Cisco 2600 InterVLAN routing (configuring subinterfaces)

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Sep 25th, 2008
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I tried to configure sub interfaces in our Cisco 2611 router as follows.

Router1(config)#interface fastEthernet 0/1.1

(config-subif)#ip address

but this gives the following error.

% Configuring IP routing on a LAN subinterface is only allowed if that

subinterface is already configured as part of an IEEE 802.10, IEEE 802.1Q,

or ISL vLAN.

what was the cause for this error?

Also the router does not provide encapsulation dot1Q 2 ...... commands in the subinterface mode.

Is this router not provide this feature??


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spremkumar Thu, 09/25/2008 - 23:04
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Hi Kosala

You need to make sure that your IOS supports inter vlan routing feature.

If it doesnt you need to upgrade it first to configure inter vlan routing.


mfreijser Thu, 09/25/2008 - 23:19
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You will need IOS 12.1(3)T or higher to use the "encapsulation dot1q ..." command.

There is a workaround if you are using a earlier version of IOS and are not able to upgrade the device. It can be found on the following page:

Please rate if the post helps!



kosalasuranjith Sun, 09/28/2008 - 19:55
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But my router, the version is newer.

Pls. check the show version output....

Cisco Internetwork Operating System Software

IOS (tm) C2600 Software (C2600-I-M), Version 12.3(17b), RELEASE SOFTWARE (fc2)

Technical Support:

Copyright (c) 1986-2006 by cisco Systems, Inc.

Compiled Mon 06-Mar-06 22:02 by dchih

Image text-base: 0x80008098, data-base: 0x80CE0844

ROM: System Bootstrap, Version 12.2(7r) [cmong 7r], RELEASE SOFTWARE (fc1)

ROM: C2600 Software (C2600-I-M), Version 12.3(17b), RELEASE SOFTWARE (fc2)

SLTiDC_DR_Router1 uptime is 6 days, 18 hours, 20 minutes

System returned to ROM by power-on


Can it be the problem...?


Jon Marshall Sun, 09/28/2008 - 21:15
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You need a minimum feature set of IP Plus to support 802.1q subinterfaces.



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