First of all I have to apologize with Henrik because I replied directly to him (I didn't noticed that Yahoo replies only to the sender by default). then it comes the repost: Ok... I do a new checksum... before changing the port I checked that the checksum Algorithm was right by comparing the system computed check with the one computed by me. Everything was right. but in the moment I change the port the packet never arrives. Here's what comes out from TCPDump fetching on port 2026 the packets (originally for port 2022) that I changed... from the first Ack on...: root@morningmoon:/home/lore# tcpdump -i wlan0 dst port 2026 -vvv tcpdump: listening on wlan0, link-type EN10MB (Ethernet), capture size 96 bytes 16:27:50.094991 IP (tos 0x0, ttl 64, id 39743, offset 0, flags [DF], proto: TCP (6), length: 60) 192.168.0.4.32788 > geronte.cs.unibo.it.2026: S, cksum 0x5034 (correct), 2890202236:2890202236(0) win 5840 <mss 1460,sackOK,timestamp 14378819 0,nop,wscale 2> 16:27:50.119230 IP (tos 0x0, ttl 64, id 625, offset 0, flags [DF], proto: TCP (6), length: 40) 192.168.0.4.32788 > geronte.cs.unibo.it.2026: R, cksum 0x36fd (correct), 2890202237:2890202237(0) win 0 16:27:52.971108 IP (tos 0x0, ttl 64, id 39745, offset 0, flags [DF], proto: TCP (6), length: 60) 192.168.0.4.32788 > geronte.cs.unibo.it.2026: S, cksum 0x447b (correct), 2890202236:2890202236(0) win 5840 <mss 1460,sackOK,timestamp 14381820 0,nop,wscale 2> 16:27:52.995399 IP (tos 0x0, ttl 64, id 626, offset 0, flags [DF], proto: TCP (6), length: 40) 192.168.0.4.32788 > geronte.cs.unibo.it.2026: R, cksum 0x36fd (correct), 2890202237:2890202237(0) win 0 Any Idea? Thanks a lot... lore --- Henrik Nordstrom <hno@xxxxxxxxxxxxxxx> ha scritto: > On Sat, 29 Oct 2005, Lore wrote: > > > and in the code I change the tcphdr->dest to 2021, > do > > a new checksum and verdict it with NF_ACCEPT. > > > > The packet get's silently dropped and I don't know > > why... > > Should work.. but make sure you get the TCP header > checksum correct... > > What does tcpdump say? > > Also beware that conntrack won't be too happy if you > modify the > "connection details" like this. If you need > conntrack loaded such mangling > of the packets is better left to NAT.. > > Regards > Henrik > ___________________________________ Yahoo! Mail: gratis 1GB per i messaggi e allegati da 10MB http://mail.yahoo.it
