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Cannot assign ip address on sub-interface C-2600

i have 1 internet router C-2600 as a gateway to internet via fastethernet. The router has 3 ports, 1 is integrated (fe0/0) and another 2 is physical card-port(sub-interface fe0/0.1 and fe0/0.2).This is supposed to be simple routing to internet via fe (external) and fe (internal local LAN). The problem is i cannot assign any IP address to sub-interface port (fe0/0.1 or fe0/0.2) as the router complains something about " cannot assign Ip address unless interface is in IEEE802.1, Trunking or IS-VLAN". I need to use 1 sub-interface port external to Internet (gateway) and another 1 port internal to local LAN (via firewall). i check the IOS and it doesn't have any option for encapsulation command.

thanks in advance


Re: Cannot assign ip address on sub-interface C-2600

I assume you have a 2620 or something similar. This router has only a single ethernet port.

To make this work you will first need a version of IOS that has 802.1q support. This is normally IPPLUS or higher. Next you will need a switch that also supports 802.1q and you must define a trunk port that has these 2 vlans defined. You then define 2 access ports on the switch one in each vlan to connect to the gateways and your firewall.

New Member

Re: Cannot assign ip address on sub-interface C-2600

Thank you for your quick reply.

Yes, it is true that the router originally comes with 1 fe port. Then later i added 2 fe port-card, identified as sub-interface fe0/0.1 & fe0/0.2 instead of fe0/1 & fe0/2 i was hoping for. Unfortunately, the router is quite the old model (2-year plus)& it doesn't have IPPLUS set s/w. It is much trublesome now to upgrade it into IPPLUS as it will cost more.

Is there any other work around on this ? Otherwise i have to replace thsi router with C 3725 with also comes equipped with FE sub-interface port.

How do we check whether the router comes with 802.1q support ?

thx in advance

Re: Cannot assign ip address on sub-interface C-2600


when u go in the sub-interface configuration u can type encapsulation and ? this will show u weather it supports it or not.and the other way is IP Plus image.



New Member

Re: Cannot assign ip address on sub-interface C-2600

There is no encapsulation (unrecognized command) when i tried to type that under sub-interface. So, i guess the router neither supports encapsulation nor IPPLus image s/w. Too bad because i just plan to implement simple routing to WAN internet GW router via FE.

So, i guess the next ection is to replace it with C3725.

TQ to all

Re: Cannot assign ip address on sub-interface C-2600

Hi Conrad

If you are deciding to go for a new router i would suggest to take a look out on Cisco 2800 series routers which are modular in nature and offers most of the features available at present...


New Member

Re: Cannot assign ip address on sub-interface C-2600

TQ mr Kumar,

In fact, i have at my disposal now Cisco 3825 (gigabit 2-GE & 2-FE) and Cisco 3725 (1-FE + 4-FE ). C3725 was purchased a long time ago together with C2600. The reason i intend to use C2600 is because the link is only 1 pipe to internet , about 4 Mbps and it is for light & simple task.

C3725 is multi-service router (FE + serial port)


Re: Cannot assign ip address on sub-interface C-2600

If I go back to your post that says you put in a 2 port fast ethernet card it becomes a questions of how you did that.

The only way to add ethernet ports to a 2600 is in the module slot. There are nm-2fe but they are not supported on a 2600. The ports on interfaces have names line e1/0 and e1/1 they are not subinterfaces. I suspect if you put a nm-2fe card in the module slot you are getting errors on boot saying the card is not supported.

You can use a nm-4e card to add ethernet ports to a 2600 router. You can also use nm-1e if you only need 1 port. These cards have become very inexpensive because they are end of life and and not supported on the 2800 routers.

These cards are much cheaper than the ipplus software if you can get it on the used market or ebay

New Member

Re: Cannot assign ip address on sub-interface C-2600

That 2-port FE card was in fact slotted into the module slot (lower part of the router). Yes, the FE on that card was marked FE1/0 & FE1/1.

I didn't get any error messages upon booting up the router. In fact, the router easily identified the card as FE0/0.1 & FE0/0.2 (sub-interface) & not FE0/1 & FE0/2 as i was hoping for. It was clearly verified by "sh int", "sh controller", "sh inventory".

Quite strange to me, the router has the necessary routing option but unfortunately no IPPLus s/w.

I know, when the port is under "sub-interface", it can only be configured together with vlan, dot801.2q or encapsulation options. The router does have none of these.

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