BGP Large Community

The BGP large communities attribute provides the capability for tagging routes and modifying BGP routing policy on routers. BGP large communities can be appended or removed selectively on the large communities attribute as the route travels from router to router. The BGP large communities are similar attributes to BGP communities, but with a twelve octet size. The large communities attribute specifies an unordered set of non-duplicated large communities. However, there are no well-known large communities as in communities. The BGP large communities are split logically into a 4 octet Global Administrator field and a 8 octet Local Administrator field. A 4 octet Autonomous System can fit into the Global Administrator field.

Information About the BGP Large Community Feature

BGP Large Community Overview

The BGP large communities attribute provides the capability for tagging routes and modifying BGP routing policy on routers. BGP large communities can be appended or removed selectively on the large communities attribute as the route travels from router to router. When large communities are specified in commands, they are specified as three non-negative decimal integers separated by colons. For example as 1:2:3. The first interger represents the Global Administrator field, and the other two integers represent the Local Administrator field.

The BGP large communities attribute behaves similar to regular communities and is used for the similar purposes. For more information on BGP large community, see the rfc8092 document.

Large Community Lists

A BGP large community list is used to create groups of large communities which can be used in a match clause of a route map. You can use large communities to control the routing policy. Routing policy allows you to filter the routes you receive or advertise, or modify the attributes of the routes you receive or advertise. You can also use a large community list to delete the large communities selectively. There are two types of large community lists:

  • Standard large community lists-—Specifies large communities.

  • Expanded large community lists—Specifies large communities using a regular expression.

A large community list can be either named or numbered. Both named and numbered large community lists can be either standard or expanded. All the rules of numbered large community lists apply to named large community lists, except that there is no limit on the number of named community lists that can be configured.


Note

A maximum of 99 (range 1-99) numbered standard large community lists and 401 (range 100-500) numbered expanded large community lists can be configured. Named large community lists do not have this limitation.

BGP Large Communities Attribute

In a BGP large community, the large community value is encoded as a 12 octet number. The following image displays the syntax of the large communities attribute.

How to Configure the BGP Large Community

Enabling BGP Large Communities

To enable large communities, perform the following steps.

SUMMARY STEPS

  1. configure terminal
  2. router bgp autonomous-system-number
  3. neighbor IP address remote-as autonomous-system-number
  4. address-family {ipv4 | ipv6} {unicast | multicast}
  5. neighbor IP address activate
  6. neighbor IP address send-community [both | extended | standard]
  7. exit
  8. exit
  9. end

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 2

router bgp autonomous-system-number

Example:


Device(config)# router bgp 64496

Enters router configuration mode for the specified routing process.

Step 3

neighbor IP address remote-as autonomous-system-number

Example:


Device(config-router)# neighbor 209.165.201.1 remote-as 100

Enters global address family configuration mode.

Step 4

address-family {ipv4 | ipv6} {unicast | multicast}

Example:


Device(config-router-neighbor)# address-family ipv4 multicast

Enters global address family configuration mode.

Note

 

It also supports other available address families.

Step 5

neighbor IP address activate

Example:


Device(config-router-af)# neighbor 209.165.201.1 activate

Enters global address family configuration mode and activates the BGP neighbor.

Step 6

neighbor IP address send-community [both | extended | standard]

Example:


Device(config-router-neighbor-af)# neighbor 209.165.201.1 send-community standard

Configures the router to send the large communities attribute to the neighbor 209.165.201.1.

  • Both—Sends extended community, large community, and standard communities attributes to the neighbor.

  • Extended—Sends the extended communities attribute to the neighbor.

  • Standard—Sends large community and also standard communities attribute to the neighbor.

    Note

     

    When configuring the command, not specifying any keyword is equivalent to configuring the standard keyword (no keyword will be displayed in the configuration). When configuring both standard keyword and extended keyword, that will be equivalent to configuring both keyword (both keyword is displayed in the configuration).

Step 7

exit

Example:


Device(config-router-neighbor-af)# exit

Exits address-family mode and enters global configuration mode.

Step 8

exit

Example:


Device(config-router)# exit

Exits router configuration mode and enters global configuration mode.

Step 9

end

Example:


Device(config)# end

Exits configuration mode and enters privileged EXEC mode.

Defining a BGP Large Community List

To define a BGP large community list, perform the following steps. BGP large community supports named and numbered community lists.

SUMMARY STEPS

  1. configure terminal
  2. ip large-community-list {list-number | standard list-name } {deny | permit } community-number large-community
  3. ip large-community-list {list-number | expanded list-name } {deny | permit} regexp
  4. end

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 2

ip large-community-list {list-number | standard list-name } {deny | permit } community-number large-community

Example:

Numbered Large Community List

Device(config)# ip large-community-list 1 permit 1:2:3 5:6:7 
Device(config)# ip large-community-list 1 permit 4123456789:4123456780:4123456788

Named Large Community List

Device(config)# ip large-community-list standard LG_ST permit 1:2:3 5:6:7
Device(config)# ip large-community-list standard LG_ST permit 4123456789:4123456780:4123456788

Defines a standard large community list. A standard large community list is composed of a set of entries, each specifying a set of large community lists.

Step 3

ip large-community-list {list-number | expanded list-name } {deny | permit} regexp

Example:

Numbered Extended Large Community List

Device(config)# ip large-community-list 100 permit ^5:.*:7$
Device(config)# ip large-community-list 100 permit ^5:.*:8$

Named Extended Large Community List

Device(config)# ip large-community-list expanded LG_EX permit ^5:.*:7$
Device(config)# ip large-community-list expanded LG_EX permit ^5:.*:8$

Defines an expanded large community list. An expanded large community list is composed of a set of entries, each specifying a regular expression used to match a set of large communities.

Step 4

end

Example:


Device(config)# end

Exits configuration mode and enters privileged EXEC mode.

Matching Large Communities

To match BGP large communities, perform the following steps.

SUMMARY STEPS

  1. configure terminal
  2. route-map map-tag [permit | deny] [sequence number]
  3. match large-community {list-name | list-numbered }
  4. exit
  5. route-map map-tag [permit | deny] [sequence number]
  6. match large-community {list-name | list-numbered } exact-match
  7. exit
  8. end

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 2

route-map map-tag [permit | deny] [sequence number]

Example:


Device(config)# route-map test permit 10

Enters route-map configuration mode.

Step 3

match large-community {list-name | list-numbered }

Example:


Device(config-route-map)# match large-community 1

Matches a large community list.

Matching a standard large community list entry means that all the large communities defined in such entry are included in the large communities attribute in the route we are trying to match.

Matching an expanded large community list entry means the regular expression defined in such entry matches the string representing (in order) all the large communities in the large communities attribute.

Matching a large community list means matching at least one of its entries with a grant permit. The entries are evaluated in order. If the first entry in matching has a grant permit, we consider the large community list has matched. If the first entry in matching has a grant deny, or there is no entry matching, we consider the large community list has not matched.

Note

 

You can specify more than one large community list. In such a case, a match of any large community list will be consider a global match for the match large community statement.

Step 4

exit

Example:


Device(config-route-map)# exit

Exits route-map configuration mode and enters global configuration mode.

Step 5

route-map map-tag [permit | deny] [sequence number]

Example:


Device(config)# route-map test permit 20

Enters the route-map configuration mode and defines the conditions for routes from one routing protocol into another.

Step 6

match large-community {list-name | list-numbered } exact-match

Example:


Device(config-route-map)# match large-community 1 exact-match

The key word exact-match ensures that there is no large community in the route that is not matched by a large community in the large community list entry. In other words, the set of large communities in the route must be an exact match of the set of large communities in the large community list entry.

Note

 

The exact-match keyword is only supported for standard large community lists.

Step 7

exit

Example:


Device(config-router-map)# exit

Exits route-map configuration mode and enters global configuration mode.

Step 8

end

Example:


Device(config)# end

Exits configuration mode and enters privileged EXEC mode.

Setting BGP Large Communities

To set large communities, perform the following steps.

SUMMARY STEPS

  1. configure terminal
  2. route-map map-tag [permit | deny] [sequence number]
  3. set large-community { none | xx1:yy1:zz1....xxn:yyn:zzn }
  4. exit
  5. route-map map-tag [permit | deny] [sequence number]
  6. set large-community xx1:yy1:zz1....xxn:yyn:zzn additive
  7. exit
  8. end

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 2

route-map map-tag [permit | deny] [sequence number]

Example:


Device(config)# route-map foo permit 10

Enters the route-map configuration mode.

Step 3

set large-community { none | xx1:yy1:zz1....xxn:yyn:zzn }

Example:


Device(config-route-map)# set large-community 1:2:3 5:6:7

This route-map set statement is used to set one or more large communities in a route. The keyword none sets an empty set of large communities. This is equivalent to an update with no large communities attribute.

Step 4

exit

Example:


Device(config-router-map)# exit

Exits route-map configuration mode and enters global configuration mode.

Step 5

route-map map-tag [permit | deny] [sequence number]

Example:


Device(config)# route-map foo permit 20

Enters the route-map configuration mode.

Step 6

set large-community xx1:yy1:zz1....xxn:yyn:zzn additive

Example:


Device(config-route-map)# set large-community 1:2:3 5:6:7 additive

This route-map set statement is used to set one or more large communities in a route in an additive manner. The keyword additive adds the speified large communities without removing the existing large communities.

Step 7

exit

Example:


Device(config-router-map)# exit

Exits route-map configuration mode and enters global configuration mode.

Step 8

end

Example:


Device(config)# end

Exits configuration mode and enters privileged EXEC mode.

Deleting Large Communities

To delete BGP large communities, perform the following steps.

SUMMARY STEPS

  1. configure terminal
  2. route-map map-tag [permit | deny] [sequence number]
  3. set largecomm-list {standard | expanded | large-community-list number } delete
  4. exit
  5. end

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 2

route-map map-tag [permit | deny] [sequence number]

Example:


Device(config)# route-map test permit 10

Enters the route-map configuration mode.

Step 3

set largecomm-list {standard | expanded | large-community-list number } delete

Example:


Device(config-route-map)# set largecomm-list 1 delete

Deletes the large communities based on the matches for the large community list.

Step 4

exit

Example:


Device(config-route-map)# exit

Exits route-map configuration mode and enters global configuration mode.

Step 5

end

Example:


Device(config)# end

Exits configuration mode and enters privileged EXEC mode.

Verifying the Configuration of the BGP Large Community

To verify the BGP large community, use the following commands.

This example displays entries in the IP version 4 (IPv4) BGP routing table. 

Device # show bgp ipv4 unicast 2.2.2.2
BGP routing table entry for 2.2.2.2/32, version 2
Paths: (1 available, best #1, table default)
Not advertised to any peer
Refresh Epoch 1
67001
19.0.101.1 from 19.0.101.1 (19.0.101.1)
Origin IGP, localpref 100, valid, external, best
Large Community: 67001:0:2
rx pathid: 0, tx pathid: 0x0
Updated on Nov 1 2020 01:18:02 PST

This example shows a list of routes that contain all of the large communities given in the command. The listed routes may contain additional large communities. 

Device# show bgp large-community 1:2:3 5:6:7
BGP table version is 17, local router ID is 1.1.1.3
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *>i 5.5.5.5/32       1.1.1.2                  0    100      0 ?
 *>i 5.5.5.6/32       1.1.1.2                  0    100      0 ?

This example displays the listed routes that contain only the given large communities when you add the keyword exact-match in the configuration. 

Device#show bgp large-community 1:2:3 5:6:7 exact-match
BGP table version is 17, local router ID is 1.1.1.3
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *>i 5.5.5.5/32       1.1.1.2                  0    100      0 ?

In the last two examples above, the routes 5.5.5.5/32 and 5.5.5.6/32 contain both the large communities 1:2:3 and 5:6:7. The route 5.5.5.6/32 contains some additional large communities.

This example displays a large community list.

Device# show ip largecommunity-list 51
Large Community standard list 51
     permit 1:2:3 5:6:7

This example displays a match with large community list.


Device# show ip bgp largecommunity-list 51 exact-match
BGP table version is 17, local router ID is 1.1.1.3
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *>i 5.5.5.5/32       1.1.1.2                  0    100      0 ?

Troubleshooting Large Communities

To debug the large communities, use debug ip bgp update command. 

Device# debug ip bgp update

*Mar 10 23:25:01.194: BGP(0): 192.0.0.1 rcvd UPDATE w/ attr: nexthop 192.0.0.1, origin ?, metric 0, merged path 1, AS_PATH , community 0:44 1:1 2:3, large-community 3:1:244 3:1:245
*Mar 10 23:25:01.194: BGP(0): 192.0.0.1 rcvd 5.5.5.1/32
*Mar 10 23:25:01.194: BGP(0): Revise route installing 1 of 1 routes for 5.5.5.1/32 -> 192.0.0.1(global) to main IP table

Memory Display

The show ip bgp summary command displays large community memory information. 

Device # show ip bgp summary
BGP router identifier 1.1.1.1, local AS number 1
BGP table version is 3, main routing table version 3
2 network entries using 496 bytes of memory
2 path entries using 272 bytes of memory
1/1 BGP path/bestpath attribute entries using 288 bytes of memory
1 BGP community entries using 40 bytes of memory
2 BGP large-community entries using 96 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 1096 total bytes of memory
BGP activity 3/1 prefixes, 3/1 paths, scan interval 60 secs
2 networks peaked at 13:04:52 Mar 11 2020 EST (00:07:25.579 ago)

Neighbor        V           AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
192.0.0.2       4            2    1245    1245        3    0    0 18:47:56        0

BGP Large Community Configuration Example

The following examples show how to configure policies used to match and manipulate the large communities attribute.

Numbered Standard Large Community List

This example shows how to configure a numbered large community list.

ip large-community-list 1 permit 1:2:3 5:6:7 
ip large-community-list 1 permit 4123456789:4123456780:4123456788

Named Standard Large Community List

This example shows how to configure a named standard large community list.

ip large-community-list standard LG_ST permit 1:2:3 5:6:7
ip large-community-list standard LG_ST permit 4123456789:4123456780:4123456788

Numbered Expanded Large Community List

This example shows how to configure a numbered expanded large community list.

ip large-community-list 100 permit ^5:.*:7$
ip large-community-list 100 permit ^5:.*:8$

Named Expanded Large Community List

This example shows how to configure a named expanded large community list.

ip large-community-list expanded LG_EX permit ^5:.*:7$
ip large-community-list expanded LG_EX permit ^5:.*:8$

Matching Large Communities

These examples show how to match large communities.

route-map foo permit 10 
 match large-community 1

route-map foo2 permit 10 
 match large-community 1 exact-match

route-map foo3 permit 10
 match large-community 100

route-map foo4 permit 10
 match large-community LG_ST exact-match

Setting Large Communities

These examples show how to add large communities to the large communities attribute. The additive keyword adds the large communities without removing the existing large communities. 

route-map foo permit 10 
 set large-community 1:2:3 5:6:7

route-map foo2 permit 10 
 set large-community 1:2:3 5:6:7 additive

Deleting Large Communities

These examples show how to remove large communities from the large communities attribute.

route-map foo
 set large-comm-list 1 delete

route-map foo2
 set largecomm-list 100 delete

route-map foo3
 set largecomm-list LG_ST delete

Additional References

Related Documents

Related Topic

Document Title

BGP commands

Cisco IOS IP Routing: BGP Command Reference

Technical Assistance

Description

Link

The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

http://www.cisco.com/cisco/web/support/index.html

Standards and RFCs

Standard/RFC

Title

RFC-8092

BGP Large Communities Attribute

Feature Information for BGP Large Communities

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Table 1. Feature Information for BGP Large Communities

Feature Name

Releases

Feature Information

BGP Large Communities

Cisco IOS XE Bengaluru 17.4.1a

 The BGP large communities attribute provides the capability for tagging routes and modifying BGP routing policy on routers.