* 2.6.0: Bad udp checksum in loopback interface
@ 2003-08-15 11:11 Ricardo Galli
2003-08-15 11:49 ` 2.6.0: Bad udp checksum in loopback interface (me too!) Catalin BOIE
2003-08-15 16:08 ` 2.6.0: Bad udp checksum in loopback interface Stephen Hemminger
0 siblings, 2 replies; 3+ messages in thread
From: Ricardo Galli @ 2003-08-15 11:11 UTC (permalink / raw)
To: linux-kernel, linux-net
tcpdump -v shows bad udp checksum in the loopback interface. But I'm not sure
if the packets is discarded or the error is ignored.
ponti:~# tcpdump -i lo -n -v
ponti:~# dig @192.168.0.3 gallimedina.net
13:02:12.360728 192.168.0.3.32827 > 192.168.0.3.53: [bad udp cksum 5e6d!]
35220+ A? gallimedina.net. (33) (DF) [ttl 0] (id 0, len 61)
13:02:12.364470 192.168.0.3.53 > 192.168.0.3.32827: 35220* 1/1/1
gallimedina.net. A 192.168.0.10 (85) (DF) [ttl 0] (id 12492, len 113)
ponti:~# dig @127.0.0.1 gallimedina.net
13:03:53.299883 127.0.0.1.32827 > 127.0.0.1.53: [bad udp cksum 167d!] 32901+
A? gallimedina.net. (33) (DF) [ttl 0] (id 0, len 61)
13:03:53.303448 127.0.0.1.53 > 127.0.0.1.32827: 32901* 1/1/1 gallimedina.net.
A 192.168.0.10 (85) (DF) [ttl 0] (id 7725, len 113)
This machine has a bridge, but I also tried in another one with netcat (nc -l
-u localhost -p 2000 and nc -u localhost 2000)
antoli:~# tcpdump -i lo -n -v
tcpdump: listening on lo
13:09:04.125385 127.0.0.1.32890 > 127.0.0.1.2000: [bad udp cksum 5a0!] udp 14
(DF) [ttl 0] (id 32006, len 42)
13:09:12.472940 127.0.0.1.2000 > 127.0.0.1.32890: [bad udp cksum 837!] udp 7
(DF) [ttl 0] (id 34086, len 35)
I saw the short message does arrive to the listening netcat, but tcpdump still
gives the bad udp error message.
Regards,
--
ricardo galli GPG id C8114D34
http://mnm.uib.es/~gallir/
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: 2.6.0: Bad udp checksum in loopback interface (me too!)
2003-08-15 11:11 2.6.0: Bad udp checksum in loopback interface Ricardo Galli
@ 2003-08-15 11:49 ` Catalin BOIE
2003-08-15 16:08 ` 2.6.0: Bad udp checksum in loopback interface Stephen Hemminger
1 sibling, 0 replies; 3+ messages in thread
From: Catalin BOIE @ 2003-08-15 11:49 UTC (permalink / raw)
To: Ricardo Galli; +Cc: linux-kernel, linux-net
Hi!
I have almost the same program.
cups sends on udp browse informations.
It sends 3 + 1 udps.
The last one has bad checksum.
> tcpdump -v shows bad udp checksum in the loopback interface. But I'm not sure
> if the packets is discarded or the error is ignored.
>
> ponti:~# tcpdump -i lo -n -v
>
> ponti:~# dig @192.168.0.3 gallimedina.net
>
> 13:02:12.360728 192.168.0.3.32827 > 192.168.0.3.53: [bad udp cksum 5e6d!]
> 35220+ A? gallimedina.net. (33) (DF) [ttl 0] (id 0, len 61)
> 13:02:12.364470 192.168.0.3.53 > 192.168.0.3.32827: 35220* 1/1/1
> gallimedina.net. A 192.168.0.10 (85) (DF) [ttl 0] (id 12492, len 113)
>
> ponti:~# dig @127.0.0.1 gallimedina.net
>
>
> 13:03:53.299883 127.0.0.1.32827 > 127.0.0.1.53: [bad udp cksum 167d!] 32901+
> A? gallimedina.net. (33) (DF) [ttl 0] (id 0, len 61)
> 13:03:53.303448 127.0.0.1.53 > 127.0.0.1.32827: 32901* 1/1/1 gallimedina.net.
> A 192.168.0.10 (85) (DF) [ttl 0] (id 7725, len 113)
>
>
>
> This machine has a bridge, but I also tried in another one with netcat (nc -l
> -u localhost -p 2000 and nc -u localhost 2000)
>
> antoli:~# tcpdump -i lo -n -v
> tcpdump: listening on lo
> 13:09:04.125385 127.0.0.1.32890 > 127.0.0.1.2000: [bad udp cksum 5a0!] udp 14
> (DF) [ttl 0] (id 32006, len 42)
> 13:09:12.472940 127.0.0.1.2000 > 127.0.0.1.32890: [bad udp cksum 837!] udp 7
> (DF) [ttl 0] (id 34086, len 35)
>
>
> I saw the short message does arrive to the listening netcat, but tcpdump still
> gives the bad udp error message.
>
> Regards,
>
> --
> ricardo galli GPG id C8114D34
> http://mnm.uib.es/~gallir/
> -
> To unsubscribe from this list: send the line "unsubscribe linux-net" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
>
---
Catalin(ux) BOIE
catab@deuroconsult.ro
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: 2.6.0: Bad udp checksum in loopback interface
2003-08-15 11:11 2.6.0: Bad udp checksum in loopback interface Ricardo Galli
2003-08-15 11:49 ` 2.6.0: Bad udp checksum in loopback interface (me too!) Catalin BOIE
@ 2003-08-15 16:08 ` Stephen Hemminger
1 sibling, 0 replies; 3+ messages in thread
From: Stephen Hemminger @ 2003-08-15 16:08 UTC (permalink / raw)
To: Ricardo Galli; +Cc: linux-kernel, linux-net
Linux turns off IP checksumming on the loopback device for performance
(unless you specifically turn on #define for LOOPBACK_MUST_CHECKSUM).
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2003-08-15 16:25 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2003-08-15 11:11 2.6.0: Bad udp checksum in loopback interface Ricardo Galli
2003-08-15 11:49 ` 2.6.0: Bad udp checksum in loopback interface (me too!) Catalin BOIE
2003-08-15 16:08 ` 2.6.0: Bad udp checksum in loopback interface Stephen Hemminger
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