Subject: `ifconfig wm3 ip4csum` creates bad cksums via tcpdump
To: None <>
From: Charlie Allom <>
List: current-users
Date: 05/19/2007 19:17:43

not a ball breaker - as everything still works... afaict.

on my quad intel cards I get all IP packets with bad cksums when
viewing via tcpdump - pf enabled or not!


% ifconfig wm3 tcp4csum udp4csum tso4 ip4csum
[[wait 34 seconds! poor sockets ]]



19:05 hadrian:~% sudo tcpdump -enlv -i wm3 |grep bad\ cksum
19:05:33.916096 00:15:17:14:ee:19 > 00:00:0c:07:ac:fb, ethertype IPv4 (0x0800), length 66: (tos 0x0, ttl  63, id 60320, offset 0, flags [DF], proto: TCP (6), length: 52, bad cksum 0 (->ea78)!) > ., cksum 0x4e88 (correct), ack 0 win 16746 <nop,nop,timestamp 109171399 3172525958>

what does that mean? cksum 0??

so I port spanned the traffic back to the same NIC, wm4, and of course
*no* bad cksums.

19:05 hadrian:~% sudo ifconfig wm3 -ip4csum
19:07 hadrian:~% sudo tcpdump -enlv -i wm3 |grep bad\ cksum
tcpdump: listening on wm3, link-type EN10MB (Ethernet), capture size 96
^C25313 packets captured
104115 packets received by filter
77966 packets dropped by kernel

all gone! can someone explain?

19:15 hadrian:~% grep wm3 /var/run/dmesg.boot 
wm3 at pci8 dev 0 function 1: Intel PRO/1000 QT (82571EB), rev. 6
wm3: interrupting at ioapic0 pin 17 (irq 5)
wm3: PCI-Express bus
wm3: 65536 word (16 address bits) SPI EEPROM
wm3: Ethernet address 00:15:17:14:ee:19
igphy1 at wm3 phy 1: Intel IGP01E1000 Gigabit PHY, rev. 0

 hail eris