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
