maximum number of outgoing connections

[Igor Sysoev]

On Mon, Aug 20, 2007 at 05:19:14PM +0100, Tom Judge wrote:

> Igor Sysoev wrote:
> >It seems that FreeBSD can not make more than
> >
> >net.inet.ip.portrange.last - net.inet.ip.portrange.first
> >
> >simultaneous outgoing connections, i.e., no more than about 64k.
> >
> >If I made ~64000 connections 127.0.0.1:XXXX > 127.0.0.1:80, then
> >connect() to an external address returns EADDRNOTAVAIL.
> >
> >net.inet.ip.portrange.randomized is 0.
> >
> >sockets, etc. are enough:
> >
> >ITEM        SIZE     LIMIT      USED      FREE  REQUESTS  FAILURES
> >socket:      356,   204809,    13915,   146443, 148189452,        0
> >inpcb:       180,   204820,    20375,   137277, 147631805,        0
> >tcpcb:       464,   204800,    13882,   142102, 147631805,        0
> >tcptw:        48,    41028,     6493,    11213, 29804665,        0
> >
> >I saw it on 6.2-STABLE.
> >
> >
> 
> In an ideal world (Not sure if this is quite correct for FreeBSD) TCP 
> connections are tracked with a pair of tupels  source-addr:src-port -> 
> dst-addr:dst-port
> 
> As your always connecting to the same destination service 127.0.0.1:80 
> and always from the same source IP 127.0.0.1 then you only have one 
> variable left to change, the source port.  If you where to use the hole 
> of the whole of the port range minus the reserved ports you would only 
> ever be able to make 64512 simultaneous connections.  In order to make 
> more connections the first thing that you may want to start changing is 
> the source IP. If you added a second IP to you lo0 interface (say 
> 127.0.0.2) and used a round robin approach to making your out bound 
> connections then you could make around 129k outbound connections.

Connections to 127.0.0.1 were via lo0, external connections are via bge0.

> I am not sure if there are any other constraints that need to be taken 
> into account such as the maximum number of sockets, RAM etc....

No, there are no constraints in memory, sockets, mbufs, clusters, etc.
If there's contraint in memory, then FreeBSD simply panics.
If there's contraint in mbuf clusters, then process stucks in zonelimit
state forever.

I suspect that local address in in_pcbbind_setup() is 0.0.0.0 so there
is 64K limit.


-- 
Igor Sysoev
http://sysoev.ru/en/