Extended Community Attributes

The extended community attribute provides a mechanism to label BGP routes. It provides two important enhancements over the standard community attribute:
  • An expanded range. Extended communities are 8-bytes wide, whereas regular communities were only 4-bytes wide. So, this ensures that extended communities can be assigned for a plethora of uses, without the fear of overlap.

  • The addition of a 'Type' field provides structure for the extended community

The following two types of extended communities are available:
  • Route Target (RT)

  • Site Of Origin (SOO)

Although these two community types are generally used in L3 VPN network setup, you can also use them in a non-L3 VPN network to control the distribution of BGP routes.

BGP does not send either the extended or standard community attributes to their neighbors by default; you must use the configuration command configure bgp neighbor send-community.