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Cisco IOS IP Addressing Services Command Reference
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accounting DHCP through clear ip route
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clear ip route dhcp through ip arp entry learn
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ip arp gratuitous through ip dhcp ping packets
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ip dhcp ping timeout through ip dhcp-client forcerenew
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ip dhcp-client network-discovery through ip nat sip-sbc
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ip nat source through iterate-ip-addrs
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lease through renew dhcp
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reserved-only through show ip irdp
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show ip masks through vrf DHCP pool
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Index
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Feedback
Contents
clear ip route dhcp through ip arp entry learn
- clear ip route dhcp
- clear ip snat sessions
- clear ip snat translation distributed
- clear ip snat translation peer
- clear ip dhcp snooping database statistics
- clear ip translation peer
- clear ipv6 dhcp
- clear ipv6 dhcp binding
- clear ipv6 dhcp client
- clear ipv6 dhcp conflict
- clear ipv6 dhcp-ldra statistics
- clear ipv6 dhcp relay binding
- clear ipv6 dhcp route
- clear ipv6 nat translation
- clear logging ip access-list cache
- clear mdns cache
- clear mdns statistics
- clear nat64 ha statistics
- clear nat64 statistics
- clear nat64 translations
- client-identifier
- client-name
- control
- data
- ddns (DDNS-update-method)
- default-mapping-rule
- default-router
- device-role (DHCPv6 Guard)
- dns forwarder
- dns forwarding
- dns forwarding source-interface
- dns-server
- dns-server (config-dhcp-global-options)
- dns-server (IPv6)
- domain list
- domain lookup
- domain multicast
- domain name
- domain-name (IPv6)
- domain name-server
- domain name-server interface
- domain resolver source-interface
- domain retry
- domain round-robin
- domain timeout
- domain-name (DHCP)
- group (firewall)
- hardware-address
- host
- host (host-list)
- http (DDNS-update-method)
- import all
- import dns-server
- import domain-name
- import information refresh
- import nis address
- import nis domain-name
- import nisp address
- import nisp domain-name
- import sip address
- import sip domain-name
- import sntp address
- information refresh
- internal (DDNS-update-method)
- interval maximum
- interval minimum
- ip address
- ip address dhcp
- ip address pool (DHCP)
- ip arp entry learn
clear ip route dhcp
To remove routes from the routing table added by the Cisco IOS Dynamic Host Configuration Protocol (DHCP) server and relay agent for the DHCP clients on unnumbered interfaces, use the clear ip route dhcpcommand in EXEC mode.
Command History
Release
Modification
12.2
This command was introduced.
12.2(33)SRA
This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX
This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.
Usage Guidelines
To remove information about global routes in the routing table, use the clear ip route dhcp command. To remove routes in the VRF routing table, use the clear ip route vrf vrf-name dhcp command.
clear ip snat sessions
To clear dynamic Stateful Network Address Translation (SNAT) sessions from the translation table, use the clear ip snat sessionscommand in EXEC mode.
Examples
The following example shows the SNAT entries before and after using the clear ip snat sessions command:
Router> show ip snat distributed SNAT:Mode PRIMARY :State READY :Local Address 10.168.123.2 :Local NAT id 100 :Peer Address 10.168.123.3 :Peer NAT id 200 :Mapping List 10 Router> clear ip snat sessions * Closing TCP session to peer:10.168.123.3 Router> show ip snat distributedclear ip snat translation distributed
clear ip snat translation peer
To clear peer Stateful Network Address Translation (SNAT) translations from the translation table, use the clear ip snat translation peercommand in EXEC mode.
Usage Guidelines
Use this command to clear peer entries from the translation table before they time out.
Examples
The following example shows the SNAT entries before and after the peer entry is cleared:
Router# show ip snat peer Pro Inside global Inside local Outside local Outside global --- 192.168.25.20 192.168.122.20 --- --- tcp 192.168.25.20:33528 192.168.122.20:33528 192.168.24.2:21 192.168.24.2:21 Router# clear ip snat translation peer 192.168.122.20clear ip dhcp snooping database statistics
clear ip translation peer
To clear or reset the Network Address Translation (NAT) entries created by the Stateful Failover of Network Address Translation (SNAT) peer router and retreive a list of NAT entries, use the clear ip translation peer command in privileged EXEC mode.
clear ipv6 dhcp
clear ipv6 dhcp binding
To delete automatic client bindings from the Dynamic Host Configuration Protocol (DHCP) for IPv6 server binding table, use the clear ipv6 dhcp binding command in privileged EXEC mode.
Command History
Release
Modification
12.3(4)T
This command was introduced.
12.4(24)T
This command was modified. It was updated to allow for clearing all address bindings associated with a client.
Cisco IOS XE Release 2.1
This command was implemented on Cisco ASR 1000 Series Routers.
12.2(33)XNE
This command was integrated into Cisco IOS Release 12.2(33)SXE.
15.1(2)S
This command was modified. The vrf vrf-name keyword and argument were added.
Cisco IOS XE Release 3.3S
This command was modified. The vrf vrf-name keyword and argument were added.
15.3(3)M
This command was integrated into Cisco IOS Release 15.3(3)M.
Usage Guidelines
The clear ipv6 dhcp binding command is used as a server function.
A binding table entry on the DHCP for IPv6 server is automatically:
- Created whenever a prefix is delegated to a client from the configuration pool.
- Updated when the client renews, rebinds, or confirms the prefix delegation.
- Deleted when the client releases all the prefixes in the binding voluntarily, all prefixes’ valid lifetimes have expired, or an administrator runs the clear ipv6 dhcp binding command.
If the clear ipv6 dhcp binding command is used with the optional ipv6-address argument specified, only the binding for the specified client is deleted. If the clear ipv6 dhcp binding command is used without the ipv6-address argument, then all automatic client bindings are deleted from the DHCP for IPv6 binding table. If the optional vrf vrf-name keyword and argument combination is used, only the bindings for the specified VRF are cleared.
clear ipv6 dhcp client
To restart the Dynamic Host Configuration Protocol (DHCP) for IPv6 client on an interface, use the clear ipv6 dhcp client command in privileged EXEC mode.
Usage Guidelines
The clear ipv6 dhcp client command restarts the DHCP for IPv6 client on specified interface after first releasing and unconfiguring previously acquired prefixes and other configuration options (for example, Domain Name System [DNS] servers).
clear ipv6 dhcp conflict
To clear an address conflict from the Dynamic Host Configuration Protocol for IPv6 (DHCPv6) server database, use the clear ipv6 dhcp conflict command in privileged EXEC mode.
Command History
Release
Modification
12.4(24)T
This command was introduced.
15.1(2)S
This command was modified. The vrf vrf-name keyword and argument were added.
Cisco IOS XE Release 3.3S
This command was modified. The vrf vrf-name keyword and argument were added.
15.3(3)M
This command was integrated into Cisco IOS Release 15.3(3)M.
Usage Guidelines
When you configure the DHCPv6 server to detect conflicts, it uses ping. The client uses neighbor discovery to detect clients and reports to the server through a DECLINE message. If an address conflict is detected, the address is removed from the pool, and the address is not assigned until the administrator removes the address from the conflict list.
If you use the asterisk (*) character as the address parameter, DHCP clears all conflicts.
If the vrf vrf-name keyword and argument are specified, only the address conflicts that belong to the specified VRF will be cleared.
clear ipv6 dhcp-ldra statistics
To clear Lightweight DHCPv6 Relay Agent (LDRA) related statistics, use the clear ipv6 dhcp-ldra statistics command in user EXEC or privileged EXEC mode.
Syntax Description
interface-type (Optional) Interface type. For more information, use the question mark (?) online help function.
number (Optional) Interface number.
Command History
Release Modification 15.1(2)SG
This command was introduced.
Cisco IOS XE Release 3.4SG
This command was integrated into Cisco IOS XE Release 3.4SG.
Usage Guidelines
The following interfaces are allowed and can be used for the interface-type argument:
clear ipv6 dhcp relay binding
To clear an IPv6 address or IPv6 prefix of a Dynamic Host Configuration Protocol (DHCP) for IPv6 relay binding, use the clear ipv6 dhcp relay binding command in privileged EXEC mode.
Cisco uBR10012 and Cisco uBR7200 Series Universal Broadband Devices
clear ipv6 dhcp relay binding { vrf vrf-name } { * | ipv6-prefix }
Command History
Release
Modification
Cisco IOS XE Release 2.6
This command was introduced.
15.1(2)S
This command was modified. The vrf vrf-name keyword-argument pair was added.
Cisco IOS XE Release 3.3S
This command was modified. The vrf vrf-name keyword-argument pair was added.
15.2(1)S
The command was modified to delete the binding or route for IPv6 addresses.
Cisco IOS XE Release 3.5S
The command was modified to delete the binding or route for IPv6 addresses.
12.2(33)SCF4
This command was implemented on Cisco uBR10012 and Cisco uBR7200 series universal broadband devices.
15.3(3)M
This command was integrated into Cisco IOS Release 15.3(3)M.
Usage Guidelines
The clear ipv6 dhcp relay binding command deletes a specific IPv6 address or IPv6 prefix of a DHCP for IPv6 relay binding. If no relay client is specified, no binding is deleted.
Examples
The following example shows how to clear the binding for a client with a specified IPv6 address:
Device# clear ipv6 dhcp relay binding 2001:0DB8:3333:4::5The following example shows how to clear the binding for a client with the VRF name vrf1 and a specified prefix on a Cisco uBR10012 universal broadband device:
Device# clear ipv6 dhcp relay binding vrf vrf1 2001:DB8:0:1::/64clear ipv6 dhcp route
To clear routes added by Dynamic Host Configuration Protocol for IPv6 (DHCPv6) on a DHCPv6 server for Internet Assigned Numbers Authority (IANA) and Identity Association for Prefix Delegation (IAPD), use the clear ipv6 dhcp route command in privileged EXEC mode.
clear ipv6 nat translation
To clear dynamic Network Address Translation--Protocol Translation (NAT-PT) translations from the dynamic state table, use the clear ipv6 nat translationcommand in privileged EXEC mode.
Usage Guidelines
Use this command to clear entries from the dynamic translation state table before they time out. Static translation configuration is not affected by this command.
Examples
The following example shows the NAT-PT entries before and after the dynamic translation state table is cleared. Note that all the dynamic NAT-PT mappings are cleared, but the static NAT-PT configurations remain.
Router# show ipv6 nat translations Prot IPv4 source IPv6 source IPv4 destination IPv6 destination --- --- --- 192.168.123.2 2001::2 --- --- --- 192.168.122.10 2001::10 tcp 192.168.124.8,11047 3002::8,11047 192.168.123.2,23 2001::2,23 udp 192.168.124.8,52922 3002::8,52922 192.168.123.2,69 2001::2,69 Router# clear ipv6 nat translation * Router# show ipv6 nat translations Prot IPv4 source IPv6 source IPv4 destination IPv6 destination --- --- --- 192.168.123.2 2001::2 --- --- --- 192.168.122.10 2001::10clear logging ip access-list cache
To clear all the entries from the Optimized ACL Logging (OAL) cache and send them to the syslog, use the clear logging ip access-list cache command in privileged EXEC mode.
Usage Guidelines
This command is supported on Cisco 7600 series routers that are configured with a Supervisor Engine 720 only.
Examples
This example shows how to clear all the entries from the OAL cache and send them to the syslog:
Router# clear logging ip access-list cacheRelated Commands
Command
Description
logging ip access-list cache (global configuration )
Configures the OAL parameters globally.
logging ip access-list cache (interface configuration )
Enables an OAL-logging cache on an interface that is based on direction.
show logging ip access-list
Displays information about the logging IP access list.
clear mdns cache
To clear multicast Domain Name System (mDNS) cache information, use the clear mdns cache command in privileged EXEC mode.
Usage Guidelines
The clear mdns cache command clears mDNS cache information corresponding to all the interfaces on the device, including all mDNS records in cache.
clear mdns statistics
To clear multicast Domain Name System (mDNS) statistics, use the clear mdns statistics command in privileged EXEC mode.
Usage Guidelines
The all keyword can be used in two forms of the clear mdns statistics command. You can clear mDNS statistics for the device using the clear mdns statistics all command form. To clear service-policy statistics, use the clear mdns statistics service-policy all command form
clear nat64 ha statistics
To clear the Network Address Translation 64 (NAT64) high availability (HA) statistics, use the clear nat64 ha statistics command in privileged EXEC mode.
Usage Guidelines
The HA statistics include the number of HA messages that are transmitted and received by the Route Processor (RP).
clear nat64 statistics
To clear the Network Address Translation 64 (NAT64) statistics, use the clear nat64 statistics command in privileged EXEC mode.
clear nat64 statistics [ failure | global | interface type number | limit global | pool pool-name | prefix [ stateful ipv6-prefix/prefix-length | stateless [ v4v6 | v6v4 ] ipv6-prefix/prefix-length ] ]
Syntax Description
failure
(Optional) Clears NAT64 failure count statistics.
global
(Optional) Clears global NAT64 statistics.
interface
(Optional) Clears interface statistics.
type
(Optional) Interface type. For more information, use the question mark (?) online help function.
number
(Optional) Interface or subinterface number. For more information about the numbering syntax for your networking device, use the question mark (?) online help function.
limit
(Optional) Clears the statistics about the maximum number of stateful NAT64 translations allowed on a router.
pool pool-name
(Optional) Clears statistics for a specified pool.
prefix
(Optional) Clears statistics for a specified prefix.
stateful
(Optional) Clears stateful NAT64 statistics.
ipv6-prefix
(Optional) IPv6 network number to include in router advertisements. This argument must be in the form documented in RFC 2373 where the address is specified in hexadecimal using 16-bit values between colons.
/prefix-length
(Optional) Length of the IPv6 prefix. A decimal value that indicates how many of the high-order contiguous bits of the address comprise the prefix (the network portion of the address). A slash mark must precede the decimal value.
stateless
(Optional) Clears stateless NAT64 statistics.
v4v6
(Optional) Clears statistics about the IPv4 address that is associated with an IPv6 host for NAT64.
v6v4
(Optional) Clears statistics about the IPv6 address that is associated with an IPv4 host for NAT64.
Command History
Release
Modification
Cisco IOS XE Release 3.2S
This command was introduced.
Cisco IOS XE Release 3.4S
This command was modified. The failure, pool, stateful, stateless, v4v6, and v6v4 keywords and the pool-name argument were added.
15.4(1)T
This command was integrated into Cisco IOS Release 15.4(1)T.
Usage Guidelines
You can use the clear nat64 statistics command to clear the statistics of a specified interface or all the interfaces for a given stateful or stateless prefix.
Related Commands
Command
Description
nat64 v4v6
Translates an IPv4 source address to an IPv6 source address and an IPv6 destination address to an IPv4 destination address for NAT64.
nat64 v6v4
Translates an IPv6 source address to an IPv4 source address and an IPv4 destination address to an IPv6 destination address for NAT64.
show nat64 statistics
Displays statistics about NAT64 interfaces and the translated and dropped packet count.
clear nat64 translations
To clear dynamic stateful Network Address Translation 64 (NAT64) translations, use the clear nat64 translations command in privileged EXEC mode.
Syntax Description
all
Clears all NAT64 translations.
redundancy group-id
Clears translations that are filtered on the basis of the specified redundancy group ID. Valid values are 1 and 2.
protocol
Clears translations that are filtered on the basis of the specified protocol.
icmp
Clears NAT64 Internet Control Message Protocol (ICMP) translations.
tcp
Clears NAT64 TCP translations.
udp
Clears NAT64 UDP translations.
client-identifier
To specify the unique identifier (in dotted hexadecimal notation) for a Dynamic Host Configuration Protocol (DHCP) client, use the client-identifier command in DHCP pool configuration mode. To delete the client identifier, use the no form of this command.
Command History
Release
Modification
12.0(1)T
This command was introduced.
12.2(33)SRA
This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX
This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.
Usage Guidelines
This command is valid for manual bindings only. DHCP clients require client identifiers instead of hardware addresses. The client identifier is formed by concatenating the media type and the MAC address. You can specify the unique identifier for the client in either of the following ways:For a list of media type codes, refer to the “Address Resolution Protocol Parameters” section of RFC 1700, Assigned Numbers.
- A 7-byte dotted hexadecimal notation. For example, 01b7.0813.8811.66, where 01 represents the Ethernet media type and the remaining bytes represent the MAC address of the DHCP client.
- A 27-byte dotted hexadecimal notation. For example, 7665.6e64.6f72.2d30.3032.342e.3937.6230.2e33.3734.312d.4661.302f.31. The equivalent ASCII string for this hexadecimal value is vendor-0024.97b0.3741-fa0/1, where vendor represents the vendor, 0024.97b0.3741 represents the MAC address of the source interface, and fa0/1 represents the source interface of the DHCP client.
You can determine the client identifier by using the debug ip dhcp server packet command.
Examples
The following example specifies the client identifier for MAC address 01b7.0813.8811.66 in dotted hexadecimal notation:
Device(dhcp-config)# client-identifier 01b7.0813.8811.66client-name
To specify the name of a Dynamic Host Configuration Protocol (DHCP) client, use the client-name command in DHCP pool configuration mode. To remove the client name, use the no form of this command.
Command History
Release
Modification
12.0(1)T
This command was introduced.
12.2(33)SRA
This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX
This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.
control
To configure the control interface type and number for a redundancy group, use the controlcommand in redundancy application group configuration mode. To remove the control interface for the redundancy group, use the no form of this command.
Examples
The following example shows how to configure the redundancy group protocol media and instance for the control Gigabit Ethernet interface:
Router# configure terminal Router(config)# redundancy Router(config-red)# application redundancy Router(config-red-app)# group 1 Router(config-red-app-grp)# control GigabitEthernet 0/0/0 protocol 1Related Commands
Command
Description
application redundancy
Enters redundancy application configuration mode.
authentication
Configures clear text authentication and MD5 authentication for a redundancy group.
data
Configures the data interface type and number for a redundancy group.
group(firewall)
Enters redundancy application group configuration mode.
name
Configures the redundancy group with a name.
preempt
Enables preemption on the redundancy group.
protocol
Defines a protocol instance in a redundancy group.
data
To configure the data interface type and number for a redundancy group, use the datacommand in redundancy application group configuration mode. To remove the configuration, use the no form of this command.
Usage Guidelines
Use the data command to configure the data interface. The data interface can be the same physical interface as the control interface.
Examples
The following example shows how to configure the data Gigabit Ethernet interface for group1:
Router# configure terminal Router(config)# redundancy Router(config-red)# application redundancy Router(config-red-app)# group 1 Router(config-red-app-grp)# data GigabitEthernet 0/0/0Related Commands
Command
Description
application redundancy
Enters redundancy application configuration mode.
authentication
Configures clear text authentication and MD5 authentication for a redundancy group.
control
Configures the control interface type and number for a redundancy group.
group(firewall)
Enters redundancy application group configuration mode.
name
Configures the redundancy group with a name.
preempt
Enables preemption on the redundancy group.
protocol
Defines a protocol instance in a redundancy group.
ddns (DDNS-update-method)
To specify an update method for address (A) Resource Records (RRs) as IETF standardized Dynamic Domain Name System (DDNS), use the ddnscommand in DDNS-update-method configuration mode. To disable the DDNS method for updating, use the no form of this command.
Usage Guidelines
If Dynamic Host Configuration Protocol (DHCP) is used to configure the IP address on the interface, a DHCP client may not perform both A and PTR RRs or any updates. Also, if the DHCP server notifies the client during the DHCP interaction that it will perform the updates, then the DHCP client will not perform the updates. The DHCP server can always override the client even if the client is configured to perform the updates.
If the interface is configured using DHCP and if the DDNS update method is configured on that interface, then the DHCP fully qualified domain name (FQDN) option is included in the DHCP packets between the client and the server. The FQDN option contains the hostname, which is used in the update as well as information about what types of updates the client has been configured to perform.
If the ddns keyword is specified, the A RRs only are updated, but if the ddns both keyword are specified, both the A and the PTR RRs are updated. Also, if the DHCP server returns the the FQDN option with an updated hostname, that hostname is used in the update instead.
default-mapping-rule
To configure Network Address Translation 64 (NAT64) mapping of addresses and ports translation (MAP-T) default domain mapping rule, use the default-mapping-rule command in NAT64 MAP-T configuration mode. To remove the NAT64 MAP-T default domain mapping rule, use the no form of this command.
Syntax Description
ipv6-prefix/prefix-mask
The IPv6 address assigned to the interface and the length of the IPv6 prefix.
The prefix-length is a decimal value that indicates how many of the high-order contiguous bits of the address comprise the prefix (the network portion of the address). A slash mark must precede the decimal value.
Usage Guidelines
MAP-T or Mapping of address and port (MAP) double stateless translation-based solution (MAP-T) provides IPv4 hosts connectivity to and across an IPv6 domain. MAP-T builds on existing stateless IPv4/IPv6 address translation techniques that are specified in RFC 6052, RFC 6144, and RFC 6145.
default-router
To specify the default router list for a Dynamic Host Configuration Protocol (DHCP) client, use the default-router command in DHCP pool configuration mode. To remove the default router list, use the no form of this command.
Command History
Release
Modification
12.0(1)T
This command was introduced.
12.2(33)SRA
This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX
This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.
Usage Guidelines
The IP address of the router should be on the same subnet as the client subnet. You can specify up to eight routers in the list. Routers are listed in order of preference (address1 is the most preferred router, address2 is the next most preferred router, and so on).
device-role (DHCPv6 Guard)
To specify the role of the device attached to the target (which can be an interface or VLAN), use the device-role command in Dynamic Host Configuration Protocol version 6 (DHCPv6) guard configuration mode. To remove the specification, use the no form of this command.
Usage Guidelines
The device-role command specifies the role of the device attached to the target (which can be an interface or VLAN) . The device role is primarily used to allow and disallow DHCP replies and DHCP advertisements when they are received on an interface with a device role other than server or relay.
dns forwarder
To add an address to the end of the ordered list of IP addresses for a Domain Name System (DNS) view to use when forwarding incoming DNS queries, use the dns forwarder command in DNS view configuration mode. To remove an IP address from the list, use the no form of this command.
dns forwarder [ vrf vrf-name ] forwarder-ip-address
no dns forwarder [ vrf vrf-name ] forwarder-ip-address
Syntax Description
Command Default
Provided that DNS forwarding (configured by using the dns forwarding command) is enabled and the interface to use when forwarding incoming DNS queries is configured (if using the dns forwarding source-interface command) and not shut down, incoming DNS queries handled using the DNS view are forwarded to one of the DNS forwarding name servers.
If no forwarding name servers are configured for the DNS view, the device uses any configured domain name server addresses.
If there are no domain name server addresses configured either, the device forwards incoming DNS queries to the limited broadcast address (255.255.255.255) so that the queries are received by all hosts on the local network segment but not forwarded by devices.
Usage Guidelines
This command can be entered multiple times to specify a maximum of six forwarding name servers. After six forwarding name servers have been specified, additional forwarding name servers cannot be specified unless an existing entry is removed.
To display the list of DNS forwarding name server addresses configured for the DNS view, use the show ip dns view command.
NoteDNS resolving name servers and DNS forwarding name servers are configured separately. The domain name-server and domain name-server interface commands are used to specify the DNS resolving name servers (the ordered list of IP addresses to use when resolving internally generated DNS queries handled using the DNS view). The dns forwarder command specifies the forwarder addresses (the ordered list of IP addresses to use when forwarding incoming DNS queries handled using the DNS view). Earlier to this command being introduced, the resolving name server list was used for resolving internal DNS queries and forwarding DNS queries received by the DNS server. For backward compatibility, if there are no forwarding name servers configured, the resolving name server list will be used instead.
Examples
The following example shows how to add three IP addresses to the list of forwarder addresses for the DNS view named user3 that is associated with the VRF vpn32:
Device(config)# ip dns view vrf vpn32 user3 Device(cfg-dns-view)# dns forwarder 192.168.2.0 Device(cfg-dns-view)# dns forwarder 192.168.2.1 Device(cfg-dns-view)# dns forwarder 192.168.2.2The following example shows how to add the IP address 192.0.2.3 to the list of forwarder addresses for the DNS view named user1 that is associated with the VRF vpn32, with the restriction that incoming DNS queries will be forwarded to 192.0.2.3 only if the queries are from the VRF named vpn1:
Device(config)# ip dns view vrf vpn32 user1 Device(cfg-dns-view)# dns forwarder vrf vpn1 192.168.2.3Related Commands
Command
Description
dns forwarding
Enables forwarding of incoming DNS queries by the DNS view.
dns forwarding source-interface
Specifies the interface to use when forwarding incoming DNS queries handled using the DNS view.
domain name-server
Specifies the ordered list of IP addresses to use when resolving internally generated DNS queries handled using the DNS view.
domain name-server interface
Specifies the interface from which the device can learn (through either DHCP or PPP interaction on the interface) a DNS resolving name server address for the DNS view.
show ip dns view
Displays information about a particular DNS view or about all configured DNS views, including the number of times the DNS view was used.
dns forwarding
To enable forwarding of incoming Domain Name System (DNS) queries handled using the DNS view, use the dns forwarding command in DNS view configuration mode. To disable forwarding and revert to the default configuration, use the no form of this command.
Command Default
The default value is inherited from the global setting configured using the ip domain lookup global configuration command. However, the dns forwarding command for the DNS view does not have a reciprocal side effect on the setting configured by the ip domain lookup command.
Usage Guidelines
This command enables forwarding of incoming DNS queries handled using the DNS view.
To display the DNS forwarding setting for a DNS view, use the show ip dns view command.
If you configure the no domain lookup command for a DNS view while the dns forwarding command has not been disabled for that view, then the dns forwarding command setting will appear in the show ip dns view command output in order to make it clear that DNS forwarding is still enabled.
If you configure the no ip domain lookup global configuration command, however, the no dns forwarding setting is automatically configured also, in order to be backward compatible with the global command form.
NoteDNS lookup and DNS forwarding are configured separately. The domain lookup command enables the resolution of internally generated DNS queries handled using the DNS view. The dns forwarding command enables the forwarding of incoming DNS queries handled using the DNS view. By default, domain lookup and DNS forwarding are both enabled for a view. If you then configure the no domain lookupcommand, DNS forwarding is still enabled. However, if you instead use the older Cisco IOS command no ip domain lookup to disable domain lookup for the global default view, then DNS forwarding is disabled automatically. This is done for backward compatibility with the functionality of the no ip domain lookup global configuration command.
Examples
The following example shows how to enable forwarding of incoming DNS queries handled using the DNS view named user3 that is associated with the VRF vpn32:
Router(config)# ip dns view vrf vpn32 user3 Router(cfg-dns-view)# dns forwardingRelated Commands
Command
Description
dns forwarding source-interface
Specifies the interface to use when forwarding incoming DNS queries handled using the DNS view.
domain lookup
Enables the IP DNS-based hostname-to-address translation for internally generated DNS queries handled using the DNS view.
ip domain lookup
Enables the IP DNS-based hostname-to-address translation.
show ip dns view
Displays information about a particular DNS view or about all configured DNS views, including the number of times the DNS view was used.
dns forwarding source-interface
To specify the interface to use when forwarding incoming Domain Name System (DNS) queries handled using the DNS view, use the dns forwarding source-interface command in DNS view configuration mode. To remove the specification of the source interface for a DNS view to use when forwarding DNS queries, use the no form of this command.
Command Default
No interface is specified for forwarding incoming DNS queries handled using the DNS view, so the router selects the appropriate source IP address automatically, according to the interface used to send the packet, when the query is forwarded.
Usage Guidelines
This command specifies the interface to use when forwarding incoming DNS queries handled using the DNS view.
To display the interface configured by this command, use the show ip dns view command.
Tip
To list all the interfaces configured on the router or access server, use the show interfaces command with the summary keyword. Use the appropriate interface specification, typed exactly as it is displayed under the Interface column of the show interfaces command output, to replace the interface argument in the dns forwarding source-interface command.
Examples
The following is sample output from the show interfaces command used with the summary keyword:
Router# show interfaces summary *: interface is up IHQ: pkts in input hold queue IQD: pkts dropped from input queue OHQ: pkts in output hold queue OQD: pkts dropped from output queue RXBS: rx rate (bits/sec) RXPS: rx rate (pkts/sec) TXBS: tx rate (bits/sec) TXPS: tx rate (pkts/sec) TRTL: throttle count Interface IHQ IQD OHQ OQD RXBS RXPS TXBS TXPS TRTL ------------------------------------------------------------------------ * FastEthernet0/0 0 0 0 0 0 0 0 0 0 FastEthernet0/1 0 0 0 0 0 0 0 0 0 ATM2/0 0 0 0 0 0 0 0 0 0 Ethernet3/0 0 0 0 0 0 0 0 0 0 Ethernet3/1 0 0 0 0 0 0 0 0 0 Ethernet3/2 0 0 0 0 0 0 0 0 0 Ethernet3/3 0 0 0 0 0 0 0 0 0 ATM6/0 0 0 0 0 0 0 0 0 0 NOTE:No separate counters are maintained for subinterfaces Hence Details of subinterface are not shownThe following example shows how to configure FastEthernet slot 0, port 1 as the interface to be used to forward DNS queries for the DNS view named user3 that is associated with the VRF vpn32:
Router(config)# ip dns view vrf vpn32 user3 Router(cfg-dns-view)# dns forwarder source-interface FastEthernet0/1Related Commands
Command
Description
dns forwarding
Enables forwarding of incoming DNS queries by the DNS view.
show interfaces
Display statistics for all interfaces configured on the router or access server.
show ip dns view
Displays information about a particular DNS view or about all configured DNS views, including the number of times the DNS view was used.
dns-server
To specify the Domain Name System (DNS) IP servers available to a Dynamic Host Configuration Protocol (DHCP) client, use the dns-server command in DHCP pool configuration mode. To remove the DNS server list, use the no form of this command.
Command Default
If DNS IP servers are not configured for a DHCP client, the client cannot correlate host names to IP addresses.
Command History
Release
Modification
12.0(1)T
This command was introduced.
12.2(33)SRA
This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX
This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.
Usage Guidelines
Servers are listed in order of preference (address1 is the most preferred server, address2 is the next most preferred server, and so on).
dns-server (config-dhcp-global-options)
To configure the Domain Name System (DNS) servers that are available to DHCP clients on request, use the dns-server command in DHCP global options configuration mode. To remove the DNS server list, use the no form of this command.
Command Default
If DNS servers are not configured for a DHCP client, the client cannot correlate hostnames to IP addresses.
Usage Guidelines
Before you configure the dns-server command, you must enter DHCP global options configuration mode by using the ip dhcp global-options command.
dns-server (IPv6)
To specify the Domain Name System (DNS) IPv6 servers available to a Dynamic Host Configuration Protocol (DHCP) for IPv6 client, use the dns-server command in DHCP for IPv6 pool configuration mode. To remove the DNS server list, use the no form of this command.
Command History
Release
Modification
12.3(4)T
This command was introduced.
Cisco IOS XE Release 2.1
This command was integrated into Cisco IOS XE Release 2.1.
12.2(33)SRE
This command was modified. It was integrated into Cisco IOS Release 12.2(33)SRE.
Command History
Usage Guidelines
Multiple Domain Name System (DNS) server addresses can be configured by issuing this command multiple times. New addresses will not overwrite old addresses.
domain list
To add a domain name to the end of the ordered list of domain names used to complete unqualified hostnames (names without a dotted-decimal domain name) in Domain Name System (DNS) queries handled using the DNS view, use the domain list command in DNS view configuration mode. To remove a name from the domain search list, use the no form of this command.
Usage Guidelines
This command adds a domain name to the end of the domain search list for the DNS view.
NoteThe domain list and domain name commands are similar, except that the domain list command can be used to define a list of domain names for the view, each to be tried in turn. If DNS lookup is enabled for the DNS view but the domain search list (specified using the domain list command) is empty, the default domain name (specified by using the domain name command) is used instead. If the domain search list is not empty, the default domain name is not used.
To display the list of domain names used to complete unqualified hostnames in DNS queries received by a DNS view, use the show hosts command or the show ip dns view command.
Examples
The following example shows how to add two domain names to the list for the DNS view named user3 that is associated with the VRF vpn32:
Router(config)# ip dns view vrf vpn32 user3 Router(cfg-dns-view)# domain list example1.com Router(cfg-dns-view)# domain list example1.orgThe following example shows how to add two domain names to the list for the DNS view and then delete one of the domain names from the list:
Router(cfg-dns-view)# domain list example2.com Router(cfg-dns-view)# domain list example2.org Router(cfg-dns-view)# no domain list example2.netRelated Commands
Command
Description
domain name
Specifies a single default domain name to use to complete unqualified hostnames in internally generated DNS queries handled using the DNS view.
show hosts
Displays the default domain name, the style of name lookup service, a list of name server hosts, and the cached list of hostnames and addresses specific to a particular DNS view or for all configured DNS views.
show ip dns view
Displays information about a particular DNS view or about all configured DNS views, including the number of times the DNS view was used.
domain lookup
To enable the IP Domain Name System (DNS)-based hostname-to-address translation for internally generated DNS queries handled using the DNS view, use the domain lookup command in DNS view configuration mode. To disable domain lookup for hostname resolution, use the no form of this command.
Command Default
The default value is inherited from the global setting configured using the ip domain lookup global command. However, the domain lookup DNS view command does not have a reciprocal side effect on the setting configured by the ip domain lookup global command.
Usage Guidelines
This command enables DNS-based hostname-to-address translation for internally generated DNS queries handled using the DNS view.
To display the DNS lookup setting for a DNS view, use the show ip dns view command.
If you configure no dns forwarding for a DNS view while domain lookup has not been disabled for that view, then the domain lookup setting will appear in the show ip dns view command output in order to make it clear that domain lookup is still enabled.
If you configure the no ip domain lookup global command, however, the no domain lookup setting is automatically configured also, in order to be backward compatible with the global command form.
NoteDNS lookup and DNS forwarding are configured separately. The domain lookup command enables the resolution of internally generated DNS queries handled using the DNS view. The dns forwarding command enables the forwarding of incoming DNS queries handled using the DNS view. By default, both domain lookup and DNS forwarding are both enabled for a view. If you then configure no domain lookup, DNS forwarding is still enabled. However, if you instead uses the older Cisco IOS command no ip domain lookup to disable domain lookup for the global default view, then DNS forwarding is disabled automatically. This is done for backward compatibility with the functionality of the no ip domain lookup global command.
Examples
The following example shows how to enable IP DNS-based hostname-to-address translation in the DNS view named user3 that is associated with the VRF vpn32:
Router(config)# ip dns view vrf vpn32 user3 Router(cfg-dns-view)# domain lookupRelated Commands
Command
Description
dns forwarding
Enables forwarding of incoming DNS queries by the DNS view.
domain name-server
Specifies the ordered list of IP addresses to use when resolving internally generated DNS queries handled using the DNS view.
domain name-server interface
Specifies the interface from which the router can learn (through either DHCP or PPP interaction on the interface) a DNS resolving name server address for the DNS view.
ip domain lookup
Enables the IP DNS-based hostname-to-address translation.
show ip dns view
Displays information about a particular DNS view or about all configured DNS views, including the number of times the DNS view was used.
domain multicast
To configure the domain name to be used when performing multicast address lookups for internally generated Domain Name System (DNS) queries handled using the DNS view, use the domain multicast command in DNS view configuration mode. To remove the specification of the domain name for multicast address lookups, use the no form of this command.
Command Default
No IP address is specified for performing multicast address lookups for the DNS view.
Usage Guidelines
This command configures the domain name to be used when performing multicast address lookups for internally generated DNS queries handled using the DNS view.
To display the domain name for multicast address lookups, use the show ip dns view command.
Examples
The following example shows how to configure the domain name www.example.com as the domain name to be used when performing multicast lookups for internally generated DNS queries handled using the DNS view named user3 that is associated with the VRF vpn32:
Router(config)# ip dns view vrf vpn32 user3 Router(cfg-dns-view)# domain multicast www.example.comdomain name
To specify the default domain for a Domain Name System (DNS) view to use to complete unqualified hostnames (names without a dotted-decimal domain name), use the domain name command in DNS view configuration mode. To remove the specification of the default domain name for a DNS view, use the no form of this command.
Usage Guidelines
This command configures the default domain name used to complete unqualified hostnames in DNS queries handled using the DNS view.
NoteThe domain list and domain name commands are similar, except that the domain list command can be used to define a list of domain names for the view, each to be tried in turn. If DNS lookup is enabled for the DNS view but the domain search list (specified using the domain list command) is empty, the default domain name (specified by using the domain name command) is used instead. If the domain search list is not empty, the default domain name is not used.
To display the default domain name configured for a DNS view, use the show hosts command or the show ip dns view command.
Examples
The following example shows how to define example.com as the default domain name for the DNS view named user3 that is associated with the VRF vpn32:
Router(config)# ip dns view vrf vpn32 user3 Router(cfg-dns-view)# domain name example.comRelated Commands
Command
Description
domain list
Defines the ordered list of default domain names to use to complete unqualified hostnames in internally generated DNS queries handled using the DNS view.
show hosts
Displays the default domain name, the style of name lookup service, a list of name server hosts, and the cached list of hostnames and addresses specific to a particular DNS view or for all configured DNS views.
show ip dns view
Displays information about a particular DNS view or about all configured DNS views, including the number of times the DNS view was used.
domain-name (IPv6)
To configure a domain name for a Dynamic Host Configuration Protocol for IPv6 (DHCPv6) client, use the domain-namecommand in DHCPv6 pool configuration mode. To return to the default for this command, use the no form of this command.
Command History
Release
Modification
12.4(9)T
This command was introduced.
Cisco IOS XE Release 2.1
This command was integrated into Cisco IOS XE Release 2.1.
12.2(33)SRE
This command was modified. It was integrated into Cisco IOS Release 12.2(33)SRE.
12.2(33)XNE
This command was modified. It was integrated into Cisco IOS Release 12.2(33)XNE.
domain name-server
To add a name server to the list of Domain Name System (DNS) name servers to be used for a DNS view to resolve internally generated DNS queries, use the domain name-server command in DNS view configuration mode. To remove a DNS name server from the list, use the no form of this command.
domain name-server [ vrf vrf-name ] name-server-ip-address
no domain name-server [ vrf vrf-name ] [ name-server-ip-address]
Syntax Description
vrf vrf-name
(Optional) The vrf-name argument specifies the name of the Virtual Private Network (VPN) routing and forwarding (VRF) instance of the forwarder-ip-address.
Note If no VRF is specified, the default is the global VRF.
name-server-ip-address
IP address of a DNS name server.
Note You can specify an IPv4 or IPv6 address for the DNS name server. Command Default
No IP address is explicitly added to the list of resolving name servers for this view, although an IP address can be added to the list if dynamic name server acquisition is enabled. If the list of resolving name servers is empty, the device will send the query to the limited broadcast address 255.255.255.255 when this view is used.
Usage Guidelines
This command can be entered multiple times to specify a maximum of six resolving name servers. After six resolving name servers have been specified, additional resolving name servers cannot be specified unless an existing entry is removed.
This method of explicitly populating the list of resolving name servers is useful in an enterprise network where the population of available DNS servers is relatively static. In an Internet service provider (ISP) environment, where primary and secondary DNS server addresses can change frequently, the device can learn a DNS server address through either DHCP or PPP on the interface. To configure the dynamic acquisition of DNS resolving name server addresses, use the domain name-server interface command. Regardless of the method or methods used to populate the list of DNS resolving name servers for the view, no more than six resolving name servers are maintained for the view.
To display the list of DNS resolving name server IP addresses configured for a DNS view, use the show hosts command or the show ip dns view command.
NoteThe DNS resolving name servers and DNS forwarding name servers are configured separately. The domain name-server and domain name-server interface commands are used to specify the DNS resolving name servers (the ordered list of IP addresses to use when resolving internally generated DNS queries for the DNS view). The dns forwarder command specifies the forwarder addresses (the ordered list of IP addresses to use when forwarding incoming DNS queries for the DNS view). If there is no DNS forwarder configuration in a view, then the domain name server list will be used when forwarding DNS queries. This is done for backward compatibility with the ip name-server global command.
Examples
The following example shows how to specify the hosts at 192.168.2.111 and 192.168.2.112 as the name servers for the DNS view named user3 that is associated with the VRF vpn32:
Device(config)# ip dns view vrf vpn32 user3 Device(cfg-dns-view)# domain name-server 192.168.2.111 Device(cfg-dns-view)# domain name-server 192.168.2.112Related Commands
Command
Description
dns forwarder
Specifies the ordered list of IP addresses to use when forwarding incoming DNS queries handled using the DNS view.
domain name-server interface
Specifies the interface from which the device can learn (through either DHCP or PPP interaction on the interface) a DNS resolving name server address for the DNS view.
ip name-server
Specifies the address of one or more name servers to use for name and address resolution.
show hosts
Displays the default domain name, the style of name lookup service, a list of name server hosts, and the cached list of hostnames and addresses specific to a particular DNS view or for all configured DNS views.
show ip dns view
Displays information about a particular DNS view or about all configured DNS views, including the number of times the DNS view was used.
domain name-server interface
To specify the interface on which the router can learn (through either DHCP or PPP) Domain Name System (DNS) a resolving name server address for the DNS view, use the domain name-server interface command in DNS view configuration mode. To remove the definition of the interface, use the no form of this command.
Command Default
No interface is used to acquire the DHCP or PPP address to be used for a DNS view to resolve internally generated DNS queries.
Usage Guidelines
This command specifies the interface from which to acquire (through DHCP or PPP interaction on the interface) the IP address of a DNS server to add to the list of DNS name servers used to resolve internally generated DNS queries for the DNS view.
The dynamic acquisition of DNS resolving name server addresses is useful in an Internet service provider (ISP) environment, where primary and secondary DNS server addresses can change frequently. To explicitly populate the list of resolving name servers in an enterprise network where the population of available DNS servers is relatively static, use the domain name-server command. Regardless of the method or methods used to populate the list of DNS resolving name servers for the view, no more than six resolving name servers are maintained for the view.
NoteThe DNS resolving name servers and DNS forwarding name servers are configured separately. The domain name-server and domain name-server interface commands are used to specify the DNS resolving name servers (the ordered list of IP addresses to use when resolving internally generated DNS queries for the DNS view). The dns forwarder command specifies the forwarder addresses (the ordered list of IP addresses to use when forwarding incoming DNS queries for the DNS view). If there is no DNS forwarder configuration in a view, then the domain name server list will be used when forwarding DNS queries. This is done for backward compatibility with the ip name-server global command.
Tip
To list all the interfaces configured on the router or access server, use the show interfaces command with the summary keyword. Use the appropriate interface specification, typed exactly as it is displayed under the Interface column of the show interfaces command output, to replace the interface argument in the domain name-server interface command.
Examples
The following is sample output from the show interfaces command used with the summary keyword:
Router# show interfaces summary *: interface is up IHQ: pkts in input hold queue IQD: pkts dropped from input queue OHQ: pkts in output hold queue OQD: pkts dropped from output queue RXBS: rx rate (bits/sec) RXPS: rx rate (pkts/sec) TXBS: tx rate (bits/sec) TXPS: tx rate (pkts/sec) TRTL: throttle count Interface IHQ IQD OHQ OQD RXBS RXPS TXBS TXPS TRTL ------------------------------------------------------------------------ * FastEthernet0/0 0 0 0 0 0 0 0 0 0 FastEthernet0/1 0 0 0 0 0 0 0 0 0 ATM2/0 0 0 0 0 0 0 0 0 0 Ethernet3/0 0 0 0 0 0 0 0 0 0 Ethernet3/1 0 0 0 0 0 0 0 0 0 Ethernet3/2 0 0 0 0 0 0 0 0 0 Ethernet3/3 0 0 0 0 0 0 0 0 0 ATM6/0 0 0 0 0 0 0 0 0 0 NOTE:No separate counters are maintained for subinterfaces Hence Details of subinterface are not shownThe following example shows how to specify a list of name servers for the DNS view named user3 that is associated with the VRF vpn32. First, the list of name server addresses is cleared, then five DNS server IP addresses are added to the list. Finally, FastEthernet slot 0, port 0 is specified as the interface on which to acquire, by DHCP or PPP interaction, a sixth DNS server IP address.
Router(config)# ip dns view vrf vpn32 user3 Router(cfg-dns-view)# no domain name-server Router(cfg-dns-view)# domain name-server 192.168.2.1 Router(cfg-dns-view)# domain name-server 192.168.2.2 Router(cfg-dns-view)# domain name-server 192.168.2.3 Router(cfg-dns-view)# domain name-server 192.168.2.4 Router(cfg-dns-view)# domain name-server 192.168.2.5 Router(cfg-dns-view)# domain name-server interface FastEthernet0/0Related Commands
Command
Description
domain name-server
Specifies the ordered list of IP addresses to use when resolving internally generated DNS queries handled using the DNS view.
show interfaces
Display statistics for all interfaces configured on the router or access server.
show ip dns view
Displays information about a particular DNS view or about all configured DNS views, including the number of times the DNS view was used.
domain resolver source-interface
To set the source IP address of the Domain Name Server (DNS) queries for the DNS resolver functionality, use the domain resolver source-interface command in DNS view configuration mode. To disable the configuration, use the no form of this command.
Usage Guidelines
Sometimes, when a source interface is configured on a router with the split DNS feature to forward DNS queries, the router does not forward the DNS queries through the configured interface. If you want the router to forward the DNS queries through a particular source interface, configure the router using the domain resolver source-interface command.
domain retry
To configure the number of retries to perform when sending or forwarding Domain Name System (DNS) queries handled using the DNS view, use the domain retry command in DNS view configuration mode. To remove the specification of the number of retries for a DNS view, use the no form of this command.
Usage Guidelines
This command configures the number of retries to perform when sending or forwarding DNS queries handled using the DNS view.
To display the number of retries configured for the DNS view, use the show ip dns view command.
domain round-robin
To enable round-robin rotation of multiple IP addresses associated with a name in the hostname cache used by the DNS view, use the domain round-robin command in DNS view configuration mode. To disable round-robin functionality for the DNS view, use the no form of this command.
Command Default
Round-robin rotation of multiple IP addresses associated with a name in the hostname cache is disabled for the DNS view.
Usage Guidelines
This command enables round-robin rotation such that each time a hostname in the internal cache is accessed, the system returns the next IP address in the cache, rotated such that the second IP address in the list becomes the first one and the first one is moved to the end of the list. For a more detailed description of round-robin functionality, see the description of the ip domain round-robin global command in the Cisco IOS IP Addressing Services Command Reference .
To display the cached list of hostnames and addresses specific to a particular DNS view or for all configured DNS views, use the show hosts command. To define static hostname-to-address mappings in the global hostname cache or VRF hostname cache for the specified DNS view, use the ip host command. To display the round-robin setting for the DNS view, use the show ip dns view command.
Examples
The following example shows how to define the hostname www.example.com with three IP addresses and then enable round-robin rotation for the default DNS view associated with the global VRF. Each time that hostname is referenced internally or queried by a DNS client sending a query to the Cisco IOS DNS server on this system, the order of the IP addresses associated with the host www.example.com will be changed. Because most client applications look only at the first IP address associated with a hostname, this results in different clients using each of the different addresses and thus distributing the load among the three different IP addresses.
Router(config)# ip host view www.example.com 192.168.2.100 192.168.2.200 192.168.2.250 Router(config)# ip dns view default Router(cfg-dns-view)# domain lookup Router(cfg-dns-view)# domain round-robinRelated Commands
Command
Description
ip host
Defines static hostname-to-address mappings in the DNS hostname cache for a DNS view.
ip domain round-robin
Enables round-robin functionality on DNS servers.
show hosts
Displays the default domain name, the style of name lookup service, a list of name server hosts, and the cached list of hostnames and addresses specific to a particular DNS view or for all configured DNS views.
show ip dns view
Displays information about a particular DNS view or about all configured DNS views, including the number of times the DNS view was used.
domain timeout
To configure the number of seconds to wait for a response to a Domain Name System (DNS) query sent or forwarded by the DNS view, use the domain timeout command in DNS view configuration mode. To remove the specification of the number of seconds for a DNS view to wait, use the no form of this command.
Usage Guidelines
This command configures the number of seconds to wait for a response to a DNS query sent or forwarded by the DNS view.
To display the number of seconds configured for the DNS view, use the show ip dns view command.
domain-name (DHCP)
To specify the domain n ame for a Dynamic Host Configuration Protocol (DHCP) client, use the domain-name command in DHCP pool configuration mode. To remove the domain name, use the no form of this command.
Command History
Release
Modification
12.0(1)T
This command was introduced.
12.2(33)SRA
This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX
This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.
group (firewall)
To enter redundancy application group configuration mode, use the group command in redundancy application configuration mode. To remove the group configuration, use the no form of this command.
hardware-address
To specify the hardware address of a BOOTP client, use the hardware-address command in DHCP pool configuration mode. To remove the hardware address, use the no form of this command.
Syntax Description
hardware-address
MAC address of the client.
protocol-type
(Optional) Protocol type. The valid entries are:
If no protocol type is specified, the default is Ethernet.
hardware-number
(Optional) ARP hardware specified in an online database at http://www.iana.org/assignments/arp-parameters. The valid range is from 0 to 255. See the table below for valid entries.
Command History
Release
Modification
12.0(1)T
This command was introduced.
12.2(33)SRA
This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX
This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.
Usage Guidelines
This command is valid for manual bindings only.
The table below lists the valid assigned hardware numbers found online at http://www.iana.org/assignments/arp-parameters.
Table 1 ARP Hardware Numbers and Types Hardware Number
Hardware Type
1
Ethernet
2
Experimental Ethernet (3Mb)
3
Amateur Radio AX.25
4
ProNET Token Ring
5
Chaos
6
IEEE 802 Networks
7
ARCNET
8
Hyperchannel
9
Lanstar
10
Autonet Short Address
11
LocalTalk
12
LocalNet (IBM PCNet or SYTEK LocalNET)
13
Ultra link
14
SMDS
15
Frame Relay
16
Asynchronous Transmission Mode (ATM)
17
HDLC
18
Fibre Channel
19
Asynchronous Transmission Mode (ATM) (RFC2225)
20
Serial Line
21
Asynchronous Transmission Mode (ATM)
22
MIL-STD-188-220
23
Metricom
24
IEEE 1394.1995
25
MAPOS and Common Air Interface (CAI)
26
Twinaxial
27
EUI-64
28
HIPARP
29
IP and ARP over ISO 7816-3
30
ARPSec
31
IPsec tunnel (RFC3456)
32
InfiniBand (RFC-ietf-ipoib-ip-over-infiniband-09.txt)
33
TIA-102 Project
Examples
The following example specifies b708.1388.f166 as the MAC address of the client:
hardware-address b708.1388.f166 ieee802Related Commands
Command
Description
client-identifier
Specifies the unique identifier of a DHCP client in dotted hexadecimal notation.
host
Specifies the IP address and network mask for a manual binding to a DHCP client.
ip dhcp pool
Configures a DHCP address pool on a Cisco IOS DHCP server and enters DHCP pool configuration mode.
host
To specify the IP address and network mask for a manual binding to a Dynamic Host Configuration Protocol (DHCP) client, use the hostcommand in DHCP pool configuration mode. To remove the IP address of the client, use the no form of this command.
Syntax Description
address
Specifies the IP address of the client.
mask
(Optional) Specifies the network mask of the client.
/ prefix-length
(Optional) Specifies the number of bits that comprise the address prefix. The prefix is an alternative way of specifying the network mask of the client. The prefix length must be preceded by a forward slash (/).
Command History
Release
Modification
12.0(1)T
This command was introduced.
12.2(33)SRA
This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX
This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.
Usage Guidelines
If the mask and prefix length are unspecified, DHCP examines its address pools. If no mask is found in the pool database, the Class A, B, or C natural mask is used. This command is valid for manual bindings only.
There is no limit on the number of manual bindings but you can configure only one manual binding per host pool.
Examples
The following example specifies 10.12.1.99 as the IP address of the client and 255.255.248.0 as the subnet mask:
host 10.12.1.99 255.255.248.0Related Commands
Command
Description
client-identifier
Specifies the unique identifier of a Microsoft DHCP client in dotted hexadecimal notation.
hardware-address
Specifies the hardware address of a DHCP client.
ip dhcp pool
Configures a DHCP address pool on a Cisco IOS DHCP server and enters DHCP pool configuration mode.
network (DHCP)
Configures the subnet number and mask for a DHCP address pool on a Cisco IOS DHCP server.
host (host-list)
To specify a list of hosts that will receive Dynamic Domain Name System (DDNS) updates of address (A) and pointer (PTR) Resource Records (RRs), use the hostcommand in host-list configuration mode. To disable the host list, use the no form of this command.
host [ vrf vrf-name ] { host-ip-address | hostname }
no host [ vrf vrf-name ] { host-ip-address | hostname }
Syntax Description
vrf vrf-name
(Optional) Specifies the virtual routing and forwarding (VRF) table. The vrf-name argument is a name with which the address pool is associated.
Note All hostnames or IP addresses specified on the same line as the vrf keyword are associated with that VRF.
host-ip-address
List of server IP addresses that will receive DDNS updates.
hostname
Specifies a hostname.
Examples
The following example shows how to configure a list of hosts:
ip host-list test host vrf abc 10.10.0.0Related Commands
Command
Description
debug dhcp
Displays debugging information about the DHCP client and monitors the status of DHCP packets.
debug ip ddns update
Enables debugging for DDNS updates.
debug ip dhcp server
Enables DHCP server debugging.
ip ddns update hostname
Enables a host to be used for DDNS updates of A and PTR RRs.
ip ddns update method
Specifies a method of DDNS updates of A and PTR RRs and the maximum interval between the updates.
ip dhcp client update dns
Enables DDNS updates of A RRs using the same hostname passed in the hostname and FQDN options by a client.
ip dhcp-client update dns
Enables DDNS updates of A RRs using the same hostname passed in the hostname and FQDN options by a client.
ip dhcp update dns
Enables DDNS updates of A and PTR RRs for most address pools.
ip host-list
Specifies a list of hosts that will receive DDNS updates of A and PTR RRs.
show ip ddns update
Displays information about the DDNS updates.
show ip ddns update method
Displays information about the DDNS update method.
show ip host-list
Displays the assigned hosts in a list.
update dns
Dynamically updates a DNS with A and PTR RRs for some address pools.
http (DDNS-update-method)
To specify an update method for address (A) and pointer (PTR) Resource Records (RRs) as HTTP and enter DDNS-HTTP configuration mode, use the httpcommand in DDNS-update-method configuration mode. To disable HTTP dynamic updates, use the no form of this command.
Syntax Description
add url-string
URL to be used to add or change a mapping between a hostname and an IP address. The url-stringargumenttakes the following form:
http://userid:password@domain-name/update-folder-name/update?system= system-name &hostname= hostname &myip= myipaddr
- userid and password--Strings for the organization website that you use for performing the A and PTR RRs updates.
- domain-name --String for the organizational URL that you are using for the updates; for example www.Cisco.com.
- update-folder-name --String of the folder name within the organizational website in which your updates are stored.
- update?system =system-name --Update system (method) being used; for example, dydns is DDNS and dyn is EasyDNS.
Note Before entering the question mark (?) character, press the control (Ctrl) key and the v key together on your keyboard. This will allow you to enter the ? without the software interpreting the ? as a help query.
- &hostname= hostname-- Hostname to update.
- &myip =myipaddr--IP address with which the specified hostname is associated, respectively.
Note There is one additional special character string, <s>, which could also be entered into the url-string. If <s> is entered, when the update is processed, the IP address of the server to which the update is being sent is substituted at that location.
remove url-string
URL to be used to remove a mapping between a hostname and an IP address. The url-string argument takes the same form as the one shown in the add keyword description.
Examples
The following example shows how to specify the DynDNS.org to process the updates:
ip ddns update method unit-test http add http://myuserid:secret@members.dyndns.org/nic/update?system=dyndns&hostname= mywebsite&myip=10.10.10.10The following are examples of URLs that can be used to update some HTTP DNS update services. These URLs are correct to the best of the knowledge of Cisco but have not been tested in all cases. Where the word “USERNAME:” appears in the URL, your account username at the HTTP site should be used. Where the word “PASSWORD” appears in the URL, your password for that account should be used:
Examples
http://USERNAME:PASSWORD@members.dyndns.org/nic/update?system=dyndns&hostname=<h>&myip=<a> !Requires “interval max 28 0 0 0" in the update method definition.Examples
http://cgi.tzo.com/webclient/signedon.html?TZOName=<h>&Email=USERNAME&TZOKey=PASSWORD&IP Address=<a>Examples
http://USERNAME:PASSWORD@members.easydns.com/dyn/ez-ipupdate.php?action=edit&myip=<a>& host_id=<h>Examples
http://USERNAME:PASSWORD@www.justlinux.com/bin/controlpanel/dyndns/jlc.pl?direst=1& username=USERNAME&password=PASSWORD&host=<h>&ip=<a>Examples
http://USERNAME:PASSWORD@www.dyns.cx/postscript.php?username=USERNAME&password=PASSWORD& host=<h>&ip=<a>Examples
http://USERNAME:PASSWORD@www.zoneedit.com/auth/dynamic.html?host=<h>&dnsto=<a>
NoteBecause these services are provided by the respective companies, the URLs may be subject to change or the service could be discontinued at any time. Cisco takes no responsibility for the accuracy or use of any of this information. The URLs were obtained using an application called “ez-ipupdate,” which is available for free on the Internet.
Related Commands
Command
Description
ddns
Specifies DDNS as the update method for A and PTR RRs.
debug dhcp
Displays debugging information about the DHCP client and monitors the status of DHCP packets.
debug ip ddns update
Enables debugging for DDNS updates.
debug ip dhcp server
Enables DHCP server debugging.
default
Specifies the command default.
host (host-list)
Specifies a list of hosts that will receive DDNS updates of A and PTR RRs.
internal
Specifies the internal Cisco IOS cache is used for DDNS updates of A and PTR RRs.
interval maximum
Specifies a maximum interval for DDNS updates of A and PTR RRs.
ip ddns update hostname
Enables a host to be used for DDNS updates of A and PTR RRs.
ip ddns update method
Enables DDNS as the update method and assigns a method name.
ip dhcp client update dns
Enables DDNS updates of A RRs using the same hostname passed in the hostname and FQDN options by a client.
ip dhcp-client update dns
Enables DDNS updates of A RRs using the same hostname passed in the hostname and FQDN options by a client.
ip dhcp update dns
Enables DDNS updates of A and PTR RRs for most address pools.
ip host-list
Specifies a list of hosts that will receive DDNS updates of A and PTR RRs.
show ip ddns update
Displays information about the DDNS updates.
show ip ddns update method
Displays information about the DDNS update method.
show ip host-list
Displays the assigned hosts in a list.
update dns
Dynamically updates a DNS with A and PTR RRs for some address pools.
import all
To import Dynamic Host Configuration Protocol (DHCP) option parameters into the DHCP server database, use the import all command in DHCP pool configuration mode. To disable this feature, use the no form of this command.
Command History
Release
Modification
12.1(2)T
This command was introduced.
12.2(33)SRA
This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX
This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.
Usage Guidelines
When the no import all command is used, the DHCP server deletes all “imported” option parameters that were added to the specified pool in the server database. Manually configured DHCP option parameters override imported DHCP option parameters.
Imported option parameters are not part of the router configuration and are not saved in NVRAM.
import dns-server
To import the Domain Name System (DNS) recursive name server option to a Dynamic Host Configuration Protocol (DHCP) for IPv6 client, use the import dns-servercommand in IPv6 DHCP pool configuration mode. To remove the available DNS recursive name server list, use the no form of this command.
Usage Guidelines
DHCP for IPv6 for stateless configuration allows a DHCP for IPv6 client to export configuration parameters (that is, DHCP for IPv6 options) to a local DHCP for IPv6 server pool. The local DHCP for IPv6 server can then provide the imported configuration parameters to other DHCP for IPv6 clients.
The DNS recursive name server option provides a list of one or more IPv6 addresses of DNS recursive name servers to which a client’s DNS resolver may send DNS queries. The DNS servers are listed in the order of preference for use by the client resolver.
The DNS recursive name server list option code is 23. For more information on DHCP options and suboptions, see the "DHCP Options" appendix in the Network Registrar User's Guide , Release 6.2.
import domain-name
To import the domain name search list option to a Dynamic Host Configuration Protocol (DHCP) for IPv6 client, use the import domain-namecommand in IPv6 DHCP pool configuration mode. To remove the domain name search list, use the no form of this command.
Usage Guidelines
DHCP for IPv6 for stateless configuration allows a DHCP for IPv6 client to export configuration parameters (that is, DHCP for IPv6 options) to a local DHCP for IPv6 server pool. The local DHCP for IPv6 server can then provide the imported configuration parameters to other DHCP for IPv6 clients.
The domain name search list option specifies the domain search list the client is to use when resolving hostnames with DNS.
The domain name search list option code is 24. For more information on DHCP options and suboptions, see the "DHCP Options" appendix in the Network Registrar User's Guide , Release 6.2.
import information refresh
To import the information refresh time option to a Dynamic Host Configuration Protocol (DHCP) for IPv6 client, use the import information refreshcommand in IPv6 DHCP pool configuration mode. To remove the specified refresh time, use the no form of this command.
Usage Guidelines
DHCP for IPv6 for stateless configuration allows a DHCP for IPv6 client to export configuration parameters (that is, DHCP for IPv6 options) to a local DHCP for IPv6 server pool. The local DHCP for IPv6 server can then provide the imported configuration parameters to other DHCP for IPv6 clients.
The information refresh time option specifies an upper bound for how long a client should wait before refreshing information retrieved from DHCP for IPv6. It is used only in Reply messages in response to Information Request messages. In other messages, there will usually be other options that indicate when the client should contact the server (for example, addresses with lifetimes).
The information refresh time option code is 32. For more information on DHCP options and suboptions, see the "DHCP Options" appendix in the Network Registrar User's Guide , Release 6.2.
import nis address
To import the network information service (NIS) address option to a Dynamic Host Configuration Protocol (DHCP) for IPv6 client, use the import nis address command in IPv6 DHCP pool configuration mode. To remove the NIS address, use the no form of this command.
Usage Guidelines
DHCP for IPv6 for stateless configuration allows a DHCP for IPv6 client to export configuration parameters (that is, DHCP for IPv6 options) to a local DHCP for IPv6 server pool. The local DHCP for IPv6 server can then provide the imported configuration parameters to other DHCP for IPv6 clients.
The NIS servers option provides a list of one or more IPv6 addresses of NIS servers available to send to the client. The client must view the list of NIS servers as an ordered list, and the server may list the NIS servers in the order of the server’s preference.
The NIS servers option code is 27. For more information on DHCP options and suboptions, see the "DHCPv6 Options" appendix in the Network Registrar User's Guide , Release 6.2.
import nis domain-name
To import the network information service (NIS) domain name option to a Dynamic Host Configuration Protocol (DHCP) for IPv6 client, use the import nis domain-name command in IPv6 DHCP pool configuration mode. To remove the domain name, use the no form of this command.
Usage Guidelines
DHCP for IPv6 for stateless configuration allows a DHCP for IPv6 client to export configuration parameters (that is, DHCP for IPv6 options) to a local DHCP for IPv6 server pool. The local DHCP for IPv6 server can then provide the imported configuration parameters to other DHCP for IPv6 clients.
The NIS domain name option provides a NIS domain name for the client.
The NIS domain name option code is 29.
import nisp address
To import the network information service plus (NIS+) servers option to a Dynamic Host Configuration Protocol (DHCP) for IPv6 client, use the import nisp address command in IPv6 DHCP pool configuration mode. To remove the NIS address, use the no form of this command.
Usage Guidelines
DHCP for IPv6 for stateless configuration allows a DHCP for IPv6 client to export configuration parameters (that is, DHCP for IPv6 options) to a local DHCP for IPv6 server pool. The local DHCP for IPv6 server can then provide the imported configuration parameters to other DHCP for IPv6 clients.
The NIS+ servers option provides a list of one or more IPv6 addresses of NIS+ servers available to send to the client. The client must view the list of NIS+ servers as an ordered list, and the server may list the NIS+ servers in the order of the server’s preference.
The NIS+ servers option code is 28. For more information on DHCP options and suboptions, see the "DHCPv6 Options" appendix in the Network Registrar User's Guide , Release 6.2.
Examples
The following example shows how to import the NIS+ address of an IPv6 server:
import nisp addressimport nisp domain-name
To import the network information service plus (NIS+) domain name option to a Dynamic Host Configuration Protocol (DHCP) for IPv6 client, use the import nisp domain-namecommand in IPv6 DHCP pool configuration mode. To remove the domain name, use the no form of this command.
Usage Guidelines
DHCP for IPv6 for stateless configuration allows a DHCP for IPv6 client to export configuration parameters (that is, DHCP for IPv6 options) to a local DHCP for IPv6 server pool. The local DHCP for IPv6 server can then provide the imported configuration parameters to other DHCP for IPv6 clients.
The NIS+ domain name option provides an NIS+ domain name for the client.
The NIS+ domain name option code is 30. For more information on DHCP options and suboptions, see the "DHCPv6 Options" appendix in the Network Registrar User's Guide , Release 6.2.
import sip address
To import the Session Initiation Protocol (SIP) server IPv6 address list option to the outbound SIP proxy server, use the import sip addresscommand in IPv6 DHCP pool configuration mode. To remove the SIP server IPv6 address list, use the no form of this command.
Usage Guidelines
Dynamic Host Configuration Protocol (DHCP) for IPv6 for stateless configuration allows a DHCP for IPv6 client to export configuration parameters (that is, DHCP for IPv6 options) to a local DHCP for IPv6 server pool. The local DHCP for IPv6 server can then provide the imported configuration parameters to other DHCP for IPv6 clients.
A SIP server is the host on which the outbound SIP proxy server is running.
The SIP server IPv6 address list option specifies a list of IPv6 addresses that indicate SIP outbound proxy servers available to the client. Servers must be listed in order of preference.
The SIP server IPv6 address list option code is 22. For more information on DHCP options and suboptions, see the "DHCP Options" appendix in the Network Registrar User's Guide , Release 6.2.
import sip domain-name
To import a Session Initiation Protocol (SIP) server domain-name list option to the outbound SIP proxy server, use the import sip domain-namecommand in IPv6 DHCP pool configuration mode. To remove the SIP server domain-name list, use the no form of this command.
Usage Guidelines
Dynamic Host Configuration Protocol (DHCP) for IPv6 for stateless configuration allows a DHCP for IPv6 client to export configuration parameters (that is, DHCP for IPv6 options) to a local DHCP for IPv6 server pool. The local DHCP for IPv6 server can then provide the imported configuration parameters to other DHCP for IPv6 clients.
A SIP server is the host on which the outbound SIP proxy server is running.
The SIP server domain-name list option contains the domain names of the SIP outbound proxy servers. Domain names must be listed in order of preference. The option may contain multiple domain names, but the client must try the records in the order listed. The client resolves the subsequent domain names only if attempts to contact the first one failed or yielded no common transport protocols between client and server or denoted a domain administratively prohibited by client policy.
The SIP server domain-name list option code is 21. For more information on DHCP options and suboptions, see the "DHCP Options" appendix in the Network Registrar User's Guide , Release 6.2.
import sntp address
To import the Simple Network Time Protocol (SNTP) address option to a Dynamic Host Configuration Protocol (DHCP) for IPv6 client, use the import sntp address command in IPv6 DHCP pool configuration mode. To remove the SNTP server address, use the no form of the command.
Usage Guidelines
DHCP for IPv6 for stateless configuration allows a DHCP for IPv6 client to export configuration parameters (that is, DHCP for IPv6 options) to a local DHCP for IPv6 server pool. The local DHCP for IPv6 server can then provide the imported configuration parameters to other DHCP for IPv6 clients.
The SNTP server option provides a list of one or more IPv6 addresses of SNTP servers available to the client for synchronization. The clients use these SNTP servers to synchronize their system time to that of the standard time servers.
Clients must treat the list of SNTP servers as an ordered list, and the server may list the SNTP servers in decreasing order of preference. The SNTP address option can be used only to configure information about SNTP servers that can be reached using IPv6.
The SNTP server option code is 31. For more information on DHCP options and suboptions, see the "DHCP Options" appendix in the Network Registrar User's Guide , Release 6.2.
information refresh
To specify the information refresh time to be sent to the client, use the information refreshcommand in IPv6 DHCP pool configuration mode. To remove the specified refresh time, use the no form of this command.
information refresh { days [ hours minutes ] | infinity }
no information refresh { days [ hours minutes ] | infinity }
Syntax Description
days
Refresh time specified in number of days. The default is 0 0 86400, which equals 24 hours.
hours
(Optional) Refresh time specified in number of hours.
minutes
(Optional) Refresh time specified in number of minutes. The minimum refresh time that can be used is 0 0 600, which is 10 minutes.
infinity
Sets the IPv6 value of 0xffffffff used to configure the information refresh time to infinity.
Command Default
Information refresh information is not sent to the client. The client refreshes every 24 hours if no refresh information is sent.
Usage Guidelines
Dynamic Host Configuration Protocol (DHCP) for IPv6 for stateless configuration allows a DHCP for IPv6 client to export configuration parameters (that is, DHCP for IPv6 options) to a local DHCP for IPv6 server pool. The local DHCP for IPv6 server can then provide the imported configuration parameters to other DHCP for IPv6 clients.
The information refresh time option specifies the maximum time a client should wait before refreshing information retrieved from DHCP for IPv6. It is only used in Reply messages in response to Information Request messages. In other messages, there will usually be other options that indicate when the client should contact the server (for example, addresses with lifetimes).
The maximum value for the information refresh period on the DHCP for IPv6 client is 7 days. The maximum value is not configurable.
The information refresh time option code is 32. For more information on DHCP options and suboptions, see the "DHCP Options" appendix in the Network Registrar User's Guide , Release 6.2.
internal (DDNS-update-method)
To specify an update method for Dynamic Domain Name System (DDNS) address (A) and pointer (PTR) Resource Records (RRs) as a Cisco IOS internal cache, use the internalcommand in DDNS-update-method configuration mode. To disable the internal dynamic updates, use the no form of this command.
Usage Guidelines
This command is useful in conjunction with turning on the internal Cisco IOS DNS name-server. The DNS name-server is enabled by using the ip dns server command. This command enables the name-server to reply to requests for an IP address associated with the hostname that was added to the internal name cache. Not all images have Cisco IOS DNS name-server functionality, so the internal command will not be available. Refer to Feature Navigator at http://www.cisco.com/go/fn to verify the name-server functionality in your image.
When the internal type of update is specified, an entry into the Cisco IOS name cache is added, which is basically the same as entering the ip host abc.com 10.0.0.1 command. The hostname “abc” and the IP address “10.0.0.1” are associated with an interface.
interval maximum
To specify a maximum interval at which Dynamic Domain Name System (DDNS) updates of address (A) and pointer (PTR) Resource Records (RRs) occur, use the interval maximumcommand in DDNS-update-method configuration mode. To disable the interval, use the no form of this command.
Syntax Description
days
Maximum interval, in days, at which updates occur. The range is from 0 to 365.
hours
Maximum interval, in hours, at which updates occur. The range is from 0 to 23.
minutes
Maximum interval, in minutes, at which updates occur. The range is from 0 to 59.
seconds
Maximum interval, in seconds, at which updates occur. The range is from 0 to 59.
Examples
The following example shows how to configure the update method, the maximum interval of the updates (globally), and the hostname on the interface:
interface ethernet1 ip ddns update hostname abc.dyndns.org ip ddns update mytest ip ddns update method mytest http add http://test:test@members.dyndns.org/nic/update?system=dyndns&hostname=myhost& myip=10.10.10.10 interval maximum 1 0 0 0interval minimum
To specify a minimum interval at which Dynamic Domain Name System (DDNS) updates of address (A) and pointer (PTR) Resource Records (RRs) occur, use the interval minimumcommand in DDNS-update-method configuration mode. To disable the minimum interval, use the no form of this command.
Syntax Description
days
Minimum interval, in days, at which updates occur. The range is from 0 to 365.
hours
Minimum interval, in hours, at which updates occur. The range is from 0 to 23.
minutes
Minimum interval, in minutes, at which updates occur. The range is from 0 to 59.
seconds
Minimum interval, in seconds, at which updates occur. The range is from 0 to 59.
Usage Guidelines
DDNS updates for interfaces acquiring their address through DHCP occur every time the DHCP lease is renewed. If the lease is renewed more often than the minimum update interval needed, then a problem may occur with the updates. Sites accepting HTTP-style updates, such as DynDNS.org, may report an error if the updates occur too often. The interval minimum command forces the system to ignore updates that would occur too often.
Currently, the DynDNS.org policy is that updates can not be made more often than once every 10 minutes. This policy is subject to change in the future. The interval minimum command helps to guarantee that updates will not be sent too often.
Examples
The following example shows how to configure the minimum interval so that updates would not be sent to DynDNS.org any more often than once every 15 minutes.
! ip ddns update method my test interval minimum 0 0 15 0 http add http://test:test@members.dyndns.org/nic/update?system=dyndns&hostname=myhostname& myip=10.10.10 .1Related Commands
Command
Description
ddns
Specifies DDNS as the update method for A and PTR RRs.
host (host-list)
Specifies a list of hosts that will receive DDNS updates of A and PTR RRs.
http
Specifies HTTP as the update method for A and PTR RRs.
internal
Specifies the internal Cisco IOS cache is used for DDNS udpates of A and PTR RRs.
interval maximum
Specifies a maximum interval at which DDNS updates of A and pointer PTR Resource RRs occur.
ip ddns update hostname
Enables a host to be used for DDNS updates of A and PTR RRs.
ip ddns update method
Enables DDNS as the update method and assigns a method name.
ip dhcp client update dns
Enables DDNS updates of A RRs using the same hostname passed in the hostname and FQDN options by a client.
ip dhcp-client update dns
Enables DDNS updates of A RRs using the same hostname passed in the hostname and FQDN options by a client.
ip dhcp update dns
Enables DDNS updates of A and PTR RRs for most address pools.
ip host-list
Specifies a list of hosts that will receive DDNS updates of A and PTR RRs.
show ip ddns update
Displays information about the DDNS updates.
show ip ddns update method
Displays information about the DDNS update method.
show ip host-list
Displays the assigned hosts in a list.
update dns
Dynamically updates a DNS with A and PTR RRs for some address pools.
ip address
To set a primary or secondary IP address for an interface, use the ip address command in interface configuration mode. To remove an IP address or disable IP processing, use the noform of this command.
ip address ip-address mask [ secondary [ vrf vrf-name ] ]
no ip address ip-address mask [ secondary [ vrf vrf-name ] ]
Syntax Description
ip-address
IP address.
mask
Mask for the associated IP subnet.
secondary
(Optional) Specifies that the configured address is a secondary IP address. If this keyword is omitted, the configured address is the primary IP address.
Note If the secondary address is used for a VRF table configuration with the vrf keyword, the vrf keyword must be specified also.
vrf
(Optional) Name of the VRF table. The vrf-name argument specifies the VRF name of the ingress interface.
Command History
Release
Modification
10.0
This command was introduced.
12.2(28)SB
The vrf keyword and vrf-name argument were introduced.
12.2(33)SRA
This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2(33)SRB
Support for IPv6 was added.
12.2(33)SXH
This command was integrated into Cisco IOS Release 12.2(33)SXH.
12.2(33)SB
This command was integrated into Cisco IOS Release 12.2(33)SB.
12.2(33)SCB
This command was integrated into Cisco IOS Release 12.2(33)SCB.
Cisco IOS XE Release 2.1
This command was introduced on Cisco ASR 1000 Series Routers.
15.1(1)S
This command was integrated into Cisco IOS Release 15.1(1)S.
15.2(3)T
This command was integrated into Cisco IOS Release 15.2(3)T.
Usage Guidelines
An interface can have one primary IP address and multiple secondary IP addresses. Packets generated by the Cisco IOS software always use the primary IP address. Therefore, all routers and access servers on a segment should share the same primary network number.
Hosts can determine subnet masks using the Internet Control Message Protocol (ICMP) mask request message. Routers respond to this request with an ICMP mask reply message.
You can disable IP processing on a particular interface by removing its IP address with the no ip address command. If the software detects another host using one of its IP addresses, it will print an error message on the console.
The optional secondary keyword allows you to specify an unlimited number of secondary addresses. Secondary addresses are treated like primary addresses, except the system never generates datagrams other than routing updates with secondary source addresses. IP broadcasts and Address Resolution Protocol (ARP) requests are handled properly, as are interface routes in the IP routing table.
Secondary IP addresses can be used in a variety of situations. The following are the most common applications:
- There may not be enough host addresses for a particular network segment. For example, your subnetting allows up to 254 hosts per logical subnet, but on one physical subnet you need 300 host addresses. Using secondary IP addresses on the routers or access servers allows you to have two logical subnets using one physical subnet.
- Many older networks were built using Level 2 bridges. The judicious use of secondary addresses can aid in the transition to a subnetted, router-based network. Routers on an older, bridged segment can be easily made aware that many subnets are on that segment.
- Two subnets of a single network might otherwise be separated by another network. This situation is not permitted when subnets are in use. In these instances, the first network is extended, or layered on top of the second network using secondary addresses.
NoteIf any router on a network segment uses a secondary address, all other devices on that same segment must also use a secondary address from the same network or subnet. Inconsistent use of secondary addresses on a network segment can very quickly cause routing loops.
NoteWhen you are routing using the Open Shortest Path First (OSPF) algorithm, ensure that all secondary addresses of an interface fall into the same OSPF area as the primary addresses.
To transparently bridge IP on an interface, you must perform the following two tasks:
- Disable IP routing (specify the no ip routing command).
- Add the interface to a bridge group, see the bridge-group command.
To concurrently route and transparently bridge IP on an interface, see the bridge crbcommand.
Examples
In the following example, 192.108.1.27 is the primary address and 192.31.7.17 and 192.31.8.17 are secondary addresses for Ethernet interface 0:
interface ethernet 0 ip address 192.108.1.27 255.255.255.0 ip address 192.31.7.17 255.255.255.0 secondary ip address 192.31.8.17 255.255.255.0 secondaryIn the following example, Ethernet interface 0/1 is configured to automatically classify the source IP address in the VRF table vrf1:
interface ethernet 0/1 ip address 10.108.1.27 255.255.255.0 ip address 10.31.7.17 255.255.255.0 secondary vrf vrf1 ip vrf autoclassify sourceRelated Commands
Command
Description
bridge crb
Enables the Cisco IOS software to both route and bridge a given protocol on separate interfaces within a single router.
bridge-group
Assigns each network interface to a bridge group.
ip vrf autoclassify
Enables VRF autoclassify on a source interface.
match ip source
Specifies a source IP address to match to required route maps that have been set up based on VRF connected routes.
route-map
Defines the conditions for redistributing routes from one routing protocol into another, or to enable policy routing.
set vrf
Enables VPN VRF selection within a route map for policy-based routing VRF selection.
show ip arp
Displays the ARP cache, in which SLIP addresses appear as permanent ARP table entries.
show ip interface
Displays the usability status of interfaces configured for IP.
show route-map
Displays static and dynamic route maps.
ip address dhcp
To acquire an IP address on an interface from the DHCP, use the ip address dhcpcommand in interface configuration mode. To remove any address that was acquired, use the no form of this command.
ip address dhcp [ client-id interface-type number ] [ hostname hostname ]
no ip address dhcp [ client-id interface-type number ] [ hostname hostname ]
Syntax Description
client-id
(Optional) Specifies the client identifier. By default, the client identifier is an ASCII value. The client-id interface-type numberoption sets the client identifier to the hexadecimal MAC address of the named interface.
interface-type
(Optional) Interface type. For more information, use the question mark (?) online help function.
number
(Optional) Interface or subinterface number. For more information about the numbering syntax for your networking device, use the question mark (?) online help function.
hostname
(Optional) Specifies the hostname.
hostname
(Optional) Name of the host to be placed in the DHCP option 12 field. This name need not be the same as the hostname entered in global configuration mode.
Command Default
The hostname is the globally configured hostname of the router. The client identifier is an ASCII value.
Command History
Release
Modification
12.1(2)T
This command was introduced.
12.1(3)T
This command was modified. The client-idkeyword and interface-type numberargument were added.
12.2(3)
This command was modified. The hostnamekeyword and hostnameargument were added. The behavior of the client-id interface-type numberoption changed. See the “Usage Guidelines” section for details.
12.2(8)T
This command was modified. The command was expanded for use on PPP over ATM (PPPoA) interfaces and certain ATM interfaces.
12.2(33)SRA
This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX
This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.
15.1(3)T
This command was modified. Support was provided on the tunnel interface.
Usage Guidelines
NotePrior to Cisco IOS Release 12.2(8)T, the ip address dhcp command could be used only on Ethernet interfaces.
The ip address dhcp command allows any interface to dynamically learn its IP address by using the DHCP protocol. It is especially useful on Ethernet interfaces that dynamically connect to an Internet service provider (ISP). Once assigned a dynamic address, the interface can be used with the Port Address Translation (PAT) of Cisco IOS Network Address Translation (NAT) to provide Internet access to a privately addressed network attached to the router.
The ip address dhcp command also works with ATM point-to-point interfaces and will accept any encapsulation type. However, for ATM multipoint interfaces you must specify Inverse ARP via the protocol ip inarp interface configuration command and use only the aa15snap encapsulation type.
Some ISPs require that the DHCPDISCOVER message have a specific hostname and client identifier that is the MAC address of the interface. The most typical usage of the ip address dhcp client-id interface-type number hostname hostname command is when interface-typeis the Ethernet interface where the command is configured and interface-type numberis the hostname provided by the ISP.
A client identifier (DHCP option 61) can be a hexadecimal or an ASCII value. By default, the client identifier is an ASCII value. The client-id interface-type numberoption overrides the default and forces the use of the hexadecimal MAC address of the named interface.
NoteBetween Cisco IOS Releases 12.1(3)T and 12.2(3), the client-id optional keyword allows the change of the fixed ASCII value for the client identifier. After Release 12.2(3), the optional client-id keyword forces the use of the hexadecimal MAC address of the named interface as the client identifier.
If a Cisco router is configured to obtain its IP address from a DHCP server, it sends a DHCPDISCOVER message to provide information about itself to the DHCP server on the network.
If you use the ip address dhcp command with or without any of the optional keywords, the DHCP option 12 field (hostname option) is included in the DISCOVER message. By default, the hostname specified in option 12 will be the globally configured hostname of the router. However, you can use the ip address dhcp hostname hostname command to place a different name in the DHCP option 12 field than the globally configured hostname of the router.
The no ip address dhcp command removes any IP address that was acquired, thus sending a DHCPRELEASE message.
You might need to experiment with different configurations to determine the one required by your DHCP server. The table below shows the possible configuration methods and the information placed in the DISCOVER message for each method.
Table 2 Configuration Method and Resulting Contents of the DISCOVER Message Configuration Method
Contents of DISCOVER Messages
ip address dhcp
The DISCOVER message contains “cisco- mac-address -Eth1” in the client ID field. The mac-address is the MAC address of the Ethernet 1 interface and contains the default hostname of the router in the option 12 field.
ip address dhcp hostname hostname
The DISCOVER message contains “cisco- mac-address -Eth1” in the client ID field. The mac-address is the MAC address of the Ethernet 1 interface, and contains hostname in the option 12 field.
ip address dhcp client-id ethernet 1
The DISCOVER message contains the MAC address of the Ethernet 1 interface in the client ID field and contains the default hostname of the router in the option 12 field.
ip address dhcp client-id ethernet 1 hostname hostname
The DISCOVER message contains the MAC address of the Ethernet 1 interface in the client ID field and contains hostname in the option 12 field.
Examples
In the examples that follow, the command ip address dhcp is entered for Ethernet interface 1. The DISCOVER message sent by a router configured as shown in the following example would contain “cisco- mac-address -Eth1” in the client-ID field, and the value abc in the option 12 field.
hostname abc ! interface Ethernet 1 ip address dhcpThe DISCOVER message sent by a router configured as shown in the following example would contain “cisco- mac-address -Eth1” in the client-ID field, and the value def in the option 12 field.
hostname abc ! interface Ethernet 1 ip address dhcp hostname defThe DISCOVER message sent by a router configured as shown in the following example would contain the MAC address of Ethernet interface 1 in the client-id field, and the value abc in the option 12 field.
hostname abc ! interface Ethernet 1 ip address dhcp client-id Ethernet 1The DISCOVER message sent by a router configured as shown in the following example would contain the MAC address of Ethernet interface 1 in the client-id field, and the value def in the option 12 field.
hostname abc ! interface Ethernet 1 ip address dhcp client-id Ethernet 1 hostname defip address pool (DHCP)
To enable the IP address of an interface to be automatically configured when a Dynamic Host Configuration Protocol (DHCP) pool is populated with a subnet from IP Control Protocol (IPCP) negotiation, use the ip address pool command in interface configuration mode. To disable autoconfiguring of the IP address of the interface, use the no form of this command.
Usage Guidelines
Use this command to automatically configure the IP address of a LAN interface when there are DHCP clients on the attached LAN that should be serviced by the DHCP pool on the router. The DHCP pool obtains its subnet dynamically through IPCP subnet negotiation.
ip arp entry learn
To specify the maximum number of learned Address Resolution Protocol (ARP) entries, use the ip arp entry learn command in global configuration mode. To return to the default settings, use the no form of this command.
Usage Guidelines
The ip arp entry learn command is available on the Cisco 7600 series routers, which can support a maximum limit of learned ARP entries of 256,000. If a memory card is installed on the router the maximum limit is extended to 512,000.
When the number of ARP entries that can be created by the system is not limited, memory exhaustion can cause system instability. The ip arp entry learn command overcomes this problem by defining a maximum number of learned ARP entries.
The limit is not enforced on nonlearned entries. Upon reaching the learn ARP entry threshold limit, or 80 percent of the configured maximum limit, the system will generate a syslog message with a priority set to Level 3 (LOG_NOTICE). Upon reaching the configured maximum limit, the system starts discarding newly learned ARP entries and generates a syslog message. The priority will be set to Level 3 (LOG_NOTICE). The system administrator will have to take appropriate action.
A syslog message is also generated when the number of learned ARP entries in the ARP table decreases from the maximum configured limit to the permit threshold limit, or 95 percent of the maximum configured limit to notify the system administrator that the ARP table is back to normal operation.
The default behavior of the system is not to enforce a maximum limit of learned ARP entries on the system.
When a user tries to configure a maximum limit value for the number of ARP entries that is lower than the current number of ARP entries in the system, the configuration will be rejected with an error message.
The following example configures a maximum limit of the number of learned ARP entries of 512,000:
Router# configure terminal Router(config)# ip arp entry learn 512000
