----- Original Message -----
From: Mipam <[EMAIL PROTECTED]>
Date: Mon, 9 Aug 2004 11:05:37 +0200 (MEST)
To: M�rtainn D�mhnallach <[EMAIL PROTECTED]>
Subject: Re: bad cksum 0! repeat line in tcpdump in 3.5
> On Sun, 8 Aug 2004, =?iso-8859-1?B?TeBydGFpbm4gRPJtaG5hbGxhY2g= ?= wrote:
>
> > Hi there,
> > I originally sent this list to comp.unix.openbsd.misc but I got no takers
> > for it. I'm trying to set up a transparent filtering bridge using pf and I get an
> > odd line when I used tcpdump to monitor what specific multicast messages come
> > through the bridge. I'm monitoring what comes
> > into the bridge (em1) and what goes out (em0).
> >
> > Every incoming multicast packet is followed by another identical packet with a
> > checksum error. It looks like pf or tcpdump is generating them. The good packet is
> > reported to leave on the em0 interface. I'm using a standard 3.5 setup straight
> > off the official disk.
> >
> > I've used Ethereal to check that the checksum failing packets are not present on
> > the LAN.
> >
> > I saw a reference to something like this on Google on bit.listserv.openbsd-pf but
> > it was dated back in January 2003.
> >
> > Any ideas if this is the same problem?
> >
> > Thanks,
> > Martin.
> >
> > The tcpdump lines:
> >
> > Aug 05 14:14:13.654484 rule 0/0(match): pass in on em1: 10.194.1.76.1026
> > > SVRLOC.MCAST.NET.svrloc: udp 124 (ttl 32, id 287) Aug 05
> > 14:14:13.654489 rule 0/0(match): pass in on em1: 10.194.1.76.1026 >
> > SVRLOC.MCAST.NET.svrloc: udp 124 (ttl 32, id 287, bad cksum 0!) Aug 05
> > 14:14:13.654492 rule 2/0(match): pass out on em0: 10.194.1.76.1026 >
> > SVRLOC.MCAST.NET.svrloc: udp 124 (ttl 32, id 287) --
>
> So this machine is serving as bridge?
> Bad udp/tcp checksums are normal when you
> enable checksum offloading, but since you're using the machine as
> bridge, this shouldnt be the case right?
> Bye,
>
> Mipam.
Hi Mipam,
The NIC is an Intel Pro/1000MT (dual port) which has HW checksum offloading
as a default as far as I can make out. If this is causing the problem have you any
idea how to turn it off?
Thanks,
Martin
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