loopback interface

Unanswered Question
Jan 17th, 2008

Hi all, If I create a loopback interface on my router/switch, can I connect to this from any vlan or any port, would my pc have to be on the same vlan ip of the port to reach the loopback, people say you can plug into any physical connection and still reach loopback, how does this work if the port is in a vlan ?

I have this problem too.
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Collin Clark Thu, 01/17/2008 - 07:12

The loopback is not really in a VLAN. For example I use loopbacks on all our routers. All the loopbacks are in the same IP Subnet. When you configure the loopback use the subnet mask of /32, a host route (this is the default BTW). You will need to add the loopback subnet to your IGP. Now this IP subnet really has a bunch of host routes (each router) and they are reachable via many different ways such as your ethernet or serial connections on the routers.


Istvan_Rabai Thu, 01/17/2008 - 18:37

Hi Carl,

Just to write some additional explanation to this:

The loopback interface behaves like a physical interface, in terms that it should be in a subnet different from other interfaces.

So you cannot connect to it direcly with your pc, but you can reach it via routing from your vlan, i.e. via layer 3 connection, not via layer 2 connection. The loopback is in a different subnet, a different broadcast domain if you like.

You should be able to ping it from your vlan.

If you still cannot reach it, just write me about your config and I will help.

Cheers: Istvan


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