lkml.org 
[lkml]   [2003]   [Aug]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Subject2.6.0: Bad udp checksum in loopback interface
Date
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-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:47    [W:0.029 / U:0.216 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site