Re: 2.2.15pre10: TCP problem

From: Willy Tarreau (willy@novworld.Novecom.Fr)
Date: Sat Feb 26 2000 - 04:26:10 EST

Hi !

I confirm a similar problem with 2.2.15pre9, 2.2.14aa[678].

I was FTPing from my notebook to an alphaserver running Digital Unix 4.0D, and
my network connection was terribly slow (13kB/s on a 100Mbps FD). I caught the
trace from tcpdump, but I've lost it in my /tmp during the reboot :-(.
As for Chris, we can see that there are long delays between each packet

There has been something very strange with this alphaserver (which works
perfectly with any other systems : solaris, tru64, nt, older linux). It
sometimes has a strange way to ACK connections : it appears that when my
notebook ( sends a SYN to this server (, sometimes
this one replies with an ACK only without a SYN nor any RST. My linux then
sends RST to it and it works when trying again. May be I'm lacking some TCP/IP
knowledge but I didn't know about this method of ACKing connections.

I've tried to play with several parameters under /proc/sys/net/ipv4 without
success (not even a change in the inter-packet delay). I was used to write 0
to tcp_sack sometimes but I don't remember if I had to do this on versions
later than stock 2.2.14. Anyway, this doesn't work here.

I don't have permanent access to this alphaserver, but if someone suggests
patches, I can occasionnaly test them.



Attached is a portion of tcpdump involving the strange ack :

10:06:37.486211 > S 869374555:869374555(0) win 32120 <mss 1460> (DF)
10:06:37.487011 > . ack 457311198 win 33579 (DF)
10:06:37.487079 > R 457311198:457311198(0) win 0
10:06:40.483316 > S 869374555:869374555(0) win 32120 <mss 1460> (DF)
10:06:40.484291 > S 30525997:30525997(0) ack 869374556 win 33580 <mss 1460> (DF)
10:06:40.484378 > . ack 1 win 32120 (DF)
10:06:40.484460 > P 1:20(19) ack 1 win 32120 (DF)
10:06:40.503979 > P 1:33(32) ack 20 win 33579 (DF)
10:06:40.504025 > . ack 33 win 32120 (DF)
10:06:40.504487 > FP 33:155(122) ack 20 win 33579 (DF)
10:06:40.504525 > . ack 156 win 31997 (DF)

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
Please read the FAQ at

This archive was generated by hypermail 2b29 : Tue Feb 29 2000 - 21:00:15 EST