tcpdump mailing list archives
Re: incorrect tcp checksum on Linux tun interfaces?
From: Michael Richardson <mcr () sandelman ca>
Date: Tue, 04 Dec 2012 11:09:43 -0500
{sorry if I'm a bit tardy at removing the emergency moderation that I turned on in order to keep junk off the list}
"Gert" == Gert Doering <gert () greenie muc de> writes:
Gert> I'm a bit irritated by a byproduct of a problem hunt today, incorrect Gert> TCP checksums on a *tun* interface... Gert> 23:17:39.862001 IP6 (hlim 64, next-header TCP (6) payload length: 40) fd00:abcd:194:7::1.33509 > fd00:abcd:194:7::1000.2: S, cksum 0x6502 (incorrect (-> 0x3962), 1541095226:1541095226(0) win 14400 <mss 1440,sackOK,timestamp 178211075 0,nop,wscale 6> What's curious to me is that the chsum is not zero. If it was being "offloaded" into a step after the PF_PACKET interface, it would be zero, right? Gert> 23:18:14.295000 IP (tos 0x10, ttl 64, id 4904, offset 0, flags [DF], proto TCP (6), length 60) 10.194.7.1.52647 > 10.194.7.6.2: S, cksum 0x23b9 (incorrect (-> 0xd832), 2395069612:2395069612(0) win 14600 <mss 1460,sackOK,timestamp 178245508 0,nop,wscale 6> Both for IPv4 and IPv6? Gert> (The tun goes into openvpn, and out of the other side's tun Gert> comes a packet openvpn does IPv6 now? I suppose the next step would be to hexdump packets from /dev/net/tun. -- ] He who is tired of Weird Al is tired of life! | firewalls [ ] Michael Richardson, Sandelman Software Works, Ottawa, ON |net architect[ ] mcr () sandelman ottawa on ca http://www.sandelman.ottawa.on.ca/ |device driver[ Kyoto Plus: watch the video <http://www.youtube.com/watch?v=kzx1ycLXQSE> then sign the petition. _______________________________________________ tcpdump-workers mailing list tcpdump-workers () lists tcpdump org https://lists.sandelman.ca/mailman/listinfo/tcpdump-workers
Current thread:
- incorrect tcp checksum on Linux tun interfaces? Gert Doering (Dec 04)
- Re: incorrect tcp checksum on Linux tun interfaces? Michael Richardson (Dec 04)
- Re: incorrect tcp checksum on Linux tun interfaces? Gert Doering (Dec 04)
- Re: incorrect tcp checksum on Linux tun interfaces? Rick Jones (Dec 10)
- Re: incorrect tcp checksum on Linux tun interfaces? Gert Doering (Dec 04)
- Re: incorrect tcp checksum on Linux tun interfaces? Michael Richardson (Dec 04)