Comments on: What is the use of Loop Back Interfaces on a Cisco Router?? http://www.routersguide.com/blog/cisco-router/what-is-the-use-of-loop-back-interfaces-on-a-cisco-router/ This blog will tell you everything that you need to know about Cisco, Juniper, Netgear, Linksys, and Foundry wireless routers. Sat, 31 Jul 2010 04:10:06 +0000 http://wordpress.org/?v=2.9.2 hourly 1 By: networkmaster http://www.routersguide.com/blog/cisco-router/what-is-the-use-of-loop-back-interfaces-on-a-cisco-router/comment-page-1/#comment-7102 networkmaster Fri, 22 Jan 2010 23:24:13 +0000 http://www.routersguide.com/blog/cisco-router/what-is-the-use-of-loop-back-interfaces-on-a-cisco-router/#comment-7102 A loopback interface is ALWAYS active and CANNOT fail, that is the reason they are used, they are always in the up/up state and this makes routing protocols such as OSPF and BGP much more stable, as opposed to using a real interface. In addition, some routing protocols like OSPF will use the highest IP address configured on the router as the router ID, but you can override this behavior by configuring a loopback address. Finally, you can use the loopback address as the "source interface" for traffic that is generated by the router, such as syslog packets, SNMP traps, and security related packets. A typical config file's loopback related commands might look like this: interface Loopback0 ip address 172.16.1.1 255.255.255.255 router ospf 100 router-id 172.16.1.1 ip tftp source-interface Loopback0 ip tacacs source-interface Loopback0 logging source-interface Loopback0 snmp-server trap-source Loopback0 A loopback interface is ALWAYS active and CANNOT fail, that is the reason they are used, they are always in the up/up state and this makes routing protocols such as OSPF and BGP much more stable, as opposed to using a real interface.

In addition, some routing protocols like OSPF will use the highest IP address configured on the router as the router ID, but you can override this behavior by configuring a loopback address.

Finally, you can use the loopback address as the "source interface" for traffic that is generated by the router, such as syslog packets, SNMP traps, and security related packets.

A typical config file’s loopback related commands might look like this:
interface Loopback0
ip address 172.16.1.1 255.255.255.255
router ospf 100
router-id 172.16.1.1
ip tftp source-interface Loopback0
ip tacacs source-interface Loopback0
logging source-interface Loopback0
snmp-server trap-source Loopback0

]]> By: Lord_of_Armenia http://www.routersguide.com/blog/cisco-router/what-is-the-use-of-loop-back-interfaces-on-a-cisco-router/comment-page-1/#comment-7103 Lord_of_Armenia Fri, 22 Jan 2010 23:24:13 +0000 http://www.routersguide.com/blog/cisco-router/what-is-the-use-of-loop-back-interfaces-on-a-cisco-router/#comment-7103 Some virtual networking applications use loopback connections to make a computer think that its connected to a network when it is really just connected to itself. There are probably other uses as well. Some virtual networking applications use loopback connections to make a computer think that its connected to a network when it is really just connected to itself.

There are probably other uses as well.

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