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Cisco IOS Interface Command Reference, Release 12.2
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About the Cisco IOS Software Documentation
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Using Cisco IOS Software
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Interface Commands - Introduction
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Interface Commands (aps-authenticate - cut-through)
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Interface Commands (dce-terminal-timing enable - interface)
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Interface Commands (interface fastethernet - loopback line)
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Interface Commands (loopback remote - service module t1 remote-loopback)
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Interface Commands (service-module t1 timeslots - show hub)
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Interface Commands (show interfaces - show interfaces vg-anylan)
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Interface Commands (show pas caim - tx-queue-limit)
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Dial Shelf Management Commands
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Online index for Cisco IOS Interface Comand Reference
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Feedback
Table Of Contents
ip director server availability
ip director server port availability
interface fastethernet
To select a particular Fast Ethernet interface for configuration, use the interface fastethernet command in global configuration mode.
Cisco 4500 and 4700 Series
interface fastethernet number
Cisco 7200 Series
interface fastethernet slot/port
Cisco 7500 Series
interface fastethernet slot/port-adapter/port
Syntax Description
Defaults
No FastEthernet interface will be configured.
Command Modes
Global configuration
Command History
11.2
This command was introduced.
11.3
The default encapsulation type was changed to ARPA.
Usage Guidelines
This command does not have a no form.
Examples
The following example configures Fast Ethernet interface 0 for standard ARPA encapsulation (the default setting) on a Cisco 4500 or 4700 series router:
Router(config)# interface fastethernet 0Related Commands
show interfaces fastethernet
Displays information about the Fast Ethernet interfaces.
interface gigabitethernet
To configure a Gigabit Ethernet interface and enter interface configuration mode, use the interface gigabitethernet slot/port command in global configuration mode.
interface gigabitethernet slot/port
To configure a Gigabit Ethernet interface and enter interface configuration mode on a Cisco 7200 VXR router used as a router shelf in an AS5800 Universal Access Server, use the interface gigabitethernet router-shelf/slot/port command in global configuration mode.
interface gigabitethernet router-shelf/slot/port
Syntax Description
router-shelf
Router shelf in a Cisco AS5800 Universal Access Server.
slot
Slot number of the interface.
port
Port number on the interface.
Defaults
No Gigabit Ethernet interface is created.
Command Modes
Global configuration
Command History
Usage Guidelines
Many features are enabled on a per-interface basis. The interface gigabitethernet global configuration command modifies the operation of the Gigabit Ethernet interface on the Cisco 7200-I/O-GE+E.
Examples
This example illustrates the command syntax for creating a Gigabit Ethernet interface:
Router(config)# interface gigabitethernet 0/0Router(config-if)#Related Commands
Checks the status and configuration settings of the Gigabit Ethernet interface of the Cisco 7200-I/O-GE+E.
interface group-async
To create a group interface that will serve as master to which asynchronous interfaces can be associated as members, use the interface group-async command in global configuration mode. To restore the default, use the no form of this command.
interface group-async unit-number
no interface group-async unit-number
Syntax Description
Defaults
No interfaces are designated as group masters.
Command Modes
Global configuration
Usage Guidelines
Using the interface group-async command, you create a single asynchronous interface to which other interfaces are associated as members using the group-range command. This one-to-many configuration allows you to configure all associated member interfaces by entering one command on the group master interface, rather than entering this command on each individual interface. You can create multiple group masters on a device; however, each member interface can be associated only with one group.
Examples
The following example defines asynchronous group master interface 0:
Router(config)# interface group-async 0Related Commands
interface multilink
To create a multilink bundle or enter multilink interface configuration mode, use the interface multilink command in global configuration mode. To remove a multilink bundle, use the no form of this command.
interface multilink group-name
no interface multilink
Syntax Description
Defaults
No interfaces are configured.
Command Modes
Global configuration
Command History
Examples
The following example shows how to create multilink bundle 1:
interface multilink 1ip address 192.168.11.4 255.255.255.192encapsulation pppppp multilinkkeepaliveRelated Commands
multilink-group
Designates an interface as part of a multilink leased line bundle.
ppp multilink fragmentation
Enables PPP multilink fragmentation.
interface port-channel
To specify a Fast EtherChannel and enter interface configuration mode, use the interface port-channel command in global configuration mode.
interface port-channel channel-number
Syntax Description
Defaults
No Fast EtherChannel is specified.
Command Modes
Global configuration
Command History
11.1 CA
This command was introduced.
12.1(5)T
This command was integrated into 12.1(5)T.
Usage Guidelines
The Fast EtherChannel feature allows multiple Fast Ethernet point-to-point links to be bundled into one logical link to provide bidirectional bandwidth of up to 800 Mbps. Fast EthernetChannel can be configured between networking devices that support EtherChannel capability.
You can configure the port-channel interface as you would do to any Fast Ethernet interface.
After you create a port-channel interface, you assign Fast Ethernet interfaces (up to four) to it. For information on how to assign a Fast Ethernet interface to a port-channel interface, refer to the channel-group interface configuration command.
CautionThe port-channel interface is the routed interface. Do not enable Layer 3 addresses on the physical Fast Ethernet interfaces. Do not assign bridge groups on the physical Fast Ethernet interfaces because it creates loops. Also, you must disable spanning tree.
Caution
As you work with the interface port-channel command, consider the following points:
•
•
•
This command does not have a no form.
Examples
The following example creates a port-channel interface with a channel group number of 1 and adds three Fast Ethernet interfaces to port-channel 1:
Router(config)# interface port-channel 1Router(config-if)# ip address 10.1.1.10 255.255.255.0Router(config)# interface fastethernet 1/0/0Router(config-if)# channel-group 1Router(config)# interface fastethernet 4/0/0Router(config-if)# channel-group 1Router(config)# interface fastethernet 5/0/0Router(config-if)# channel-group 1Related Commands
interface pos
To specify the Packet OC-3 interface on the Packet-over-SONET (POS) interface processor and enter interface configuration mode, use the interface pos command in global configuration mode.
Cisco 7000 and Cisco 7500 Series Routers with VIPs
interface pos slot/port-adapter/port
Cisco 7200 Series Routers
interface pos slot/port
Syntax Description
Defaults
No POS interface is specified.
Command Modes
Global configuration
Command History
Usage Guidelines
This command does not have a no form.
Examples
The following example specifies the single Packet OC-3 interface on the POS OC-3 port adapter in slot 2:
Router(config)# interface pos 2/0interface range
To execute commands on multiple subinterfaces at the same time, use the interface range command in global configuration command mode.
interface range {fastethernet interfacenumber - interfacenumber | gigabitethernet interfacenumber - interfacenumber | loopback number | tunnel number | port-channel number | vlan number | macro word}
Syntax Description
Defaults
No default behavior or values
Command Modes
Global configuration
Command History
Usage Guidelines
Configuration Changes
All configuration changes made to a range of subinterfaces are saved to NVRAM, but the range itself does not get savedto NVRAM. Use the define interface-range command to create and save a range.
You can enter the range in two ways:
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You can specify either the interfaces or the name of a range macro. A range must consist of the same interface type, and the interfaces within a range cannot span slots.
You cannot specify both an interface range and a macro keyword in the same command. After creating a macro, the CLI does not allow you to enter additional ranges. Likewise, if you have already entered an interface range, the CLI does not allow you to enter a macro.
The spaces around the dash in the interface range command syntax are required. For example, using a Catlyst 6500 router, the command interface range fastethernet 1 - 6 is valid; the command interface range fastethernet 1-6 is not valid.
VLAN Ranges
When you define a Catalyst Vlans, valid values are from 1 to 4094. The last VLAN number cannot exceed 4094.
You cannot use the interface range command to create switch virtual interfaces (SVIs). You must create SVIs with individual interface VLAN commands. You can use the interface range command on existing VLAN SVIs. To display VLAN SVIs, enter the show running-config command. VLANs not displayed cannot be used in the interface range command.
The commands entered under the interface range command are applied to all existing VLAN SVIs.
Examples
The following example shows how to use the interface range command to configure a fastethernet range:
Router(config)# interface range fastethernet5/1 - 4Router(config-if-range)#
The following example shows how to set a vlan:
Cisco-65K(config)#interface range vlan 123Cisco-65K(config-if-range)#The following example configures the Fast Ethernet subinterfaces within the range from 5/1.1 to 5/1.4 and applies the following VLAN IDs to those subinterfaces:
Fast Ethernet5/1.1 = VLAN ID 301 (vlan-id)Fast Ethernet5/1.2 = VLAN ID 302 (vlan-id = 301 + 2 - 1 = 302)Fast Ethernet5/1.3 = VLAN ID 303 (vlan-id = 301 + 3 - 1 = 303)Fast Ethernet5/1.4 = VLAN ID 304 (vlan-id = 301 + 4 - 1 = 304)Router(config)# interface range fastethernet5/1 - 4Router(config-if)# encapsulation dot1q 301Router(config-if)# no shutdownRouter(config-if)#*Oct 6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet5/1.1, changed state to up*Oct 6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet5/1.2, changed state to up*Oct 6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet5/1.3, changed state to up*Oct 6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet5/1.4, changed state to up*Oct 6 08:24:36: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet5/1.1, changed state to up*Oct 6 08:24:36: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet5/1.2, changed state to up*Oct 6 08:24:36: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet5/1.3, changed state to up*Oct 6 08:24:36: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet5/1.4, changed state to upThe following example shows how to execute a range macro:
Router(config)# interface range macro macro1The following exampe shows how to set a gigabitethernet range:
Router(config)# interface range gigabitethernet1/1 - 6Router(config-if-range)#
The following example shows how to use the loopback interface:
Router(config)# interface range loopback 34567Router(config-if-range)#
The following example shows how to use the tunnel interface:
Router(config)# interface range tunnel 55555Router(config-if-range)#
The following example shows how to use the port-channel interface:
Router(config)# interface range port-channel 343Router(config-if-range)#
Related Commands
interface vg-anylan
To specify the interface on a 100VG-AnyLAN port adapter and enter interface configuration mode on Cisco 7200 series routers and Cisco 7500 series routers, use the interface vg-anylan command in global configuration mode.
Cisco 7200 Series Routers
interface vg-anylan slot/port
Cisco 7500 Series Routers with VIPs
interface vg-anylan slot/port-adapter/port
Syntax Description
Defaults
No interfaces are specified.
Command Modes
Global configuration
Command History
Usage Guidelines
The 100VG-AnyLAN port adapter provides a single interface port that is compatible with and specified by IEEE 802.12. The 100VG-AnyLAN port adapter provides 100 Mbps over Category 3 or Category 5 unshielded twisted-pair (UTP) cable with RJ-45 terminators, and supports IEEE 802.3 Ethernet packets.
You configure the 100VG-AnyLAN port adapter as you would any Ethernet or Fast Ethernet interface. The 100VG-AnyLAN port adapter can be monitored with the IEEE 802.12 Interface MIB.
This command does not have a no form.
Examples
The following example specifies the 100VG-AnyLAN port adapter in the first port adapter in slot 1:
Router(config)# interface vg-anylan 1/0/0Related Commands
international bit
To set the E3 international bit in the G.751 frame used by the PA-E3 port adapter, use the international bit command in interface configuration mode. To return to the default international bit, use the no form of this command.
international bit {0 | 1} {0 | 1}
no international bit
Syntax Description
0 | 1
Specifies the value of the first international bit in the G.751 frame. The default is 0.
0 | 1
Specifies the value of the second international bit in the G.751 frame. The default is 0.
Defaults
The default value for each bit is 0.
Command Modes
Interface configuration
Command History
Usage Guidelines
The international bit command sets bits 6 and 8, respectively, of set II in the E3 frame.
To verify the international bit configured on the interface, use the show controllers serial EXEC command.
Examples
The following example sets the international bit to 1 1 on the PA-E3 port adapter in slot 1, port adapter slot 0, interface 0:
Router(config)# interface serial 1/0/0Router(config-if)# international bit 1 1Related Commands
national bit
Sets the E3 national bit in the G.751 frame used by the PA-E3 port adapter.
show controllers serial
Displays information that is specific to the interface hardware.
invert data
To invert the data stream, use the invert data command in interface configuration mode. This command applies only to the Cisco 7000 series routers with the RSP7000 and RSP7000CI, Cisco 7200 series routers, and Cisco 7500 series routers. To disable inverting the data stream, use the no form of this command.
invert data
no invert data
Syntax Description
This command has no arguments or keywords.
Defaults
Data is not inverted.
Command Modes
Interface configuration
Command History
Usage Guidelines
T1 Line Without B8ZS Encoding
If the interface on the PA-8T and PA-4T+ synchronous serial port adapters and the PA-T3 and PA-2T3 synchronous serial port adapters is used to drive a dedicated T1 line that does not have B8ZS encoding (a method to avoid 15 zeros), the data stream must be inverted (both transmitting and receiving data) either in the connecting CSU/DSU or in the interface.
Inverting is a method of avoiding excessive zeroes that is superseded by the use of B8ZS encryption. This option could be needed for use with legacy equipment that supports this option. By inverting the High-Level Data Link Control (HDLC) data stream, the HDLC zero insertion algorithm becomes a ones insertion algorithm that satisfies the T1 requirements. Be careful not to invert data both on the interface and on the CSU/DSU because two data inversions will cancel each other out.
AMI Line Coding
If the interface on the CT3IP uses alternate mark inversion (AMI) line coding, you must also invert the data on the T1 channel. For more information, see the t1 linecode controller configuration command.
Examples
The following example inverts data on serial interface 3/1/0:
Router(config)# interface serial 3/1/0Router(config-if)# invert dataRelated Commands
t1 linecode
Specifies the type of linecoding used by the T1 channels on the CT3IP in Cisco 7500 series routers.
invert rxclock
To configure UIO serial port 0 or 1 on the Cisco MC3810 when the cable connected is DCE type, use the invert rxclock command in interface configuration mode. The command inverts the phase of the RX clock on the UIO serial interface, which does not use the T1/E1 interface. To disable the phase inversion, use the no form of this command.
invert rxclock
no invert rxclock
Syntax Description
This command has no arguments or keywords.
Defaults
The receive clock signal is not inverted.
Command Modes
Interface configuration
Command History
Examples
The following example inverts the clock signal on serial interface 1:
Router(config)# interface serial 1Router(config-if)# invert rxclockinvert-transmit-clock
The invert-transmit-clock command is replaced by the invert txclock command. See the description of the invert-txclock command in this chapter for information on the transmit clock signal.
invert txclock
To invert the transmit (TX) clock signal, use the invert txclock command in interface configuration mode. To return the TX clock signal to its initial state, use the no form of this command.
invert txclock
no invert txclock
Syntax Description
This command has no arguments or keywords.
Defaults
Transmit clock signal is not inverted.
Command Modes
Interface configuration
Command History
10.0
This command was introduced.
11.3
The invert-transmit-clock command was replaced by the invert txclock command.
Usage Guidelines
Delays between the serial clock transmit external (SCTE) clock and data transmission indicate that the transmit clock signal might not be appropriate for the interface rate and length of cable being used. Different ends of the wire can have variances that differ slightly. The invert txclock command compensates for these variances. This command replaces the invert-transmit-clock command.
Systems that use long cables or cables that are not transmitting the TxC signal (transmit echoed clock line, also known as TXCE or SCTE clock) can experience high error rates when operating at the higher transmission speeds. For example, if a PA-8T synchronous serial port adapter is reporting a high number of error packets, a phase shift might be the problem. Inverting the clock might correct this shift.
When a PA-8T or PA-4T+ port adapter interface is DTE, the invert txclock command inverts the TxC signal it received from the remote DCE. When the PA-8T or PA-4T+ port adapter interface is DCE, this command changes the signal back to its original phase.
Examples
The following example inverts the clock signal on serial interface 3/0:
Router(config)# interface serial 3/0Router(config-if)# invert txclockip director default-weights
To configure default weight metrics for the DistributedDirector, use the ip director default-weights command in global configuration mode. To restore the default, use the no form of this command.
ip director default-weights {[drp-int n] [drp-ext n] [drp-ser n] [drp-rtt n] [random n] [admin n] [portion n] [availability n] [route-map n]}
no ip director default-weights {[drp-int n] [drp-ext n] [drp-ser n] [drp-rtt n] [random n] [admin n] [portion n] [availability n] [route-map n]}
Syntax Description
Defaults
The availability default value is 65,535.
Command Modes
Global configuration
Command History
11.1(18)IA
This command was introduced.
12.1(5)T
The availability and route-map metrics were added.
Usage Guidelines
Not all of the metrics need to be configured; however, at least one metric must be configured when this command is used.
Default weights are used for all host names sorted by the DistributedDirector. To override default weights for a certain host, specify host-specific weights in the private DNS server configuration.
When the associated metric is referenced in the sorting decision, it will always be multiplied by the appropriate metric weight. In this way, you can specify that some metrics be weighted more than others. You may determine the weights that you want to use through experimentation. The weights given do not need to add up to 100.
The new availability metric allows the DistributedDirector to attempt to create a TCP connection to each distributed server on a configured port over a configurable time interval.
Examples
The following command configures default weights for the internal and external metrics:
ip director default-weights drp-int 10 drp-ext 90Related Commands
ip director dfp
To configure the DistributedDirector Dynamic Feedback Protocol (DFP) agent with which the DistributedDirector should communicate, use the ip director dfp command in global configuration mode. To turn off the DFP agent, use the no form of this command.
ip director dfp ip-address [port] [retry n] [attempts n] [timeout n]
no ip director dfp ip-address [port] [retry n] [attempts n] [timeout n]
Syntax Description
Syntax Description
The port default value is 8080.
The retry default value is 5 attempts.
The attempts default value is 10,000 seconds.
The timeout default value is 10,000 seconds.
Command Modes
Global configuration
Command History
Usage Guidelines
A connection is attempted a specified number of times with a delay of a specified number of seconds between each attempt. Once a connection is established, the DFP protocol will run. If a time interval update has not occurred for this DFP session, the connection breaks and is reestablished as described above.
Examples
The following example configures the DistributedDirector to communicate with a specified DFP agent:
ip director dfp 10.0.0.1 retry 3 attempts 60 timeout 6000
ip director dfp security
To configure a security key for use when connecting to the Dynamic Feedback Protocol (DFP) client named, use the ip director dfp security command in global configuration mode. To turn off the security key, use the no form of this command.
ip director dfp security ip-address md5 string [timeout]
no ip director dfp security ip-address md5 string [timeout]
Syntax Description
Defaults
The timeout default value is 0 seconds.
Command Modes
Global configuration
Command History
Usage Guidelines
The ip director dfp security command should be entered before configuring the ip director dfp command, resulting in a connection being made, but it can be entered independently of making a connection.
DFP allows servers to take themselves Out-of-Service and place themselves back In-Service. This function could result in a security risk because a network that is hacked could be shut down even though all the servers are still performing. An optional security vector is included in DFP to allow each message to be verified. The security vector is used to describe the security algorithm being used and to provide the data for that algorithm. The security vector itself is also extensible in that it specifies which security algorithm is being used. This specification allows different levels of security from MD5 to Data Encryption Standard (DES) to be used without overhauling the protocol and disrupting any installed base of equipment. If a receiving unit is configured for the specified security type, all DFP packets must contain that security vector or they are ignored. If a receiving unit is not configured for any security type, the security vector does not have to be present, and if it is present, it is ignored while the rest of the message is processed normally.
Examples
The following example configures the security key hello:
ip director dfp security 10.0.0.1 md5 hello 60Related Commands
Configures the DistributedDirector DFP agent with which the DistributedDirector should communicate.
ip director host priority
To configure the order in which the DistributedDirector considers metrics when picking a server, use the ip director host priority command in global configuration mode. To turn off metric priorities, use the no form of this command.
ip director host host-name priority {[drp-int n] [drp-ext n] [drp-ser n] [drp-rtt n] [random n] [admin n] [portion n] [availability n] [route-map n]}
no ip director host host-name priority {[drp-int n] [drp-ext n] [drp-ser n] [drp-rtt n] [random n] [admin n] [portion n] [availability n] [route-map n]}
Syntax Description
Defaults
The availability default value is 65,535.
Command Modes
Global configuration
Command History
11.1(18)IA
This command was introduced.
12.1(5)T
The availability and route-map metrics were added.
Usage Guidelines
Not all of the metrics need to be specified, but at least one must be specified.
The new availability metric allows the DistributedDirector to attempt to create a TCP connection to each distributed server on a configured port over a configurable time interval.
If multiple servers end up with the same metric value, the next metric is considered to determine the "best" server. If multiple metrics have the same priority value, the metrics are added to obtain a composite metric. For example, if two metrics have the same priority value, they are first multiplied by their weight values (if specified) and then added together to form the composite metric.
If you do not specify weights for a group of distributed servers, there are no default weights for the Director, and if you have specified priority values, the weight values are set to 1.
Any metrics that have a nonzero weight and that are assigned no priority value are set to a priority value of 101. They are considered after all other metrics that have priority values. As a result, if no priority values are specified for any metric, metrics are treated additively to form one composite metric.
If you do not use priority and multiple servers have the same metric value, the server whose last IP address was looked at will be returned as the "best" server. If you want to return a random IP address in the case of a tie, use metric priority with the random metric as the last criterion.
To turn off all priorities on all metrics associated with the defined host name, use the no ip director host priority command. You can turn off the priority for a specific metric or metrics using the no ip director host host-name priority [drp-int n] [drp-ext n] [drp-ser n] [drp-rtt n] [random n] [admin n] [portion n] [availability n] [route-map n] command.
Examples
The following example sets the external metric as the first priority and the administrative metric as the second priority:
ip director host www.xyz.com priority drp-ext 1 admin 2Related Commands
ip director host connect
Enables the DistributedDirector to verify that a server is available.
show ip director hosts
Displays the DistributedDirector host information.
ip director host weights
To set host-specific weights for the metrics that the DistributedDirector uses to determine the best server within a specific host name, use the ip director host weights command in global configuration mode. To turn off weights for a host, use the no form of this command.
ip director host host-name weights {[drp-int n] [drp-ext n] [drp-ser n] [drp-rtt n] [random n] [admin n] [portion n] [availability n] [route-map n]}
no ip director host host-name weights {[drp-int n] [drp-ext n] [drp-ser n] [drp-rtt n] [random n] [admin n] [portion n] [availability n] [route-map n]}
Syntax Description
Note
Defaults
The availability default value is 65,535.
Command Modes
Global configuration
Command History
11.1(25)IA
This command was introduced.
12.0(3)T
This command was integrated into Cisco IOS Release 12.0(3)T.
12.1(5)T
The availability and route-map metrics were added.
Usage Guidelines
Use host-specific weights when you want to use different metric weights for different virtual host names (for example, www.xyz.com and ftp.xyz.com).
The new availability metric allows the DistributedDirector to attempt to create a TCP connection to each distributed server on a configured port over a configurable time interval.
If desired, host-specific weights can instead be configured on the DistributedDirector default DNS server.
For example, you could configure host-specific weights with the following DNS TXT record:
hostname in txt "ciscoDD: weights {[drp-int n] [drp-ext n] [drp-ser n] [random n] [admin n]}"To use the default weights for all metrics associated with this host name, use the no ip director host weights command. To use the default weights for a specific metric or metrics, use the no ip director host host-name weights [drp-int n] [drp-ext n] [drp-ser n] [drp-rtt n] [random n] [admin n] [portion n] [availability n] [route-map n] command.
Examples
The following example sets the DRP internal metric to 4:
ip director host www.xyz.com weights drp-int 4Related Commands
Configures default weight metrics for the DistributedDirector.
Displays information about the current status of the DistributedDirector connections with a particular DFP agent.
ip director server availability
To configure a default availability value for all ports on a server, use the ip director server availability command in global configuration mode. To restore the default, use the no form of this command.
ip director server ip-address availability {availability-value | dfp [availability-value]}
no ip director server ip-address availability {availability-value | dfp [availability-value]}
Syntax Description
Defaults
The availability default value is 65,535.
Command Modes
Global configuration
Command History
Usage Guidelines
There are two methods for specifying a default availability value. These two methods exist because the LocalDirector and the DistributedDirector deal with values in two different ways. All metrics for the DistributedDirector are arranged such that lower is better; however the LocalDirector load information is calculated such that higher is better. Thus, the DistributedDirector translates the metric value upon receipt from the LocalDirector by subtracting the availability from the maximum possible value of 65,535.
Examples
To configure a default availability to be used if there is no other valid availability information, the following configuration would suffice. The following example shows how to specify the LocalDirector load and DistributedDirector availability, respectively:
ip director server 10.0.0.1 availability dfp 1ip director server 10.0.0.1 availability 65534To make the availability clear and to allow for specifying numbers in both schemes easily, there are two methods of specifying availability information. If the servers are running multiple serves, it may be necessary to configure the default availability value on a per-port basis by using the ip director server port availability command.
ip director server 10.0.0.1 port availability dfp 65535ip director server 10.0.0.20 port availability dfp 65535Related Commands
ip director server port availability
To configure a default availability value for a specific port on a server, use the ip director server port availability command in global configuration mode. To restore the default, use the no form of this command.
ip director server ip-address port availability {availability-value | dfp [availability-value]}
no ip director server ip-address port availability {availability-value | dfp [availability-value]}
Syntax Description
Defaults
The availability default value is 65,535.
Command Modes
Global configuration
Command History
Usage Guidelines
There are two methods for specifying a default availability value. These two methods exist because the LocalDirector and the DistributedDirector deal with values in two different ways. All metrics for the DistributedDirector are arranged such that lower is better; however the LocalDirector load information is calculated such that higher is better. Thus, the DistributedDirector translates the metric value upon receipt from the LocalDirector by subtracting the availability from the maximum possible value of 65,535.
Examples
To make the availability clear and to allow for specifying numbers in both schemes easily, there are two methods of specifying availability information. If the servers are running multiple serves, it may be necessary to configure the default availability value on a per-port basis by using the ip director server port availability command.
ip director server 10.0.0.1 port availability dfp 65535ip director server 10.0.0.20 port availability dfp 65535To configure a default availability to be used if there is no other valid availability information, the following configuration would suffice. The following example shows how to specify the LocalDirector load and DistributedDirector availability, respectively:
ip director server 10.0.0.1 availability dfp 1ip director server 10.0.0.1 availability 65534Related Commands
keepalive
To enable keepalive packets and to specify the number of times that the Cisco IOS software tries to send keepalive packets without a response before bringing down the interface, or before bringing the tunnel protocol down for a specific interface, use the keepalive command in interface configuration mode. When the keepalive feature is enabled, a keepalive packet is sent at the specified time interval to keep the interface active. To turn off keepalive packets entirely, use the no form of this command.
keepalive [period [retries]]
no keepalive [period [retries]]
Syntax Description
Defaults
seconds: 10 seconds
retries: 5
Command Modes
Interface configuration
Command History
Usage Guidelines
Keepalive Time Interval
You can configure the keepalive time interval, which is the frequency at which the Cisco IOS software sends messages to itself (Ethernet and Token Ring) or to the other end (serial and tunnel), to ensure that a network interface is alive. The interval is adjustable in 1-second increments down to 1 second. An interface is declared down after three update intervals have passed without receiving a keepalive packet unless the retry value is set higher.
Note
Setting the keepalive timer to a low value is very useful for rapidly detecting Ethernet interface failures (transceiver cable disconnecting, cable not terminated, and so on).
Line Failure
A typical serial line failure involves losing Carrier Detect (CD) signal. Because this sort of failure is typically noticed within a few milliseconds, adjusting the keepalive timer for quicker routing recovery is generally not useful.
Keepalive Packets with Tunnel Interfaces
GRE keepalive packets may be sent from both sides of a tunnel, or from just one side. If they are sent from both sides, the period and retry parameters can be different at each side of the link. If you configure keepalives on only one side of the tunnel, the tunnel interface on the sending side might perceive the tunnel interface on the receiving side to be down because the sending interface is not receiving keepalives. From the receiving side of the tunnel, the link appears normal because no keepalives were enabled on the second side of the link.
Dropped Packets
Keepalive packets are treated as ordinary packets, so it is possible that they will be dropped. To reduce the chance that dropped keepalive packets will cause the tunnel interface to be taken down, increase the number of retries.
Note
GRE Tunnels with IPsec
When using GRE with IPsec, the keepalives are encrypted like any other traffic. As with user data packets, if the IKE and IPsec security associations are not already active on the GRE tunnel, the first GRE keepalive packet will trigger IKE/IPsec initialization.
Default Behaviors
If you enter only the keepalive command with no arguments, defaults for both arguments are used.
If you enter only the keepalive command and the timeout parameter, the default number of retries (3) is used.
If you enter the no keepalive command, keepalive packets are disabled on the interface.
Examples
The following example sets the keepalive interval to 3 seconds:
Router(config)# interface ethernet 0Router(config-if)# keepalive 3The following example sets the keepalive interval to 3 seconds and the retry value to 7:
Router(config)# interface tunnel 1Router(config-if)# keepalive 3 7lbo
To set a cable length longer than 655 feet for a DS-1 link, use the lbo command in interface configuration mode on the interface for a T1 link. To delete the lbo long value, use the no form of this command.
lbo {long {gain26 | gain36} {-15db | -22.5db | -7.5db | 0db} | short {133 | 266 | 399 | 533 | 655}}
no lbo
Syntax Description
Defaults
gain26 and 0db
Command Modes
Interface configuration
Command History
Usage Guidelines
This command is supported on T1 links only.
Each T1 port can operate in long-haul or short-haul mode. In long haul mode, the user must specify the gain and the line build out. In short-haul mode, the user must specify the cable length in feet.
The transmit attenuation value is best obtained by experimentation. If the signal received by the far-end equipment is too strong, reduce the transmit level by entering additional attenuation.
Examples
On Cisco 7100 or 7200 series routers, the following example specifies a pulse gain of 36 decibels and a decibel pulse rate of -7.5 decibels:
interface atm 1/2lbo long gain36 -7.5dblex burned-in-address
To set the burned-in MAC address for a LAN Extender interface, use the lex burned-in-address command in interface configuration mode. To clear the burned-in MAC address, use the no form of this command.
lex burned-in-address ieee-address
no lex burned-in-address
Syntax Description
Defaults
No burned-in MAC address is set.
Command Modes
Interface configuration
Command History
Usage Guidelines
Use this command only on a LAN Extender interface that is not currently active (not bound to a serial interface).
Examples
The following example sets the burned-in MAC address on LAN Extender interface 0:
Router(config)# interface serial 4Router(config-if)# encapsulation pppRouter(config)# interface lex 0Router(config-if)# lex burned-in-address 0000.0c00.0001Router(config-if) ip address 10.108.172.21 255.255.255.0lex input-address-list
To assign an access list that filters on MAC addresses, use the lex input-address-list command in interface configuration mode. To remove an access list from the interface, use the no form of this command.
lex input-address-list access-list-number
no lex input-address-list
Syntax Description
access-list-number
Number of the access list assigned with the access-list global configuration command. It can be a number from 700 to 799.
Defaults
No access lists are preassigned to a LAN Extender interface.
Command Modes
Interface configuration
Command History
Usage Guidelines
Use the lex input-address-list command to filter the packets that are allowed to pass from the LAN Extender to the core router. The access list filters packets on the basis of the source MAC address.
The LAN Extender interface does not process MAC-address masks. Therefore, you should omit the mask from the access-list commands.
For LAN Extender interfaces, an implicit permit everything entry is automatically defined at the end of an access list. Note that this default differs from other access lists, which have an implicit deny everything entry at the end of each access list.
Examples
The following example applies access list 710 to LAN Extender interface 0. This access list denies all packets from MAC address 0800.0214.2776 and permits all other packets.
Router(config-if)# access-list 710 deny 0800.0214.2776Router(config)# interface lex 0Router(config-if)# lex input-address-list 710Related Commands
access-list
Configures the access list mechanism for filtering frames by protocol type or vendor code.
lex input-type-list
To assign an access list that filters Ethernet packets by type code, use the lex input-type-list command in interface configuration mode. To remove an access list from an interface, use the no form of this command.
lex input-type-list access-list-number
no lex input-type-list
Syntax Description
access-list-number
Number of the access list that you assigned with the access-list command. It can be a number in the range 200 to 299.
Defaults
No access lists are preassigned to a LAN Extender interface.
Command Modes
Interface configuration
Command History
Usage Guidelines
Filtering is done on the LAN Extender chassis.
The LAN Extender interface does not process masks. Therefore, you should omit the mask from the access-list commands.
For LAN Extender interfaces, an implicit permit everything entry is automatically defined at the end of an access list. Note that this default differs from other access lists, which have an implicit deny everything entry at the end of each access list.
Examples
The following example applies access list 220 to LAN Extender interface 0. This access list denies all AppleTalk packets (packets with a type field of 0x809B) and permits all other packets.
Router(config-if)# access-list 220 deny 0x809B 0x0000Router(config)# interface lex 0Router(config-if)# lex input-type-list 220Related Commands
access-list
Configures the access list mechanism for filtering frames by protocol type or vendor code.
lex priority-group
To activate priority output queueing on the LAN Extender, use the lex priority-group command in interface configuration mode. To disable priority output queueing, use the no form of this command.
lex priority-group group
no lex priority-group
Syntax Description
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
To define queueing priorities, use the priority-list protocol global configuration command. Note that you can use only the following forms of this command:
priority-list list protocol protocol {high | medium | normal | low}
priority-list list protocol bridge {high | medium | normal | low} list list-number
If you specify a protocol that does not have an assigned Ethernet type code, such as x25, stun, or pad, it is ignored and will not participate in priority output queueing.
Examples
The following example activates priority output queueing on LAN Extender interface 0:
Router(config-if)# priority-list 5 protocol bridge medium list 701Router(config-if)# lex interface 0Router(config-if)# lex priority-group 5Related Commands
priority-list protocol
Establishes queueing priorities based on the protocol type.
lex retry-count
To define the number of times to resend commands to the LAN Extender chassis, use the lex retry-count command in interface configuration mode. To return to the default value, use the no form of this command.
lex retry-count number
no lex retry-count number
Syntax Description
number
Number of times to retry sending commands to the LAN Extender. It can be a number in the range 0 to 100. The default is 10.
Defaults
10 retries
Command Modes
Interface configuration
Command History
Usage Guidelines
After the router has sent a command the specified number of times without receiving an acknowledgment from the LAN Extender, it stops sending the command altogether.
Examples
The following example resends commands 20 times to the LAN Extender:
Router(config-if)# lex interface 0Router(config-if)# lex retry-count 20Related Commands
lex timeout
Defines the amount of time to wait for a response from the LAN Extender.
lex timeout
To define the amount of time to wait for a response from the LAN Extender, use the lex timeout command in interface configuration mode. To return to the default time, use the no form of this command.
lex timeout milliseconds
no lex timeout [milliseconds]
Syntax Description
milliseconds
Time, in milliseconds, to wait for a response from the LAN Extender before resending the command. It can be a number in the range 500 to 60,000. The default is 2000 ms.
Defaults
2000 ms (2 seconds)
Command Modes
Interface configuration
Command History
Usage Guidelines
The lex timeout command defines the amount of time that the router waits to receive an acknowledgment after having sent a command to the LAN Extender.
Examples
The following example causes unacknowledged packets to be resent at 4-second intervals:
Router(config-if)# lex interface 0Router(config-if)# lex timeout 4000Related Commands
lex retry-count
Defines the number of times to resend commands to the LAN Extender chassis.
linecode
To select the line-code type for T1 or E1 lines, use the linecode command in controller configuration mode.
linecode {ami | b8zs | hdb3}
Syntax Description
Defaults
AMI is the default for T1 lines.
High-density bipolar 3 is the default for E1 lines.
Command Modes
Controller configuration
Command History
Usage Guidelines
Use this command in configurations in which the router or access server must communicate with T1 fractional data lines. The T1 service provider determines which line-code type, either ami or b8zs, is required for your T1 circuit. Likewise, the E1 service provider determines which line-code type, either ami or hdb3, is required for your E1 circuit.
This command does not have a no form.
Examples
The following example specifies B8ZS as the line-code type:
Router(config-controller)# linecode b8zsline-termination
To specify the line termination for the E1 port on a trunk card, use the line-termination command in controller configuration mode. To return to the default line termination, use the no form of this command.
line-termination {75-ohm | 120-ohm}
no line-termination
Syntax Description
75-ohm
Specifies 75-ohm unbalanced termination.
120-ohm
Specifies 120-ohm balanced termination. This is the default.
Defaults
120-ohms
Command Modes
Controller configuration
Command History
Usage Guidelines
To determine the line termination setting for the port, use the show controllers e1 command.
Examples
In the following example, the line termination is set to 75 ohms for the E1 port located in shelf 6, slot 0, port 0:
Router# configure terminalRouter(config)# controller e1 6/0/0Router(config-controller)# line-termination 75-ohmRouter(config-controller)# exitRouter(config)# exitRouter#Related Commands
show controllers e1
Displays information about the E1 links supported by the NPM (Cisco 4000) or MIP (Cisco 7500 series).
link-test
To reenable the link-test function on a port on an Ethernet hub of a Cisco 2505 or Cisco 2507 router, use the link-test command in hub configuration mode. Use the no form of this command to disable this feature if a pre-10BaseT twisted-pair device not implementing link test is connected to the hub port.
link-test
no link-test
Syntax Description
This command has no arguments or keywords.
Defaults
Enabled
Command Modes
Hub configuration
Command History
Usage Guidelines
This command applies to a port on an Ethernet hub only. Disable this feature if a 10BaseT twisted-pair device at the other end of the hub does not implement the link test function.
Examples
The following example disables the link test function on hub 0, ports 1 through 3:
Router(config)# hub ethernet 0 1 3Router(config-hub)# no link-testRelated Commands
hub
Enables and configures a port on an Ethernet hub of a Cisco 2505 or Cisco 2507 router.
local-lnm
To enable Lanoptics Hub Networking Management of a PCbus Token Ring interface, use the local-lnm command in interface configuration mode. To disable Lanoptics Hub Networking Management, use the no form of this command.
local-lnm
no local-lnm
Syntax Description
This command has no arguments or keywords.
Defaults
Management is not enabled.
Command Modes
Interface configuration
Command History
Usage Guidelines
The Token Ring interface on the AccessPro PC card can be managed by a remote LAN manager over the PCbus interface. At present, the Lanoptics Hub Networking Management software running on an IBM compatible PC is supported.
Examples
The following example enables Lanoptics Hub Networking Management:
Router(config-if)# local-lnmlogging event
To enable notification of interface, subinterface, and Frame Relay data link connection identifier (DLCI) data link status changes, use the logging event command in interface configuration mode. To disable notification, use the no form of this command.
logging event {dlci-status-change | link-status | subif-link-status [ignore-bulk]}
no logging event {dlci-status-change | link-status | subif-link-status [ignore-bulk]}
Syntax Description
Defaults
For system images, notification of interface, subinterface, and Frame Relay DLCI data link status changes is enabled by default.
For boot images, notification of Frame Relay subinterface and DLCI data link status changes is disabled by default. Notification of interface data link status changes is enabled by default.
Command Modes
Interface configuration
Command History
Examples
The following example shows how to enable notification of subinterface link status changes:
Router(config-if)# logging event subif-link-statusThe following are examples of Frame Relay DLCI and subinterface status change notification messages filtered by the logging event command:
00:16:22: %FR-5-DLCICHANGE: Inteface Serial3/0/0:1 - DLCI 105 state changed to INACTIVE00:16:22: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial3/0/0:1.5, changed state to downlogging-events
to print typical T3 controller Up and Down messages on a Channelized T3 Port Adapter, use the logging-events command in T3 controller configuration mode. Use the no form of this command to disable printing of the T3 controller Up and Down messages.
logging-events [detail]
[no] logging-events
Syntax Description
detail
(Optional) Enables printing the reason code when a T3 controller changes from the Up to Down state.
Defaults
The logging-events command is the default.
Command Modes
T3 controller configuration
Command History
Usage Guidelines
When the no logging-events command disables printing of the T3 controller Up and Down messages, these messages will neither appear on the console nor in the logs.
Examples
The following example uses the logging-events [detail] command to show the Out-of-Frame (OOF) reason code when the T3 controller changes from an Up state to a Down state:
Router(config-controller)# logging-events detail*Jun 19 17:47:50: %CONTROLLER-5-DOWNDETAIL: Controller T3 4/1, changed state to down due to OOFRelated Commands
t1 logging-events
Prints the typical T1 controller Up and Down messages on a channelized T3 port adapter.
loopback (interface)
To diagnose equipment malfunctions between the interface and device, use the loopback command in interface configuration mode. To disable the test, use the no form of this command.
loopback
no loopback
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
Loopback on HSSI Cards
On High-Speed Serial Interface (HSSI) cards, the loopback function configures a two-way internal and external loop on the HSA applique of the specific interface.
Loopback on MCI and SCI Serial Interface Cards
On MCI and SCI serial interface cards, the loopback functions when a CSU/DSU or equivalent device is attached to the router or access server. The loopback command loops the packets through the CSU/DSU to configure a CSU loop, when the device supports this feature.
Loopback on MCI and MEC Ethernet Cards
On the MCI and MEC Ethernet cards, the interface receives back every packet it sends when the loopback command is enabled. Loopback operation has the additional effect of disconnecting network server functionality from the network.
Loopback on CSC-FCI FDDI Cards
On the CSC-FCI FDDI card, the interface receives back every packet it sends when the loopback command is enabled. Loopback operation has the additional effect of disconnecting network server functionality from the network.
Loopback on Token Ring Interface Cards
On all Token Ring interface cards (except the 4-megabit CSC-R card), the interface receives back every packet it sends when the loopback command is enabled. Loopback operation has the additional effect of disconnecting network server functionality from the network.
Active Loopback Interfaces
To show interfaces currently in loopback operation, use the show interfaces loopback EXEC command.
Note
Examples
The following example configures the loopback test on Ethernet interface 4:
Router(config)# interface ethernet 4Router(config-if)# loopbackRelated Commands
down-when-looped
Configures an interface to inform the system it is down when loopback is detected.
show interfaces loopback
Displays information about the loopback interface.
loopback (E3/T3 interface)
To loop the serial interface on a PA-E3 or PA-T3 port adapter, use the loopback command in interface configuration mode. To remove the loopback, use the no form of this command.
PA-E3 Port Adapter
loopback {dte | local | network {line | payload}}
no loopback
PA-T3 Port Adapter
loopback {dte | local | network {line | payload} | remote}
no loopback
Syntax Description
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
Use this command for troubleshooting purposes.
To verify that a loopback is configured on the interface, use the show interfaces serial or show interfaces loopback EXEC command.
Examples
The following example configures the serial interface located in slot 3/0/0 for a local loopback:
Router(config)# interface serial 3/0/0Router(config-if)# loopback localRelated Commands
loopback (T1 interface)
To loop individual T1 channels on the CT3IP in Cisco 7000 series routers with the RSP7000 and RSP7000CI and in Cisco 7500 series routers, use the loopback command in interface configuration mode. To remove the loopback, use the no form of this command.
loopback [local | network {line | payload} | remote {line {fdl {ansi | bellcore} | inband} | payload [fdl] [ansi]}]
no loopback
Syntax Description
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
Use this command for troubleshooting purposes.
To better diagnose T1 provisioning problems, you can place the remote CSU or remote SmartJack into loopback. The loopback remote line fdl interface configuration command allows you to place either the CSU or the SmartJack into loopback:
•
•
When both are configured, transmission of LOF indication (yellow alarm) takes priority over transmission of some FDL messages.
If the remote loopback appears not to be working, use the show controllers t3 command to determine if the given T1 is currently attempting to transmit a LOF indication (yellow alarm):
Router# show controllers t3 0/0/0:2T3 0/0/0 is up.CT3 H/W Version: 5, CT3 ROM Version: 1.2, CT3 F/W Version: 2.5.9Mx H/W version: 2, Mx ucode ver: 1.34T1 2 is down, speed: 1536 kbs, non-inverted datatimeslots: 1-24FDL per AT&T 54016 spec.Transmitter is sending LOF Indication.Receiver is getting AIS.If the transmitter is sending a LOF indication, as in the previous example, stop the transmission of the LOF indication (yellow alarm) with the no t1 yellow generation configuration command as shown in the following example:
Router(config)# controllers t3 0/0/0Router(config-controll)# no t1 2 yellow generationRouter(config-controll)# Ctrl-DTo verify that the transmission of the LOF indication (yellow alarm) has stopped, use the show controllers t3 command:
Router# show controlloers t3 0/0/0:2T3 0/0/0 is up.CT3 H/W Version: 5, CT3 ROM Version: 1.2, CT3 F/W Version: 2.5.9Mx H/W version: 2, Mx ucode ver: 1.34T1 2 is down, speed: 1536 kbs, non-inverted datatimeslots: 1-24FDL per AT&T 54016 spec.Receiver is getting AIS.Framing is ESF, Line Code is B8ZS, Clock Source is Internal.Yellow Alarm Generation is disabledThen retry the remote loopback command. When diagnosis is complete, remember to reenable the LOF indication (yellow alarm).
You can also loopback all the T1 channels by using the loopback (CT3IP) interface configuration command.
Examples
The following example configures T1 channel 5 for a local loopback:
Router(config)# interface serial 3/0/0:5Router(config-if)# loopback localRelated Commands
loopback (T3 controller)
To loop the entire T3 (all 28 T1 channels) on the CT3 in a Cisco AS5800 universal access server or on the CT3IP in Cisco 7500 series routers, use the loopback command in controller configuration mode. To remove the loopback, use the no form of this command.
loopback [local | network | remote]
no loopback
Syntax Description
Defaults
Disabled
Command Modes
Controller configuration
Command History
Usage Guidelines
Use this command for troubleshooting purposes.
You can also loopback each T1 channel by using the loopback interface configuration command for T1.
For more information, refer to the "Troubleshoot the T3 and T1 Channels" section in the "Configuring Serial Interfaces" chapter of the Cisco IOS Interface Configuration Guide.
Examples
The following example configures the CT3 or CT3IP for a local loopback:
Router(config)# controller t3 3/0/0Router(config-controller)# loopback localRelated Commands
loopback applique
To configure an internal loop on the High Speed Serial Interface (HSSI) applique, use the loopback applique command in interface configuration mode. To remove the loop, use the no form of this command.
loopback applique
no loopback applique
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
This command loops the packets within the applique to provide a way to test communication within the router or access server. It is useful for sending pings to yourself to check functionality of the applique.
To show interfaces that are currently in loopback operation, use the show interfaces loopback EXEC command.
Examples
The following example configures the loopback test on the HSSI applique:
Router(config)# interface serial 1Router(config-if)# loopback appliqueRelated Commands
loopback dte
To loop packets back to the DTE from the CSU/DSU, when the device supports this feature, use the loopback dte command in interface configuration mode. To remove the loop, use the no form of this command.
loopback dte
no loopback dte
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
This command is useful for testing the DTE-to-DCE cable.
This command is used to test the performance of the integrated CSU/DSU. Packets are looped from within the CSU/DSU back to the serial interface of the router. Send a test ping to see if the packets successfully looped back. To cancel the loopback test, use the no loopback dte command.
When using the 4-wire 56/64-kbps CSU/DSU module, an out-of-service signal is transmitted to the remote CSU/DSU.
To show interfaces that are lcurrently in loopback operation, use the show interfaces loopback EXEC command.
Examples
The following example configures the loopback test on the DTE interface:
Router(config)# interface serial 0Router(config-if)# loopback dteRelated Commands
loopback line
To loop packets completely through the CSU/DSU to configure the CSU loop, use the loopback line command in interface configuration mode. To remove the loop, use the no form of this command.
loopback line [payload]
no loopback line [payload]
Syntax Description
payload
(Optional) Configures a loopback point at the DSU and loops data back to the network on an integrated CSU/DSU.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
This command is useful for testing the DCE device (CSU/DSU) itself. When the loopback line command is configured on the 2-wire 56-kbps CSU/DSU module or the 4-wire 56/64-kbps CSU/DSU modules, the network data loops back at the CSU and the router data loops back at the DSU. If the CSU/DSU is configured for switched mode, you must have an established connection to perform a payload-line loopback. To loop the received data through the minimum amount of CSU/DSU circuitry, issue the loopback line command.
When you issue the loopback line payload command on an integrated CSU/DSU module, the router cannot transmit data through the serial interface for the duration of the loopback. Choosing the DSU as a loopback point loops the received-network data through the maximum amount of CSU/DSU circuitry. Data is not looped back to the serial interface. An active connection is required when operating in switched mode for payload loopbacks.
If you enable the loopback line command on the fractional T1/T1 module, the CSU/DSU performs a full-bandwidth loopback through the CSU portion of the module and data transmission through the serial interface is interrupted for the duration of the loopback. No reframing or corrections of bipolar violation errors or cyclic redundancy check (CRC) errors are performed. When you configure the loopback line payload command on the FT1/T1 module, the CSU/DSU performs a loopback through the DSU portion of the module. The loopback line payload command reframes the data link, regenerates the signal, and corrects bipolar violations and Extended Super Frame CRC errors.
When performing a T1-line loopback with Extended Super Frame, communication over the facilities data link is interrupted, but performance statistics are still updated. To show interfaces currently in loopback operation, use the show service-module EXEC command.
To show interfaces that are currently in loopback operation on other routers, use the show interfaces loopback EXEC command.
Examples
The following example configures the loopback test on the DCE device:
Router(config)# interface serial 1Router(config-if)# loopback lineThe following example shows how to configure a payload loopback on a Cisco 2524 or 2525 router:
Router1(config-if)# loopback line payloadLoopback in progressRouter1(config-if)# no loopback lineThe following example shows the output on a Cisco 2524 or 2525 router when you loop a packet in switched mode without an active connection:
Router1(config-if)# service-module 56k network-type switchedRouter1(config-if)# loopback line payloadNeed active connection for this type of loopback% Service module configuration command failed: WRONG FORMAT.Related Commands
show interfaces loopback
Displays information about the loopback interface.
show service-module
Displays the performance report for an integrated CSU/DSU.
