Loopback what your role is? How does it work?
This interface is one of the most widely used virtual interface, in almost every router on use,
In the following USES,
1, as the address of a router management system administrator to complete the network planning, in order to facilitate the management, will be for each router to create a loopback interface, and separately on the interface specifies an IP address as the management, the administrator can use the address of the router Telnet (Telnet), the address is actually played a similar device name kind of function, but also exists in each router interface and address, why not chosen at random from among a? Here's why: because the Telnet command using TCP packet, there are the following: the one interface of the router because of a malfunction dropped down, but it still can Telnet other interface, that is, to the router TCP connection remains, so choose the Telnet address must be never down off, and virtual interfaces to satisfy such requirements, because this kind of interface with no connectivity needs to end, so in order to save the address resources, loopback interface address usually designated as a 32-bit mask,
2, using the interface address as a dynamic routing protocol OSPF, BGP of dynamic routing protocol OSPF router id, BGP in the running process need to specify a router id for the agreement, as a unique identifier of the router, and demand throughout the autonomous system only, as the router id is a 32-bit unsigned integer, this and are very similar to the IP address, and IP address is not duplicate phenomenon, so usually the router, the router id is specified as an interface with the equipment at the same address, due to the IP address of the loopback interface is often viewed as the router's identity, so also is the best choice of the router id,
3, using the interface address as a TCP connection to BGP source address
In BGP protocol, two run BGP neighbor relationships between routers is done through a TCP connection is established, the configuration when the neighbors usually specify the loopback interface as a source address (usually only used to establish a TCP connection
IBGP, with 2.1, is to enhance the robustness of a TCP connection)
Configuration commands are as follows:
The router id 61.235.66.1
Interface loopback 0
IP address 61.235.66.1 255.255.255.255
The router BGP 100
Neighbor 61.235.66.7 remote - as 200
Neighbor 61.235.66.7 update - source LoopBack0