The main purpose of loopback interfaces is to provide one or more permanent addresses to a network device, regardless of which network interfaces are up. A loopback address is typically announced into the routing tables, and can therefore be used as a management address instead of a physical interface address. This is preferable since a loopback interface is independent from any physical interface and is, therefore, always available. This also enables to configure unnumbered point-to-point interfaces (for example with a PPPv4 server) A loopback address will typically be used in IPv4 packets. Finally, a prefix configured on a loopback interface can be used to announce some directly connected networks via dynamic routing protocols.
To configure loopback, enter the context
loopback from the
VRF in which you plan to define a loopback logical interface.
vsr running vrf main# interface loopback loop0 vsr running loopback loop0# commit
Let’s fetch the state after committing this configuration:
vsr running vrf main# interface loopback loop0 vsr running loopback loop0# show state loopback loop0 oper-status UP enabled true mtu 1500 counters in-octets 0 out-octets 0 in-errors 0 in-unicast-pkts 0 in-discards 0 out-unicast-pkts 0 out-errors 0 out-discards 0 .. ethernet mac-address 26:16:54:8d:10:0a .. ipv6 address fe80::2416:54ff:fe8d:100a/64 .. ..
The same configuration can be made using this NETCONF XML configuration:
vsr running loopback loop0# show config xml absolute <config xmlns="urn:6wind:vrouter"> <vrf> <name>main</name> <interface xmlns="urn:6wind:vrouter/interface"> <loopback xmlns="urn:6wind:vrouter/loopback"> <name>loop0</name> (...) </loopback> </interface> </vrf> </config>
The command reference for details.