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Table Of Contents
BGP Prefix-Based Outbound Route Filtering
Prerequisites for BGP Prefix-Based Outbound Route Filtering
Restrictions for BGP Prefix-Based Outbound Route Filtering
Information About BGP Prefix-Based Outbound Route Filtering
BGP Prefix-Based Outbound Route Filtering Overview
Enabling BGP Prefix-Based Outbound Route Filtering
Benefits of BGP Prefix-Based Outbound Route Filtering
How to Configure BGP Prefix-Based Outbound Route Filtering
Configuring BGP Prefix-Based Outbound Route Filtering
Verifying BGP Prefix-Based Outbound Route Filtering
Verifying the Local BGP Prefix-Based Outbound Route Filtering Configuration
Verifying the BGP Prefix-Based Outbound Route Filtering Configuration of a Remote Peer
Verifying the Receipt of the Outbound Filter by the Remote Peer
neighbor capability orf prefix-list
BGP Prefix-Based Outbound Route Filtering
The BGP Prefix-Based Outbound Route Filtering feature uses Border Gateway Protocol (BGP) outbound route filter (ORF) send and receive capabilities to minimize the number of BGP updates that are sent between BGP peers. Configuring this feature can help reduce the amount of system resources required for generating and processing routing updates by filtering out unwanted routing updates at the source. For example, this feature can be used to reduce the amount of processing required on a router that is not accepting full routes from a service provider network.
Feature History for BGP Prefix-Based Outbound Route Filtering
Finding Support Information for Platforms and Cisco IOS Software Images
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Contents
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Prerequisites for BGP Prefix-Based Outbound Route Filtering
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Prerequisites for BGP Prefix-Based Outbound Route Filtering
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Restrictions for BGP Prefix-Based Outbound Route Filtering
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Information About BGP Prefix-Based Outbound Route Filtering
To configure BGP prefix-based outbound route filtering, you must understand the following concepts:
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BGP Prefix-Based Outbound Route Filtering Overview
The BGP Prefix-Based Outbound Route Filtering feature uses Border Gateway Protocol (BGP) outbound route filter (ORF) send and receive capabilities to minimize the number of BGP updates that are sent between BGP peers. Configuring this feature can help reduce the amount of system resources required for generating and processing routing updates by filtering out unwanted routing updates at the source. For example, this feature can be used to reduce the amount of processing required on a router that is not accepting full routes from a service provider network.
Enabling BGP Prefix-Based Outbound Route Filtering
The BGP Prefix-Based Outbound Route Filtering feature is enabled through the advertisement of ORF capabilities to peer routers. The advertisement of the ORF capability indicates that a BGP speaker will accept a prefix list from a neighbor and apply the prefix list to locally configured ORFs (if any exist). When this capability is enabled, the BGP speaker can install the inbound prefix list filter to the remote peer as an outbound filter, which reduces unwanted routing updates.
The BGP Prefix-Based Outbound Route Filtering feature can be configured with send and/or receive ORF capabilities. The local peer advertises the ORF capability in send mode. The remote peer receives the ORF capability in receive mode and applies the filter as an outbound policy. The local and remote peers exchange updates to maintain the ORF on each router. Updates are exchanged between peer routers by address family depending on the ORF prefix list capability that is advertised. The remote peer starts sending updates to the local peer after a route refresh has been configured with the clear ip bgp command or after an ORF prefix list with immediate status is processed. The BGP speaker will continue to apply the inbound prefix list to received updates after the speaker pushes the inbound prefix list to the remote peer.
Benefits of BGP Prefix-Based Outbound Route Filtering
The BGP Prefix-Based Outbound Route Filtering feature can limit the number of unwanted routing updates, which will reduce the amount of resources required for routing update generation and processing. This feature also reduces the amount of resources required to receive and discard routes that would otherwise be filtered out.
How to Configure BGP Prefix-Based Outbound Route Filtering
This section contains the following procedures:
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Configuring BGP Prefix-Based Outbound Route Filtering
The BGP Prefix-Based Outbound Route Filtering supports prefix length matching, wild-card based prefix matching, and exact address prefix matching for address family support. This feature can be configured on a router to send or receive ORF capabilities with either the send or receive keywords. This feature can also be configured on a router to both send and receive ORF capabilities with the both keyword.
Prerequisites
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Restrictions
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SUMMARY STEPS
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DETAILED STEPS
Examples
Router-A Configuration (Sender)
The following example creates an outbound route filter and configures Router-A (10.1.1.1) to advertise the filter to Router-B (172.16.1.2). An IP prefix list named FILTER is created to specify the 192.168.1.0/24 subnet for outbound route filtering. The ORF send capability is configured on Router-A so that Router-A can advertise the outbound route filter to Router-B.
ip prefix-list FILTER seq 10 permit 192.168.1.0/24!router bgp 100address-family ipv4 unicastneighbor 172.16.1.2 remote-as 200neighbor 172.16.1.2 ebgp-multihopneighbor 172.16.1.2 capability orf prefix-list sendneighbor 172.16.1.2 prefix-list FILTER inexitRouter-B Configuration (Receiver)
The following example configures Router-B to advertise the ORF receive capability to Router-A. Router-B will install the outbound route filter, defined in the FILTER prefix list, after ORF capabilities have been exchanged. An inbound soft reset is initiated on Router-B at the end of this configuration to activate the outbound route filter.
router bgp 200address-family ipv4 unicastneighbor 10.1.1.1 remote-as 100neighbor 10.1.1.1 ebgp-multihop 255neighbor 10.1.1.1 capability orf prefix-list receiveendclear ip bgp 10.1.1.1 in prefix-filter!
Note
What to Do Next
You can verify that this feature is configured correctly with the show running-config and show ip bgp neighbors command. Go to the Verifying BGP Prefix-Based Outbound Route Filtering section for instructions and example output.
Verifying BGP Prefix-Based Outbound Route Filtering
This section provides verification examples for the BGP Prefix-Based Outbound Route Filtering feature. In each example, the relevant lines of the output are shown in bold text.
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Verifying the Local BGP Prefix-Based Outbound Route Filtering Configuration
The following example output from the show running-config privileged EXEC command shows the local configuration of a router. The router is configured to advertise the ORF send mode capability to the 172.16.1.2 neighbor.
Router# show running-config | begin bgprouter bgp 100bgp log-neighbor-changesneighbor 172.16.1.2 remote-as 200neighbor 172.16.1.2 ebgp-multihop 255!address-family ipv4neighbor 172.16.1.2 activateneighbor 172.16.1.2 capability orf prefix-list sendneighbor 172.16.1.2 prefix-list FILTER inno auto-summaryno synchronizationexit-address-family!Verifying the BGP Prefix-Based Outbound Route Filtering Configuration of a Remote Peer
The following is sample output from the show ip bgp neighbors privileged EXEC command. The output show if ORF capability exchange is enabled on the local router and the specified peer. Send mode and receive mode capabilities are shown as advertised or received or as both advertised and received.
The output shows that 10.1.1.1 neighbor is advertising the send mode ORF capability and has received an announcement that the local router is advertising both send and receive mode capabilities:
Router# show ip bgp neighbors 10.1.1.1BGP neighbor is 10.1.1.1, remote AS 100, external linkBGP version 4, remote router ID 172.16.1.2BGP state = Established, up for 00:13:27Last read 00:00:27, hold time is 180, keepalive interval is 60 secondsNeighbor capabilities:Route refresh:advertised and received(new)Address family IPv4 Unicast:advertised and receivedReceived 36 messages, 0 notifications, 0 in queueSent 36 messages, 0 notifications, 0 in queueDefault minimum time between advertisement runs is 30 secondsFor address family:IPv4 UnicastBGP table version 13, neighbor version 13Index 1, Offset 0, Mask 0x2AF-dependant capabilities:Outbound Route Filter (ORF) type (128) Prefix-list:Send-mode:advertised, receivedReceive-mode:receivedRoute refresh request:received 4, sent 22 accepted prefixes consume 80 bytesPrefix advertised 8, suppressed 0, withdrawn 2Verifying the Receipt of the Outbound Filter by the Remote Peer
The following is sample output from the show ip bgp neighbors command entered with the received prefix-filter keyword. The IP prefix list that defines the outbound route filter will be displayed as a prefix list entry on the specified router. The output shows that the 172.16.1.2 neighbor has received an IP prefix list that defines an outbound route filter for the 192.168.1.0/24 subnet.
Router# show ip bgp neighbor 172.16.1.2 received prefix-filterAddress family:IPv4 Unicastip prefix-list 172.16.1.2:1 entriesseq 5 permit 192.168.1.0/24
Additional References
The following sections provide references related to BGP Prefix-Based Outbound Route Filtering feature.
Related Documents
The BGP Prefix-Based Outbound Route Filtering feature is an extension of the BGP routing protocol. For more information about configuring BGP, route filtering, and IP prefix lists refer to the "Configuring BGP" chapter of the Cisco IOS IP Configuration Guide and the Cisco IOS IP Command Reference.
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Standards
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.
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MIBs
RFCs
Technical Assistance
Technical Assistance Center (TAC) home page, containing 30,000 pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content.
TAC Home Page:
http://www.cisco.com/public/support/tac/home.shtml
BGP Support Page:
http://www.cisco.com/pcgi-bin/Support/browse/psp_view.pl?p=Internetworking:BGP
Command Reference
This section documents new and modified commands. All other commands used with this feature are documented in the Cisco IOS command reference publications.
New Commands
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Modified Commands
clear ip bgp in prefix-filter
To initiate an inbound soft reset to clear a BGP outbound route filter (ORF), use the clear ip bgp in prefix-filter command in privileged EXEC mode.
clear ip bgp {ip-address | *} in prefix filter
Syntax Description
*
Clears all ORFs and resets all inbound BGP sessions.
ip-address
(Optional) IP address of the network about which to clear dampening information.
Defaults
The prefix-filter keyword will be ignored and a normal inbound route refresh will be performed if ORF capabilities have not been enabled locally or received from a BGP peer.
Command Modes
Privileged EXEC
Command History
Usage Guidelines
This command is used to push out the existing ORF prefix list so that a new route refresh will be received from a neighbor (including the current ORF prefix list). When this command is used without the prefix-filter keyword, a normal route refresh is performed. This command should be used when inbound routing policy changes other than a prefix list filter occur, such as a route map change.
Examples
The following example initiates an inbound soft reset to clear BGP ORFs received from the 192.168.0.1 neighbor:
Router# clear ip bgp 192.168.0.1 in prefix-filterRelated Commands
Enables outbound route filter (ORF) capability exchange and advertise ORF capabilities to a BGP peer.
Displays information about the TCP and BGP connections to neighbors.
neighbor capability orf prefix-list
To enable outbound route filter (ORF) capability exchange and advertise ORF capabilities to a BGP peer, use the neighbor capability orf prefix-list command in address family configuration mode. To disable ORF capability exchange, use the no form of this command.
neighbor ip-address capability orf prefix-list {both | receive | send}
no neighbor ip-address capability orf prefix-list {both | receive | send}
Syntax Description
Defaults
Disabled
Command Modes
Address family configuration
Command History
Usage Guidelines
The neighbor capability orf prefix command is used to advertise ORF send and/or receive capabilities to minimize the number of BGP updates that are processed and sent between BGP peers. The outbound route filter is defined in an IP prefix list (distribute lists and IP access lists are not supported). The ORF capability is enabled both locally and on the remote peer. The send keyword configures a router to advertise the ORF send capability, the receive keyword configures a router to advertise the ORF receive capabilities, and the both keyword configures a router to advertise both send and receive capabilities.
In most configurations, this command will be used to advertise both send and receive ORF capabilities. However this feature can be configured in one direction between two routers with one router configured to send ORF capabilities and another router configured to receive ORF capabilities.
Examples
Send Mode Configuration Example
The following example creates an outbound route filter and configures Router-A (10.1.1.1) to advertise the filter to Router-B (172.16.1.2). An IP prefix list named FILTER is created to specify the 192.168.1.0/24 subnet for outbound route filtering. The ORF send capability is configured on Router-A so that Router-A will advertise the outbound route filter to Router-B.
ip prefix-list FILTER seq 10 permit 192.168.1.0/24!router bgp 100address-family ipv4 unicastneighbor 172.16.1.2 remote-as 200neighbor 172.16.1.2 ebgp-multihopneighbor 172.16.1.2 capability orf prefix-list sendneighbor 172.16.1.2 prefix-list FILTER inexitReceive Mode Configuration Example
The following example configures Router-B to advertise the ORF receive capability to Router-A. Router-B will install the outbound route filter, defined in the FILTER prefix list, after ORF capabilities have been exchanged. An inbound soft reset is initiated on Router-B at the end of this configuration to activate the outbound route filter.
router bgp 200address-family ipv4 unicastneighbor 10.1.1.1 remote-as 100neighbor 10.1.1.1 ebgp-multihop 255neighbor 10.1.1.1 capability orf prefix-list receiveendclear ip bgp 10.1.1.1 in prefix-filter!
Related Commands
Initiates an inbound soft reset to clear BGP outbound route filters.
ip prefix-list
Creates an entry in a prefix list.
show ip bgp neighbors
To display information about the TCP and Border Gateway Protocol (BGP) connections to neighbors, use the show ip bgp neighbors command in EXEC mode.
show ip bgp neighbors [neighbor-address] [received-routes | routes | advertised-routes | {paths regexp} | dampened-routes] [received prefix-filter]
Syntax Description
Command Modes
EXEC
Command History
10.0
This command was introduced.
11.2
The received-routes keyword was added.
12.2(4)T
12.2(14S
12.0(22)S
The received prefix-filter keyword was added.
Examples
The following is sample output from the show ip bgp neighbors command in privileged EXEC mode:
Router# show ip bgp neighbors 172.16.232.178BGP neighbor is 172.16.232.178, remote AS 35, external linkBGP version 4, remote router ID 192.168.3.3BGP state = Established, up for 1w1dLast read 00:00:53, hold time is 180, keepalive interval is 60 secondsNeighbor capabilities:Route refresh: advertised and receivedAddress family IPv4 Unicast: advertised and receivedAddress family IPv4 Multicast: advertised and receivedReceived 12519 messages, 0 notifications, 0 in queueSent 12523 messages, 0 notifications, 0 in queueRoute refresh request: received 0, sent 0Minimum time between advertisement runs is 30 secondsFor address family: IPv4 UnicastBGP table version 5, neighbor version 5Index 1, Offset 0, Mask 0x2Community attribute sent to this neighborInbound path policy configuredOutbound path policy configuredRoute map for incoming advertisements is uni-inRoute map for outgoing advertisements is uni-out3 accepted prefixes consume 108 bytesPrefix advertised 6, suppressed 0, withdrawn 0For address family: IPv4 MulticastBGP table version 5, neighbor version 5Index 1, Offset 0, Mask 0x2Inbound path policy configuredOutbound path policy configuredRoute map for incoming advertisements is mul-inRoute map for outgoing advertisements is mul-out3 accepted prefixes consume 108 bytesPrefix advertised 6, suppressed 0, withdrawn 0Connections established 2; dropped 1Last reset 1w1d, due to Peer closed the sessionConnection state is ESTAB, I/O status: 1, unread input bytes: 0Local host: 172.16.232.178, Local port: 179Foreign host: 172.16.232.179, Foreign port: 11002Enqueued packets for retransmit: 0, input: 0 mis-ordered: 0 (0 bytes)Event Timers (current time is 0x2CF49CF8):Timer Starts Wakeups NextRetrans 12518 0 0x0TimeWait 0 0 0x0AckHold 12514 12281 0x0SendWnd 0 0 0x0KeepAlive 0 0 0x0GiveUp 0 0 0x0PmtuAger 0 0 0x0DeadWait 0 0 0x0iss: 273358651 snduna: 273596614 sndnxt: 273596614 sndwnd: 15434irs: 190480283 rcvnxt: 190718186 rcvwnd: 15491 delrcvwnd: 893SRTT: 300 ms, RTTO: 607 ms, RTV: 3 ms, KRTT: 0 msminRTT: 0 ms, maxRTT: 300 ms, ACK hold: 200 msFlags: passive open, nagle, gen tcbsDatagrams (max data segment is 1460 bytes):Rcvd: 24889 (out of order: 0), with data: 12515, total data bytes: 237921Sent: 24963 (retransmit: 0), with data: 12518, total data bytes: 237981Table 1 describes the significant fields shown in the display.
The following is sample output from the show ip bgp neighbors command with the advertised-routes keyword in privileged EXEC mode:
Router# show ip bgp neighbors 172.16.232.178 advertised-routesBGP table version is 27, local router ID is 172.16.232.181Status codes: s suppressed, d damped, h history, * valid, > best, i - internalOrigin codes: i - IGP, e - EGP, ? - incompleteNetwork Next Hop Metric LocPrf Weight Path*>i110.0.0.0 172.16.232.179 0 100 0 ?*> 200.2.2.0 0.0.0.0 0 32768 iThe following is sample output from the show ip bgp neighbors command with the routes keyword in privileged EXEC mode:
Router# show ip bgp neighbors 172.16.232.178 routesBGP table version is 27, local router ID is 172.16.232.181Status codes: s suppressed, d damped, h history, * valid, > best, i - internalOrigin codes: i - IGP, e - EGP, ? - incompleteNetwork Next Hop Metric LocPrf Weight Path*> 10.0.0.0 172.16.232.178 40 0 10 ?*> 20.0.0.0 172.16.232.178 40 0 10 ?Table 2 describes the significant fields shown in the displays.
The following is sample output from the show ip bgp neighbors command with the paths keyword in privileged EXEC mode:
Router# show ip bgp neighbors 171.69.232.178 paths ^10Address Refcount Metric Path0x60E577B0 2 40 10 ?Table 3 describes the significant fields shown in the display.
The following is sample output from the show ip bgp neighbors command with the received prefix-filter keyword in privileged EXEC mode:
Router# show ip bgp neighbor 192.168.20.72 received prefix-filterAddress family:IPv4 Unicastip prefix-list 192.168.20.72:1 entriesseq 5 deny 10.0.0.0/8 le 32Table 4 describes the significant fields shown in the display.
Table 4 show ip bgp neighbors paths Field Descriptions
Address family:
The configured address family mode.
ip prefix-list...
The configured prefix list for the specified neighbor.
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