Benimaur Gao wrote:
Dear all,
I tried to capture http traffic by the following command:
# tcpdump -Ani eth1 'host 10.20.156.9 and tcp port 9003 and
(((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)'
(the web application didn't not serve at the conventional 80 port)
but different results was given by two hosts:
skyshouter:~# tcpdump -Ani eth1 'host 10.20.156.9 and tcp port 9003
and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)'
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
...
# tcpdump -Ani eth0 'host 10.20.141.138 and tcp port 6100 and
(((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)'
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
Lets examine the last line of each of the above outputs:
listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
I'm willing to bet that not much interesting data makes it into the first
96 bytes of a HTTP packet and that you'll need to use "-s 65535" on
the second system in order to get reliable output.
Darren
-
This is the tcpdump-workers list.
Visit https://cod.sandelman.ca/ to unsubscribe.
