Re: CDP tunneling: why doesn't far end switch show near end

From: Jonathan Greenwood II (gwood83@gmail.com)
Date: Wed Aug 06 2008 - 13:32:53 ART

You need to change the switchport mode from access to dot1q-tunnel.

On Wed, Aug 6, 2008 at 11:27 AM, Hobbs <deadheadblues@gmail.com> wrote:

> Hello,
>
> I am trying get my head around a semi-complex protocol tunneling task, but
> I
> have some questions on the basics.
>
> Here's the topology
>
> "Near end host": BB1
> "Far end switch": CAT2
>
> [BB1]f0/1-----f0/11[CAT1]f0/23-----dot1q
> trunk-----f0/23[CAT2]f0/1-----f0/1[R1]
>
> To get cdp tunneling to work (and it does work) I enable this on CAT1 and
> CAT2 access ports:
>
> CAT1:
> interface f0/11
> switchport mode access
> switchport access vlan 100
> l2protocol-tunneling cdp
> no cdp enable
>
> CAT2:
> interface f0/1
> switchport mode access
> switchport access vlan 100
> l2protocol-tunneling cdp
> no cdp enable
>
> The trunk between CAT1 and CAT2 carries vlan 100 as well as others.
>
> This is what I understand so far:
>
> BB1 sends a multicast CDP packet on it's port to CAT1.
> Since CAT1 has cdp tunneling enabled, it forwards it rather than processes
> it. Is this correct?
> CAT1 sends this packet out all trunk links that have vlan 100 allowed AND
> any access ports on VLAN100. Is this correct?
> The packet still has the cisco CDP destination MAC. Is this correct?
> The packet is dot1q tagged and sent out port fa0/23 and still has cisco CDP
> destination MAC address. Is this correct?
>
> Question:
>
> CAT2 doesn't have tunneling on port fa0/23.
> Why doesn't CAT2 now process this CDP packet and show BB1 has a CDP
> neighbor
> on fa0/23?
> Does trunking override this behavior?
> Does CAT2 treat this packet differently because it is a tagged CDP packet?
>
> Thanks,
>
>
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