Subinterface encapsulation on Cisco 2651 Router

Posted on 2008-11-08
Last Modified: 2012-08-13
I am setting up my home lab for VLAN routing and I wish to configure a subinterface on my 2651 router.

 It does have 2 10/100 FE ports.

I am able to created the sub interface (using INTERFACE FA0/1.10 command) but when I go to set the encapsulation is says that command is not recognized.  Below is a SHO VER and error messages.
R1(config-if)#do sho ver

Cisco Internetwork Operating System Software

IOS (tm) C2600 Software (C2600-I-M), Version 12.3(6a), RELEASE SOFTWARE (fc4)

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

Compiled Fri 02-Apr-04 19:17 by kellythw

Image text-base: 0x80008098, data-base: 0x80C83D68

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

R1 uptime is 46 minutes

System returned to ROM by power-on

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

cisco 2651 (MPC860P) processor (revision 0x200) with 126976K/4096K bytes of memory.

Processor board ID JAB05380CRG (3611485969)

M860 processor: part number 5, mask 2

Bridging software.

X.25 software, Version 3.0.0.

2 FastEthernet/IEEE 802.3 interface(s)

1 Serial network interface(s)

32K bytes of non-volatile configuration memory.

16384K bytes of processor board System flash (Read/Write)

Configuration register is 0x2102


R1(config)#interface fa0/1.10

R1(config-subif)# encapsulation


% Invalid input detected at '^' marker.

R1(config-subif)#ip address

% 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.


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Question by:every1isevil2
    LVL 23

    Expert Comment

    show run int fa0/1

    You need to make sure that  the configuration of the FastEthernet0/1  base  interface itself is comptaible with 802.1q

    For example:
    int fa0/1
     no ip address
     duplex auto
     speed auto
     no shutdown
    LVL 4

    Author Comment

    Mysidia:  thanks for the reply.

    Are you saying that the base interface (Fa0/1) cannot have an IP address, and must be set to auto duplex?
    It would seem that this is not the case as the study guide I am using the instructor set an IP address, and duplex to full on the router interface.   At any case I tried this and still have the same problem.
    LVL 23

    Expert Comment

    duplex/speed is not an issue,  but  is there by default:  duplex/speed should match the configuration of the other side of the link.
    If the other side of the link has duplex set to 'auto',  then it must be auto on this side, etc.

    The IP address _is_  an issue.
    It is  inconsistent with  subinterface naming for fa0/1 to have an  IP address.

    You may actually be able to do it on some models/software versions if you have an encapsulation such as:
    encapsulation dot1Q  1 native

    On the  fa0/1 interface.

    But in my experience, you cannot (in most cases) have a .1q  subinterface, if the base interface is populated with addressing as a router port.

    You cannot properly mix  dot-1q  and  non-VLAN  interfaces on the same physical port
    (Although you can have an 802.1q  native vlan interface)

    LVL 50

    Accepted Solution

    You're running the IP feature set. You'll need at least IP Plus to support trunking.
    LVL 4

    Author Closing Comment

    Thanks I have obtained this and am flashing my router now!

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