Virtual Loopback Interface

[zekwueme1]

I have just been hit with a loopback interface scheme at a new job. I do not quite understand it that much, since it is very different from loopback addressing of 127.0.0.1 Could someone tell me more. How is it used? what is it used for? You could also point me to a link to read up on it.

[spremkumar]

Hi

Hope this helps..

http://www.cisco.com/en/US/products/sw/iosswrel/ps1828/products_configuration_guide_chapter09186a0080087da4.html#3302

regds

[Collin Clark]

Loopback interfaces are very useful. We use them for SNMP, logging, terminal sessions, and TACACs. A loopback interface never goes down. It provides consistency for the above protocols. We took a private class C address space and assigned the loopback an address out of that. (ie 192.168.10.44 /32). The major benefit is when you have redundant connections. If you always SSH to a serial interface for management and the interface goes down, you now have to SSH to the ethernet side of the router. With the loopback, if the serial interface goes down, the routing protocol still advertises the host route through the redundant connections and you can get to it. It's also used in OSPF, but that's another story.

HTH and please rate.

[Jitez1234]

Just to put more light to the loopback interface regarding its use in ospf. It is recommended that loopback interfaces should be used for ospf configs, since they never go down, reason being that the router ID (RID) will first be applied to it, if they are not configured then physical interfaces are used.