From: Hobbs (deadheadblues@gmail.com)
Date: Sat Jan 31 2009 - 17:30:59 ARST
Jared,
Thanks for the reply, but the issue isn't with R5, I was using it test
my monitoring by running debug ip packet. I can remove as needed and
the issue remains.
The issue is with SW1 seeing R2 as a CDP neighbor - THIS should not be
happening. Suppose I had a monitoring device on SW1....why does SW1
see R2 as a neighbor?
thanks,
On Sat, Jan 31, 2009 at 12:21 PM, Jared Scrivener
<jscrivener@ipexpert.com> wrote:
> Hey Hobbs,
>
> It appears that your switch is copying ALL frames (from layer 2) received
> via R2 and outputting them to R5. That includes CDP frames.
>
> R5 thinks that R2 is a CDP neighbor as a result of this. CDP adjacencies
> require duplex to be matching (as they assume that CDP adjacencies are on
> the same physical link) but it appears that R2 is half-duplex. This is
> giving you CDP errors.
>
> My first question is "why" are you doing this (spanning a router to another
> router), but I'm sure you're doing it to learn something new. :)
>
> Just disable CDP on R2's interface and your issue should resolve itself
> (assuming changing the duplex on R2 doesn't help).
>
> Cheers,
>
> Jared Scrivener CCIE3 #16983 (R&S, Security, SP), CISSP
> Technical Instructor - IPexpert, Inc.
> Telephone: +1.810.326.1444
> Fax: +1.810.454.0130
> Mailto: jscrivener@ipexpert.com
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Hobbs
> Sent: Saturday, 31 January 2009 2:02 PM
> To: Cisco certification
> Subject: RSPAN causing an l2protocol tunnel-like effect
>
> Hello,
>
> I have the following:
>
> R5---sw1---sw2---R2
>
> Afetr setting up RSPAN on the switches (3560s), sw1 sees R2 as a CDP
> neighbor.
>
> I have a monitor session on sw2 destined for a remote vlan as follows:
>
> SW2#sho run | inc mon
> monitor session 1 source interface Fa0/2
> monitor session 1 destination remote vlan 999
>
> On sw1 I start getting these messages:
>
> 00:50:32: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on
> FastEthernet0/13 (not half duplex), with R2 Ethernet0/0 (half duplex).
> 00:51:32: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on
> FastEthernet0/13 (not half duplex), with R2 Ethernet0/0 (half duplex).
>
> Sure enough, Sw1 now sees R2 as a cdp neighbor on the port connected to sw2
>
> SW1#sho cdp ne | inc 0/13
> SW2 Fas 0/13 125 R S I
> WS-C3560-2Fas 0/13
> R2 Fas 0/13 165 R S I 3640
> Eth 0/0
>
> fyi, sw1 has the following config:
>
> SW1#sho run | inc mon
> monitor session 1 destination interface Fa0/5 ingress untagged vlan 100
> monitor session 1 source remote vlan 999
>
> I have define vlan 999 as a remote-span vlan.
>
> Any ideas?
>
> thank you
>
>
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