bad checksum problem: HELP!?!

[Jeremias]

I got a high network traffic as an answer of:

mount //server/media /mnt/media -t smbfs -o username=user,password=pw

without doing something!

I captured some packages with ethereal/tcpdump and got a lot of bad checksum errors on udp and tcp protocols, only on packages sent out of my pc. But ifconfig and netstat shows no error.

[user@pc ~]$ ifconfig eth0
eth0      Link encap:Ethernet  HWaddr 00:50:04:45:F7:E0
          inet addr:192.168.6.11  Bcast:192.168.6.255  Mask:255.255.255.0
          inet6 addr: fe80::250:4ff:fe45:f7e0/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1245 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1150 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:825385 (806.0 KiB)  TX bytes:190450 (185.9 KiB)
          Interrupt:9 Base address:0xb000

[user@pc ~]$ netstat -in
Kernel Interface table
Iface       MTU Met    RX-OK RX-ERR RX-DRP RX-OVR    TX-OK TX-ERR TX-DRP TX-OVR Flg
eth0       1500   0     1242      0      0      0     1147      0      0      0 BMRU

[user@pc ~]$ tcpdump eth1 | grep cksum
09:44:27.978790 IP (tos 0x0, ttl  64, id 47122, offset 0, flags [DF], proto 17, length: 70) 192.168.6.244.32780 > router.hometown.domain: [bad udp cksum 53dc!]  63908+ PTR? 1.6.168.192.in-addr.arpa. (42)
09&#58;44&#58;28.019048 IP &#40;tos 0x0, ttl  64, id 59335, offset 0, flags &#91;DF&#93;, proto 6, length&#58; 52&#41; 192.168.6.244.35520 > server.hometown.microsoft-ds&#58; . &#91;tcp sum ok&#93; 279&#58;279&#40;0&#41; ack 545 win 1460 <nop,nop,timestamp 2537531 61868669>
0
...
09&#58;17&#58;31.282177 IP &#40;tos 0x0, ttl  64, id 53098, offset 0, flags &#91;DF&#93;, proto 6, length&#58; 57&#41; 192.168.6.244.54166 > baym-cs237.msgr.hotmail.com.1863&#58; P &#91;bad tcp cksum 9d13 &#40;->af9e&#41;!&#93; 10&#58;15&#40;5&#41; ack 17 win 2264 <nop,nop,timestamp 920548 2261424>
09&#58;18&#58;19.539379 IP &#40;tos 0x0, ttl  64, id 51308, offset 0, flags &#91;DF&#93;, proto 17, length&#58; 60&#41; 192.168.6.244.32780 > router.hometown.domain&#58; &#91;bad udp cksum d8be!&#93;  19895+ AAAA? foxtown.ath.cx. &#40;32&#41;
09&#58;18&#58;19.703905 IP &#40;tos 0x0, ttl  64, id 51473, offset 0, flags &#91;DF&#93;, proto 17, length&#58; 69&#41; 192.168.6.244.32780 > router.hometown.domain&#58; &#91;bad udp cksum 31a1!&#93;  36005+ AAAA? foxtown.ath.cx.hometown. &#40;41&#41;
...
205.188.8.200.5190&#58; P &#91;bad tcp cksum 9e41 &#40;->9613&#41;!&#93; 18&#58;24&#40;6&#41; ack 1 win 20400
09&#58;18&#58;31.282043 IP &#40;tos 0x0, ttl  64, id 53102, offset 0, flags &#91;DF&#93;, proto 6, length&#58; 57&#41; 192.168.6.244.54166 > baym-cs237.msgr.hotmail.com.1863&#58; P &#91;bad tcp cksum 9d13 &#40;->c2d0&#41;!&#93; 15&#58;20&#40;5&#41; ack 25 win 2264 <nop,nop,timestamp 980557 2262023>
09&#58;19&#58;27.544287 IP &#40;tos 0x0, ttl  64, id 47298, offset 0, flags &#91;DF&#93;, proto 6, length&#58; 46&#41; 192.168.6.244.49319 > 205.188.8.200.5190&#58; P &#91;bad tcp cksum 9e41 &#40;->960c&#41;!&#93; 24&#58;30&#40;6&#41; ack 1 win 20400
09&#58;19&#58;31.281721 IP &#40;tos 0x0, ttl  64, id 53106, offset 0, flags &#91;DF&#93;, proto 6, length&#58; 57&#41; 192.168.6.244.54166 > baym-cs237.msgr.hotmail.com.1863&#58; P &#91;bad tcp cksum 9d13 &#40;->d600&#41;!&#93; 20&#58;25&#40;5&#41; ack 33 win 2264 <nop,nop,timestamp 1040566 2262624>
0
...

I'm running FC4, with Kernel 2.6.12-1.1447_FC4 on a 800MHz Intel Pentium III
NIC1: 3Com, XL PCI, Fast Etherlink, 3C905B-TX
NIC2: 3Com, XL PCI, Fast Etherlink, 3C905B-TX
else: Hauppauge WinTV, ATI Rage

Thanks for help!

[SteveA]

I hope you solved your problem long ago, but for the record ...

ethereal examines outgoing packets before they exit through your ethernet chip. Most modern ethernet chips calculate the checksums on outgoing packets, so the software stack does not.

It is normal to see most OUTGOING packets declared as "bad checksum".