Subject: Re: bridge(4) and silent data corruption :-(
To: Sean Doran <>
From: Michael Richardson <>
List: tech-net
Date: 04/29/2002 16:35:08

>>>>> "Sean" == Sean Doran <> writes:
    Sean> mcr writes:

    Sean> |   Presumeably, if packets are getting corrupted, that TCP checksumming should
    Sean> | really be catching this, unless the bridge is "fixing" them in some way...

    Sean> It sure looks like that...  However, I haven't figured out why local traffic
    Sean> through the bridge works OK but non-local doesn't.

  Could it be the router?
  I haven't used bridge(4) [I don't not presently even have a machine with
the man page]. Is it doing proxy-arp'ing for other IPs, or is this a layer-2 switch? 
  I wonder if the router gets confused by two hosts with the same MAC?

    Sean> |   Maybe a tcpdump from both sides of the bridge? Too bad there isn't a good
    Sean> | program to coorelate and compare packets!

    Sean> No kidding...  Here's a complete dump of world->station-a (it fails
    Sean> nice and quickly) during Topology 3.

    Sean> (tcpdump -w x -vvv -s 1500 -i en0 -ttt host world; tcpdump -r x
    Sean>  yeah, station-a is a mac os x laptoy...).

  I can't really see anything wrong there... with -vvv it should be checking
the TCP checksums, so they are okay.... There isn't any NAT occuring on
"router" is there?

]       ON HUMILITY: to err is human. To moo, bovine.           |  firewalls  [
]   Michael Richardson, Sandelman Software Works, Ottawa, ON    |net architect[
] |device driver[
] panic("Just another NetBSD/notebook using, kernel hacking, security guy");  [

Version: 2.6.3ia
Charset: latin1
Comment: Finger me for keys