[Nottingham] Linux number of forwarded net connections limit

Martin martin at ml1.co.uk
Wed Oct 12 10:58:28 UTC 2011


On 12 October 2011 10:29, Sergiusz Pawlowicz <sergiusz at pawlowicz.name> wrote:
> martin, imho limiting amount of concurrent connections is rather
> against the idea of tcp/ip, and to be honest, i cannot understand what
> precisely you want to achieve? is it a theoretical game or you want to
> do something practically, eg. limit bandwidth?

For a home worker, I'm trying to make use of their 'poorly
implemented' ADSL modem-router whereby just two users surfing the web
can cause the thing to crash! My best guess is that it falls over with
too many connections. Too small a NAT table?... Hence I'm wanting to
see if I can insert a linux box to act as a gateway to limit the max
number of connections. A second problem is that one of those users
chokes everything up with torrents.

I can easily throttle the bandwidth and do traffic management with tc,
for example to allow VoIP a good connection, but not if everything
falls over due to too many connections killing the modem-router.

Obviously, the Linux 32k max connections (thanks Dylan) is no problem
as a limit. However, I suspect that most (all) home modem-routers will
easily fail on high simultaneous connection counts. The "high" might
be as low as just 20 to 50 NATed streams...

For the home modem routers, is that a problem of cheap design using
minimal hardware? Or a deliberate limit by the ISP? And ADSL appears
to be rather unreliable at the best of times! The sooner we abandon
the ancient tech of telephone poles the better!!

(At least on cable you can use just a 'dumb' modem and let a proper
Linux box do all the cleverness. You also get a consistent connection.
Then again, are not most modem-routers running some cut-down version
of Linux?...)


More information about the Nottingham mailing list