[263] in linux-net channel archive
Re: lcp-echo-failure doesn't work?
daemon@ATHENA.MIT.EDU (Alexander Terczka)
Wed May 3 06:35:01 1995
From: alex@terz.via.at (Alexander Terczka)
To: linux-net@vger.rutgers.edu
Date: Wed, 3 May 1995 09:48:33 +0100 (MET DST)
Hello,
>
> Hello all!
>
[cut]
>
> .... This does NOT fix the problem with the PPP link dropping dead
> periodically! I have seen this complained about by several individuals
> over the last several months. The usual remark they get is "oh you must
> be having a modem problem". Wrong again. At this point, I have been able
> to confirm that the modem is in an operational state. Flow control is
> NOT in a blocking state, the modem continues to receive data fine (implying
> that the modem has not gone brain-dead and the error correcting link is
> still fully functional) and that interrupts are proceeding properly.
> The higher level code seems to have lost track of what it is doing and is
> no longer able to send data!
>
> I've mentioned this to a couple of others, including Alan Cox
> when I was looking at some things in the latest network snapshots. So
> far, the best I can figure out is that it is some sort of timing problem.
> It seems to primarily occur, on my system, when there are a high number of
> connections being established and broken (you guessed it - WWW and Netscape).
>
> As has been reported by others, this problem has seemed to come
> and go over a large number of patch levels. Some have indicated that
> it got much worse around 1.1.6[345] or there abouts. I can confirm that.
> It also seemed to get somewhat better with the 1.2.4 version but I can't
> find anything in those patches that would acount for it. It seems much
> worse on a 28.8 link than a 14.4 link (I have one of each), but that may
> be a bogus observation since I don't have the same level of Web traffic
> over the 14.4 link; just telnet, ftp, and smtp and at a lower frequency.
>
...
> Right now, it's just a minor annoyance, since pppd can now detect
> the problem and recover from it. It would be nice to figure out where
> the problem is and fix it though. I've been pawing through serial code,
> ppp code, and network code but have come up empty handed. Anyone with some
> more suggestions as to where to look, let me know and I check'm out.
>
I had lockups on ppp-connections for a long time. The error was, that
TCP in the Linux kernel and TCP in a Cisco router (V ~9.1) didn't like
each other. It has to do with the windowing mechanism in the TCP layer.
I know, this would not lock up the whole connection, but only one TCP
connection. But perhaps it looks like a total modem lock in your
situation. To fix the problem I simply said "PC/TCP compatibility mode : YES"
Alan told me, that there is a real patch that linux tcp can handle ciscos,
and that I should try it, but as my IP-provider upgrade the cisco software
to 10.2 I can't reproduce the bug even without the patch.
btw: linux is the best OS I ever used. :)
AlexT
(alext@cslab.tuwien.ac.at)
