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Cisco IOS IP Routing Protocols Command Reference
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Introduction
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BGP Commands: A through B
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BGP Commands: C through I
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BGP Commands: M through neighbor soo
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BGP Commands: neighbor timers through show bgp nsap summary
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BGP Commands: show ip bgp through T
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EIGRP Commands: A through I
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EIGRP Commands: M through V
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Integrated IS-IS Commands: A through I
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Integrated IS-IS Commands: L through V
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On-Demand Routing Commands
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OSPF Commands: A through ip ospf demand-circuit
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OSPF Commands: ip ospf flood-reduction through R
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OSPF Commands: show ip ospf through T
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IP Routing Protocol-Independent Commands: A through R
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IP Routing Protocol-Independent Commands: S through T
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RIP Commands
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Table Of Contents
bgp bestpath cost-community ignore
bgp bestpath med missing-as-worst
bgp client-to-client reflection
BGP Commands
address-family ipv4 (BGP)
To enter address family or router scope address family configuration mode to configure a routing session using standard IP Version 4 address prefixes, use the address-family ipv4 command in router configuration or router scope configuration mode. To exit address family configuration mode and remove the IPv4 address family configuration from the running configuration, use the no form of this command.
Syntax Available Under Router Configuration Mode
address-family ipv4 [mdt | multicast | tunnel | unicast [vrf vrf-name] | vrf vrf-name]
no address-family ipv4 [mdt | multicast | tunnel | unicast [vrf vrf-name] | vrf vrf-name]
Syntax Available Under Router Scope Configuration Mode
address-family ipv4 [mdt | multicast | unicast]
no address-family ipv4 [mdt | multicast | unicast]
Syntax Description
Command Default
IP Version 4 address prefixes are not enabled.
Command Modes
Router configuration (config-router)
Router scope configuration (config-router-scope)Command History
Usage Guidelines
The address-family ipv4 command replaces the match nlri and set nlri commands. The address-family ipv4 command places the router in address family configuration mode (prompt: config-router-af), from which you can configure routing sessions that use standard IP Version 4 address prefixes. To leave address family configuration mode and return to router configuration mode, type exit.
Note
Routing information for address family IPv4 is advertised by default for each BGP routing session configured with the neighbor remote-as command unless you enter the no bgp default ipv4-unicast command before configuring the neighbor remote-as command.
The tunnel keyword is used to enable the tunnel subaddress family identifier (SAFI) under the IPv4 address family identifier. This SAFI is used to advertise the tunnel endpoints and the SAFI-specific attributes (which contain the tunnel type and tunnel capabilities). Redistribution of tunnel endpoints into the BGP IPv4 tunnel SAFI table occurs automatically when the tunnel address family is configured. However, peers need to be activated under the tunnel address family before the sessions can exchange tunnel information.
The mdt keyword is used to enable the MDT SAFI under the IPv4 address family identifier. This SAFI is used to advertise tunnel endpoints for inter-AS multicast VPN peering sessions.
In Cisco IOS Release 12.2(33)SRB and later releases, the ability to use address family configuration under the router scope configuration mode was introduced. The scope hierarchy can be defined for BGP routing sessions and is required to support Multi-Topology Routing (MTR). To enter the router scope configuration mode, use the scope command, which can apply globally or for a specific VRF. When using the scope for a specific VRF, only the unicast keyword is available.
Examples
The following example places the router in address family configuration mode for the IP Version 4 address family:
Router(config)# router bgp 50000Router(config-router)# address-family ipv4Router(config-router-af)#Multicast Example
The following example places the router in address family configuration mode and specifies only multicast address prefixes for the IP Version 4 address family:
Router(config)# router bgp 50000Router(config-router)# address-family ipv4 multicastRouter(config-router-af)#Unicast Example
The following example places the router in address family configuration mode and specifies unicast address prefixes for the IP Version 4 address family:
Router(config)# router bgp 50000Router(config-router)# address-family ipv4 unicastRouter(config-router-af)#VRF Example
The following example places the router in address family configuration mode and specifies cisco as the name of the VRF instance to associate with subsequent IP Version 4 address family configuration mode commands:
Router(config)# router bgp 50000Router(config-router)# address-family ipv4 vrf ciscoRouter(config-router-af)#
Note
Tunnel Example
The following example places the router in tunnel address family configuration mode:
Router(config)# router bgp 100Router(config-router)# address-family ipv4 tunnelRouter(config-router-af)#MDT Example
The following example shows how to configure a router to support an IPv4 MDT address-family session:
Router(config)# router bgp 45000Router(config-router)# address-family ipv4 mdtRouter(config-router-af)#Router Scope Configuration Mode Example
The following example shows how to configure the IPv4 address family under router scope configuration mode. In this example, the scope hierarchy is enabled globally. The router enters router scope address family configuration mode, and only multicast address prefixes for the IP Version 4 address family are specified:
Router(config)# router bgp 50000Router(config-router)# scope globalRouter(config-router-scope)# address-family ipv4 multicastRouter(config-router-scope-af)#Related Commands
address-family l2vpn
To enter address family configuration mode to configure a routing session using Layer 2 Virtual Private Network (L2VPN) endpoint provisioning address information, use the address-family l2vpn command in router configuration mode. To remove the L2VPN address family configuration from the running configuration, use the no form of this command.
address-family l2vpn [vpls]
no address-family l2vpn [vpls]
Syntax Description
vpls
(Optional) Specifies L2VPN Virtual Private LAN Service (VPLS) endpoint provisioning address information.
Command Default
No L2VPN endpoint provisioning support is enabled.
Command Modes
Router configuration
Command History
Usage Guidelines
The address-family l2vpn command places the router in address family configuration mode (prompt: config-router-af), from which you can configure routing sessions that support L2VPN endpoint provisioning.
BGP support for the L2VPN address family introduces a BGP-based autodiscovery mechanism to distribute L2VPN endpoint provisioning information. BGP uses a separate L2VPN routing information base (RIB) to store endpoint provisioning information, which is updated each time any Layer 2 (L2) virtual forwarding instance (VFI) is configured. Prefix and path information is stored in the L2VPN database, allowing BGP to make best-path decisions. When BGP distributes the endpoint provisioning information in an update message to all its BGP neighbors, the endpoint information is used to set up a pseudowire mesh to support L2VPN-based services.
The BGP autodiscovery mechanism facilitates the setting up of L2VPN services, which are an integral part of the Cisco IOS Virtual Private LAN Service (VPLS) feature. VPLS enables flexibility in deploying services by connecting geographically dispersed sites as a large LAN over high-speed Ethernet in a robust and scalable IP MPLS network.
Note
Examples
In this example, two provider edge (PE) routers are configured with VPLS endpoint provisioning information that includes L2 VFI, VPN, and VPLS IDs. BGP neighbors are configured and activated under L2VPN address family to ensure that the VPLS endpoint provisioning information is saved to a separate L2VPN RIB and then distributed to other BGP peers in BGP update messages. When the endpoint information is received by the BGP peers, a pseudowire mesh is set up to support L2VPN-based services.
Router A
enableconfigure terminall2 vfi customerA autodiscoveryvpn id 100vpls-id 45000:100exitl2 vfi customerB autodiscoveryvpn id 200vpls-id 45000:200exitrouter bgp 45000no bgp default ipv4-unicastbgp log-neighbor-changesneighbor 172.16.1.2 remote-as 45000neighbor 172.21.1.2 remote-as 45000address-family l2vpn vplsneighbor 172.16.1.2 activateneighbor 172.16.1.2 send-community extendedneighbor 172.21.1.2 activateneighbor 172.21.1.2 send-community extendedendRouter B
enableconfigure terminall2 vfi customerA autodiscoveryvpn id 100vpls-id 45000:100exitl2 vfi customerB autodiscoveryvpn id 200vpls-id 45000:200exitrouter bgp 45000no bgp default ipv4-unicastbgp log-neighbor-changesneighbor 172.16.1.1 remote-as 45000neighbor 172.22.1.1 remote-as 45000address-family l2vpn vplsneighbor 172.16.1.1 activateneighbor 172.16.1.1 send-community extendedneighbor 172.22.1.1 activateneighbor 172.22.1.1 send-community extendedendRelated Commands
neighbor activate
Enables the exchange of information with a BGP neighboring router.
show ip bgp l2vpn
Displays L2VPN address family information.
address-family nsap
To enter address family configuration mode to configure Connectionless Network Service (CLNS)-specific parameters for Border Gateway Protocol (BGP) routing sessions, use the address-family nsap command in router configuration mode. To exit address family configuration mode and remove the CLNS address family configuration from the running configuration, use the no form of this command.
address-family nsap [unicast]
no address-family nsap [unicast]
Syntax Description
Command Default
NSAP prefix support is not enabled.
Note
Command Modes
Router configuration
Command History
12.2(8)T
This command was introduced.
12.2(33)SRB
This command was integrated into Cisco IOS Release 12.2(33)SRB.
Usage Guidelines
The address-family nsap command enters address family configuration mode (prompt: config-router-af)#, from which you can configure routing sessions that use standard NSAP address prefixes; you must enter NSAP address family configuration mode to configure BGP for CLNS prefixes.
To leave address family configuration mode and return to router configuration mode without removing the existing configuration, enter the exit-address-family command.
Examples
The following example enters NSAP address family configuration mode under BGP:
Router(config)# router bgp 50000Router(config-router)# address-family nsapRouter(config-router-af)#Related Commands
address-family vpnv4
To enter address family configuration mode to configure a routing session using Virtual Private Network (VPN) Version 4 address prefixes, use the address-family vpnv4 command in router configuration mode. To exit address family configuration mode and remove the VPNv4 address family configuration from the running configuration, use the no form of this command.
address-family vpnv4 [unicast]
no address-family vpnv4 [unicast]
Syntax Description
Defaults
Unicast prefix support is enabled by default when this command is entered without any optional keywords.
Note
Command Modes
Router configuration
Command History
12.0(5)T
This command was introduced.'
12.2(33)SRA
This command was integrated into Cisco IOS Release 12.2(33)SRA.
Usage Guidelines
The address-family vpnv4 command replaces the match nlri and set nlri commands.
The address-family vpnv4 command places the router in address family configuration mode (prompt: config-router-af)#, from which you can configure routing sessions that use VPN Version 4 address prefixes.
To leave address family configuration mode and return to router configuration mode without removing the existing configuration, enter the exit-address-family command.
Examples
The following example places the router in address family configuration mode for the VPN Version 4 address family:
Router(config)# router bgp 50000Router(config-router)# address-family vpnv4Router(config-router-af)#The following example places the router in address family configuration mode for the unicast VPN Version 4 address family:
Router(config)# router bgp 50000Router(config-router)# address-family vpnv4 unicastRouter(config-router-af)#Related Commands
aggregate-address
To create an aggregate entry in a Border Gateway Protocol (BGP) database, use the aggregate-address command in address family or router configuration mode. To disable this function, use the no form of this command.
aggregate-address address mask [as-set] [summary-only] [suppress-map map-name] [advertise-map map-name] [attribute-map map-name]
no aggregate-address address mask [as-set] [summary-only] [suppress-map map-name] [advertise-map map-name] [attribute-map map-name]
Syntax Description
Command Default
The atomic aggregate attribute is set automatically when an aggregate route is created with this command unless the as-set keyword is specified.
Command Modes
Address family configuration
Router configurationCommand History
Usage Guidelines
You can implement aggregate routing in BGP and mBGP either by redistributing an aggregate route into BGP or mBGP, or by using the conditional aggregate routing feature.
Using the aggregate-address command with no keywords will create an aggregate entry in the BGP or mBGP routing table if any more-specific BGP or mBGP routes are available that fall within the specified range. (A longer prefix which matches the aggregate must exist in the RIB.) The aggregate route will be advertised as coming from your autonomous system and will have the atomic aggregate attribute set to show that information might be missing. (By default, the atomic aggregate attribute is set unless you specify the as-set keyword.)
Using the as-set keyword creates an aggregate entry using the same rules that the command follows without this keyword, but the path advertised for this route will be an AS_SET consisting of all elements contained in all paths that are being summarized. Do not use this form of the aggregate-address command when aggregating many paths, because this route must be continually withdrawn and updated as autonomous system path reachability information for the summarized routes changes.
Using the summary-only keyword not only creates the aggregate route (for example, 192.*.*.*) but also suppresses advertisements of more-specific routes to all neighbors. If you want to suppress only advertisements to certain neighbors, you may use the neighbor distribute-list command, with caution. If a more-specific route leaks out, all BGP or mBGP routers will prefer that route over the less-specific aggregate you are generating (using longest-match routing).
Using the suppress-map keyword creates the aggregate route but suppresses advertisement of specified routes. You can use the match clauses of route maps to selectively suppress some more-specific routes of the aggregate and leave others unsuppressed. IP access lists and autonomous system path access lists match clauses are supported.
Using the advertise-map keyword selects specific routes that will be used to build different components of the aggregate route, such as AS_SET or community. This form of the aggregate-address command is useful when the components of an aggregate are in separate autonomous systems and you want to create an aggregate with AS_SET, and advertise it back to some of the same autonomous systems. You must remember to omit the specific autonomous system numbers from the AS_SET to prevent the aggregate from being dropped by the BGP loop detection mechanism at the receiving router. IP access lists and autonomous system path access lists match clauses are supported.
Using the attribute-map keyword allows attributes of the aggregate route to be changed. This form of the aggregate-address command is useful when one of the routes forming the AS_SET is configured with an attribute such as the community no-export attribute, which would prevent the aggregate route from being exported. An attribute map route map can be created to change the aggregate attributes.
Examples
AS-Set Example
In the following example, an aggregate BGP address is created in router configuration mode. The path advertised for this route will be an AS_SET consisting of all elements contained in all paths that are being summarized.
Router(config)# router bgp 50000Router(config-router)# aggregate-address 10.0.0.0 255.0.0.0 as-setSummary-Only Example
In the following example, an aggregate BGP address is created in address family configuration mode and applied to the multicast database (SAFI) under the IP Version 4 address family. Because the summary-only keyword is configured, more-specific routes are filtered from updates.
Router(config)# router bgp 50000Router(config-router)# address-family ipv4 multicastRouter(config-router-af)# aggregate-address 10.0.0.0 255.0.0.0 summary-onlyConditional Aggregation Example
In the following example, a route map called MAP-ONE is created to match on an as-path access list. The path advertised for this route will be an AS_SET consisting of elements contained in paths that are matched in the route map.
Router(config)# ip as-path access-list 1 deny ^1234_Router(config)# ip as-path access-list 1 permit .*Router(config)# !Router(config)# route-map MAP-ONERouter(config-route-map)# match ip as-path 1Router(config-route-map)# exitRouter(config)# router bgp 50000Router(config-router)# address-family ipv4Router(config-router-af)# aggregate-address 10.0.0.0 255.0.0.0 as-set advertise-map MAP-ONERouter(config-router-af)# endRelated Commands
auto-summary (BGP)
To configure automatic summarization of subnet routes into network-level routes, use the auto-summary command in address family or router configuration mode. To disable automatic summarization and send subprefix routing information across classful network boundaries, use the no form of this command.
auto-summary
no auto-summary
Syntax Description
This command has no arguments or keywords.
Command Default
Automatic summarization is disabled by default (the software sends subprefix routing information across classful network boundaries).
BGP automatically summarizes to classful network boundaries when this command is enabled.
Command Modes
Address family configuration
Router configurationCommand History
Usage Guidelines
Route summarization is used to reduce the amount of routing information in routing tables.
Note
By default, BGP does not accept subnets redistributed from an Interior Gateway Protocol (IGP). To allow Cisco IOS Software to create summary subprefixes to the classful network boundary when crossing classful network boundaries, use the auto-summary command. To advertise and carry subnet routes in BGP when automatic summarization is enabled, use an explicit network command statement to advertise the subnet.
Examples
In the following example, automatic summarization is enabled for IPv4 address family prefixes:
Router(config)# router bgp 50000Router(config-router)# address-family ipv4 unicastRouter(config-router-af)# auto-summaryRelated Commands
bgp always-compare-med
To enable the comparison of the Multi Exit Discriminator (MED) for paths from neighbors in different autonomous systems, use the bgp always-compare-med command in router configuration mode. To disallow the comparison, use the no form of this command.
bgp always-compare-med
no bgp always-compare-med
Syntax Description
This command has no arguments or keywords.
Command Default
Cisco IOS software does not compare the MED for paths from neighbors in different autonomous systems if this command is not enabled or if the no form of this command is entered. The MED is compared only if the autonomous system path for the compared routes is identical.
Command Modes
Router configuration
Command History
Usage Guidelines
The MED, as stated in RFC 1771, is an optional nontransitive attribute that is a four octet non-negative integer. The value of this attribute may be used by the BGP best path selection process to discriminate among multiple exit points to a neighboring autonomous system.
The MED is one of the parameters that is considered when selecting the best path among many alternative paths. The path with a lower MED is preferred over a path with a higher MED. During the best-path selection process, MED comparison is done only among paths from the same autonomous system. The bgp always-compare-med command is used to change this behavior by enforcing MED comparison between all paths, regardless of the autonomous system from which the paths are received.
The bgp deterministic-med command can be configured to enforce deterministic comparison of the MED value between all paths received from within the same autonomous system.
Examples
In the following example, the local BGP routing process is configured to compare the MED from alternative paths, regardless of the autonomous system from which the paths are received:
Router(config)# router bgp 500000Router(config-router)# bgp always-compare-medRelated Commands
bgp deterministic-med
Enforces deterministic comparison of the MED value between all paths received from within the same autonomous system
bgp asnotation dot
To change the default display and regular expression match format of Border Gateway Protocol (BGP) 4-byte autonomous system numbers from asplain (decimal values) to dot notation, use the bgp asnotation dot command in router configuration mode. To reset the default 4-byte autonomous system number display and regular expression match format to asplain, use the no form of this command.
bgp asnotation dot
no bgp asnotation dot
Syntax Description
This command has no arguments or keywords.
Command Default
BGP autonomous system numbers are displayed using asplain (decimal value) format in screen output, and the default format for matching 4-byte autonomous system numbers in regular expressions is asplain.
Command Modes
Router configuration (config-router)
Command History
Usage Guidelines
Prior to January 2009, BGP autonomous system numbers that were allocated to companies were 2-octet numbers in the range from 1 to 65535 as described in RFC 4271, A Border Gateway Protocol 4 (BGP-4). Due to increased demand for autonomous system numbers, the Internet Assigned Number Authority (IANA) will start in January 2009 to allocate four-octet autonomous system numbers in the range from 65536 to 4294967295. RFC 5396, Textual Representation of Autonomous System (AS) Numbers, documents three methods of representing autonomous system numbers. Cisco has implemented the following two methods:
•
•
For details about the third method of representing autonomous system numbers, see RFC 5396.
In Cisco IOS Release 12.0(32)SY8, 12.2(33)SXI1, 12.0(33)S3, Cisco IOS XE Release 2.4, and later releases, the Cisco implementation of 4-byte autonomous system numbers uses asplain as the default display format for autonomous system numbers, but you can configure 4-byte autonomous system numbers in both the asplain and asdot format. In addition, the default format for matching 4-byte autonomous system numbers in regular expressions is asplain, so you must ensure that any regular expressions to match 4-byte autonomous system numbers are written in the asplain format. If you want to change the default show command output to display 4-byte autonomous system numbers in the asdot format, use the bgp asnotation dot command under router configuration mode. When the asdot format is enabled as the default, any regular expressions to match 4-byte autonomous system numbers must be written using the asdot format, or the regular expression match will fail. Table 8 and Table 9 show that although you can configure 4-byte autonomous system numbers in either asplain or asdot format, only one format is used to display show command output and control 4-byte autonomous system number matching for regular expressions, and the default is asplain format. To display 4-byte autonomous system numbers in show command output and to control matching for regular expressions in the asdot format, you must configure the bgp asnotation dot command. After enabling the bgp asnotation dot command, a hard reset must be initiated for all BGP sessions by entering the clear ip bgp * command.
Note
Examples
The following output from the show ip bgp summary command shows the default asplain format of the 4-byte autonomous system numbers. Note the asplain format of the 4-byte autonomous system numbers, 65536 and 65550.
Router# show ip bgp summaryBGP router identifier 172.17.1.99, local AS number 65538BGP table version is 1, main routing table version 1Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down Statd192.168.1.2 4 65536 7 7 1 0 0 00:03:04 0192.168.3.2 4 65550 4 4 1 0 0 00:00:15 0The following configuration is performed to change the default output format to the asdot notation format:
configure terminalrouter bgp 65538bgp asnotation dotendclear ip bgp *After the configuration is performed, the output is converted to asdot notation format as shown in the following output from the show ip bgp summary command. Note the asdot format of the 4-byte autonomous system numbers, 1.0 and 1.14 (these are the asdot conversions of the 65536 and 65550 autonomous system numbers).
RouterB# show ip bgp summaryBGP router identifier 172.17.1.99, local AS number 1.2BGP table version is 1, main routing table version 1Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down Statd192.168.1.2 4 1.0 9 9 1 0 0 00:04:13 0192.168.3.2 4 1.14 6 6 1 0 0 00:01:24 0After the bgp asnotation dot command is configured, the regular expression match format for 4-byte autonomous system paths is changed to asdot notation format. Although a 4-byte autonomous system number can be configured in a regular expression using either asplain format or asdot format, only 4-byte autonomous system numbers configured using the current default format are matched. In the first example, the show ip bgp regexp command is configured with a 4-byte autonomous system number in asplain format. The match fails because the default format is currently asdot format and there is no output. In the second example using asdot format, the match passes and the information about the 4-byte autonomous system path is shown using the asdot notation.
Note
RouterB# show ip bgp regexp ^65536$RouterB# show ip bgp regexp ^1\.0$BGP table version is 2, local router ID is 172.17.1.99Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,r RIB-failure, S StaleOrigin codes: i - IGP, e - EGP, ? - incompleteNetwork Next Hop Metric LocPrf Weight Path*> 10.1.1.0/24 192.168.1.2 0 0 1.0 iRelated Commands
bgp bestpath as-path ignore
To configure Border Gateway Protocol (BGP) to not consider the autonomous system (AS) path during best path route selection, use the bgp bestpath as-path ignore command in router configuration mode. To restore default behavior and configure BGP to consider the AS-path during route selection, use the no form of this command.
bgp bestpath as-path ignore
no bgp bestpath as-path ignore
Syntax Description
This command has no arguments or keywords.
Command Default
The AS-path is considered during BGP best path selection.
Command Modes
Router configuration
Command History
Examples
In the following example, the BGP routing process is configured to not consider the AS-path during best path selection:
Router(config)# router bgp 40000Router(config-router)# bgp bestpath as-path ignoreRelated Commands
show ip bgp ipv4
Displays information about the TCP and BGP connections to neighbors.
bgp bestpath compare-routerid
To configure a Border Gateway Protocol (BGP) routing process to compare identical routes received from different external peers during the best path selection process and to select the route with the lowest router ID as the best path, use the bgp bestpath compare-routerid command in router configuration mode. To return the BGP routing process to the default operation, use the no form of this command.
bgp bestpath compare-routerid
no bgp bestpath compare-routerid
The behavior of this command is disabled by default; BGP selects the route that was received first when two routes with identical attributes are received.
Command HistoryRouter configuration
Usage Guidelines
The bgp bestpath compare-routerid command is used to configure a BGP routing process to use the router ID as the tie breaker for best path selection when two identical routes are received from two different peers (all the attributes are the same except for the router ID). When this command is enabled, the lowest router ID will be selected as the best path when all other attributes are equal.
In the following example, the BGP routing process is configured to compare and use the router ID as a tie breaker for best path selection when identical paths are received from different peers:
Router(config)# router bgp 50000Router(config-router)# bgp bestpath compare-routeridRelated Commands
bgp bestpath cost-community ignore
To configure a router that is running the Border Gateway Protocol (BGP) to not evaluate the cost community attribute during the best path selection process, use the bgp bestpath cost-community ignore command in router configuration mode. To return the router to default operation, use the no form of this command.
bgp bestpath cost-community ignore
no bgp bestpath cost-community ignore
Syntax Description
This command has no keywords or arguments.
Command Default
The behavior of this command is enabled by default until the cost community attribute is manually configured.
Command Modes
Address family configuration
Router configurationCommand History
Usage Guidelines
The bgp bestpath cost-community ignore command is used to disable the evaluation of the cost community attribute to help isolate problems and troubleshoot issues that relate to BGP path selection. This command can also be used to delay the activation of cost community attribute evaluation so that cost community filtering can be deployed in a large network at the same time.
Examples
The following example shows how to configure a router to not evaluate the cost community attribute during the best path selection process:
router bgp 50000address-family ipv4 unicastbgp bestpath cost-community ignoreRelated Commands
set extcommunity cost
Creates a set clause to apply the cost community attribute to routes that pass through a route map.
show ip bgp
Displays entries in the BGP routing table.
bgp bestpath med confed
To configure a Border Gateway Protocol (BGP) routing process to compare the Multi Exit Discriminator (MED) between paths learned from confederation peers, use the bgp bestpath med confed command in router configuration mode. To disable MED comparison of paths received from confederation peers, use the no form of this command.
bgp bestpath med confed [missing-as-worst]
no bgp bestpath med confed [missing-as-worst]
Syntax Description
missing-as-worst
(Optional) Assigns the value of infinity to received routes that do not carry the MED attribute, making these routes the least desirable.
Defaults
Cisco IOS software does not consider the MED attribute when choosing among paths learned from confederation peers if this command is not enabled or if the no form of this command is entered.
Command Modes
Router configuration
Command History
Usage Guidelines
The MED comparison between confederation peers occurs only if no external autonomous systems are in the path (an external autonomous system is an autonomous system that is not within the confederation). If an external autonomous system in the path, then the external MED is passed transparently through the confederation, and the comparison is does not occur.
For example, assume that autonomous system 65000, 65001, 65002, and 65004 are part of the confederation; autonomous system 1 is not; and we are comparing route A with four paths. If the bgp bestpath med confed command is enabled, path 1 would be chosen. The fourth path has a lower MED, but it is not involved in the MED comparison because there is an external autonomous system in this path. The following list displays the MED for each autonomous system.
path = 65000 65004, med = 2
path = 65001 65004, med = 3
path = 65002 65004, med = 4
path = 65003 1, med = 1
Examples
In the following example, the BGP routing process is configured to compare MED values for paths learned from confederation peers:
Router(config)# router bgp 50000Router(config-router)# bgp bestpath med confedRelated Commands
show ip bgp
Displays entries in the BGP routing table.
show ip bgp ipv4
Displays information about the TCP and BGP connections to neighbors.
bgp bestpath med missing-as-worst
To configure a Border Gateway Protocol (BGP) routing process to assign a value of infinity to routes that are missing the Multi Exit Discriminator (MED) attribute (making the path without a MED value the least desirable path), use the bgp bestpath med missing-as-worst command in router configuration mode. To return the router to the default behavior (assign a value of 0 to the missing MED), use the no form of this command.
bgp bestpath med missing-as-worst
no bgp bestpath med missing-as-worst
Syntax Description
This command has no arguments or keywords.
Defaults
Cisco IOS software assigns a value of 0 to routes the are missing the MED attribute, causing the route with the missing MED attribute to be considered the best path.
Command Modes
Router configuration
Command History
Examples
In the following example, the BGP router process is configured to consider a route with a missing MED attribute as having a value of infinity (4294967294), making this path the least desirable path:
Router(config)# router bgp 50000Router(config-router)# bgp bestpath med missing-as-worstRelated Commands
show ip bgp
Displays entries in the BGP routing table.
show ip bgp ipv4
Displays information about the TCP and BGP connections to neighbors.
bgp client-to-client reflection
To enable or restore route reflection from a BGP route reflector to clients, use the bgp client-to-client reflection command in router configuration mode. To disable client-to-client route reflection, use the no form of this command.
bgp client-to-client reflection
no bgp client-to-client reflection
Syntax Description
This command has no arguments or keywords.
Defaults
Client-to-client route reflection is enabled by default; when a route reflector is configured, the route reflector reflects routes from a client to other clients.
Command Modes
Router configuration
Command History
Usage Guidelines
By default, the clients of a route reflector are not required to be fully meshed and the routes from a client are reflected to other clients. However, if the clients are fully meshed, route reflection is not required. In this case, use the no bgp client-to-client reflection command to disable client-to-client reflection.
Examples
In the following example, the local router is a route reflector, and the three neighbors are fully meshed. Because the neighbors are fully meshed, client-to-client reflection is disabled with the no bgp client-to-client reflection command.
Router(config)# router bgp 50000Router(config-router)# neighbor 10.24.95.22 route-reflector-clientRouter(config-router)# neighbor 10.24.95.23 route-reflector-clientRouter(config-router)# neighbor 10.24.95.24 route-reflector-clientRouter(config-router)# no bgp client-to-client reflectionRouter(config-router)# endRelated Commands
bgp cluster-id
To set the cluster ID on a route reflector in a route reflector cluster, use the bgp cluster-id command in router configuration mode. To remove the cluster ID, use the no form of this command.
bgp cluster-id cluster-id
no bgp cluster-id cluster-id
Syntax Description
cluster-id
Cluster ID of this router acting as a route reflector; maximum of 4 bytes. The ID can be specified in dotted or decimal format.
Defaults
The local router ID of the route reflector is used as the cluster ID when no ID is specified or when the no form of this command is entered.
Command Modes
Router configuration
Command History
Usage Guidelines
Together, a route reflector and its clients form a cluster. When a single route reflector is deployed in a cluster, the cluster is identified by the router ID of the route reflector.
The bgp cluster-id command is used to assign a cluster ID to a route reflector when the cluster has one or more route reflectors. Multiple route reflectors are deployed in a cluster to increase redundancy and avoid a single point of failure. When multiple route reflectors are configured in a cluster, the same cluster ID is assigned to all route reflectors. This allows all route reflectors in the cluster to recognize updates from peers in the same cluster and reduces the number of updates that need to be stored in BGP routing tables.
Note
Examples
In the following example, the local router is one of the route reflectors serving the cluster. It is configured with the cluster ID to identify the cluster.
Router(config)# router bgp 50000Router(config-router)# neighbor 192.168.70.24 route-reflector-clientRouter(config-router)# bgp cluster-id 10.0.1.2Related Commands
bgp confederation identifier
To specify a BGP confederation identifier, use the bgp confederation identifier command in router configuration mode. To remove the confederation identifier, use the no form of this command.
bgp confederation identifier autonomous-system-number
no bgp confederation identifier autonomous-system-number
Syntax Description
Command Default
No BGP confederation identifier is identified.
Command Modes
Router configuration (config-router)
Command History
Usage Guidelines
The bgp confederation identifier command is used to configure a single autonomous system number to identify a group of smaller autonomous systems as a single confederation.
A confederation can be used to reduce the internal BGP (iBGP) mesh by dividing a large single autonomous system into multiple subautonomous systems and then grouping them into a single confederation. The subautonomous systems within the confederation exchange routing information like iBGP peers. External peers interact with the confederation as if it is a single autonomous system.
Each subautonomous system is fully meshed within itself and has a few connections to other autonomous systems within the confederation. Next hop, Multi Exit Discriminator (MED), and local preference information is preserved throughout the confederation, allowing you to retain a single Interior Gateway Protocol (IGP) for all the autonomous systems.
In Cisco IOS Release 12.0(32)SY8, 12.2(33)SXI1, 12.0(33)S3, Cisco IOS XE Release 2.4, and later releases, the Cisco implementation of 4-byte autonomous system numbers uses asplain—65538 for example—as the default regular expression match and output display format for autonomous system numbers, but you can configure 4-byte autonomous system numbers in both the asplain format and the asdot format as described in RFC 5396. To change the default regular expression match and output display of 4-byte autonomous system numbers to asdot format, use the bgp asnotation dot command followed by the clear ip bgp * command to perform a hard reset of all current BGP sessions.
In Cisco IOS Release 12.0(32)S12, 12.4(24)T, and Cisco IOS XE Release 2.3, the Cisco implementation of 4-byte autonomous system numbers uses asdot—1.2 for example—as the only configuration format, regular expression match, and output display, with no asplain support.
If one member of a BGP confederation is identified using a 4-byte autonomous system number, all other members of a BGP confederation must be upgraded to support 4-byte autonomous system numbers.
Examples
In the following example, the routing domain is divided into autonomous systems 50001, 50002, 50003, 50004, 50005, and 50006 and identified by the confederation identifier 50000. Neighbor 10.2.3.4 is a peer inside of the routing domain confederation. Neighbor 10.4.5.6 is a peer outside of the routing domain confederation. To external peers and routing domains, the confederation appears as a single autonomous system with the number 50000.
router bgp 50000bgp confederation identifier 50000bgp confederation peers 50001 50002 50003 50004 50005 50006neighbor 10.2.3.4 remote-as 50001neighbor 10.4.5.6 remote-as 40000endIn the following example, the routing domain is divided into autonomous systems using 4-byte autonomous system numbers 65538, 65536, and 65550 and identified by the confederation identifier 65545. Neighbor 192.168.1.2 is a peer inside of the routing domain confederation. Neighbor 192.168.2.2 is a peer outside of the routing domain confederation. To external peers and routing domains, the confederation appears as a single autonomous system with the number 65545. This example requires Cisco IOS Release 12.0(32)SY8, 12.2(33)SXI1, 12.0(33)S3, Cisco IOS XE Release 2.4, or later release.
router bgp 65550bgp confederation identifier 65545bgp confederation peers 65538 65536 65550neighbor 192.168.1.2 remote-as 65536neighbor 192.168.2.2 remote-as 65547endIn the following example, the routing domain is divided into autonomous systems using 4-byte autonomous system numbers 1.2, 1.0, and 1.14 in asdot format and is identified by the confederation identifier 1.9. Neighbor 192.168.1.2 is a peer inside of the routing domain confederation. Neighbor 192.168.2.2 is a peer outside of the routing domain confederation. To external peers and routing domains, the confederation appears as a single autonomous system with the number 1.9. This example requires Cisco IOS Release 12.0(32)S12, 12.4(24)T, or Cisco IOS XE Release 2.3 where asdot notation is the only format for 4-byte autonomous system numbers. This configuration can also be performed using Cisco IOS Release 12.0(32)SY8, 12.2(33)SXI1, 12.0(33)S3, Cisco IOS XE Release 2.4, or later releases.
router bgp 1.14bgp confederation identifier 1.9bgp confederation peers 1.2 1.0 1.14neighbor 192.168.1.2 remote-as 1.0neighbor 192.168.2.2 remote-as 1.11endRelated Commands
bgp confederation peers
To configure subautonomous systems to belong to a single confederation, use the bgp confederation peers command in router configuration mode. To remove an autonomous system from the confederation, use the no form of this command.
bgp confederation peers autonomous-system-number [... autonomous-system-number]
no bgp confederation peers autonomous-system-number [... autonomous-system-number]
Syntax Description
Command Default
No BGP peers are configured to be members of a BGP confederation.
Command Modes
Router configuration (config-router)
Command History
Usage Guidelines
The bgp confederation peers command is used to configure multiple autonomous systems as a single confederation. The ellipsis (...) in the command syntax indicates that your command input can include multiple values for the as-number argument.
The autonomous systems specified in this command are visible internally to the confederation. Each autonomous system is fully meshed within itself. The bgp confederation identifier command specifies the confederation to which the autonomous systems belong.
In Cisco IOS Release 12.0(32)SY8, 12.2(33)SXI1, 12.0(33)S3, Cisco IOS XE Release 2.4, and later releases, the Cisco implementation of 4-byte autonomous system numbers uses asplain—65538 for example—as the default regular expression match and output display format for autonomous system numbers, but you can configure 4-byte autonomous system numbers in both the asplain format and the asdot format as described in RFC 5396. To change the default regular expression match and output display of 4-byte autonomous system numbers to asdot format, use the bgp asnotation dot command followed by the clear ip bgp * command to perform a hard reset of all current BGP sessions.
In Cisco IOS Release 12.0(32)S12, 12.4(24)T, and Cisco IOS XE Release 2.3, the Cisco implementation of 4-byte autonomous system numbers uses asdot—1.2 for example—as the only configuration format, regular expression match, and output display, with no asplain support.
If one member of a BGP confederation is identified using a 4-byte autonomous system number, all other members of a BGP confederation must be upgraded to support 4-byte autonomous system numbers.
Examples
In the following example, autonomous systems 50001, 50002, 50003, 50004, and 50005 are configured to belong to a single confederation under the identifier 50000:
router bgp 50000bgp confederation identifier 50000bgp confederation peers 50001 50002 50003 50004 50005In the following example, the routing domain is divided into autonomous systems using 4-byte autonomous system numbers 65538, 65536, and 65550 and is identified by the confederation identifier 65545. Neighbor 192.168.1.2 is a peer inside of the routing domain confederation. Neighbor 192.168.2.2 is a peer outside of the routing domain confederation. To external peers and routing domains, the confederation appears as a single autonomous system with the number 65545. This example requires Cisco IOS Release 12.0(32)SY8, 12.2(33)SXI1, 12.0(33)S3, Cisco IOS XE Release 2.4, or a later release.
router bgp 65550bgp confederation identifier 65545bgp confederation peers 65538 65536 65550neighbor 192.168.1.2 remote-as 65536neighbor 192.168.2.2 remote-as 65547endIn the following example, the routing domain is divided into autonomous systems using 4-byte autonomous system numbers 1.2, 1.0, and 1.14 and is identified by the confederation identifier 1.9. Neighbor 192.168.1.2 is a peer inside of the routing domain confederation. Neighbor 192.168.2.2 is a peer outside of the routing domain confederation. To external peers and routing domains, the confederation appears as a single autonomous system with the number 1.9. This example requires Cisco IOS Release 12.0(32)S12, 12.4(24)T, or Cisco IOS XE Release 2.3 where asdot notation is the only format for 4-byte autonomous system numbers. This configuration can also be performed using Cisco IOS Release 12.0(32)SY8, 12.2(33)SXI1, 12.0(33)S3, Cisco IOS XE Release 2.4, or a later release.
router bgp 1.14bgp confederation identifier 1.9bgp confederation peers 1.2 1.0 1.14neighbor 192.168.1.2 remote-as 1.0neighbor 192.168.2.2 remote-as 1.11endRelated Commands
bgp dampening
To enable BGP route dampening or change BGP route dampening parameters, use the bgp dampening command in address family or router configuration mode. To disable BGP dampening, use the no form of this command.
bgp dampening [half-life reuse suppress max-suppress-time | route-map map-name]
no bgp dampening [half-life reuse suppress max-suppress-time | route-map map-name]
Syntax Description
Defaults
BGP dampening is disabled by default. The following values are used when this command is enabled without configuring any optional arguments:
half-life: 15 minutes
reuse: 750
suppress: 2000
max-suppress-time: 4 times half-lifeCommand Modes
Address family configuration
Router configurationCommand History
Usage Guidelines
The bgp dampening command is used to enable BGP route dampening. This command can be entered without any arguments or keywords. The half-life, reuse, suppress, and max-suppress-time arguments are position-dependent; meaning that if any of these arguments are entered, then all optional arguments must be entered.
When BGP dampening is configured and a prefix is withdrawn, BGP considers the withdrawn prefix as a flap and increases the penalty by a 1000. If BGP receives an attribute change, BGP increases the penalty by 500. If then the prefix has been withdrawn, BGP keeps the prefix in the BGP table as a history entry. If the prefix has not been withdrawn by the neighbor and BGP is not using this prefix, the prefix is marked as dampened. Dampened prefixes are not used in the BGP decision process and not installed to the routing table.
Examples
In the following example, the BGP dampening values are set to 30 minutes for the half life, 1500 for the reuse value, 10000 for the suppress value, and 120 minutes for the maximum suppress time:
Router(config)# router bgp 5Router(config-router)# address-family ipv4 unicastRouter(config-router-af)# bgp dampening 30 1500 10000 120Router(config-router-af)# endIn the following example, BGP dampening is applied to prefixes filtered through the route-map named BLUE:
Router(config)# ip prefix-list RED permit 10.0.0.0/8Router(config)# !Router(config)# route-map BLUERouter(config-route-map)# match ip address ip prefix-list REDRouter(config-route-map)# exitRouter(config)# router bgp 50000Router(config-router)# address-family ipv4Router(config-router-af)# bgp dampening route-map BLUERouter(config-router-af)# endRelated Commands
bgp default ipv4-unicast
To set the IP version 4 (IPv4) unicast address family as default for BGP peering session establishment, use the bgp default ipv4-unicast command in router configuration mode. To disable default IPv4 unicast address family for peering session establishment, use the no form of this command.
bgp default ipv4-unicast
no bgp default ipv4-unicast
Syntax Description
This command has no arguments or keywords.
Command Default
IPv4 address family routing information is advertised by default for each BGP routing session configured with the neighbor remote-as command, unless you first configure the no bgp default ipv4-unicast command before configuring the neighbor remote-as command.
Command Modes
Router configuration
Command History
Usage Guidelines
The bgp default ipv4-unicast command is used to enable the automatic exchange of IPv4 address family prefixes. The neighbor activate address family configuration command must be entered in each IPv4 address family session before prefix exchange will occur.
Examples
In the following example, the automatic exchange of IP version 4 unicast address family routing information is disabled:
Router(config)# router bgp 50000Router(config-router)# no bgp default ipv4-unicastRelated Commands
neighbor activate
Enables the exchange of information with a neighboring router.
bgp default local-preference
To change the default local preference value, use the bgp default local-preference command in router configuration mode. To return the local preference value to the default setting, use the no form of this command.
bgp default local-preference number
no bgp default local-preference number
Syntax Description
Command Default
Cisco IOS software applies a local preference value of 100 if this command is not enabled or if the no form of this command is entered.
Command Modes
Router configuration
Command History
Usage Guidelines
The local preference attribute is a discretionary attribute that is used to apply the degree of preference to a route during the BGP best path selection process. This attribute is exchanged only between iBGP peers and is used to determine local policy. The route with the highest local preference is preferred.
Examples
In the following example, the local preference value is set to 200:
Router(config)# router bgp 50000Router(config-router)# bgp default local-preference 200Related Commands
set local-preference
Specifies a preference value for the autonomous system path.
bgp deterministic-med
To enforce the deterministic comparison of the Multi Exit Discriminator (MED) value between all paths received from within the same autonomous system, use the bgp deterministic-med command in router configuration mode. To disable the required MED comparison, use the no form of this command.
bgp deterministic-med
no bgp deterministic-med
Syntax Description
This command has no arguments or keywords.
Command Default
Cisco IOS software does not enforce the deterministic comparison of the MED variable between all paths received from the same autonomous system.
Command Modes
Router configuration
Command History
Usage Guidelines
The bgp always-compare-med command is used to enable the comparison of the Multi Exit Discriminator (MED) for paths from neighbors in different autonomous systems. After the bgp always-compare-med command is configured, all paths for the same prefix that are received from different neighbors, which are in the same autonomous system, will be grouped together and sorted by the ascending MED value (received-only paths are ignored and not grouped or sorted). The best path selection algorithm will then pick the best paths using the existing rules; the comparison is made on a per neighbor autonomous system basis and then global basis. The grouping and sorting of paths occurs immediately after this command is entered. For correct results, all routers in the local autonomous system must have this command enabled (or disabled).
Examples
In the following example, BGP is configured to compare the MED during path selection for routes advertised by the same subautonomous system within a confederation:
Router(config)# router bgp 50000Router(config-router)# bgp deterministic-medThe following example show ip bgp command output shows how route selection is affected by the configuration of the bgp deterministic-med command. The order in which routes are received affects how routes are selected for best path selection when the bgp deterministic-med command is not enabled. The following sample output from the show ip bgp command shows three paths that are received for the same prefix (10.100.0.0), and the bgp deterministic-med command is not enabled:
Router# show ip bgp 10.100.0.0BGP routing table entry for 10.100.0.0/16, version 40Paths: (3 available, best #3, advertised over IBGP, EBGP)109192.168.43.10 from 192.168.43.10 (192.168.43.1)Origin IGP, metric 0, localpref 100, valid, internal2051192.168.43.22 from 192.168.43.22 (192.168.43.2)Origin IGP, metric 20, localpref 100, valid, internal2051192.168.43.3 from 192.168.43.3 (10.4.1.1)Origin IGP, metric 30, valid, external, bestIf the bgp deterministic-med feature is not enabled on the router, the route selection can be affected by the order in which the routes are received. Consider the following scenario in which a router received three paths for the same prefix:
The clear ip bgp * command is entered to clear all routes in the local routing table.
Router# clear ip bgp *The show ip bgp command is issued again after the routing table has been repopulated. Note that the order of the paths changed after clearing the BGP session. The results of the selection algorithm also changed because the order in which the paths were received was different for the second session.
Router# show ip bgp 10.100.0.0BGP routing table entry for 10.100.0.0/16, version 2Paths: (3 available, best #3, advertised over EBGP)109 192.168.43.10 from 192.168.43.10 (192.168.43.1)Origin IGP, metric 0, localpref 100, valid, internal2051192.168.43.3 from 192.168.43.3 (10.4.1.1)Origin IGP, metric 30, valid, external2051192.168.43.22 from 192.168.43.22 (192.168.43.2)Origin IGP, metric 20, localpref 100, valid, internal, bestIf the bgp deterministic-med command is enabled, then the result of the selection algorithm will always be the same, regardless of the order in which the paths are received by the local router. The following output is always generated when the bgp deterministic-med command is entered on the local router in this scenario:
Router# show ip bgp 10.100.0.0BGP routing table entry for 10.100.0.0/16, version 15Paths: (3 available, best #1, advertised over EBGP)109192.168.43.10 from 192.168.43.10 (192.168.43.1)Origin IGP, metric 0, localpref 100, valid, internal, best 3192.168.43.22 from 192.168.43.22 (192.168.43.2)Origin IGP, metric 20, localpref 100, valid, internal 3192.168.43.3 from 192.168.43.3 (10.4.1.1)Origin IGP, metric 30, valid, externalRelated Commands
bgp dmzlink-bw
To configure BGP to distribute traffic proportionally over external links with unequal bandwidth when multipath load balancing is enabled, use the bgp dmzlink-bw command in address family configuration mode. To disable traffic distribution that is proportional to the link bandwidth, use the no form of this command.
bgp dmzlink-bw
no bgp dmzlink-bw
Syntax Description
This command has no arguments or keywords.
Command Default
BGP traffic is not distributed proportionally over external links with unequal bandwidth.
Command Modes
Address family configuration
Command History
Usage Guidelines
The bgp dmzlink-bw command is used to configure BGP to distribute traffic proportionally to the bandwidth of external links. This command is configured for multipath load balancing between directly connected external BGP (eBGP) neighbors. This command is used with BGP multipath features to configure load balancing over links with unequal bandwidth. The neighbor dmzlink-bw command must also be configured for each external link through which multipath load balancing is configured to advertise the link bandwidth as an extended community. The neighbor send-community command must be configured to exchange the link bandwidth extended community with internal BGP (iBGP) peers.
Examples
The following example shows how to configure the bgp dmzlink-bw command to allow multipath load balancing to distribute link traffic proportionally to the bandwidth of each external link and to advertise the bandwidth of these links to iBGP peers as an extended community:
Router(config)# router bgp 45000Router(config-router)# neighbor 10.10.10.1 remote-as 100Router(config-router)# neighbor 10.10.10.1 update-source Loopback 0Router(config-router)# neighbor 10.10.10.3 remote-as 100Router(config-router)# neighbor 10.10.10.3 update-source Loopback 0Router(config-router)# neighbor 172.16.1.1 remote-as 200Router(config-router)# neighbor 172.16.1.1 ebgp-multihop 1Router(config-router)# neighbor 172.16.2.2 remote-as 200Router(config-router)# neighbor 172.16.2.2 ebgp-multihop 1Router(config-router)# address-family ipv4Router(config-router-af)# bgp dmzlink-bwRouter(config-router-af)# neighbor 10.10.10.1 activateRouter(config-router-af)# neighbor 10.10.10.1 next-hop-selfRouter(config-router-af)# neighbor 10.10.10.1 send-community bothRouter(config-router-af)# neighbor 10.10.10.3 activateRouter(config-router-af)# neighbor 10.10.10.3 next-hop-selfRouter(config-router-af)# neighbor 10.10.10.3 send-community bothRouter(config-router-af)# neighbor 172.16.1.1 activateRouter(config-router-af)# neighbor 172.16.1.1 dmzlink-bwRouter(config-router-af)# neighbor 172.16.2.2 activateRouter(config-router-af)# neighbor 172.16.2.2 dmzlink-bwRouter(config-router-af)# maximum-paths ibgp 6Router(config-router-af)# maximum-paths 6Related Commands
bgp enforce-first-as
To configure a router to deny an update received from an external BGP (eBGP) peer that does not list its autonomous system number at the beginning of the AS_PATH in the incoming update, use the bgp enforce-first-as command in router configuration mode. To disable this behavior, use the no form of this command.
bgp enforce-first-as
no bgp enforce-first-as
Syntax Description
This command has no arguments or keywords.
Defaults
The behavior of this command is enabled by default.
Command Modes
Router configuration
Command History
Usage Guidelines
The bgp enforce-first-as command is used to deny incoming updates received from eBGP peers that do not list their autonomous system number as the first segment in the AS_PATH attribute. Enabling this command prevents a misconfigured or unauthorized peer from misdirecting traffic (spoofing the local router) by advertising a route as if it was sourced from another autonomous system.
Examples
In the following example, all incoming updates from eBGP peers are examined to ensure that the first autonomous system number in the AS_PATH is the local AS number of the transmitting peer. In the follow example, updates from the 10.100.0.1 peer will be discarded if the first AS number is not 65001.
Router(config)# router bgp 50000Router(config-router)# bgp enforce-first-asRouter(config-router)# address-family ipv4Router(config-router-af)# neighbor 10.100.0.1 remote-as 65001Router(config-router-af)# endbgp fast-external-fallover
To configure a Border Gateway Protocol (BGP) routing process to immediately reset external BGP peering sessions if the link used to reach these peers goes down, use the bgp fast-external-fallover command in router configuration mode. To disable BGP fast external fallover, use the no form of this command.
bgp fast-external-fallover
no bgp fast-external-fallover
Syntax Description
This command has no arguments or keywords.
Command Default
BGP fast external fallover is enabled by default in Cisco IOS software.
Command Modes
Router configuration
Command History
Usage Guidelines
The bgp fast-external-fallover command is used to disable or enable fast external fallover for BGP peering sessions with directly connected external peers. The session is immediately reset if link goes down. Only directly connected peering sessions are supported.
If BGP fast external fallover is disabled, the BGP routing process will wait until the default hold timer expires (3 keepalives) to reset the peering session. BGP fast external fallover can also be configured on a per-interface basis using the ip bgp fast-external-fallover interface configuration command.
Examples
In the following example, the BGP fast external fallover feature is disabled. If the link through which this session is carried flaps, the connection will not be reset.
Router(config)# router bgp 50000Router(config-router)# no bgp fast-external-falloverRelated Commands
bgp graceful-restart
To enable the Border Gateway Protocol (BGP) graceful restart capability globally for all BGP neighbors, use the bgp graceful-restart command in router configuration mode. To disable the BGP graceful restart capability globally for all BGP neighbors, use the no form of this command.
bgp graceful-restart [restart-time seconds | stalepath-time seconds] [all]
no bgp graceful-restart
Syntax Description
Command Default
The following default values are used when this command is entered without any keywords or arguments:
restart-time: 120 seconds
stalepath-time: 360 seconds
Note
Command Modes
Address-family configuration
Router configuration (router-config)Command History
Usage Guidelines
The bgp graceful-restart command is used to enable or disable the graceful restart capability globally for all BGP neighbors in a BGP network. The graceful restart capability is negotiated between nonstop forwarding (NSF)-capable and NSF-aware peers in OPEN messages during session establishment. If the graceful restart capability is enabled after a BGP session has been established, the session will need to be restarted with a soft or hard reset.
The graceful restart capability is supported by NSF-capable and NSF-aware routers. A router that is NSF-capable can perform a stateful switchover (SSO) operation (graceful restart) and can assist restarting peers by holding routing table information during the SSO operation. A router that is NSF-aware functions like a router that is NSF-capable but cannot perform an SSO operation.
The BGP graceful restart capability is enabled by default when a supporting version of Cisco IOS software is installed. The default timer values for this feature are optimal for most network deployments. We recommend that they are adjusted only by experienced network operators. When adjusting the timer values, the restart timer should not be set to a value greater than the hold time that is carried in the OPEN message. If consecutive restart operations occur, routes (from a restarting router) that were previously marked as stale will be deleted.
Note
Examples
In the following example, the BGP graceful restart capability is enabled:
Router# configure terminalRouter(config)# router bgp 65000Router(config-router)# bgp graceful-restartIn the following example, the restart timer is set to 130 seconds:
Router# configure terminalRouter(config)# router bgp 65000Router(config-router)# bgp graceful-restart restart-time 130In the following example, the stalepath timer is set to 350 seconds:
Router# configure terminalRouter(config)# router bgp 65000Router(config-router)# bgp graceful-restart stalepath-time 350Related Commands
show ip bgp
Displays entries in the BGP routing table.
show ip bgp neighbors
Displays information about the TCP and BGP connections to neighbors.
bgp inject-map
To configure conditional route injection to inject more specific routes into a Border Gateway Protocol (BGP) routing table, use the bgp inject-map command in address family or router configuration mode. To disable a conditional route injection configuration, use the no form of this command.
bgp inject-map inject-map exist-map exist-map [copy-attributes]
no bgp inject-map inject-map exist-map exist-map
Syntax Description
Command Default
No specific routes are injected into a BGP routing table.
Command Modes
Address family configuration
Router configurationCommand History
Usage Guidelines
The bgp inject-map command is used to configure conditional route injection. Conditional route injection allows you to originate a more specific prefix into a BGP routing table without a corresponding match. Two route maps (exist-map and inject-map) are configured in global configuration mode and then specified with the bgp inject-map command in address family or router configuration mode.
The exist-map argument specifies a route map that defines the prefix that the BGP speaker will track. This route map must contain a match ip address prefix-list command statement to specify the aggregate prefix and a match ip route-source prefix-list command statement to specify the route source.
The inject-map argument defines the prefixes that will be created and installed into the routing table. Injected prefixes are installed in the local BGP RIB. A valid parent route must exist; Only prefixes that are equal to or more specific than the aggregate route (existing prefix) can be injected.
The optional copy-attributes keyword is used to optionally configure the injected prefix to inherit the same attributes as the aggregate route. If this keyword is not entered, the injected prefix will use the default attributes for locally originated routes.
Examples
In the following example, conditional route injection is configured. Injected prefixes will inherit the attributes of the aggregate (parent) route.
Router(config)# ip prefix-list ROUTE permit 10.1.1.0/24Router(config)# ip prefix-list ROUTE_SOURCE permit 10.2.1.1/32Router(config)# ip prefix-list ORIGINATED_ROUTES permit 10.1.1.0/25Router(config)# ip prefix-list ORIGINATED_ROUTES permit 10.1.1.128/25Router(config)# route-map LEARNED_PATH permit 10Router(config-route-map)# match ip address prefix-list ROUTERouter(config-route-map)# match ip route-source prefix-list ROUTE_SOURCERouter(config-route-map)# exitRouter(config)# route-map ORIGINATE permit 10Router(config-route-map)# set ip address prefix-list ORIGINATED_ROUTESRouter(config-route-map)# set community 14616:555 additiveRouter(config-route-map)# exitRouter(config)# router bgp 50000Router(config-router)# address-family ipv4Router(config-router-af)# bgp inject-map ORIGINATE exist-map LEARNED_PATH copy-attributesRouter(config-router-af)# endRelated Commands
bgp listen
To associate a subnet range with a Border Gateway Protocol (BGP) peer group and activate the BGP dynamic neighbors feature, use the bgp listen command in router configuration mode. To disable the BGP dynamic neighbors feature, use the no form of this command.
bgp listen [limit max-number | range network/length peer-group peer-group-name]
no bgp listen [limit | range network/length peer-group peer-group-name]
Syntax Description
Command Default
No subnets are associated with a BGP listen range group, and the BGP dynamic neighbor feature is not activated.
Command Modes
Router configuration (config-router)
Command History
Usage Guidelines
Use the limit keyword and max-number argument to define the global maximum number of BGP dynamic neighbors that can be created.
BGP dynamic neighbors are configured using a range of IP addresses and BGP peer groups. Each range can be configured as a subnet IP address. After a subnet range is configured for a BGP peer group, and a TCP session is initiated for an IP address in the subnet range, a new BGP neighbor is dynamically created as a member of that group. The new BGP neighbor will inherit any configuration for the peer group. Only IPv4 peering is supported. The output for three show commands has been updated to display information about dynamic neighbors. The commands are show ip bgp neighbors, show ip bgp peer-group, and the show ip bgp summary command.
Examples
The following example configures a subnet range of 192.168.0.0/16 and associates this listen range with a BGP peer group. Note that the listen range peer group that is configured for the BGP dynamic neighbor feature can be activated in the IPv4 address family using the neighbor activate command. After the initial configuration on Router 1, when Router 2 starts a BGP router session and adds Router 1 to its BGP neighbor table, a TCP session is initiated and Router 1 creates a new BGP neighbor dynamically because the IP address of the new neighbor is within the listen range subnet.
Router 1
enableconfigure terminalrouter bgp 45000bgp log-neighbor-changesneighbor group192 peer-groupbgp listen range 192.168.0.0/16 peer-group group192neighbor group192 remote-as 40000 alternate-as 50000address-family ipv4 unicastneighbor group192 activateendRouter 2
enableconfigure terminalrouter bgp 50000neighbor 192.168.3.1 remote-as 45000exitIf the show ip bgp summary command is now entered on Router 1, the output shows the dynamically created BGP neighbor, 192.168.3.2.Router1# show ip bgp summaryBGP router identifier 192.168.3.1, local AS number 45000BGP table version is 1, main routing table version 1Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd*192.168.3.2 4 50000 2 2 0 0 0 00:00:37 0* Dynamically created based on a listen range commandDynamically created neighbors: 1/(100 max), Subnet ranges: 1BGP peergroup group192 listen range group members:192.168.0.0/16Related Commands
bgp log-neighbor-changes
To enable logging of BGP neighbor resets, use the bgp log-neighbor-changes command in router configuration mode. To disable the logging of changes in BGP neighbor adjacencies, use the no form of this command.
bgp log-neighbor-changes
no bgp log-neighbor-changes
Syntax Description
This command has no arguments or keywords.
Command Default
No default behavior or values
Command Modes
Router configuration
Command History
Usage Guidelines
The bgp log-neighbor-changes command enables logging of BGP neighbor status changes (up or down) and resets for troubleshooting network connectivity problems and measuring network stability. Unexpected neighbor resets might indicate high error rates or high packet loss in the network and should be investigated.
Using the bgp log-neighbor-changes command to enable status change message logging does not cause a substantial performance impact, unlike, for example, enabling per BGP update debugging. If the UNIX syslog facility is enabled, messages are sent to the UNIX host running the syslog daemon so that the messages can be stored and archived. If the UNIX syslog facility is not enabled, the status change messages are retained in the internal buffer of the router, and are not stored to disk. You can set the size of this buffer, which is dependent upon the available RAM, using the logging buffered command.
The neighbor status change messages are not tracked if the bgp log-neighbor-changes command is not enabled, except for the reset reason, which is always available as output of the show ip bgp neighbors and show bgp ipv6 neighbors commands.
The eigrp log-neighbor-changes command enables logging of Enhanced Interior Gateway Routing Protocol (EIGRP) neighbor adjacencies, but messages for BGP neighbors are logged only if they are specifically enabled with the bgp log-neighbor-changes command.
Use the show logging command to display the log for the BGP neighbor changes.
Examples
The following example logs neighbor changes for BGP in router configuration mode:
Router(config)# bgp router 40000Router(config-router)# bgp log-neighbor-changesRelated Commands
bgp maxas-limit
To configure Border Gateway Protocol (BGP) to discard routes that have a number of AS-path segments that exceed the specified value, use the bgp maxas-limit command in router configuration mode. To return the router to default operation, use the no form of this command.
bgp maxas-limit number
no bgp maxas-limit
Syntax Description
Command Default
No routes are discarded.
Command Modes
Router configuration
Command History
Usage Guidelines
The bgp maxas-limit command is used to limit the number of AS-path segments that are permitted in inbound routes. If a route is received with an AS-path segment that exceeds the configured limit, the BGP routing process will discard the route.
Examples
In the following example, the maximum AS-path segment length is set to 30:
Router(config)# router bgp 40000Router(config-router-af)# bgp maxas-limit 30Related Commands
bgp nexthop
To configure Border Gateway Protocol (BGP) next-hop address tracking, use the bgp nexthop command in address family or router configuration mode. To disable BGP next-hop address tracking, use the no form of this command.
bgp nexthop {trigger {delay seconds | enable} | route-map map-name}
no bgp nexthop {trigger {delay | enable} | route-map map-name}
Syntax Description
Command Default
BGP next-hop address tracking is enabled by default for IPv4 and VPNv4 address families.
Command Modes
Address family configuration
Router configurationCommand History
Usage Guidelines
BGP next-hop address tracking is event driven. BGP prefixes are automatically tracked as peering sessions are established. Next-hop changes are rapidly reported to BGP as they are updated in the routing information base (RIB). This optimization improves overall BGP convergence by reducing the response time to next-hop changes for routes installed in the RIB. When a best-path calculation is run in between BGP scanner cycles, only the changes are processed and tracked.
Note
Note
Use the trigger keyword with the delay keyword and seconds argument to change the delay interval between routing table walks for BGP next-hop address tracking. You can increase the performance of BGP next-hop address tracking by tuning the delay interval between full routing table walks to match the tuning parameters for the IGP. The default delay interval is 5 seconds, which is an optimal value for a fast-tuned IGP. In the case of an IGP that converges more slowly, you can change the delay interval to 20 seconds or more, depending on the IGP convergence time.
Use the trigger keyword with the enable keyword to enable BGP next-hop address tracking. BGP next-hop address tracking is enabled by default.
Use the route-map keyword and map-name argument to allow a route map to be used. The route map is used during the BGP best-path calculation and is applied to the route in the routing table that covers the Next_Hop attribute for BGP prefixes. If the next-hop route fails the route-map evaluation, the next-hop route is marked as unreachable. This command is per address family, so different route maps can be applied for next-hop routes in different address families.
Note
Examples
The following example shows how to change the delay interval between routing table walks for BGP next-hop address tracking to occur every 20 seconds under an IPv4 address family session:
router bgp 50000address-family ipv4 unicastbgp nexthop trigger delay 20endThe following example shows how to disable next-hop address tracking for the IPv4 address family:
router bgp 50000address-family ipv4 unicastno bgp nexthop trigger enableendThe following example shows how to configure a route map that permits a route to be considered as a next-hop route only if the address mask length is more than 25. This configuration will avoid any prefix aggregates being considered as a next-hop route.
router bgp 45000address-family ipv4 unicastbgp nexthop route-map CHECK-NEXTHOPexit-address-familyexitip prefix-list FILTER25 seq 5 permit 0.0.0.0/0 le 25route-map CHECK-NEXTHOP permit 10match ip address prefix-list FILTER25endRelated Commands
match ip address
Matches IP addresses defined by a prefix list.
match source-protocol
Matches the route type based on the source protocol.
bgp redistribute-internal
To configure iBGP redistribution into an interior gateway protocol (IGP), such as IS-IS or OSPF, use the bgp redistribute-internal command in address family or router configuration mode. To return the router to default behavior and stop iBGP redistribution into IGPs, use the no form of this command.
bgp redistribute-internal
no bgp redistribute-internal
Syntax Description
This command has no arguments or keywords.
Defaults
IBGP routes are not redistributed into IGPs.
Command Modes
Address family configuration
Router configurationCommand History
Usage Guidelines
The bgp redistribute-internal command is used to configure iBGP redistribution into an IGP. The clear ip bgp command must be entered to reset BGP connections after this command is configured.
When redistributing BGP into any IGP, be sure to use IP prefix-list and route-map statements to limit the number of prefixes that are redistributed.
Caution
Examples
In the following example, BGP to OSPF route redistribution is enabled:
Router(config)# router ospf 300Router(config-router)# redistribute bgp 200Router(config-router)# exitRouter(config)# router bgp 200Router(config-router)# address-family ipv4Router(config-router-af)# bgp redistribute-internalRouter(config-router-af)# endRouter# clear ip bgp *Related Commands
bgp regexp deterministic
To configure Cisco IOS software to use the deterministic processing time regular expression engine, use the bgp regexp deterministic command in router configuration mode. To configure Cisco IOS software to use the default regular expression engine, use the no form of this command.
bgp regexp deterministic
no bgp regexp deterministic
Syntax Description
This command has no arguments or keywords.
Command Default
The default regular expression engine is enabled.
Command Modes
Router configuration (config-router)
Command History
Usage Guidelines
The default Cisco IOS regular expression engine uses a recursive algorithm. This engine is effective but uses more system resources as the complexity of regular expressions increases. The recursive algorithm works well for simple regular expressions, but is less efficient when processing very complex regular expressions because of the backtracking that is required by the default engine to process partial matches. In some cases, CPU watchdog timeouts and stack overflow traces have occurred because of the length of time that the default engine requires to process very complex regular expressions.
The deterministic processing time regular expression engine does not replace the default regular expression engine. The deterministic processing time regular expression engine employs an improved algorithm that eliminates excessive backtracking and greatly improves performance when processing complex regular expressions. When the deterministic processing time regular expression engine is enabled, complex regular expressions are evaluated more quickly, and CPU watchdog timeouts and stack overflow traces will not occur. However, the deterministic processing time regular expression engine takes longer to process simple regular expressions than the default engine.
We recommend that you use the deterministic processing time regular expression engine if you need to evaluate complex regular expressions or if you have observed problems related to evaluating regular expressions. We recommend that you use the default regular expression engine if you use only simple regular expressions. The deterministic processing time regular expression engine can be enabled by entering the bgp regexp deterministic command under a Border Gateway Protocol (BGP) routing process. The default regular expression engine can be reenabled by entering the no form of this command.
Examples
The following example shows how to configure Cisco IOS software to use the deterministic processing time regular expression engine:
Router(config)# router bgp 50000Router(config-router)# bgp regexp deterministicThe following examples shows how to configure Cisco IOS software to use the default regular expression engine:
Router(config)# router bgp 50000Router(config-router)# no bgp regexp deterministicRelated Commands
router bgp
Configures the BGP routing process.
show ip bgp regexp
Displays routes matching the autonomous system path regular expression.
bgp router-id
To configure a fixed router ID for the local Border Gateway Protocol (BGP) routing process, use the bgp router-id command in router or address family configuration mode. To remove the fixed router ID from the running configuration file and restore the default router ID selection, use the no form of this command.
Router Configuration
bgp router-id {ip-address | vrf auto-assign}
no bgp router-id [vrf auto-assign]
Address Family Configuration
bgp router-id {ip-address | auto-assign}
no bgp router-id
Syntax Description
Command Default
The following behavior determines local router ID selection when this command is not enabled:
•
•
Command Modes
Router configuration (config-router)
Address family configuration (config-router-af)Command History
Usage Guidelines
The bgp router-id command is used to configure a fixed router ID for the local BGP routing process. The router ID is entered in IP address format. Any valid IP address can be used, even an address that is not locally configured on the router. If you use an IP address from a local interface, we recommend that you use the address of a loopback interface rather than the address of a physical interface. (A loopback interface is more effective than a fixed interface as an identifier because there is no physical link to go down.) Peering sessions are automatically reset when the router ID is changed.
In Cisco IOS Release 12.2(33)SRA, 12.2(31)SB2, 12.2(33)SXH, 12.4(20)T, and later releases, the Per-VRF Assignment of BGP Router ID feature introduced VRF-to-VRF peering in BGP on the same router. BGP is designed to refuse a session with itself because of the router ID check. The per-VRF assignment feature allows a separate router ID per VRF. The router ID can be manually configured for each VRF or automatically assigned either for each VRF or globally under address family configuration mode.
Examples
The following example shows how to configure the local router with a fixed BGP router ID of 192.168.254.254:
router bgp 50000bgp router-id 192.168.254.254The following example shows how to configure a BGP router ID for the VRF named VRF1. This configuration is done under address family IPv4 VRF configuration mode.
router bgp 45000address-family ipv4 vrf VRF1bgp router-id 10.1.1.99The following example shows how to configure an automatically assigned VRF BGP router ID for all VRFs. This configuration is done under BGP router configuration mode.
router bgp 45000bgp router-id vrf auto-assignThe following example shows how to configure an automatically assigned VRF BGP router ID for a single VRF. This configuration is done under address family IPv4 VRF configuration mode.
router bgp 45000address-family ipv4 vrf VRF2bgp router-id auto-assignRelated Commands
show ip bgp
Displays entries in the BGP routing table.
show ip bgp vpnv4
Displays VPNv4 address information from the BGP routing table.
bgp rr-group
To create a route-reflector group and enable automatic inbound filtering for VPN version 4 (VPNv4) updates based on the allowed route target (RT) extended communities, use the bgp rr-group command in address family configuration mode. To disable a route-reflector group, use the no form of this command.
bgp rr-group extcom-list-number
no bgp rr-group extcom-list-number
Syntax Description
Defaults
No default behavior or values
Command Modes
VPNv4 address family configuration
Command History
Usage Guidelines
The bgp rr-group command is used to partition large VPNv4 Border Gateway Protocol (BGP) networks into smaller route-reflector groups. Each route-reflector group permits only routes from route targets defined in an extended community list. Only one extended community list can be configured for each route-reflector group.
Examples
In the following example, a route-reflector group is created. The route target is associated with the VRF and then defined in an extended community list. This route reflector will accept routes from only route target 50000:1024.
Router(config)# ip vrf REDRouter(config-vrf)# rd 50000:10000Router(config-vrf)# route-target both 50000:10000Router(config-vrf)# route-target export 50000:1024Router(config-vrf)# exitRouter(config)# ip extcommunity-list 1 permit rt 50000:1024Router(config)# router bgp 50000Router(config-router)# address family vpnv4Router(config-router-af)# bgp rr-group 1Router(config-router-af)# neighbor 192.168.0.1 activateRouter(config-router-af)# neighbor 192.168.0.1 route-reflector-clientRouter(config-router-af)# neighbor 192.168.0.1 send-community extendedRouter(config-router-af)# endRelated Commands
bgp soft-reconfig-backup
To configure a Border Gateway Protocol (BGP) speaker to perform inbound soft reconfiguration for peers that do not support the route refresh capability, use the bgp soft-reconfig-backup command in address-family or r outer configuration mode. To disable this function, use the no form of this command.
bgp soft-reconfig-backup
no bgp soft-reconfig-backup
Syntax Description
This command has no arguments or keywords.
Command Default
Inbound soft reconfiguration for peers that do not support the route refresh capability is not performed.
Command Modes
Address-family configuration
Router configurationCommand History
Usage Guidelines
The bgp soft-reconfig-backup command is used to configure BGP to perform inbound soft reconfiguration for peers that do not support the route refresh capability. The configuration of this command allows you to configure BGP to store updates (soft reconfiguration) only as necessary. Peers that support the route refresh capability are unaffected by the configuration of this command.
Use the show ip bgp neighbors command to determine if a peer supports the route refresh capability. If supported, the following will be displayed in the output:
Route refresh: advertised and received(new)Use the show ip bgp command to determine if the BGP speaker is storing inbound updates for peer that does not support the route refresh capability. If updates are stored, the following will be displayed in the output:
(received-only)Examples
The following example, starting in Global configuration mode, configures the router perform inbound soft reconfiguration only if the peer does not support the route refresh capability:
Router(config)# router bgp 50000Router(config-router)# bgp soft-reconfig-backupRouter(config-router)# neighbor 10.1.1.1 remote-as 40000Router(config-router)# neighbor 192.168.1.1 remote-as 60000Related Commands
bgp suppress-inactive
To suppress the advertisement of routes that are not installed in the routing information base (RIB), use the bgp suppress-inactive command in address family or router configuration mode.
bgp suppress-inactive
no bgp suppress inactive
Syntax Description
This command has no arguments or keywords.
Command Default
No routes are suppressed.
Command Modes
Address family configuration
Router configurationCommand History
Usage Guidelines
The bgp suppress-inactive command is used to prevent routes that are not installed in the RIB (inactive routes) from being advertised to peers. If this feature is not enabled or if the no form of this command is used, Border Gateway Protocol (BGP) will advertise inactive routes.
Note
Examples
In the following example, the BGP routing process is configured to not advertise routes that are not installed in the RIB:
Router(config)# router bgp 500000Router(config-router)# address-family ipv4Router(config-router)# bgp suppress-inactiveRelated Commands
clear ip bgp
Resets a BGP connection using BGP soft reconfiguration.
show ip bgp rib-failure
Display BGP routes were not installed in the RIB.
bgp transport
To enable TCP transport session parameters globally for all Border Gateway Protocol (BGP) sessions, use the bgp transport command in router configuration mode. To disable TCP transport session parameters globally for all BGP sessions, use the no form of this command.
bgp transport path-mtu-discovery
no bgp transport path-mtu-discovery
Syntax Description
Command Default
TCP path MTU discovery is enabled by default for all BGP sessions.
Command Modes
Router configuration (config-router)
Command History
Usage Guidelines
This command is enabled by default because it is used to allow BGP sessions to take advantage of larger MTU links, which can be very important for internal BGP (iBGP) sessions. Use the show ip bgp neighbors command to ensure that TCP path MTU discovery is enabled.
Examples
The following example shows how to disable TCP path MTU discovery for all BGP sessions:
router bgp 45000no bgp transport path-mtu-discoveryThe following example shows how to enable TCP path MTU discovery for all BGP sessions:
router bgp 45000bgp transport path-mtu-discoveryRelated Commands
neighbor transport
Enables transport session parameters for a BGP neighbor session.
show ip bgp neighbors
Displays information about BGP and TCP connections to neighbors.
bgp update-delay
To set the maximum initial delay period before a Border Gateway Protocol (BGP)-speaking networking device sends its first updates, use the bgp update-delay command in router configuration mode. To remove the bgp update-delay command from the configuration file and restore the initial delay to its default value, use the no form of this command.
bgp update-delay seconds
no bgp update-delay
Syntax Description
seconds
The maximum delay, in seconds, before a BGP-speaking networking device sends its updates. The range is from 0 to 3600. The default is 120 seconds.
Command Default
If this command is not configured, the default initial delay value is 120 seconds.
Command Modes
Router configuration
Command History
Usage Guidelines
When BGP is started, it waits a specified period of time for its neighbors to be established themselves and to begin sending their initial updates. Once that period is complete, or when the time expires, the best path is calculated for each route, and the software starts sending advertisements out to its peers. This behavior improves convergence time because, if the software were to start sending advertisements out immediately, it would have to send extra advertisements if it later received a better path for the prefix from another peer.
The bgp update-delay command is used to tune the maximum time the software will wait after the first neighbor is established until it starts calculating best paths and sending out advertisements. This command can be used when configuring the bgp graceful-restart command as part of the Nonstop Forwarding (NSF) capability.
Examples
The following example sets the maximum initial delay to 240 seconds:
router bgp 65000bgp update-delay 240Related Commands
bgp upgrade-cli
To upgrade a Network Layer Reachability Information (NLRI) formatted router configuration file to the address-family identifier (AFI) format and set the router command-line interface (CLI) to use only AFI commands, use the bgp upgrade-cli command in router configuration mode.
bgp upgrade-cli
Syntax Description
This command has no keywords or arguments.
Command Default
NLRI commands are not upgraded to the AFI format.
Command Modes
Router configuration
Command History
Usage Guidelines
The bgp upgrade-cli command is used to upgrade a router that is running in the NLRI formatted CLI to the AFI CLI format. The upgrade is automatic and does not require any further configuration by the network operator, and no configuration information is lost but you cannot return to the NLRI configuration because a no form does not exist for this command. Several NLRI-based commands do not exist under the AFI format but have equivalent commands under the AFI format. See Table 1 for NLRI to AFI command mapping.
Examples
In the following example, the existing NLRI router configuration file is converted to the AFI format and the router is configured to use only AFI format commands:
Router(config)# router bgp 5Router(config-router)# bgp upgrade-clibgp-policy
To enable Border Gateway Protocol (BGP) policy accounting or policy propagation on an interface, use the bgp-policy command in interface configuration mode. To disable BGP policy accounting or policy propagation, use the no form of this command.
bgp-policy {accounting [{input | output} [source]] | destination {ip-prec-map | ip-qos-map} | source {ip-prec-map | ip-qos-map}}
no bgp-policy {accounting [input | output] | destination {ip-prec-map | ip-qos-map} |
source {ip-prec-map | ip-qos-map}}Syntax Description
Command Default
BGP policy accounting and policy propagation are not enabled on an interface.
Command Modes
Interface configuration
Command History
Usage Guidelines
For BGP policy propagation to function, you must enable BGP and either Cisco Express Forwarding (CEF) or distributed CEF (dCEF).
To specify the QoS policy based on the IP precedence or a QoS group, the proper route-map configuration must be in place (for example, the set ip precedence or set qos-group route-map configuration command). To display QoS policy information for the interface, use the show ip interface command.
Note
To specify the accounting policy, the proper route-map configuration must be in place matching specific BGP attributes using the set traffic-index command. In BGP router configuration mode, use the table-map command to modify the accounting buckets when the IP routing table is updated with routes learned from BGP. To display accounting policy information, use the show cef interface policy-statistics, show ip bgp, and show ip cef detail EXEC commands.
Examples
In the following example, the BGP policy propagation feature is enabled on an interface based on the source address and the IP precedence setting:
Router(config)# interface ethernet 4/0/0Router(config-int)# bgp-policy source ip-prec-mapRouter(config-int)# endIn the following example, the BGP policy accounting feature is configured using a source address on input traffic being enabled on GE-WAN interface 9/1. The policy is classified by autonomous system paths.
Router(config)# router bgp 50000Router(config-router)# no synchronizationRouter(config-router)# table-map bucketsRouter(config-router)# exitRouter(config)# ip as-path access-list 1 permit _10_Router(config)# ip as-path access-list 2 permit _11_Router(config)# route-map buckets permit 10Router(config-route-map)# match as-path 1Router(config-route-map)# set traffic-index 1Router(config-route-map)# exitRouter(config)# route-map buckets permit 20Router(config-route-map)# match as-path 2Router(config-route-map)# set traffic-index 2Router(config-route-map)# exitRouter(config)# route-map buckets permit 80Router(config-route-map)# set traffic-index 7Router(config-route-map)# exitRouter(config)# interface GE-WAN9/1Router(config-int)# ip address 10.0.2.2 255.255.255.0Router(config-int)# bgp-policy accounting input sourceRouter(config-int)# no negotiation autoRouter(config-int)# endRelated Commands
