![]() ![]() 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. ![]() On a host, the loopback address is used for applications to talk to other applications running on the local system. This may seem strange, as hosts always use the loopback addresses 127.0.0.1 (IPv4) and ::1 (IPv6). 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 iBGP sessions to and from those addresses go down, even though routers 1 and 3 can still communicate by going through routers 2 and 4.įigure 2: iBGP sessions using interface addresses in a larger networkīy using loopback addresses as the source and destination of iBGP sessions, there is no longer any dependency on a particular interface of a router. Suppose that in the network in Figure 2 the link between routers 1 and 3 goes down. However, in a larger network the BGP routers typically don’t sit right next to each other so it can simply be assumed that the link between them never goes down. 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 iBGP setup is to simply configure it much the same as an eBGP session: by using the interface address of the other router as the neighbor address, as displayed in Figure 1.įigure 1: an iBGP session using interface addresses in a small network. #Standard loopback address full
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