Using eBGP Multihop
You want to use BGP to exchange routes with an external peer router that is more than one hop away because the router at the edge of the network doesn’t support BGP.
Cisco provides a useful option called eBGP Multihop, which allows you to establish eBGP peer relationships between routers that aren’t directly connected to one another:
configure terminalEnter configuration commands, one per line. End with CNTL/Z. Router1(config)#
172.20.1.2 255.255.255.255 192.168.1.5 2
In this example, we have shown the configuration for only one of the routers, although you will need to configure the ebgp-multihop keyword for the corresponding peer device as well.
This feature isn’t a standard part of the BGP protocol, but several router vendors implement it. The standard behavior requires eBGP routers to be adjacent to one another.
You might want to use this feature, for example, if the router at the edge of either your AS or the AS you are connecting to doesn’t support BGP. The router will also need to have a route to the destination device because it is not directly connected. We have included a static route for this purpose.
The ebgp-multihop keyword takes an optional ...