Information
The use of a loopback interface is recommended for use in all routing protocols. This recommendation describes the configuration of the loopback interface. Routing protocol specific configurations are described under the respective routing protocols.
Rationale:
Loopback interfaces are always up, and so are not dependent on physical interface link state issues (cabling or other link issues for instance). This means traffic sourced from a loopback interface can take any valid path to establish a routing relationship or to route traffic. Loopback interfaces by their nature cannot 'flap' (toggle between up and down states). Depending on the error condition, most physical interfaces are susceptible to interface flapping.
Impact:
Using a loopback interface makes a routing device much less susceptible to intermittent or permanent interface failures.
Solution
Creating the loopback interface is a simple process. Addressing the loopback, in particular computing the subnet mask will vary by the organization and application. Often smaller subnets can be used for loopbacks, depending on how many potential peers are possible.
switch(config)# int loopback 0
switch(config-if)# ip address 10.11.11.1 255.255.255.252
In order to use the loopback interface (rather than the closest interface to the routing peer), it must be explicitly configured in the routing protocol. This is described in the recommendations for each respective routing protocol.
Default Value:
By default no loopback interfaces are created on NX-OS devices.