Loopback port Function

This type of interface is the most widely used virtual interface, which is used on almost every vro. Regular
See the following usage.
1 As the management address of a vro
After the system administrator completes the network planning,
Loopback interface, and specify an IP address as the management address on this interface. The Administrator will
Use this address to remotely log on to the vrotelnet (Telnet). The address actually starts with the name of a similar device.
Class 1 functions.
But there are usually many interfaces and addresses on each vro. Why don't you choose one of them?
The reason is as follows: Because the Telnet command uses TCP packets, the following situations may occur:
The interface is down due to a fault, but other interfaces can still be telnet, that is
The TCP connection to this vro still exists. Therefore, the selected telnet address must never be
And the Virtual Interface meets this requirement. Because these interfaces are not interconnected with the peer end
To save Address Resources, the address of the loopback interface is usually specified as a 32-bit mask.
2. Use this interface address as the router ID of the Dynamic Routing Protocol OSPF and BGP
During the operation of the Dynamic Routing Protocol OSPF and BGP, you must specify a router ID for the Protocol.
The router must be unique in the autonomous system. Because the router ID is
A 32-bit unsigned integer, which is very similar to an IP address. And the IP address is unique.
The router ID is usually the same as the address of an interface on the device.
. Because the IP address of the loopback interface is generally regarded as the identifier of the router
The best choice for the router ID.
3. Use this interface address as the source address of the bgp tcp Connection
In the BGP protocol, two routers running BGP establish a neighbor relationship through TCP
Completed.
When configuring a neighbor, the loopback interface is often specified as the source address for establishing a TCP connection (usually used only
Ibgp, for the same reason as 2.1, is used to enhance the robustness of TCP connections)
The configuration command is as follows:
Router ID 61.235.66.1
Interface loopback 0
IP address 61.235.66.1 255.255.255.255
Router BGP 100
Neighbor 61.235.66.7 remote as 200
Neighbor 61.235.66.7 Update-source loopback0