Re: Linux 2.2.x outgoing TCP connects hang after several hours of use

Dan Hopper (eusdbho@rtp.ericsson.se)
Wed, 4 Aug 1999 16:36:14 -0400

Jordan Mendelson <jordy@wserv.com> remarked:
> Dan Hopper wrote:
> >
> > Howdy,
> >
> > I've been noticing a TCP connect problem on a masquerading gateway
> > box for a few months now, first running 2.2.7, and more recently
> > 2.2.10 and 2.2.11pre2. They behavior is basically that outgoing TCP
> > connections originating on the gateway box itself fail, but that
> > incoming TCP connects succeed. Outgoing TCP connects that are
> > masqueraded via this box succeed as well. The interfaces are eth0
> > for the local private net and ppp0 for everything else.
>
> I have a similar setup, but with two ethernet cards. I telnet from my internal
> machine to my gateway box and then use it's telnet out to the Internet (no
> quality SSL telnet client for windows). The gateway masqs my internal lan to a
> single IP acquired via a DHCP server.
>
> I have not noticed this problem, I have telnet sessions open for weeks on end
> without any trouble.
>
> However, I did for a long time use a setup identical to this and I can give you
> some information based on some of the problems I had...
>
> Are you sure it's not modem failure? Double-check to see what your modems
> upload/download rate is after several hours, a large portion of modems will
> retrain down their outgoing or incoming connection rates and have bugs in their
> firmware which cause connection rates to spiral down. Try limiting your
> connection rate to 1200/2400 baud less than what you normally connect at...

Relatively sure. Pings and UDP packets originating from the the
gateway work as expected, as do all packets originating from a
masqueraded box. I've done all the usual cycling of the interface
and modem while debugging anyway.

> Also you might want to check your pppd which can cause these problems as well.
> There were some problems with older versions of pppd flaking out.

ppp 2.3.7 - a relatively stock RH6 setup at the moment.

> Make the MTU/MRU on your ppp0 and eth0 lines equal and see if that makes a
> difference (mtu 1500/mru 1500 in your pppd options file).

I believe they already are, but I'll double check that my current
scripts still do that when I'm home this evening.

> I've also heard some problems with asyncmaps on some modems, add "asyncmap
> 0x00000000" to your pppd options file and see what happens.

Actually already have that in there - left over from a previous ISP
where it was actually necessary.

I also have been running masqueraded boxes for awhile - since around
1996 or so. This is the first time I've seen this type of problem.
Switched to the 2.2.x kernels when they came out, and didn't have
any such problems for several months. I will try to back down to
the earlier 2.2.x kernels as a test, though, and try one of the
later 2.3.x kernels just for completeness.

Thanks for the response anyway,
Dan

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