Unanswered Question
Mar 14th, 2007
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My company has requested me to install a switch on a WAN link.

They requested I configure a loopback address.

I configured the switch vlan1 with an ip/mask and no shut it.

The WAN link goes through the switch no problem.

When I configure an Loopback addrees ie

switch#config t

switch(config)#interface loopback 1

switch(config)#int loopback 1


% Invalid input detected at '^' marker.

However if you question mark int ?

switch(config)#int ?

looback is shown as a vaild command.

any one have any ideas?

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Overall Rating: 4.5 (4 ratings)
ankbhasi Wed, 03/14/2007 - 05:16
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Hi Friend,

2950 is a pure layer 2 switch so it does not need a loopback interface. The command will be present because 2950 works on basic IOS train which have this command but 2950 platform does not support this command.



*Please rate helpfull post

Richard Burts Wed, 03/14/2007 - 08:39
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Ankur gives a good explanation that the 2950 as a layer 2 switch does not support loopback interfaces and that loopback does show in help because it works out of a standard template for help in IOS.

In addition it may be helpful to point out that layer 2 switches can have only a single active virtual interface with an IP address. You indicate that you have configured VLAN 1 and given it an IP address. If you were to configure another VLAN (perhaps VLAN 2) and give it an IP address your would find that VLAN 1 shuts down. There can be only 1 active virtual interface with an IP address on the layer 2 switch.



fattyawan Sun, 09/07/2008 - 19:50
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Hello ankur,

I am also have the same problem.

I wonder why i can input the command interface loopback 0 on ios c2950-i6q4l2-mz.121-9.EA1.bin

but not on c2950-i6q4l2-mz.121-12c.EA1.bin


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