Bug#498409: Some TCP connections are not established, incoming SYN/ACK-package is seemingly not regarded as valid.
Package: linux-image-2.6.18-6-686
(On Debian Stable)
Trying to connect to some hosts via TCP, no connection is
established. SYN packages are sent repeatedly although a package with
no flag should (?) be sent to accept the connection since the
SYN/ACK-package corresponding to the SYN-package already arrived.
This is an example 'tcpdump' output while doing 'telnet
www.wikipedia.org 80' (the same happens while trying to connect from a
web browser):
(some empty lines inserted to make it better readable)
till:/home/olaf# tcpdump -i ppp0 -vvv host www.wikipedia.org
tcpdump: listening on ppp0, link-type LINUX_SLL (Linux cooked), capture size 96 bytes
19:36:01.309287 IP (tos 0x10, ttl 64, id 15523, offset 0, flags [DF], proto: TCP (6), length: 44) p54B8C1A5.dip.t-dialin.net.45289 > rr.knams.wikimedia.org.www: S, cksum 0x4d02 (correct), 575226067:575226067(0) win 5808 <mss 1452>
19:36:01.359890 IP (tos 0x0, ttl 49, id 0, offset 0, flags [DF], proto: TCP (6), length: 44) rr.knams.wikimedia.org.www > p54B8C1A5.dip.t-dialin.net.45289: S, cksum 0xf2c0 (correct), 1073551891:1073551891(0) ack 575226068 win 5840 <mss 1452>
19:36:04.305824 IP (tos 0x10, ttl 64, id 15524, offset 0, flags [DF], proto: TCP (6), length: 44) p54B8C1A5.dip.t-dialin.net.45289 > rr.knams.wikimedia.org.www: S, cksum 0x4d02 (correct), 575226067:575226067(0) win 5808 <mss 1452>
19:36:04.357651 IP (tos 0x0, ttl 49, id 0, offset 0, flags [DF], proto: TCP (6), length: 44) rr.knams.wikimedia.org.www > p54B8C1A5.dip.t-dialin.net.45289: S, cksum 0xf2c0 (correct), 1073551891:1073551891(0) ack 575226068 win 5840 <mss 1452>
19:36:05.664477 IP (tos 0x0, ttl 49, id 0, offset 0, flags [DF], proto: TCP (6), length: 44) rr.knams.wikimedia.org.www > p54B8C1A5.dip.t-dialin.net.45289: S, cksum 0xf2c0 (correct), 1073551891:1073551891(0) ack 575226068 win 5840 <mss 1452>
19:36:10.306201 IP (tos 0x10, ttl 64, id 15525, offset 0, flags [DF], proto: TCP (6), length: 44) p54B8C1A5.dip.t-dialin.net.45289 > rr.knams.wikimedia.org.www: S, cksum 0x4d02 (correct), 575226067:575226067(0) win 5808 <mss 1452>
19:36:10.356971 IP (tos 0x0, ttl 49, id 0, offset 0, flags [DF], proto: TCP (6), length: 44) rr.knams.wikimedia.org.www > p54B8C1A5.dip.t-dialin.net.45289: S, cksum 0xf2c0 (correct), 1073551891:1073551891(0) ack 575226068 win 5840 <mss 1452>
19:36:11.664530 IP (tos 0x0, ttl 49, id 0, offset 0, flags [DF], proto: TCP (6), length: 44) rr.knams.wikimedia.org.www > p54B8C1A5.dip.t-dialin.net.45289: S, cksum 0xf2c0 (correct), 1073551891:1073551891(0) ack 575226068 win 5840 <mss 1452>
19:36:22.306952 IP (tos 0x10, ttl 64, id 15526, offset 0, flags [DF], proto: TCP (6), length: 44) p54B8C1A5.dip.t-dialin.net.45289 > rr.knams.wikimedia.org.www: S, cksum 0x4d02 (correct), 575226067:575226067(0) win 5808 <mss 1452>
19:36:22.358369 IP (tos 0x0, ttl 49, id 0, offset 0, flags [DF], proto: TCP (6), length: 44) rr.knams.wikimedia.org.www > p54B8C1A5.dip.t-dialin.net.45289: S, cksum 0xf2c0 (correct), 1073551891:1073551891(0) ack 575226068 win 5840 <mss 1452>
19:36:22.376944 IP (tos 0x0, ttl 49, id 0, offset 0, flags [DF], proto: TCP (6), length: 44) rr.knams.wikimedia.org.www > p54B8C1A5.dip.t-dialin.net.36826: S, cksum 0xa0f5 (correct), 4219996580:4219996580(0) ack 301537506 win 5840 <mss 1452>
19:36:23.665007 IP (tos 0x0, ttl 49, id 0, offset 0, flags [DF], proto: TCP (6), length: 44) rr.knams.wikimedia.org.www > p54B8C1A5.dip.t-dialin.net.45289: S, cksum 0xf2c0 (correct), 1073551891:1073551891(0) ack 575226068 win 5840 <mss 1452>
12 packets captured
16 packets received by filter
0 packets dropped by kernel
till:/home/olaf#
Thus the kernel behaves as if the peer would not respond at all. Not
quite, since the SYN/ACK packages of the peer are logged (why?). This
is the corresponding part of the 'messages' log file:
Sep 9 19:36:01 till kernel: IN=ppp0 OUT= MAC= SRC=91.198.174.2 DST=84.184.193.165 LEN=44 TOS=0x00 PREC=0x00 TTL=49 ID=0 DF PROTO=TCP SPT=80 DPT=45289 WINDOW=5840 RES=0x00 ACK SYN URGP=0
Sep 9 19:36:22 till last message repeated 5 times
Sep 9 19:36:22 till kernel: IN=ppp0 OUT= MAC= SRC=91.198.174.2 DST=84.184.193.165 LEN=44 TOS=0x00 PREC=0x00 TTL=49 ID=0 DF PROTO=TCP SPT=80 DPT=36826 WINDOW=5840 RES=0x00 ACK SYN URGP=0
Sep 9 19:36:23 till kernel: IN=ppp0 OUT= MAC= SRC=91.198.174.2 DST=84.184.193.165 LEN=44 TOS=0x00 PREC=0x00 TTL=49 ID=0 DF PROTO=TCP SPT=80 DPT=45289 WINDOW=5840 RES=0x00 ACK SYN URGP=0
The problem does _not_ occur from a different computer with a faster
internet connection (with linux-image-2.6.18-6-amd64 of Debian Stable).
Olaf
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