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Deleting BGP Communities

Routing filters allow to clear BGP communities by using "delete" command. Delete command accepts several parameters based on the type of the community type:

• communities: 
  • "wk" - will match and remove well known communities
  • "other" - will match and remove other communities that are not well known 
  • "regexp" - regexp pattern to match communities that should be deleted
  • "<community-list name>" - deletes communities from specified community-list
• ext-communities:
  • "rt" - will match and remove RouteTarget
  • "soo" - will match and remove Site-of-Origin
  • "other" - will match and remove other ext communities that are not RT or SSO 
  • "regexp" - regexp pattern to match ext communities that should be deleted
  • "<community-ext-list name>" - deletes communities from specified community-ext-list
• large-communities:
  • "all" - removes everything
  • "regexp" - regexp pattern to match large communities that should be deleted
  • "<community-large-list name>" - deletes large communities from specified community-large-list

It is possible to specify multiple community types, for example delete all SSOs, other type of ext communities and specific RTs from the community-ext list:

/routing/filter/community-ext-list
add list=myRTList communities="rt:1.1.1.1:222"
/routing/filter/rule/add 
chain=myChain rule="delete bgp-ext-communities sso,other,myRTList;"

AS-PATH Regexp Matching

AS Path is the sequence of autonomous system numbers (ASNs), for example AS Path 123 456 789 would indicate, that route originated from AS with the number 789, and to reach the destination, the packet would need to travel through two autonomous systems: 456 and 789. To apply specific routing policies administrator might want to match specific AS numbers or set of numbers in the AS Path (for example, reject prefixes that travel through AS 456), which can be achieved using regular expression (regexp).

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