
Configuring IP Services
5-6
To establish a peer-to-peer connection between Router A and Router B, you must
do the following:
1. Choose a numbered interface on each router for the peer-to-peer
connection. Note the network/subnet that each interface is on.
In Figure 5-2, Router A has a numbered interface to Network 1. Router B has
a numbered interface to Network 3. The network administrator has chosen
these two interfaces to support the peer-to-peer connection.
2. If the two routers are in different ASs, enable multihop EBGP
connections.
For instructions on enabling multihop EBGP, see the Multi-hop EBGP
Connection parameter on page 5-32.
3. If no IGP protocol (RIP or OSPF) is running over the unnumbered link,
configure a static route on each router to the other router’s network and
subnet.
Since the routers do not share a numbered subnet, each BGP peer needs to
know a route to the network/subnet of the interface that the other BGP peer is
using. If there is an IGP protocol (RIP or OSPF) running over the unnumbered
link, RIP or OSPF will learn the route and store it in the routing table.
Otherwise, you need to configure a static route on each router to the other
BGP peer’s network/subnet. The route should point to the unnumbered link.
4. Configure the BGP connection on each router.
Initiating a Connection
A BGP speaker that wants to initiate peer-to-peer connections periodically issues
an Open message (see “Open Message” on page 5-9).
BGP speakers respond to connection requests by returning an Open message. In
Figure 5-3, for example, BGP Speaker A sends an Open message to BGP Speaker
B to request a connection; BGP Speaker B responds by sending an Open message
to BGP Speaker A.
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