Rt updating bgp 0 0 0 0 0

However, things do get more complex in networks that span multiple locations and have routers that communicate with other networks over e BGP in more than one location.

In those networks, it’s important to think about the following: When a network only has two BGP routers and those routers are connected using a connection that is very unlikely to go down, the most straightforward i BGP setup is to simply configure it much the same as an e BGP session: by using the interface address of the other router as the neighbor address, as displayed in the link between routers 1 and 3 goes down.

This means that address 10.0.1.1 on router 1 and address 10.0.1.2 on router 3 are no longer reachable, so all i BGP sessions to and from those addresses go down, By using loopback addresses as the source and destination of i BGP sessions, there is no longer any dependency on a particular interface of a router.

This may seem strange, as hosts always use the loopback addresses 127.0.0.1 (IPv4) and ::1 (IPv6).

However, in order for remote systems to reach a loopback address, it must be injected into an interior routing protocol such as OSPF.

So in , if the link between routers 1 and 3 goes down, the i BGP session (and all data packets between routers 1 and 3) will flow through routers 2 and 4.

The difference between a loopback address and the address configured on a regular interface is that the loopback address is always up, while an interface address becomes unreachable when the interface it’s configured on goes down.

However, on routers, loopback interfaces have a regular address, which can be used for management and control communication.

However, when router 1 propagates these prefixes to router 2 over i BGP, they’ll still have next hop address 172.31.0.1, and router 2 doesn’t have a route to that address.

Figure 4: e BGP and i BGP on router 1 for the i BGP session towards router 2.

This makes for a very simple BGP setup, where each router has the requisite filters to make sure only the network’s own IP address block(s) are advertised to the outside world over e BGP (external BGP), an all of one i BGP (internal BGP) session between the two BGP routers.

Adding a third and maybe even a fourth router in the same location doesn’t change that picture very much.