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Enabling MED comparison for routes from confederation peers
This task enables BGP to compare the MEDs of routes received from confederation peers. However,
if a route received from a confederation peer has an AS number that does not belong to the
confederation, BGP does not compare the route with other routes. For example, a confederation has
three AS numbers 65006, 65007, and 65009. BGP receives three routes from different confederation
peers. The AS_PATH attributes of these routes are 65006 65009, 65007 65009, and 65008 65009,
and the MED values of them are 2, 3, and 1. Because the third route's AS_PATH attribute contains
AS number 65008 that does not belong to the confederation, BGP does not compare it with other
routes. As a result, the first route becomes the optimal route.
To enable MED comparison for routes from confederation peers:
1. Enter system view.
system-view
N/A
2. Enter BGP instance view or
BGP-VPN instance view.
• Enter BGP instance view:
bgp as-number [ instance
instance-name ]
• Enter BGP-VPN instance
view:
a. bgp as-number
[ instance
instance-name ]
b. ip vpn-instance
N/A
3. Enable MED comparison for
routes from confederation
peers.
bestroute med-confederation
By default, MED comparison for
routes from confederation peers is
disabled.
Configuring the NEXT_HOP attribute
By default, a BGP router does not set itself as the next hop for routes advertised to an IBGP peer or
peer group. In some cases, however, you must configure the advertising router as the next hop to
ensure that the BGP peer can find the correct next hop.
For example, as shown in Figure 61, Router A and Router B establish an EBGP neighbor
relationship, and Router B and Router C establish an IBGP neighbor relationship. If Router C has no
route destined for IP address 1.1.1.1/24, you must configure Router B to set itself 3.1.1.1/24 as the
next hop for the network 2.1.1.1/24 advertised to Router C.
Figure 61 NEXT_HOP attribute configuration
If a BGP router has two peers on a broadcast network, it does not set itself as the next hop for routes
sent to an EBGP peer by default. As shown in Figure 62, Router A and Router B establish an EBGP
neighbor relationship, and Router B and Router C establish an IBGP neighbor relationship. They are
on the same broadcast network 1.1.1.0/24. When Router B sends EBGP routes to Router A, it does
not set itself as the next hop by default. However, you can configure Router B to set it (1.1.1.2/24) as
the next hop for routes sent to Router A by using the peer next-hop-local command as needed.
Router A
EBGP
AS 200
2.1.1.1/24
Router B
Router C
AS 100
1.1.1.1/24
1.1.1.2/24 3.1.1.1/24 3.1.1.2/24
IBGP
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