3Com S7906E - Switch, Руководство по настройке

Страница: 798 / 2621

1-29
Enable the comparison of MED of routes from confederation peers
Follow these steps to enable the comparison of MED of routes from confederation peers:
To do… Use the command… Remarks
Enter system view system-view
—
Enter BGP view bgp as-number
—
Enable the comparison of MED of
routes from confederation peers bestroute
med-confederation
Optional
Not enabled by default
The MED attributes of routes from confederation peers are not compared if their AS-path attributes
contain AS numbers that don’t belong to the confederation. For example, there are three routes:
AS-path attributes of them are 65006 65009, 65007 65009 and 65008 65009, and MED values of them
are 2, 3, and 1. Because the third route contains an AS number that does not belong to the
confederation, the first route becomes the optimal route.
Configuring the Next Hop Attribute
By default, when advertising routes to an iBGP peer/peer group, a BGP router does not set itself as the
next hop. However, to ensure a BGP peer can find the correct next hop in some cases, you need to
configure the router as the next hop for routes sent to the peer.
For example, as shown in the figure below, Router A and Router B establish an eBGP neighbor
relationship, and Router B and Router C establish an iBGP neighbor relationship. When Router B
advertises a network learned from Router A to Router C, if Router C has no route to IP address
1.1.1.1/24, you need to configure Router B to set itself as the next hop (3.1.1.1/24) for the route to be
sent to Router C.
Figure 1-17 Next hop attribute configuration
If a BGP router has two peers on a common broadcast network, it does not set itself as the next hop for
routes sent to an eBGP peer by default. As shown below, 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 as the nexthop
(1.1.1.2/24) for routes sent to Router A by using the peer next-hop-local command as needed.