From: Jared Scrivener (jscrivener@ipexpert.com)
Date: Sat Jan 31 2009 - 17:52:17 ARST
That's definitely odd and not something I've encountered before.
If you do "sh vlan remote-span" on both switches are they both aware it is
an RSPAN VLAN?
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: Hobbs [mailto:deadheadblues@gmail.com]
Sent: Saturday, 31 January 2009 2:36 PM
To: jscrivener@ipexpert.com
Cc: Cisco certification
Subject: Re: RSPAN causing an l2protocol tunnel-like effect
Ok, just to remove any doubt. I got my laptop connected to SW1 now and
removed R5 :)
So now R2 packets are being sent to remote-span VLAN999, to sw1 and
then along to my laptop, monitoring is working...but sw1 still sees R2
as cdp neighbor.
I would think that SW1 is supposed to know that vlan 999 is an
rspan-vlan not take everything literal....
On Sat, Jan 31, 2009 at 12:30 PM, Hobbs <deadheadblues@gmail.com> wrote:
> 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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>>
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