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Date: Thu, 12 Aug 2004 16:09:17 +0300
From: Ruslan Ermilov <ru@freebsd.org>
To: Chris Stenton <jacs@gnome.co.uk>
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cc: FreeBSD Current <freebsd-current@freebsd.org>
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Subject: Re: bad tcp cksum on outgoing packets
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[Cc: freebsd-net]

On Thu, Aug 12, 2004 at 12:50:58PM +0100, Chris Stenton wrote:
> I have just been doing some debugging on my 5.2.1 box and noticed that
> outgoing tcp packets on the box are coming up with bad checksums on
> tcpdump. I am using the nge interface.
>=20
> Here is a sample output.
>=20
> 12:44:29.458021 0:4:e2:10:60:83 0:c:6e:4e:a0:cc ip 82:
> hawk.gnome.co.uk.ssh > kite.gnome.co.uk.2167: P [bad tcp cksum 9420!]
> 2071:2099(28) ack 753 win 65535 (DF) [tos 0x10]  (ttl 64, id 35623, len
> 68, bad cksum 0!)
>=20
> 12:44:29.642088 0:c:6e:4e:a0:cc 0:4:e2:10:60:83 ip 60:
> kite.gnome.co.uk.2167 > hawk.gnome.co.uk.ssh: . [tcp sum ok] 753:753(0)
> ack 2099 win 64956 (DF) (ttl 128, id 44852, len 40)
>=20
>=20
> Any ideas whats going on as the packet does not seem to be resent?
>=20
You don't have hardware checksums enabled, do you?  I barely
recall they are incompatible with bpf(4).


Cheers,
--=20
Ruslan Ermilov
ru@FreeBSD.org
FreeBSD committer

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