i believe the most effective way to simulate routing loops is via
configuration errors, the way they appear in real life (mutual
redistribution between ospf & rip without any filtering seems pretty
effective).
I suspect that the supported parameters vary wildly by IOS version; I've
seen cases where investigating problems with explicitly configured MTU
sizes of an unacceptably small magnitude yielded little beyond failure or
success. Unfortunately, the best data i have for those cases were sniffer
traces from end-user systems and NOT router feedback.
"Chuck Larrieu" @groupstudy.com on 07/03/2001 06:58:02
PM
Please respond to "Chuck Larrieu"
Sent by: [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
cc: (bcc: Kevin Cullimore)
Subject: RE: ping replies [7:10910]
methodology questions - see in line:
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
Priscilla Oppenheimer
Sent: Tuesday, July 03, 2001 2:47 PM
To: [EMAIL PROTECTED]
Subject: ping replies [7:10910]
M Fragmentation was needed and the don't fragment (DF) bit was set.
& A time-to-live exceeded message was received.
I The user interrupted the test.
? An unknown packet was received.
C A packet was received with the congestion-experienced bit set.**
Questions:
Has anyone ever seen M? I couldn't get this to happen in my lab. Is M even
for real or was that an error in one of the versions of the documentation?
CL: curiousity, PO - are you setting the MTU on a segment at some low
number, then using extended ping with a large packed size and setting DF?
just thinking out loud how I would attempt an experiment
Has anyone every seen &? I couldn't get that one to happen either.
CL: how are you testing this one? best I can come up with is to
deliberately
create a routing loop someplace along the line. I'm just mulling over how
to
do so. static routes between two routers pointing to eachother as the place
where the destination network resides?
How about I? That doesn't happen on my routers. Plus one version of the
documentation said it was |, not I.
CL: never, and I interrupt all the time
And how about the mysterious C? I found out that it's related to RFC 2481,
an experimental protocol that adds explicit congestion notification to IP.
Maybe some internal developer asked for this. Cisco clearly favors helping
developers troubleshoot over helping customers troubleshoot. (Sorry, but
this ping research has made me angry at Cisco.)
CL: Cisco been very very good to me :->
Thanks for your help.
Priscilla
________________________
Priscilla Oppenheimer
http://www.priscilla.com
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