H3C Technologies H3C SecPath F1000-E - Manual (Page 333)

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Figure 8 MED attribute
In general, BGP compares MEDs of routes received from the same AS only.
5. LOCAL_PREF
The LOCAL_PREF attribute is exchanged between iBGP peers only, and thus is not advertised to any other
AS. It indicates the priority of a BGP router.
LOCAL_PREF is used to determine the best route for traffic leaving the local AS. When a BGP router
obtains from several iBGP peers multiple routes to the same destination but with different next hops, it
considers the route with the highest LOCAL_PREF value as the best route. As shown below, traffic from
AS20 to AS10 travels through Device C that is selected according to LOCAL_PREF.
Figure 9 LOCAL_PREF attribute
6. COMMUNITY
The COMMUNITY attribute is used to simplify routing policy usage and ease management and
maintenance. It identifies a collection of destination addresses having identical attributes, without
physical boundaries in between, and having nothing to do with the local AS. Well known community
attributes involve:
• Internet: By default, all routes belong to the Internet community. Routes with this attribute can be
advertised to all BGP peers.