client socket and source port selection

client socket and source port selection

[joël Winteregg]

HI,

For the project i'm doing, i must know how the Linux kernel allocate
sockets source port (from the dynamic range of the (2**16)-1 ports). I
looked on the Web but it's really hard to find the algoritm of the
source port allocation...

Someone maybe know how it's work or if there is a paper on the web that
explain this source port selection ?

Thanks a lot for your help !


Joël.W

Re: client socket and source port selection

[Jan Engelhardt]

>HI,
>
>For the project i'm doing, i must know how the Linux kernel allocate
>sockets source port (from the dynamic range of the (2**16)-1 ports). I
>looked on the Web but it's really hard to find the algoritm of the
>source port allocation...
>
>Someone maybe know how it's work or if there is a paper on the web that
>explain this source port selection ?

I think it starts at 1024 when it boots, and increments whenever a socket is
created.


Jan Engelhardt
-- 
Gesellschaft für Wissenschaftliche Datenverarbeitung
Am Fassberg, 37077 Göttingen, www.gwdg.de

Re: client socket and source port selection

[Roberto Nibali]

Hello,

> For the project i'm doing, i must know how the Linux kernel allocate
> sockets source port (from the dynamic range of the (2**16)-1 ports). I
> looked on the Web but it's really hard to find the algoritm of the
> source port allocation...

Check the source ;). There is a proc-fs entry which relates to the 
source port range setting. Over this entry point you get in case of TCP 
sockets to ../net/ipv4/tcp_ipv4.c:tcp_v4_get_port(...). For UDP sockets 
you need to peek into ../net/ipv4/udp.c:udp_v4_get_port().

> Someone maybe know how it's work or if there is a paper on the web that
> explain this source port selection ?

Not likely, but reading the source should help. You can set the local 
port range via /proc/sys/net/ipv4/ip_local_port_range. It's documented.

HTH and best regards,
Roberto Nibali, ratz
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