The difference between a router and a loopback address on a PC

The

PC local loopback address

127.0.0.1 is often referred to as the local loopback address (the loop back addressing), which represents the device's local virtual interface, so the default is seen as an interface that never goes down.

also has a similar definition in the Windows operating system, so it is usually possible to ping this local loopback address before installing the NIC. It is generally used to check whether the local network protocol, the IP stack within the system, the basic data interface, and so on are normal. The

Local loop has the following effects:

1. As an administrative address for a router

system administrator completes network planning and, for ease of administration, creates an loopback interface for each router and assigns a separate IP on the interface Address as an administrative address, the administrator uses this address to remotely log on to the router (telnet), which actually acts like a device name.

There are usually many interfaces and addresses on each router, so why not choose one from among them?

for the following reasons: Because the Telnet command uses a TCP message, one of the router's interfaces is down because of a failure, but other interfaces can still telnet, meaning that the TCP connection to the router still exists. Therefore, the selected Telnet address must never be down, and the virtual interface satisfies such requirements. Because such interfaces do not require interoperability with the end-to-end, the address of the loopback interface is usually specified as a 32-bit mask in order to conserve address resources.

2. Use this interface address as a dynamic routing protocol OSPF, BGP router ID

Dynamic routing protocol OSPF, BGP need to specify a router ID for the protocol to be used as the router's unique identifier and require the entire autonomous system The only one in the EC. Because the router ID is a 32-bit unsigned integer, this is very much like an IP address. Also, the IP address is not duplicated, so the router's router ID is typically specified as the same as the address of an interface on the device. Because the IP address of the loopback interface is usually considered a router's identity, it is also the best choice for the router ID.

3. Use this interface address to establish the source address
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of a TCP connection as BGP in the BGP protocol, the establishment of a neighbor relationship between the two routers running BGP is done through TCP connection.

typically specifies that the loopback interface is the source address for establishing a TCP connection when configuring a neighbor.