Operation Manual – Routing ProtocolH3C S5600 Series Ethernet Switches Chapter 5 BGP Configuration5-10EBGPRouter BRouter ARouter CRouter DD=8.0.0.0NEXT_HOP=3.1.1.1LOCAL_PREF=200IBGPIBGPIBGPEBGP2.1.1.18.0.0.0LOCAL_PREF=100NEXT_HOP=2.1.1.1LOCAL_PREF=100LOCAL_PREF=2003.1.1.1AS 20AS 10Figure 5-9 LOCAL_PREF attribute6) COMMUNITYThe Community attribute is used to simplify routing policy application and ease themaintenance and management of routing policy. Community is a set of destinationaddresses with the same features. It is not restricted to physical boundary and isindependent of AS. The Community attribute can be one of the following.z INTERNET. By default, the value of the COMMUNITY attributes of all routes isINTERNET. That is, all routes belong to the Internet community by default.Routes with this attribute can be advertised to all BGP peers.z No_EXPORT. Routes with this attribute cannot be sent to routers outside thelocal AS. With the presence of the confederation, routes of this kind cannot beadvertised outside the confederation, they can only be advertised in the sub-ASsin the confederation. (For information about confederation, refer to section 5.1.4"Problems in Large-Scale BGP Network”.)z No_ADVERTISE. Routes with this attribute cannot be advertised to any otherBGP peers after being received by a BGP router.z No_EXPORT_SUBCONFED. Routes with this attribute can neither beadvertised outside the local AS nor be advertised to other sub-ASs inside theconfederation after being received.5.1.3 BGP Routing PolicyI. BGP routing policyz A BGP router filters routes in the following order.z Drops the NEXT_HOP unreachable route.z With Prefered-value specified, chooses the route with highest Prefered-valuevalue.z Prefers the route with highest LOCAL_PREF value.z Prefers the routes starting from the local router.
