TCP blockage with PPP?

Frank van de Pol (F.K.W.van.de.Pol@inter.nl.net)
Sat, 8 Aug 1998 23:16:48 +0200 (MET DST)


John Hayward-Warburton wrote:
>
>
> Hello, all. A strange thing happened today on 2.1.112 with a recent
> CVS ipppd working with a Teles/Siemens ISDN 16.3 driver.
>
> The machine had been up for a few days, no problems; then, while
> uploading by ftp a large file to my ISP, all the TCP stuff seemed to
> choke after a very short time. Pings worked fine, but ftp, telnet,
> http, all crawled rather than ran. It seemed as if the ftp queue
> filling up choked all TCP... yet nothing was flowing (as measured by
> ifconfig). Any idea how I can diagnose this?

I experience the same problem. Seen it with all recent kernels I tried:
2.1.109, 2.1.111, 2.1.115. Using PPP 2.3.5 over an analogue 28k8 modem
connection. Downloading (isp->me) works like a charm, until I try to upload
(me->isp) some files. Uploading appears to trigger the 'stall'.

Watching "pppstat -w 1" shows that during the stall no packets are going in
or out for a long period of time. Every 15-60s a single or a few packets are
send (only 100 bytes or so). Before the stall, during uploading the ppp link
seems to be saturated with outgoing data.

> Pings working, and quickly too, was the strange thing. A reboot
> (ouch! Too much like a famous company's product) cured everything.

Same here, ping (even ping -f) works during the stall. To cure the problem I
do not have to reboot. Putting the ppp link down and up (ie. establishing
new connection to my isp) temporarily "cures" the problem.

> One more query... when FTP-ing something, and turning 'hash on', the
> ftp program gives me about thirty hash-es immediately, as if
> measuring what has been sent into some buffer rather than measuring
> how many 1024-byte blocks had actually arrived. Should I be
> expecting this?

Experiencing the same thing. But I only notice this on PPP connections.

Hints to diagnose (tcpdump magic?) or even solve this problem are
appreciated. This is really a show stopper!

Regards,
Frank.

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