The function Encyclopedia of router loopback port

The loop port has a very wide application in practice, and this article is about the use of loopback mouth.

BGP Update-source

Because the loopback mouth as long as the router is still alive, it will always remain active, so as long as the BGP peer loopback to meet the route can be reached, BGP can be established, in general, BGP use of loopback port can improve the robustness of the network.

　　neighbor 215.17.1.35 update-source loopback 0

Router ID

Use this interface address as the OSPF, BGP Router-id, as the unique identifier of this router, and requires that within the entire autonomous system, the Router-id of the BGP/OSPF in Ipv6 is still a 32-bit IP address. The router priority in OSPF is set manually under the interface, followed by the comparison of OSPF Router-id (Router-id's election is not much said here, PS: After a router starts the OSPF routing protocol, The maximum IP address of the physical interface is selected as its routerid, but if the loopback interface is configured, select from loopback The largest IP address is routerid. In addition, once the ROUTERID,OSPF is selected to ensure stability, it is not easy to change unless the Routerid IP address is removed or OSPF is restarted, and Router-id in both OSPF and BGP can be set manually in routing configuration mode.

　　OSPF: Router-ID *.*.*.*
BGP:BGP Router-ID *.*.*.*

IP unnumbered Interfaces

The loopback address can be used to save the distribution of network IP address by using the strong port address. Example:

　　interface loopback 0
ip address 215.17.3.1 255.255.255.255
!
interface Serial 5/0
bandwidth 128
ip unnumbered loopback 0

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