[Serusers] TCP sockets and NATs

[Andrei Pelinescu-Onciul]

On Feb 01, 2006 at 09:20, Teemu Harju <teemu.harju at gmail.com> wrote:
> Hi,
> 
> This is a question that has been bugging me for some time now. If I use SER
> and the clients connected to it use only TCP, will there be a problem with
> the number of sockets that can be open at the same time, if these clients
> are behind NAT? I mean that for NAT bindings to stay open, each client has
> to keep open TCP connection to SER all the time after registration. What is
> the maximum number of open sockets that Linux can handle at the same time?

First of all if you can, use UDP. tcp is more resource demanding (CPU
wasted looking for the Content-Length, CPU wasted snychronizing writes
to reuse the same connection, file descriptors and kernel tcp memory
wasted to keep all the connections) and more DOS-prone (it's much easier to
use tcp to try to DOS your sip server).
If you have to use tcp, then if you use ser 0.9.x, it cannot handle more
 then 1024 connections (in fact it's a little less then 1024).
> 
> I've changed the maximum number of open files to 65535 (ulimit -n 65535).
> Doesn't this also mean the maximum number of sockets? Is this the absolute
> maximum? Also, does this mean the maximum number of clients that can connect
> to my proxy?

No, it's not that easy :-)
You would need to use ser unstable (CVS HEAD), set
tcp_max_connections=65535, start ser with a lot of shared memory
 and/or decrease TCP_BUF_SIZE to something smaller (e.g. 10k) and
 recompile ser.
You should also watch for /proc/sys/fs/file-max (should be >=65535).
If you have lots of disconnects (clients closing connections) you might
also want to enable /proc/sys/net/ipv4/tcp_tw_recycle.

I was able to open 50K connections on the same machine (and if you have
lots of RAM you could go further).


Andrei
P.S.: if you want to use unstable, then better wait a few weeks, I'm
currently working on the tcp code