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Need help on Loopback Ip Address


Can anyone please help me on how to configure a router with only a loopback ip address.

And without any ip address on both the lan interfaces.

I want to connect a router which has only 1 loopback ip address to my core switch 1 and core swicth 2.

Using both the LAN insterface on the router.

Thank You in advance,



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Last update:
‎10-09-2009 12:29 AM
Updated by:
New Member

Hi Subash,

A loopback IP address is just for self testing and if you are not going to configure the router interface (e.g. fa0/0/1) with an IP address then the entire communication is not possible.

A network packet need source ip and destination ip in order to reach to it's destination.

Anyone correct me if i am wrong.



New Member

Hi Subash,

for me it is not clear what you want to achieve with this config.

In my eyes you could configure the two LAN interfaces with bridging and the Layer 3 interface would then be a BVI (bridged virtual interface).

Then you have a direct Layer 2 connection between your two LAN interfaces as well as between your two core switches.

I don't think that an "ip unnumbered Lo0" on both LAN interfaces will have success because then you have the same subnet on two interfaces.


New Member

Hi Guys,

What i am trying to achieve is to create a loopback ip address on the router. And all communication to the router will be to the loopback ip address.


Loopback ip :

Gi 0/1 : Connected to core 1 (vlan 10 =

Gi 0/2 : Connected to core 2 (vlan 10 =

Basicly, it is just a physical layer redundancy.

Thank You/

New Member

Hi Subash,

in my eyes you can not do this with only the loopback.

You can try the following:

interface Gigabit 0/2
bridge-group 1
interface gigabit 0/1
bridge-group 1
interface BVI 1
ip address
bridge irb
bridge 1 protocol ieee
bridge 1 route ip

With this config the router will take part in the spanning tree.

Perhaps this helps.