From: Scott Morris (smorris@internetworkexpert.com)
Date: Fri Aug 08 2008 - 17:10:44 ART
Step back a second and think about what traffic goes where. Let's start
with ANY broadcast or multicast traffic (don't just think IP, think which L2
stuff there is) and then think about what a switch/bridge does with such
traffic.
Sends out any/all available non-receiving port. So as you trace this
through your network, how's it look? When it comes to things like
L2Tunneling and Q-in-Q, you are forwarding things over normally
non-participating paths. So make sure there are no mistakes along the way
causing stuff to be "deposited" back into a path that will cause one switch
to re-receive a frame and therefore freak out about loopguard detection.
Like I said. It's not much fun, and quite tedious to do. But a very good
exercise in pulling one's hair out!
Scott
_____
From: Igor Manassypov [mailto:imanassypov@rogers.com]
Sent: Friday, August 08, 2008 3:59 PM
To: cciestudy; 'Igor Manassypov'; 'GS CCIE-Lab'
Cc: 'Scott Morris'
Subject: RE: IE Lab 20
Study,
The stp tunnelling is for S1-S3 across S4, its got nothing to do with S2
being shut down... l2p tunnel stp is granted to make s1-s3 share one common
tree. I cant reason why SW2, having three trunks in parallel run to SW4 is
being shut down. Those three are the only paths up from SW2, so honestly I
am lost here completely.
cciestudy <cciestudy@mid-world.net> wrote:
From what I understand (I am not even close to an expert), is that the
keepalive is the loop detection mechanism on the switch. Turn it off and
the loop doesn't go away, it just doesn't detect. The STP addition was the
fix to detect and block the loop.
Scott. Correct me if I am wrong on this.
_____
From: Igor Manassypov [mailto:imanassypov@rogers.com]
Sent: Friday, August 08, 2008 2:08 PM
To: Igor Manassypov; cciestudy; 'GS CCIE-Lab'
Subject: RE: IE Lab 20
Besides, how does interface keepalive relate to spantree loops?
Igor Manassypov <imanassypov@rogers.com> wrote:
Hmm, whats the mechanism behind the interface keepalives that triggers the
interface to shutdown? Besides, I really doubt that just by disabling the
interface keepalive you avoid the loop, its just might stop going into
errdisable but the loop will still occur if there is one (?)
cciestudy <cciestudy@mid-world.net> wrote:
I finished that lab a few weeks ago. All I can say is it was a bugger to
solve. The IE message board has some good insight into why it was
occurring. I believe turning off interface keep-alives resolved the looping
problem. I believe it was SW4, F0/13, F0/15, F0/19, F0/21. Also, I tried
doing L2protocol-tunnel on STP also...
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Igor
Manassypov
Sent: Friday, August 08, 2008 9:58 AM
To: GS CCIE-Lab
Subject: IE Lab 20
Hi Gang,
Has anyone done internetwork expert's lab 20 recently? I am having a hard
time on the first section with STP where it keeps flipping interfaces to
err-disabled mode due to 'loopback error'. I am wondering if anyone was able
to solve it.
Thanks!
Igor M., M.Eng, P.Eng
Network Architect
Blogs and organic groups at http://www.ccie.net
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