H3C S5600 Series Operation Manual page 392

Operation Manual – Routing Protocol
H3C S5600 Series Ethernet Switches
When a BGP speaker advertises a route generated by itself to all its neighbors, it
sets the NEXT_HOP attribute of the routing information to the address of its own
interface connecting to the peer.
When a BGP speaker sends a received route to one of its EBGP peer, it sets the
NEXT_HOP attribute of the routing information to the address of its interface
connecting to the EBGP peer.
When a BGP speaker sends a route received from one of its EBGP peer to one
of its IBGP neighbor, it does not change the NEXT_HOP attribute of the routing
information. But with load balancing enabled, the NEXT_HOP attribute is
changed when the BGP route is sent to a IBGP neighbor.
Figure 5-7 The NEXT_HOP attribute
4) MED (MULTI_EXIT_DISC)
The MED attribute is only valid between two neighboring ASs. The AS receiving this
attribute will not advertise this attribute to a third AS.
The MED attribute is used to determine the optimal route for traffic flows to enter an
AS. It acts the same as the metrics used in IGP. For multiple routes a BGP router
receives from different EBGP peers, if they have the same destination address but
different next hops, the route with the smallest MED value is chosen as the optimal
route provided other conditions are the same. As shown in
chose as the ingress for traffic from AS 10 to AS 20.
5-8
Chapter 5 BGP Configuration
Figure 5-8, Router B is