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Re: debugging SLP problems on Mac OS 9/X
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Re: debugging SLP problems on Mac OS 9/X


  • Subject: Re: debugging SLP problems on Mac OS 9/X
  • From: Smith Kennedy <email@hidden>
  • Date: Wed, 9 Feb 2005 08:03:30 -0700

Hi Glen,

If they were unique messages being sent out, what fields in the various headers (IP, UDP, etc.) would be changing each time? If they were the same packets just being re-cast over the network, which fields would be the same? I have been looking at some of my networking books, but haven't found anything yet that tips me off one way or the other.

TIA,
Smith


On Feb 8, 2005, at 7:43 PM, Glenn Anderson wrote:

At 7:15 PM -0700 2/8/05, Smith Kennedy wrote:
I was wondering if anyone might have any insight into a problem we are having with Mac systems on our site. The problem seems to involve SLP on both Mac OS 9 and Mac OS X.

I posted a related message to the client-management ML a while ago, but got no meaningful replies (thanks to John Welch for trying, though).

A couple of months ago, for several days, there were these "multicast packet squalls" that would occur periodically, and would be visible on all our subnets on the site. Each "squall" consists of 250K or so SLP service request queries being made within 1-2 minutes. All queries in a particular "squall" would emanate from the same system, and the system was always a Mac OS 9 or Mac OS X system.

<snip>

My questions are these:

- Does anybody have any hunches why this would be happening?

I have seen something like this happen before, it was some sort of ethernet switch problem causing a multicast loop. If you are seeing the same problem, it is not the Mac going crazy, it is one packet from the Mac being looped back and forth between a couple of ethernet switches. One way to tell is the packet storm will continue even if you unplug the Mac that started it. The network where I saw this was too complex to try and track down the problem in the time available, we ended up solving it by rate limiting multicast packets on the main switch. As it was just one packet going 'round and 'round, as soon as it hit the rate limit the packet was discarded, and this stopped the storms in a fraction of a second. My guess is it was some sort of layer 3 IGMP and/or spanning tree problem with one or more ethernet switches.


Glenn.

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