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Can't set encapsulation on Sub-Interaces - 2621 Router

I am studying for my CCNA, playing around with a few of the dirfferent concepts with my hardware. I am trying to setup a router on a stick configuration using a 2600 router and a 2900 catalyst switch.

I have the FastEthernet 0/1 port plugged into Fa0/1 on the switch. The switch has three vlans setup with a client on each vlan

I have set the port on the switch as follows:

Switch(config-if)#switchport mode Trunk

Switch(config-if)#switchport trunk native vlan 1

Switch(config-if)#switchport trunk encapsulation isl

When I try to set the router, I get this:

rt01(config)#int fa0/1

rt01(config-if)#no ip add


rt01(config)#int fa0/1.1

rt01(config-subif)#encapsulation isl


% Invalid input detected at '^' marker.

I cannot set the encapsulation on the sub interface, ISL or dot1q - it doesn't recognize the "encapsulation command" command at all.

My show version is below. I can't confirm one way or another if this image supports IP Plus (which I've been told may be the problem), but based on the message I get when trying to set the IP address on the subif I would think it does..?

My router sh ver shows:

Cisco Internetwork Operating System Software

IOS (tm) C2600 Software (C2600-I-M), Version 12.3(6), RELEASE SOFTWARE (fc3)

Copyright (c) 1986-2004 by cisco Systems, Inc.

Compiled Wed 11-Feb-04 19:24 by kellythw

Image text-base: 0x80008098, data-base: 0x80C83E28

ROM: System Bootstrap, Version 12.1(3r)T2, RELEASE SOFTWARE (fc1)

rt01 uptime is 1 day, 51 minutes

System returned to ROM by reload

System image file is "flash:c2600-i-mz.123-6.bin"

cisco 2621 (MPC860) processor (revision 0x200) with 61440K/4096K bytes of memory


Processor board ID JAD050309VG (2886660437)

M860 processor: part number 0, mask 49

Bridging software.

X.25 software, Version 3.0.0.

2 FastEthernet/IEEE 802.3 interface(s)

32K bytes of non-volatile configuration memory.

8192K bytes of processor board System flash (Read/Write)

Configuration register is 0x2102

Super Bronze

Re: Can't set encapsulation on Sub-Interaces - 2621 Router


c2600-i-mz.123-6.bin is the IP (not IP Plus) version of software. This doesn't support dot1q or ISL trunks.

The IP Plus would be required for this feature (image name for the plus equivalent of your image would be c2600-is-mz.12.3-6.bin)



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Aaron Please remember to rate helpful posts to identify useful responses, and mark 'Answered' if appropriate!
Community Member

Re: Can't set encapsulation on Sub-Interaces - 2621 Router

Thank you for the reply. At least I know what the "problem" is now.

Is there anyway I can get the IP Plus IOS from Cisco or elsewhere? As far as I can tell, I can't register to download it from Cisco as an individual. I purchased the router from a hardware salvage place so i don't have any kind of licensing or purchase info to use...

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