Messages in this thread | | | Date | Thu, 19 Aug 1999 22:20:59 +0000 | From | Marc Mutz <> | Subject | _Very_ strange network delay over dialup-ISDN in 2.2.11. |
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Hi out there!
I just experienced a very wierd network delay: I use a ISDN dialup line to my university. Normally I do not run ping, so this is - apart from a similar occurence with up to 20 sec lags in 2.2.10 - the first time I noticed this behaviour. But this time I wanted to keep the connection established. So I fired up ping, and saw that it reported a round-trip time of 1 second (1000 ms)! Usually it is somewhere around 50 ms and under heavy load (ftp) it sometimes increases to a few hundred ms, also up to one second but only for some few packets. Now the funny thing started, as I started an ftp session: round-trip times dropped to around 100ms ?! After the transfer was completed, I shut down the link and opened it again. Ran ping, same result: 1000ms. Then I ran a second ping, to another host on the same ethernet segment in the university. It inherited the huge round-trip time, but the first ping came down to around 100ms. Curiosly I pinged another host, which is quite close (topologically) to the dialin server. That ping was from the beginning <~ 100ms, the second ping stayed at 1000ms and the first was reduced even further (60-90 ms).
Now this seems funny and strange to me and it could only be resolved by shutting down the ISDN system (/sbin/init.d/i4l stop) and starting it again.
Some more infos I can give: - I switched off tcp_timestamping as it results in poor transfer network performance (see article of me some days ago). - due to our university's news server being so slow between 23:00 and 0:00 local time, the ISDN line timed out with a TCP connection to the news server still open. So now there lurks a connection in FIN_WAIT IIRC (it has apparently timed out now, as I took the ISDN subsystem down) that cannot be completed due to differing assigned IP numbers on every login.
I can provide tcpdumps (tcpdump -i ippp0 -n) of a normal session and the weird one on request, but they are too big to be posted (14 and 27K, resp.). cannot test pre-12's, because I first have to fix my raid stuff to use new semantics.
Anyone got a clue?
Marc -- Marc Mutz <Marc@Mutz.com> http://marc.mutz.com/ University of Bielefeld, Dep. of Mathematics / Dep. of Physics
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