Loopback interface ????

[amey.dixit]

Hey Gang,

Why we use Loopback interface, in Routing Protocol??? Like as in OSPF, EIGRP, BGP.

I know as we can Configure Manual Router-id in Ospf..... apart from That Technically What is Other Reason????

Thanks in Advance.

AD

[Vaibhava Varma]

Hi Amey

From my personal understanding Router-ID is a non-routable entitiy in the RPs such as OSPF,ISIS,BGP but they are just needed to start the particular routing protocol process.

Router-ID can be picked via manual commands under the protocol context or by automatically picking up the highest IP address of a active physical interface or highest loopback IP.

The router-id once picked up will not change untill unless the OSPF process is reset.

So from RID perspective Loopback is not must.

But from looking at some protcol operation such as iBGP and MPLS-TE its always better to form neighbourship over loopback interface as it be reachable via multiple IGP paths available and will only be unreachable if the router itself goes down. So again it comes to High Availability of an iBGP or MPLS-TE we need loopbacks.

Regards

Varma

[Ganesh Hariharan]

Currently Being Moderated
Loopback interface ????
Hey Gang,
Why we use Loopback interface, in Routing Protocol??? Like as in OSPF, EIGRP, BGP.
I know as we can Configure Manual Router-id in Ospf..... apart from That Technically What is Other Reason????
Thanks in Advance.
AD

Amey,

The advantage of coding a loopback interface is that it enables you to have an IP address on the router which is always up rather than being dependant on the physical interface being up.loopback interface always remain up and play a major role in maintaining a stable adjancy between routing peers like ospf.

Coming to Loop-back address in OSPF "The RID will be the highest physical interface on the router ... unless a loopback interface has been configured. If a loop is configured, the RID will be the highest loop address."

Also loopback play a good role in forming a DR in ospf routing protocol.

Hope to Help !!

Ganeshh Iyer

[Latchum Naidu]

Hi Amey,

As we know, VLAN interfaces are generally used for management on switches. Loop-backs are often used for management on routers.

It has long been recommended that a loop-back address be used for management on routers. The thinking behind that is that if there is any way to your router you can get to the loop-back - if you used a real interface address if that was the interface that was down, you would lose access.

The main reason for using a loop-back on a switch as the management address is that it would fall in line with a simple policy "we always use lo0 as management, lo1 - 9 as tunnel end points" sort of thing, and there is no need to modify the policy for routers or switches, and standard security configs may be a little easier.

Please rate the helpfull posts.
Regards,
Naidu.