2611XM/3548XL - Subinterfaces and VLANs

Posted on 2006-04-19
Last Modified: 2008-02-20
I am experiencing issues assigning IP address when attempting to trunk multiple VLANs up to a single CISCO 2611 using subinterfaces.....

I have a CISCO 2611 XM and a CISCO 3548 XL...I am trying to use FA 0/0 with subinterfaces (2611) and vlan access [desired ports] (3548) to carry multiple VLANs. [VLAN 100 on the 3548] [VLAN 200 on the 3548]

int fa 0/0.1
encap dot1q 100
ip address

int fa 0/0.2
encap dot1q 200
ip address

int fa 0/1
switchport mode trunk (allowed all)

int fa 0/3
switchport mode access
switchport access vlan 100

I do not have any speed/duplex issues or any up/down issues.....I have dhcp pools setup for both and dhcp-server/networks setup per VLAN (problem ???)....I currently have no L3 management IP established on the 3548 so int VLAN1 remains up up....Obviously as soon as I revert back to a single network on fa 0/0 with no sub-ifs it works fine.

I have seen several proposed solution regarding "secondary" interfaces resolving several peoples issues with physical interface limitations but unfortunately that hasn't worked for me.
Question by:ciscowannabe
    LVL 12

    Accepted Solution

    What is the problem?  Amongst other things, you might need "swit tru enc dot1q" (and if so, "swit tru enc dot1q non" would probably be better) on 3548 int f0/1 to force the trunking protocol.  Routers don't participate in DTP, so a switch expecting DTP might not trunk or might attempt ISL instead of dot1q.

    You may also want to shutdown the 3548 int VLAN1 and create/setup an int VLAN 100 ...OR... 200, so that you can telnet to the 3548.
    LVL 20

    Expert Comment

      Look at your configured IPs on the subinterfaces:
    int fa 0/0.1
    ip address  <- network address; should be something like ...

    int fa 0/0.2
    ip address  <- network address; should be something like ...

      Then you can deal with routing between VLANs:
    Workstations on VLAN 100 would have their default gateway set to:
    Workstations on VLAN 200 would have their default gateway set to:

    On the switch, you could do this in order to remotely manage it:
      int vlan 100
      ip address
      no shut

      ip default-gateway


    Author Comment

    calvinetter - The IP addresses on the sub-ifs are .1 - sorry for the misinformation.

    I'm checking into the above solution recommendations. Thanks,

    Author Comment

    Forgetting about lack of DTP was it....I forced trunk encap and that did it....thanks pjtemplin.

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