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Cisco IOS IP Command Reference, Volume 2 of 4: Routing Protocols, Release 12.3 T
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IP Routing Protocol Commands: T Through V
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Introduction
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IP Routing Protocol Commands: A
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IP Routing Protocol Commands: B
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IP Routing Protocols Commands: C through H
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IP Routing Protocols Commands: ignore lsa mospf through ip ospf transmit-delay
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IP Routing Protocol Commands: ip policy route-map through is-type
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IP Routing Protocols Commands: K through M
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IP Routing Protocols Commands: N
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IP Routing Protocols Commands: O through R
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IP Routing Protocols Commands: send-lifetime through set-overload-bit
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IP Routing Protocols Commands: show bgp nsap through show ip bgp update-group
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IP Routing Protocols Commands: show ip cache policy through show ip local policy
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IP Routing Protocol Commands: show ip ospf through synchronization
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Table Of Contents
bgp bestpath cost-community ignore
bgp bestpath med missing-as-worst
bgp client-to-client reflection
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.
Defaults
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 AS 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 non-transitive 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 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.
Defaults
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
Syntax Description
This command has no arguments or keywords.
Defaults
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 Modes
Router configuration
Command History
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.
Examples
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.
Defaults
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
In the following example, a router that is configured to not evaluate the cost community attribute during the best path selection process:
Router(config)# router bgp 50000Router(config-router)# address-family ipv4 unicastRouter(config-router-af)# bgp 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
11.1
This command was introduced.
12.0(7)T
Address family configuration mode support was added.
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
All route reflectors must maintain stable sessions between all peers in the cluster. If stable sessions cannot be maintained, then overlay route reflector clusters should be used instead (route reflectors with different cluster IDs).
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 as-number
no bgp confederation identifier as-number
Syntax Description
as-number
Autonomous system number to be configured to internally include multiple autonomous systems.
Defaults
No default behavior or values
Command Modes
Router configuration
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 enables to you to retain a single Interior Gateway Protocol (IGP) for all the autonomous systems.
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(config)# router bgp 50000Router(config-router)# bgp confederation identifier 50000Router(config-router)# bgp confederation peers 50001 50002 50003 50004 50005 50006Router(config-router)# neighbor 10.2.3.4 remote-as 50001Router(config-router)# neighbor 10.4.5.6 remote-as 40000Router(config-router)# endRelated Commands
bgp confederation peers
Configures subautonomous systems to belong to a single confederation
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 as-number [... as-number]
no bgp confederation peers as-number [... as-number]
Syntax Description
Defaults
No default behavior or values
Command Modes
Router configuration
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.
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(config)# router bgp 50000Router(config-router)# bgp confederation identifier 50000Router(config-router)# bgp confederation peers 50001 50002 50003 50004 50005Related 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
11.0
This command was introduced.
12.0(7)T
Address family configuration mode support was added.
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.
Defaults
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
Defaults
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.
Defaults
Cisco IOS software does not enforce the deterministic comparison of the MED variable between all paths received from the same autonomous system when this command is not enabled or when the no form of this command is entered.
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 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 (AS) 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 AS 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 AS number in the AS_PATH is the local AS number of the transmitting peer. In the example below, 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.
Defaults
BGP fast external fallover is enabled by default in Cisco IOS software.
Command Modes
Router configuration
Command History
10.0
This command was introduced.
12.0(7)T
Address family configuration mode support was added.
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, use the bgp graceful-restart command in router configuration mode. To disable the BGP graceful restart capability, use the no form of this command.
bgp graceful-restart [restart-time seconds | stalepath-time seconds]
no bgp graceful-restart [restart-time seconds | stalepath-time seconds]
Syntax Description
Defaults
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
Router configuration
Command History
12.0(22)S
This command was introduced.
12.2(15)T
This command was integrated into Cisco IOS Release 12.2(15)T.
Usage Guidelines
The bgp graceful-restart command is used to configure or disable the graceful restart capability on a router in a BGP network. The graceful restart capability is negotiated between 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 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.
Examples
In the following example, the BGP graceful restart capability is enabled:
Router# configure terminalRouter(config)# router bgp 101Router(config-router)# bgp graceful-restartIn the following example, the restart timer is set to 240 seconds:
router# configure terminalrouter(config)# router bgp 101router(config-router)# bgp graceful-restart restart-time 130In the following example, the stalepath timer is set to 240 seconds:
router# configure terminalrouter(config)# router bgp 101router(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 [copy-attributes]
Syntax Description
Defaults
No default behavior or values
Command Modes
Address family configuration
Router configurationCommand History
12.0(14)ST
This command was introduced.
12.2(4)T
This command was integrated into Cisco IOS Release 12.2(4)T.
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 specifies 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 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 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 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.
Defaults
No default behavior or values
Command Modes
Router configuration
Command History
11.1 CC
This command was introduced.
12.0
This command was integrated into Cisco IOS release 12.0.
12.0(7)T
Address family configuration mode support was added.
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 command.
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
number
Specifies the number of autonomous system segments. The value that can be entered for this argument is a number from 1 to 2000.
Defaults
The default value in Cisco IOS software for the number argument is 75.
Command Modes
Router configuration
Command History
12.2
This command was introduced.
12.0(17)S
This command was integrated into Cisco IOS Release 12.0(17)S.
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 next-hop
To configure a loopback interface as the next hop for routes associated with a VPN routing and forwarding instance (VRF), use the bgp next-hop command in VRF configuration mode. To return the router to default operation, use the no form of this command.
bgp next-hop loopback number
no bgp next-hop
Syntax Description
loopback number
Specifies the number of the loopback interface. The value that can be entered for this argument is a number from 1 to 2147483647.
Defaults
The IP address of the source interface, from which the route was advertised is set as the next hop when this command is not enabled.
Command Modes
VRF configuration
Command History
Usage Guidelines
The bgp next-hop command is used in Multiprotocol Label Switching (MPLS) Virtual Private Network (VPN) and Tunnel Engineering (TE) configurations. This command allows you to configure a loopback interface as the next hop for routes that are associated with the specified VRF. This command can be used, for example, to configure VPN traffic to use a specific Label Switched Path (LSP) through an MPLS core network.
Examples
In the following example, loopback interface 0 is configured as the next hop for VPN traffic associated with VRF RED:
Router(config)# ip vrf REDRouter(config-vrf)# rd 40000:1Router(config-vrf)# route-target import 40000:2Router(config-vrf)# route-target export 40000:2Router(config-vrf)# bgp next-hop loopback 0Related Commands
ip vrf
Configures a VRF routing table.
show ip vrf
Displays the set of defined VRFs and associated interfaces.
bgp nexthop trigger enable
To enable Border Gateway Protocol (BGP) next-hop address tracking, use the bgp nexthop trigger enable 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 enable
no bgp nexthop trigger enable
Syntax Description
This command has no keywords or arguments.
Defaults
BGP next-hop address tracking is enabled by default under IPv4 and VPNv4 address-family sessions.
Command Modes
Address family configuration
Router ConfigurationCommand History
12.0(29)S
This command was introduced.
12.3(14)T
This command was integrated into Cisco IOS Release 12.3(14)T.
Usage Guidelines
The bgp nexthop trigger enable command is used to enable the BGP Support for Next-Hop Address Tracking feature. 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 RIB. This optimization improves overall BGP convergence by reducing the response time to next-hop changes for routes installed in the RIB. When a bestpath calculation is run in between BGP scanner cycles, only the changes are processed and tracked.
Note
Note
Examples
In the following example, next-hop address tracking is disabled under the IPv4 address family session:
Router(config)# router bgp 50000Router(config-router)# address-family ipv4 unicastRouter(config-router-af)# no bgp nexthop trigger enableRouter(config-router-af)# endRelated Commands
bgp nexthop trigger delay
To adjust the delay interval between routing table walks for Border Gateway Protocol (BGP) next-hop address tracking, use the bgp nexthop trigger delay command in address family or router configuration mode. To set the delay interval between routing table walks to the default value, use the no form of this command.
bgp nexthop trigger delay seconds
no bgp nexthop trigger delay
Syntax Description
seconds
The number of seconds for the delay. The range of values that can be entered is from 0 to 100 seconds.
Defaults
The routing table is walked every 5 seconds.
Command Modes
Address family configuration
Router ConfigurationCommand History
12.0(29)S
This command was introduced.
12.3(14)T
This command was integrated into Cisco IOS Release 12.3(14)T.
Usage Guidelines
The bgp nexthop trigger delay command is used to adjust the delay interval between routing table walks for BGP next-hop address tracking. You can increase the performance of this feature by tuning the delay interval between full routing table walks to match the tuning parameters for the Interior Gateway protocol (IGP). The default delay interval is 5 seconds. This value is optimal 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.
Note
Examples
In the following example, the delay interval is set to occur every 20 seconds under an IPv4 address family session:
Router(config)# router bgp 50000Router(config-router)# address-family ipv4 unicastRouter(config-router-af)# bgp nexthop trigger delay 20Router(config-router-af)# endRelated Commands
bgp nexthop trigger enable
Enables or disables BGP next-hop address tracking
neighbor fall-over
Configures BGP to use fast session deactivation for the specified peering session.
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 keywords or arguments.
Defaults
The default regular expression engine is enabled.
Command Modes
Router configuration
Command History
12.0(26)S
This command was introduced.
12.3(4)T
This command was integrated into Cisco IOS Release 12.3(4)T.
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 new engine employs an improved algorithm that eliminates excessive backtracking and greatly improves performance when processing complex regular expressions. When the new engine is enabled, complex regular expressions are evaluated more quickly, and CPU watchdog timeouts and stack overflow traces will not occur. However, the new regular expression engine takes longer to process simple regular expressions than the default engine.
We recommend that you use the new 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 new 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
In the following example, Cisco IOS software is configured to use the deterministic processing time regular expression engine:
Router(config)# router bgp 50000Router(config-router)# bgp regexp deterministicIn the following example, Cisco IOS software configured to use the default regular expression engine:
Router(config)# router bgp 50000Router(config-router)# no bgp regexp deterministicbgp 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 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.
bgp router-id ip-address
no bgp router-id ip-address
Syntax Description
Defaults
The following behavior determines local router ID selection when this command is not enabled:
•
•
Command Modes
Router configuration
Command History
Usage Guidelines
The bgp router-id command is used to configure a fixed router ID for a local BGP routing process. The router ID is entered in the 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 a physical interface. (The 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.
Examples
In the following example, the local router configured with a fixed router ID of 192.168.254.254:
Router(config)# router bgp 50000Router(config-router)# bgp router-id 192.168.254.254Related Commands
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 only accept routes from 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.
Defaults
No default behavior or values
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 keywords or arguments.
Defaults
No default behavior or values
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, BGP will advertise inactive routes.
Note
Examples
In the following example, 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 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.
Defaults
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 an NLRI formatted router configuration file to the address-family identifier (AFI) format and set the router 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.
Defaults
Address family commands are enabled. NLRI commands are no longer valid after the upgrade is complete.
Command Modes
Address family configuration
Router configurationCommand 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. No configuration information lost. 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 | destination [ip-prec-map] | [ip-qos-map]} [input | output] [source ip-prec-map | ip-qos-map]
no bgp-policy {accounting | destination [ip-prec-map] | [ip-qos-map]} [input | output] [source ip-prec-map | ip-qos-map]
Syntax Description
Defaults
No default behavior or values
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 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)# !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
