yes, I neglected the crucial '-s' parameter... thank you!
On Fri, Apr 1, 2011 at 1:10 PM, Darren Reed <[email protected]> wrote: > 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. > - This is the tcpdump-workers list. Visit https://cod.sandelman.ca/ to unsubscribe.
