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Cisco IOS XR Routing Command Reference, Release 3.5
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Preface
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BGP Commands on Cisco IOS XR Software
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EIGRP Commands on Cisco IOS XR Software
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IS-IS Commands on Cisco IOS XR Software
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OSPF Commands on Cisco IOS XR Software
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OSPFv3 Commands on Cisco IOS XR Software
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RIB Commands on Cisco IOS XR Software
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RIP Commands on Cisco IOS XR Software
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Routing Policy Language Commands on Cisco IOS XR Software
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Static Routing Commands on Cisco IOS XR Software
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Index
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Table Of Contents
BGP Commands on Cisco IOS XR Software
bgp auto-policy-soft-reset disable
bgp bestpath cost-community ignore
bgp bestpath med missing-as-worst
bgp client-to-client reflection disable
bgp fast-external-fallover disable
bgp graceful-restart graceful-reset
bgp graceful-restart purge-time
bgp graceful-restart restart-time
bgp graceful-restart stalepath-time
bgp log neighbor changes disable
clear bgp nexthop performance-statistics
clear bgp nexthop registration
clear bgp performance-statistics
default-information originate (BGP)
show bgp truncated-communities
BGP Commands on Cisco IOS XR Software
This chapter describes the commands used to configure and monitor Border Gateway Protocol (BGP) for IP Version 4 (IPv4), IP Version 6 (IPv6), and Virtual Private Network Version 4 (VPNv4), VPN Version 6 (VPNv6), and multicast distribution tree (MDT) (MVPN) routing sessions.
For detailed information about BGP concepts, configuration tasks, and examples, see Implementing BGP on Cisco IOS XR Software in Cisco IOS XR Routing Configuration Guide.
address-family (BGP)
To enter various address family configuration modes while configuring Border Gateway Protocol (BGP), use the address-family command in an appropriate configuration mode. To disable support for an address family, use the no form of this command.
address-family {ipv4 unicast | ipv4 multicast | ipv4 labeled-unicast | ipv4 tunnel | ipv4 mdt | ipv6 unicast | ipv6 multicast | ipv6 labeled-unicast | vpnv4 unicast | vpnv6 unicast}
no address-family {ipv4 unicast | ipv4 multicast | ipv4 labeled-unicast | ipv4 tunnel | ipv4 mdt | ipv6 unicast | ipv6 multicast | ipv6 labeled-unicast | vpnv4 unicast | vpnv6 unicast}
Syntax Description
Defaults
An address family must be explicitly configured in the router configuration mode for the address family to be active in BGP. Similarly, an address family must be configured under the neighbor for the BGP session to be established for that address family. An address family must be configured in router configuration mode before it can be configured under a neighbor.
Command Modes
Router configuration
Neighbor configuration
Neighbor group configuration
VRF configuration
VRF neighbor configuration (IPv4 address families)Command History
Usage Guidelines
To use this command, you must be in a user group associated with a task group that includes the proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.
Use the address-family command to enter various address family configuration modes while configuring BGP routing sessions. When you enter the address-family command from router configuration mode, you enable the address family and enter global address family configuration mode.
The IPv4 unicast address family must be configured in router configuration mode before configuring the IPv4 labeled-unicast address family for a neighbor in neighbor configuration mode. The IPv6 unicast address family must be configured in router configuration mode before configuring the IPv6 labeled-unicast address family for a neighbor in neighbor configuration mode.
When you enter the address-family command from neighbor configuration mode, you activate the address family on the neighbor and enter neighbor address family configuration mode.
IPv4 neighbor sessions support IPv4 unicast, multicast, labeled-unicast, and VPNv4 unicast address families. IPv6 neighbor sessions support IPv6 unicast and multicast address families.
Note
It is not necessary to have an address family configured in router configuration mode for either an IPv4 or IPv6 neighbor to be configured. However, to be able to configure an address family under a neighbor, the same address family must be configured in router configuration mode. It is not possible to bring up a session for a neighbor under a specific address family unless the address family is configured for the neighbor.
Task ID
Examples
The following example shows how to place the router in global address family configuration mode for the IPv4 address family:
RP/0/RP0/CPU0:router# configureRP/0/RP0/CPU0:router(config)# router bgp 100RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 unicastRP/0/RP0/CPU0:router(config-bgp-af)#The following example shows how to activate IPv4 multicast for neighbor 10.0.0.1 and place the router in neighbor address family configuration mode for the IPv4 multicast address family:
RP/0/RP0/CPU0:router# configureRP/0/RP0/CPU0:router(config)# router bgp 1RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 multicastRP/0/RP0/CPU0:router(config-bgp-af)# exitRP/0/RP0/CPU0:router(config-bgp)# neighbor 10.0.0.1RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 1RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv4 multicastRP/0/RP0/CPU0:router(config-bgp-nbr-af)#The following example shows how to place the router in global address family configuration mode for the IPv4 address family:
RP/0/RP0/CPU0:router# configureRP/0/RP0/CPU0:router(config)# router bgp 12RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 tunnelRP/0/RP0/CPU0:router(config-bgp-af)#advertisement-interval
To set the minimum interval between the sending of Border Gateway Protocol (BGP) routing updates, use the advertisement-interval command in an appropriate configuration mode. To remove the advertisement-interval command from the configuration file and restore the system to its default interval values, use the no form of this command.
advertisement-interval seconds
no advertisement-interval [seconds]
Syntax Description
Defaults
Default minimum interval:
For internal BGP (iBGP) peers is 0 seconds
For external BGP (eBGP) peers is 30 seconds
For customer edge (CE) peers is 0 secondsCommand Modes
Neighbor configuration
Neighbor group configuration
Session group configuration
VRF neighbor configurationCommand History
Usage Guidelines
To use this command, you must be in a user group associated with a task group that includes the proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.
If this command configures a neighbor group or session group, all neighbors using the group inherit the configuration. Values of commands configured specifically for a neighbor override inherited values.
Task ID
Examples
The following example shows how to set the minimum time between sending BGP routing updates to 10 seconds:
RP/0/RP0/CPU0:router(config)# router bgp 5RP/0/RP0/CPU0:router(config-bgp)# neighbor 10.1.1.1RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 100RP/0/RP0/CPU0:router(config-bgp-nbr)# advertisement-interval 10Related Commands
Creates a neighbor group and enters neighbor group configuration mode.
Creates a session group and enters session group configuration mode.
af-group
To create an address family group for Border Gateway Protocol (BGP) neighbors and enter address family group configuration mode, use the af-group command in router configuration mode. To remove an address family group, use the no form of this command.
af-group af-group-name address-family {ipv4 unicast | ipv4 multicast | ipv4 labeled-unicast | ipv4 tunnel | ipv4 mdt | ipv6 unicast | ipv6 multicast | ipv6 labeled-unicast | vpnv4 unicast | vpnv6 unicast}
no af-group af-group-name address-family {ipv4 unicast | ipv4 multicast | ipv4 labeled-unicast | ipv4 tunnel | ipv4 mdt | ipv6 unicast | ipv6 multicast | ipv6 labeled-unicast | vpnv4 unicast | vpnv6 unicast}
Syntax Description
Defaults
No BGP address family group is configured.
Command Modes
Router configuration
Command History
Usage Guidelines
To use this command, you must be in a user group associated with a task group that includes the proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.
Use the af-group command to group address family-specific neighbor commands within an IPv4 or IPv6 address family. Neighbors that have address family configuration are able to use the address family group. Further, neighbors inherit the configuration parameters of the entire address family group.
You cannot define two address family groups with the same name in different address families.
Task ID
Examples
The following example shows how to create address family group group1 and enter address family group configuration mode for IPv4 unicast. Group1 contains the next-hop-self feature, which is inherited by neighbors that use address family group1.
RP/0/RP0/CPU0:router(config)# router bgp 100RP/0/RP0/CPU0:router(config-bgp)# af-group group1 address-family ipv4 unicastRP/0/RP0/CPU0:router(config-bgp-afgrp)# next-hop-selfRelated Commands
aggregate-address
To create an aggregate entry in a Border Gateway Protocol (BGP) routing table, use the aggregate-address command in an appropriate configuration mode. To remove the aggregate-address command from the configuration file and restore the system to its default condition, use the no form of this command.
aggregate-address address/mask-length [as-set] [as-confed-set] [summary-only] [route-policy route-policy-name]
no aggregate-address address/mask-length [as-set] [as-confed-set] [summary-only] [route-policy route-policy-name]
Syntax Description
Defaults
When you do not specify this command, no aggregate entry is created in the BGP routing table.
Command Modes
IPv4 address family configuration
IPv6 address family configuration
VRF IPv4 address family configuration
VRF IPv6 address family configurationCommand History
Usage Guidelines
To use this command, you must be in a user group associated with a task group that includes the proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.
You can implement aggregate routing in BGP either by redistributing an aggregate route into BGP using the network command or the aggregate-address command.
Use the aggregate-address command without optional arguments to create an aggregate entry in the BGP routing table if any more-specific BGP routes are available that fall in the specified range. The aggregate route is advertised as coming from your autonomous system and has 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.)
Use of the as-set keyword creates an aggregate entry using the same rules that the command follows without this keyword. However, the advertised path for this route is an AS_SET, a set of all autonomous systems 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.
Use the as-confed-set keyword to create an AS_CONFED_SET in the autonomous system path of the aggregate from any confederation segments in the paths being summarized. This keyword takes effect only if the as-set keyword is also specified.
Use of the summary-only keyword creates an aggregate entry (for example, 10.0.0.0/8) but suppresses advertisements of more-specific routes to all neighbors. If you want to suppress only advertisements to certain neighbors, use the route-policy (BGP) command in neighbor address family configuration mode with caution. If a more-specific route leaks out, all BGP speakers (the local router) prefer that route over the less-specific aggregate you generate (using longest-match routing).
Use the route-policy keyword to specify a routing policy for the aggregate entry. The route-policy keyword is used to select which more-specific information to base the aggregate entry on and which more-specific information to suppress. You can also use the keyword to modify the attributes of the aggregate entry.
Task ID
Examples
The following example shows how to create an aggregate address. The path advertised for this route is an autonomous system set consisting of all elements contained in all paths that are being summarized.
RP/0/RP0/CPU0:router(config)# router bgp 100RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 unicastRP/0/RP0/CPU0:router(config-bgp-af)# aggregate-address 10.0.0.0/8 as-setRelated Commands
allocate-label
To allocate Multiprotocol Label Switching (MPLS) labels for specific IPv4 unicast or VPN routing and forwarding (VRF) IPv4 unicast routes so that the BGP router can send labels with BGP routes to a neighboring router configured for labeled-unicast sessions, use the allocate-label command in the appropriate configuration mode. To restore the system to its default condition, use the no form of this command.
allocate-label {route-policy route-policy-name | all}
no allocate-label {route-policy route-policy-name | all}
Syntax Description
Defaults
No default behavior or values
Command Modes
IPv4 address family configuration
IPv6 address family configuration
VRF IPv4 address family configuration
VRF IPv6 address family configurationCommand History
Usage Guidelines
To use this command, you must be in a user group associated with a task group that includes the proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.
Use the allocate-label command with a route policy to trigger BGP to allocate labels for all or a filtered set of global IPv4 routes (as dictated by the route policy). The command enables autonomous system border routers (ASBRs) that have labeled IPv4 unicast sessions to exchange Multiprotocol Label Switching (MPLS) labels with the IPv4 routes to the other autonomous system (AS) in Layer 3 Virtual Private Network (L3VPN) inter-AS deployments.
Note
See Cisco IOS XR Multiprotocol Label Switching Configuration Guide for information on using the allocate-label command for L3VPN inter-AS deployments and carrier-supporting-carrier IPv4 BGP label distribution.
Task ID
Examples
The following example shows how to enable allocating labels for IPv4 routes:
RP/0/0/CPU0:router(config)# router bgp 6RP/0/0/CPU0:router(config-bgp)# address family ipv4 unicastRP/0/0/CPU0:router(config-bgp-af)# allocate-label route-policy policy_Aallowas-in
To allow an AS path with the provider edge (PE) autonomous system number (ASN) a specified number of times, use the allowas-in command in an appropriate configuration mode. To restore the system to its default condition, use the no form of this command.
allowas-in [as-occurrence-number]
no allowas-in [as-occurrence-number]
Syntax Description
Defaults
No default behavior or values
Command Modes
Address family group configuration
Neighbor address family configurationCommand History
Release 3.3.0
This command was introduced on the Cisco CRS-1 and Cisco XR 12000 Series Router.
Release 3.4.0
No modification.
Release 3.5.0
No modification.
Usage Guidelines
To use this command, you must be in a user group associated with a task group that includes the proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.
Hub and spoke VPN networks require looping back of routing information to the hub PE through the hub customer edge (CE). See Cisco IOS XR Multiprotocol Label Switching Configuration Guide for information on hub and spoke VPN networks. This looping back, in addition to the presence of the PE ASN, causes the looped-back information to be dropped by the hub PE.
The allowas-in command prevents the looped-back information from being dropped by replacing the neighbor autonomous system number (ASN) with the PE ASN in the AS path. This allows the VPN customer to see a specified number of occurrences of the PE ASN in the AS path.
Task ID
Examples
The following example shows how to allow five occurrences of the PE ASN:
RP/0/RP0/CPU0:router(config)# router bgp 6RP/0/RP0/CPU0:router(config-bgp)# af-group group_1 address-family vpnv4 unicastRP/0/RP0/CPU0:router(config-bgp-afgrp)# allowas-in 5as-override
To configure a provider edge (PE) router to override the autonomous system number (ASN) of a site with the ASN of a provider, use the as-override command in VRF neighbor address family configuration mode. To restore the system to its default condition, use the no form of this command.
as-override [disable]
no as-override [disable]
Syntax Description
Defaults
Automatic override of the ASN is disabled.
Command Modes
VRF neighbor address family configuration
Command History
Release 3.3.0
This command was introduced on the Cisco CRS-1 and Cisco XR 12000 Series Router.
Release 3.4.0
No modification.
Release 3.5.0
No modification.
Usage Guidelines
To use this command, you must be in a user group associated with a task group that includes the proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.
Use the as-override command in conjunction with the site-of-origin (SoO) feature, identifying the site where a route originated, and preventing routing loops between routers within a VPN.
Task ID
Examples
The following example shows how to configure an ASN override:
RP/0/RP0/CPU0:router(config)# router bgp 6RP/0/RP0/CPU0:router(config-bgp)# vrf vrf_ARP/0/RP0/CPU0:router(config-bgp-vrf)# neighbor 192.168.70.24RP/0/RP0/CPU0:router(config-bgp-vrf-nbr)# remote-as 10RP/0/RP0/CPU0:router(config-bgp-vrf-nbr)# address-family ipv4 unicastRP/0/RP0/CPU0:router(config-bgp-vrf-nbr-af)# as-overrideRelated Commands
bgp as-path-loopcheck
To enable loop checking in the autonomous system path of the prefixes advertised by internal Border Gateway Protocol (iBGP) peers, use the bgp as-path-loopcheck command in an appropriate configuration mode. To restore the system to its default condition, use the no form of this command.
bgp as-path-loopcheck
no bgp as-path-loopcheck
Syntax Description
This command has no arguments or keywords.
Defaults
When you do not specify this command, loop checking is performed only for external peers.
Command Modes
Router configuration
Command History
Usage Guidelines
To use this command, you must be in a user group associated with a task group that includes the proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.
Task ID
Examples
The following example shows how to configure an autonomous system path for loop checking iBGP peers:
RP/0/RP0/CPU0:router(config)# router bgp 6RP/0/RP0/CPU0:router(config-bgp)# bgp as-path-loopcheckbgp attribute-download
To enable Border Gateway Protocol (BGP) attribute download, use the bgp attribute-download command in an appropriate configuration mode. To disable BGP attribute download, use the no form of this command.
bgp attribute-download
no bgp attribute-download
Syntax Description
This command has no arguments or keywords.
Defaults
BGP attribute download is not enabled.
Command Modes
IPv4 unicast address family configuration
Command History
Usage Guidelines
To use this command, you must be in a user group associated with a task group that includes the proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.
When BGP attribute download is enabled using the bgp attribute-download command, BGP reinstalls all routes whose attributes are not currently in the RIB. Likewise, if the user disables BGP attribute download using the no form of the command, BGP reinstalls previously installed routes with a null key, and removes the attributes from the RIB.
Use the bgp attribute-download command to enable the Netflow BGP data export function. When attribute download is enabled, BGP downloads the attribute information for prefixes (community, extended community, and as-path) to the Routing Information Base (RIB) and Forwarding Information Base (FIB). This enables FIB to associate the prefixes with attributes and send the Netflow statistics along with the associated attributes.
Task ID
Examples
The following example shows the BGP routes before and after BGP attribute download is enabled and shows how to enable BGP attribute download on BGP router 50:
RP/0/RP0/CPU0:router# show route bgpB 100.0.1.0/24 [200/0] via 10.0.101.1, 00:00:37B 100.0.2.0/24 [200/0] via 10.0.101.1, 00:00:37B 100.0.3.0/24 [200/0] via 10.0.101.1, 00:00:37B 100.0.4.0/24 [200/0] via 10.0.101.1, 00:00:37B 100.0.5.0/24 [200/0] via 10.0.101.1, 00:00:37RP/0/RP0/CPU0:router(config)# router bgp 50RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 unicastRP/0/RP0/CPU0:router(config-bgp-af)# bgp attribute-download!!!RP/0/RP0/CPU0:router# show route bgpB 100.0.1.0/24 [200/0] via 10.0.101.1, 00:00:01Attribute ID 0x2B 100.0.2.0/24 [200/0] via 10.0.101.1, 00:00:01Attribute ID 0x2B 100.0.3.0/24 [200/0] via 10.0.101.1, 00:00:01Attribute ID 0x2B 100.0.4.0/24 [200/0] via 10.0.101.1, 00:00:01Attribute ID 0x2B 100.0.5.0/24 [200/0] via 10.0.101.1, 00:00:01Attribute ID 0x2bgp auto-policy-soft-reset disable
To disable an automatic soft reset of Border Gateway Protocol (BGP) peers when their configured route policy is modified, use the bgp auto-policy-soft-reset disable command in an appropriate configuration mode. To re-enable automatic soft reset of BGP peers, use the no form of this command.
bgp auto-policy-soft-reset disable
no bgp auto-policy-soft-reset disable
Syntax Description
This command has no arguments or keywords.
Defaults
Automatic soft reset of peers is enabled.
Command Modes
Router configuration
VRF configurationCommand History
Usage Guidelines
To use this command, you must be in a user group associated with a task group that includes the proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.
Note
Task ID
Examples
The following example shows how to disable an automatic soft reset of BGP peers when their configured route policy is modified:
RP/0/RP0/CPU0:router(config)# router bgp 6RP/0/RP0/CPU0:router(config-bgp)# bgp auto-policy-soft-reset disablebgp bestpath as-path ignore
To ignore the autonomous system path length when calculating preferred paths, use the bgp bestpath as-path ignore command in an appropriate configuration mode. To return the software to the default state in which it considers the autonomous system path length when calculating preferred paths, 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 autonomous system path length is used (not ignored) when a best path is selected.
Command Modes
Router configuration
VRF configurationCommand History
Usage Guidelines
To use this command, you must be in a user group associated with a task group that includes the proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.
Use the bgp bestpath as-path ignore command to ignore the length of autonomous system paths when the software selects a preferred path. When the best path is selected, if this command is specified, all steps are performed as usual except comparison of the autonomous path length between candidate paths.
Task ID
Examples
The following example shows how to configure the software to ignore the autonomous system length when performing best-path selection:
RP/0/RP0/CPU0:router(config)# router bgp 65000RP/0/RP0/CPU0:router(config-bgp)# bgp bestpath as-path ignoreRelated Commands
bgp bestpath compare-routerid
To compare identical routes received from external BGP (eBGP) peers during the best-path selection process and select the route with the lowest router ID, use the bgp bestpath compare-routerid command in an appropriate configuration mode. To disable comparing identical routes received from eBGP peers during best-path selection, 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 software does not select a new best path if it is the same as the current best path (according to the BGP selection algorithm) except for the router ID.
Command Modes
Router configuration
VRF configurationCommand History
Usage Guidelines
To use this command, you must be in a user group associated with a task group that includes the proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.
Use the bgp bestpath compare-routerid command to affect how the software selects the best path, in the case where there are two paths of equal cost according to the BGP selection algorithm. This command is used to force the software to select the path with the lower router ID as the best path. If this command is not used, the software continues to use whichever path is currently the best path, regardless of which has the lower router ID.
Task ID
Examples
The following example shows how to configure the BGP speaker in autonomous system 500 to compare the router IDs of similar paths:
RP/0/RP0/CPU0:router(config)# router bgp 500RP/0/RP0/CPU0:router(config-bgp)# 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 an appropriate configuration mode. To restore the system to its default condition, use the no form of this command.
bgp bestpath cost-community ignore
no bgp bestpath cost-community ignore
Syntax Description
This command has no arguments or keywords.
Defaults
The behavior of this command is enabled by default until the cost community attribute is manually configured.
Command Modes
Router configuration
VRF configurationCommand History
Release 3.3.0
This command was first supported on the Cisco CRS-1 and Cisco XR 12000 Series Router.
Release 3.4.0
No modification.
Release 3.5.0
No modification.
Usage Guidelines
To use this command, you must be in a user group associated with a task group that includes the proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.
Use the bgp bestpath cost-community ignore command 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.
Task ID
Examples
The following example shows how to configure a router to not evaluate the cost community attribute during the best-path selection process:
RP/0/RP0/CPU0:router(config)# router bgp 500RP/0/RP0/CPU0:router(config-bgp)# bgp bestpath cost-community ignoreRelated Commands
bgp bestpath med always
To allow the comparison of the Multi Exit Discriminator (MED) for paths from neighbors in different autonomous systems, use the bgp bestpath med always command in an appropriate configuration mode. To disable considering the MED attribute in comparing paths, use the no form of this command.
bgp bestpath med always
no bgp bestpath med always
Syntax Description
This command has no arguments or keywords.
Defaults
The software does not compare MEDs for paths from neighbors in different autonomous systems.
Command Modes
Router configuration
VRF configurationCommand History
Usage Guidelines
To use this command, you must be in a user group associated with a task group that includes the proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.
The MED is one of the parameters that is considered by the software when selecting the best path among many alternative paths. The software chooses the path with the lowest MED.
By default, during the best-path selection process, the software makes a MED comparison only among paths from the same autonomous system. This command changes the default behavior of the software by allowing comparison of MEDs among paths regardless of the autonomous system from which the paths are received.
When the bgp bestpath med always command is not enabled and distributed BGP is configured, speakers calculate partial best paths only (executes the best-path steps up to the MED comparison) and send them to BGP Routing Information Base (bRIB). bRIB calculates the final best path (executes all the steps in the best-path calculation). When the bgp bestpath med always command is enabled and distributed BGP is configured, speakers can compare the MED across all ASs, allowing the speaker to calculate a single best path to send it to bRIB. bRIB is the ultimate process that calculates the final best path, but when the bgp bestpath med always command is enabled, the speakers send a single best path instead of pote
