Hi,
I've been regularly losing my IRC connections going over my PPP/PPPoE/ADSL
IPv6 connection with static addresses for quite some time now. I haven't
found any obvious correlation with PPP reconnects or anything else one
would expect to cause this - now, I've had a look at it using tcpdump
and it looks to me pretty much like it's linux's TCP implementation that
fails to retransmit lost segments on some occasions.
The two occasions I captured so far look pretty similar, so here is
one of them:
| 03:34:56.061190 2002::1.6667 > 2001::1.2214: P 42984:43037(53) ack 17052 win
5712 <nop,nop,timestamp 2372706322 98778470>
| 03:34:56.061470 2001::1.2214 > 2002::1.6667: . ack 43037 win 6888
<nop,nop,timestamp 98778484 2372706322>
| 03:35:57.004547 2001::1.2214 > 2002::1.6667: P 17052:17073(21) ack 43037 win
6888 <nop,nop,timestamp 98793722 2372706322>
| 03:38:58.062458 2001::1.2214 > 2002::1.6667: F 17073:17073(0) ack 43037 win
6888 <nop,nop,timestamp 98838992 2372706322>
| 03:38:58.118258 2002::1.6667 > 2001::1.2214: . ack 17052 win 5712
<nop,nop,timestamp 2372730527 98778484,nop,nop,sack sack 1 {17073:17074} >
| 03:38:58.657355 2002::1.6667 > 2001::1.2214: P 43037:43059(22) ack 17052 win
5712 <nop,nop,timestamp 2372730581 98778484,nop,nop,sack sack 1 {17073:17074} >
| 03:38:58.657759 2001::1.2214 > 2002::1.6667: R 130103887:130103887(0) win 0
(The addresses are not the original ones, obviously.)
Note in particular the third and the fourth lines (which is when irssi
decides to close the connection because of a ping timeout):
No retransmission takes place for (more than) three minutes even though
the segment sent in the third line is not acknowledged.
Tcpdump was running on 2001::1 and it reported no dropped packets, so
I suppose that no packets are missing from this dump (unless there is
a bug in there(, too), of course ...).
2001::1 is running a linux kernel version 2.6.16, 2002::1 is an IRC
server i've got no control over - but I suppose that it's not at fault
here anyway, so that probably doesn't matter ...
I've previously been observing similar behaviour with 2.4 kernels
already (that is, IRC connections on that internet connection getting
lost, but I've never had a close look at it then), so I suppose it's
not just a faulty compilation or something like that ...
Well - in case there is anything I can provide you with that would
help you with fixing this, let me know (nope, no clue yet how to
reproduce this except for waiting for my IRC connections to time
out ;-) - simply dropping some packets in ip6tables's filter/OUTPUT
chain did not do the trick ...).
Florian
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