I got these messages (along with many 'syn-ack rtx', but those are normal)
while working in a telnet session over a fast (<5ms) ethernet connection:
Nov 16 20:12:22 moisil kernel: syn_ack rtx 1
Nov 16 21:50:42 moisil kernel: syn timeout
Nov 16 21:51:21 moisil kernel: syn timeout
Nov 16 21:52:12 moisil last message repeated 3 times
Nov 16 21:53:02 moisil last message repeated 2 times
Nov 16 21:54:10 moisil kernel: syn timeout
Nov 16 21:55:19 moisil kernel: syn timeout
Nov 16 21:56:09 moisil kernel: syn timeout
Nov 16 22:45:20 moisil kernel: syn_ack rtx 1
More precisely, the machine had to send a large amount of data, once
because of a large copy_and_paste using the mouse, and once (the one
showed above) because of something scrolling quickly on the tty. In both
cases, the session got really stuck, (although I could open another telnet
just fine), and got under way several minutes later. netstat indicated
that the send-q was rather large - 23000 or something like that. During
that interval of 5-6 minutes, every now and then (most likely once
a minute, in sync with the syn timeout messages) several packets made it
through, but since the application was queuing more stuff, it didn't help
- the send-q stayed at or around 23000.
Also, on a related issue, netstat was showing several incoming connections
(smtp and auth) in an UNKNOWN state, with send-q = recv_q = 1. Most of
them were more than 12 hours old, and seemed to have just stuck there.
They were definitely _not_ syn-flood traces, as 1. they originated from
different hosts; 2. those hosts were "trusted" (one being a machine
I have root on, and another being vger itself with a smtp connection); 3.
they were just a few (10-12) and didn't prevent in any way other
connections.
Ionut
--
Ionut Badulescu - Columbia College '98 E-mail:ib42@columbia.edu
Phone: (212)853-7875 Snail mail: 4A4 Wallach Hall
Fax: (212)695-5560 1116 Amsterdam Ave
PGP key available on request New York, NY 10027
It is better to keep your mouth shut and be thought a fool,
than to open it and remove all doubt.