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Dell Configuration Guide for the S4048–ON System 9.14.2.6

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Configuring IP Community Lists

Within Dell EMC Networking OS, you have multiple methods of manipulating routing attributes.

One attribute you can manipulate is the COMMUNITY attribute. This attribute is an optional attribute that is defined for a group of destinations. In Dell EMC Networking OS, you can assign a COMMUNITY attribute to BGP routers by using an IP community list. After you create an IP community list, you can apply routing decisions to all routers meeting the criteria in the IP community list.
IETF RFC 1997 defines the COMMUNITY attribute and the predefined communities of INTERNET, NO_EXPORT_SUBCONFED, NO_ADVERTISE, and NO_EXPORT. All BGP routes belong to the INTERNET community. In the RFC, the other communities are defined as follows:
  • All routes with the NO_EXPORT_SUBCONFED (0xFFFFFF03) community attribute are not sent to CONFED-EBGP or EBGP peers, but are sent to IBGP peers within CONFED-SUB-AS.
  • All routes with the NO_ADVERTISE (0xFFFFFF02) community attribute must not be advertised.
  • All routes with the NO_EXPORT (0xFFFFFF01) community attribute must not be advertised outside a BGP confederation boundary, but are sent to CONFED-EBGP and IBGP peers.

Dell EMC Networking OS also supports BGP Extended Communities as described in RFC 4360 — BGP Extended Communities Attribute.

To configure an IP community list, use these commands.

  1. Create a community list and enter COMMUNITY-LIST mode.
    CONFIGURATION mode
    ip community-list community-list-name
  2. Configure a community list by denying or permitting specific community numbers or types of community.
    CONFIG-COMMUNITYLIST mode
    {deny | permit} {community-number | local-AS | no-advertise | no-export | quote-regexp regular-expression-list | regexp regular-expression}
    • community-number: use AA:NN format where AA is the AS number (2 Bytes or 4 Bytes) and NN is a value specific to that autonomous system.
    • local-AS: routes with the COMMUNITY attribute of NO_EXPORT_SUBCONFED.
    • no-advertise: routes with the COMMUNITY attribute of NO_ADVERTISE.
    • no-export: routes with the COMMUNITY attribute of NO_EXPORT.
    • quote-regexp: then any number of regular expressions. The software applies all regular expressions in the list.
    • regexp: then a regular expression.

Example of the show ip community-lists Command

To view the configuration, use the show config command in CONFIGURATION COMMUNITY-LIST or CONFIGURATION EXTCOMMUNITY LIST mode or the show ip {community-lists | extcommunity-list} command in EXEC Privilege mode.
DellEMC#show ip community-lists
ip community-list standard 1
  deny 701:20
  deny 702:20
  deny 703:20
  deny 704:20
  deny 705:20
  deny 14551:20
  deny 701:112
  deny 702:112
  deny 703:112
  deny 704:112
  deny 705:112
  deny 14551:112
  deny 701:667
  deny 702:667
  deny 703:667
  deny 704:666
  deny 705:666
  deny 14551:666
DellEMC#

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