Encapsulation problem

Unanswered Question
Sep 8th, 2007

I should be able to create a sub-interface on the router and give it an encapsulation type, like dot1q or isl. But after I've created the sub-interface, there are no encapsulation options. I even typed a "?" at the prompt, and "encapsulation" didn't appear. I'm reading right out of Cisco's book right now, and I know that sequence and procedure is right, so I'm puzzled as to why it won't accept it. And if I try and assign an IP address to a sub-interface, I get the message:

Configuring IP routing on a LAN subinterface is only allowed if that subinterface is already configured as part of an IEEE 802.10 or ISL vLAN.


I have this problem too.
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scottmac Sat, 09/08/2007 - 15:36

What hardware platform, and what version of IOS?

Chances are you'll have to update your IOS to 12.{something}

Good Luck


jlhainy Fri, 09/14/2007 - 17:04

There are also some IOSes that support 802.1q by default and do not support ISL, thus the encapsulation command is not needed because it will assume that all vlans will use 802.1q. I have such an IOS on a 6500.

crunchyhippo Sat, 09/15/2007 - 03:52

Well, according to this link, I discovered that my switch(s) doesn't even support trunking, so trying to do VLANs doesn't get me far. I'll probably wind up selling them back on eBay, then cough up a little more hard-earned cash and get some 2950s like I should have done in the first place, instead of skimping and getting 2924s.


crunchyhippo Fri, 09/14/2007 - 08:26

Here are some additional details about the switch which may shed some light; I input these commands, and I show the results:

*Config t*

Switch#config t

Enter configuration commands, one per line. End with CNTL/Z.


*Interface fastethernet 0/1*

Switch(config)#int fa 0/1


*Switchport mode trunk*

Switch(config)#int fa 0/1

Switch(config-if)#switchport mode trunk


% Invalid input detected at '^' marker.


*Switchport trunk encapsulation*

Switch(config-if)#switchport trunk encapsulation


% Invalid input detected at '^' marker.


*Switchport ?*

Switch(config-if)#switchport ?

access Set access mode characteristics of the interface

mode Set trunking mode of the interface

multi Set characteristics when in multi-VLAN mode

*Switchport mode ?*

Switch(config-if)#switchport mode ?

access Set trunking mode to ACCESS unconditionally

multi Set trunking mode to multi-VLAN mode

cyphur353 Fri, 09/14/2007 - 08:34

Mohammed has already given you the link to the tool which will allow you to find the IOS image that you need, as well as the topic you should search for. You will have to investigate to find an image which supports your required services, and doesn't exceed your flash memory capacity.


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