[AG-TECH] multicast problem

Andrew Daviel andrew at andrew.triumf.ca
Wed Jun 23 18:23:38 CDT 2004


On Wed, 23 Jun 2004, Zeppy B. Vilan wrote:

> hello people,
>
> i would like to ask your help regarding my multicast problem. i can
> recieve and transmit using multicast in access grid lobby. but every 1
> to 2 minutes i got freeze and after 1 to 2 minute it will back again?

I attended one of the Internet2 Multicast Workshops (highly recommended,
if rather technical...) and one of the instructors mentioned that timing
is very important when reporting/diagnosing problems. I.e. the 2 minute
cycles correlate with timeouts of IGMP or PIM state on a router.
Offhand I'd not disagree with John and Mike's replies that it may be a PIM
problem - but I'm still not an expert.

I've had weird checksum problems here with some Nortel equipment - PIM
packets with bad checksum rejected by a Juniper upstream, but only if the
first packet had an odd packet length. I read also of some older Cisco
versions that got checksums wrong. (I don't think that's your problem,
it's just an FYI for the archive...)

I have some links to tools, RFCs etc at
http://andrew.triumf.ca/AG/multicast/
The original Internet2 presentation is available at
http://multicast.internet2.edu/workshops/vancouver/ and includes some good
troubleshooting guides

My problems were with joining, and the beacon wasn't much help (once
joined, the client stayed joined), so I wrote some simple test tools in C
and Perl to send/receive packets on arbitrary groups then look with
tcpdump and log on to the routers to check state. I later found similar
things online (e.g. mping.exe for DOS)

I'd suggest initially testing across a single network segment or across
your campus to make quite sure it works 100% there, before getting
involved with WAN issues. I imagine you already did that...

-- 
Andrew Daviel, TRIUMF, Canada
Tel. +1 (604) 222-7376
security at triumf.ca




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