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Date: Mon, 5 Apr 2004 15:52:06 +0200 (MET DST)
From: Mipam <mipam@ibb.net>
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Subject: bad tcp/udp checksums with broadcom cards.
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Hi,

(I allready posted this message without a subject, which isnt nice so i
post it again, forgive me).

I've some dell poweredges with broadcomcards in them:

bge0: <Broadcom BCM5704C Dual Gigabit Ethernet, ASIC rev. 0x2002> mem
0xfcd20000
-0xfcd2ffff,0xfcd30000-0xfcd3ffff irq 16 at device 0.0 on pci2
bge0: Ethernet address: 00:0b:db:93:c5:c4
miibus0: <MII bus> on bge0
brgphy0: <BCM5704 10/100/1000baseTX PHY> on miibus0
brgphy0:  10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, 1000baseTX,
1000baseTX-FDX, auto

However on all of these systems i encounter this in tcpdump:

14:51:49.845 x.x.x.x.22 > x.x.x.x.3599: P 444:784(340) ack
53 win 32850 (DF) [tos 0x10]  (ttl 64, id 21535, len 380, bad cksum 0!)
14:51:49.863740 x.x.x.x.3599 > x.x.x.x.22: P 53:105(52) ack 280
win 64128 (ttl 126, id 24085, len 92)
14:51:49.864327 x.x.x.x.3599 > x.x.x.x.22: . [tcp sum ok]
105:105(0) ack 784 win 63624 (ttl 126, id 24086, len 40)
14:51:49.865208 x.x.x.x.3599 > x.x.x.x.22: P 105:157(52) ack
784 win 63624 (ttl 126, id 24088, len 92)
14:51:49.865231 x.x.x.x.22 > x.x.x.x.3599: . [bad tcp cksum
505b!] 784:784(0) ack 157 win 32824 (DF) [tos 0x10]  (ttl 64, id 21536,
len 40, bad cksum 0!)

Has this to do with tcp checksum offloading?
Should i turn it off? And if so, how to turn it off?
Or is this correct and no problem?
Does this card got segmentation offload and other offloads?
Any hints?
Bye,

Mipam.