SOO - BGP Extended Community

SOO -BGP Extended Community used in MPLS

AS path-based BGP loop prevention is bypassed with AS-override and allowas-in features.

In these scenarios, to avoid loops,

BGP extended community attributes such as site of origin (SOO) can also be applied to the MP-iBGP update prior to propagation. The SOO attribute is used to identify the specific site from which the PE learns the route and it  is used to identify and prevent the routing loops. The SOO is a BGP extended communities attribute used to identify routes that have originated from a site so that the re-advertisement of that prefix back to the source site can be prevented, thus preventing routing loops. .

The SOO extended community uniquely identifies the site from which a PE router has learned a route. SOO enables filtering of traffic based on the site from which it was originated. SOO filtering manages MPLS VPN traffic and prevents routing loops from occurring in complex and mixed network topologies in which the customer sites might have connectivity across the MPLS VPN backbone as well as have backdoor links between sites.

*SOO loop prevention mechanism are needed only for customer’s networks with Multihomed sites. Loops can never occur in customer networks that have only stub sites.

• The SOO is needed only of Multihomed sites.
• When EBGP is run between PE and CE routers, The SOO is configured through a route-map command.
• For other routing protocols, the SOO can be applied to routes learned through a particular VRF interface during the redistribution into BGP

Example:

Creates a route map that sets the SOO attribute.

PE(config)#

route-map SOO permit seq

match conditions

set extcommunity soo extended-community-value

Apply the route-map

Router(config-router-af)#

neighbor ip-address route-map name in

Router(config-router-af)#neighbor 10.1.1.1 route-map SOO in

route-map SOO permit 10

set extcommunity soo 65000:100