Bug 168843

Summary:	FreeBSD
Product:	Base System	Reporter:	Nikolay Denev <ndenev>
Component:	kern	Assignee:	freebsd-bugs (Nobody) <bugs>
Status:	Closed FIXED
Severity:	Affects Only Me
Priority:	Normal
Version:	8.3-STABLE
Hardware:	Any
OS:	Any

Description Nikolay Denev 2012-06-08 11:50:13 UTC

It seems that our FreeBSD hosts are sending TCP packets with FIN flag and no ACK set, which is triggering
alerts on some firewalls.

[14:31]root@vpn1.location:/home/ndenev# tcpdump -s0 -vni em1 '(tcp[tcpflags] & tcp-ack == 0) && (tcp[tcpflags] & tcp-fin != 0)'
tcpdump: listening on em1, link-type EN10MB (Ethernet), capture size 65535 bytes
15:18:31.771578 IP (tos 0x0, ttl 62, id 44503, offset 0, flags [DF], proto TCP (6), length 40)
    10.16.1.5.53083 > Y.Y.Y.Y.9998: Flags [F], cksum 0x29a6 (correct), seq 2205738519, win 65535, length 0
15:22:02.517922 IP (tos 0x0, ttl 62, id 56317, offset 0, flags [DF], proto TCP (6), length 40)
    10.16.1.5.37719 > Y.Y.Y.Y.9998: Flags [F], cksum 0x192b (correct), seq 2125215587, win 65535, length 0
15:24:13.215171 IP (tos 0x0, ttl 62, id 36930, offset 0, flags [DF], proto TCP (6), length 40)
    10.16.1.5.25125 > Y.Y.Y.Y.9998: Flags [F], cksum 0x6998 (correct), seq 1370309927, win 65535, length 0
15:25:17.010082 IP (tos 0x0, ttl 62, id 61513, offset 0, flags [DF], proto TCP (6), length 40)
    10.16.1.5.48897 > Y.Y.Y.Y.9998: Flags [F], cksum 0x16c2 (correct), seq 2650795726, win 65535, length 0
15:29:19.979799 IP (tos 0x0, ttl 62, id 15471, offset 0, flags [DF], proto TCP (6), length 40)
    10.16.1.5.31685 > Y.Y.Y.Y.9998: Flags [F], cksum 0x218d (correct), seq 2057063075, win 65535, length 0
15:35:50.005156 IP (tos 0x0, ttl 62, id 27760, offset 0, flags [DF], proto TCP (6), length 40)
    10.16.1.5.50568 > Y.Y.Y.Y.9998: Flags [F], cksum 0x6df3 (correct), seq 2102571459, win 65535, length 0
15:38:28.252143 IP (tos 0x0, ttl 62, id 22995, offset 0, flags [DF], proto TCP (6), length 40)
    10.16.1.5.30441 > Y.Y.Y.Y.9998: Flags [F], cksum 0xced9 (correct), seq 4232454280, win 65535, length 0
15:39:35.362371 IP (tos 0x0, ttl 62, id 46525, offset 0, flags [DF], proto TCP (6), length 40)
    10.16.1.5.15067 > Y.Y.Y.Y.9998: Flags [F], cksum 0x9d94 (correct), seq 1322466127, win 65535, length 0
15:52:27.833978 IP (tos 0x0, ttl 62, id 30955, offset 0, flags [DF], proto TCP (6), length 40)
    10.16.1.5.21254 > Y.Y.Y.Y.9998: Flags [F], cksum 0x36a1 (correct), seq 3524593365, win 65535, length 0

Where 10.16.1.5 runs 8.3-STABLE

I have a PCAP that I can send privately if needed.

Fix: 

none
How-To-Repeat: Haven't tracked it down yet.

Comment 1 Sergey Matveychuk freebsd_committer

2012-06-08 16:40:03 UTC

State Changed
From-To: open->closed

Duplicate to kern/168842