L2 switch Loopback address configuration.

Unanswered Question
Jan 6th, 2008

Is it possible to configure the loopback address in cisco 2950 switch. The command is there in switch,but when i am entering the correct syntax to configure the same I am getting the below mentioned

Switch(config)#int loopback 0

^

% Invalid input detected at '^' marker.

Please suggest what should we do configure the loopback address in L2 sw.

the existing IOS is c2950-i6q4l2-mz.121-22.EA9.bin"

is it required to upgarade?

I have this problem too.
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Jon Marshall Sun, 01/06/2008 - 23:51

Hi

The 2950 switch is a layer 2 switch only so even though the option on the command line is there you can't use it on a 2950.

The way to manage the 2950 is to have one L3 vlan interface, by default it is vlan 1 but you can change this.

Jon

ankbhasi Mon, 01/07/2008 - 00:47

Hi Friend,

As Jon updated this is a layer 2 switch it will not support loopback interface. The command is available because the BASE IOS is same for 2950 and most of the layer 3 switches but layer 2 switch hardware itself will not support this interface.

HTH

Ankur

Alex_Gibson Sun, 09/18/2011 - 01:57

Okay this is an old thread but I have the same question

and it appears that loopback interfaces can be configurered and work on 2950's

I can set and ping the loopback interface

interface Loopback1

ip address 10.10.10.252  255.255.255.255

no ip route-cache

And in an old config on one of my 2950's(from previous corp owner)

they had a loopback interface set.

What reasons would you do this on a layer 2 switch ?

The ccna books don't really explain it other than to say its for OSPF or BGP, and it makes them more efficenet to have an interface that never goes down and can be used to check a router/layer3 switch is up.

Searched around abit.

So on a layer 2 device a loopback interface is just used for management and monitoring ?

Jon Marshall Sun, 09/18/2011 - 05:59

Alex

Loopbacks are generally used on a devices that are L3 capable. That could be a router or a L3 switch. Loopbacks can be used as router-ids for OSPF, for BGP peering, for management etc.

However on a L2 switch it is generally not of much use. A L2 switch doesn't run routing protocols. It is general practice therefore to use one L3 vlan interface on a L2 switch for management. This L3 vlan interface (by default vlan 1 but it can be changed) is only used for management ie. it is never used as a default-gateway for end devices such as PCs/servers/printers.

I have used loopbacks on L3 switches but only when the network was running L3 from the access-layer. This was useful there because there were not vlans going across the uplinks to the distro switches so you could not have a managment vlan common to all switches.

 

Jon

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