help on broadcast data lost in linux tcp/ip stack

i have a server, which broadcast data to a client. in the client,
there're two processes waiting on the same port, with SO_REUSEADDR set,
receiving the data comes from server. everytime one client send a
request to the server, it broadcasts at the most 128KB data. after the
client has received all the data, it sends the next request.

the two machine are equiped with gigabit ethernet, 1GB memory and
1.6GHz P4. the client's receiving buffer is set to 20MB by
setsockopt(), i think it 's large enough.


what happens strangely is (somtines) when one process successfully
receives the packet, but the anoter not. and the value of InErrors in
/proc/net/snmp increasing greatly everytime the processes are run.

i have google the related question, some one said that, packet will
loss intra-stack. is there some method to handle this.

thanks in advance.

Zhang Huan wrote:
> i have a server, which broadcast data to a client. in the client,
> there're two processes waiting on the same port,

Port identifies a process. Only one process is ever likely to receive
data for the same port.

> with SO_REUSEADDR set,

You misunderstand the purpose of SO_REUSEADDR. It is intended for TCP
servers doing active close only. Read man ip(7).

Maxim Yegorushkin wrote:
> Zhang Huan wrote:
> > i have a server, which broadcast data to a client. in the client,
> > there're two processes waiting on the same port,
>
> Port identifies a process. Only one process is ever likely to receive
> data for the same port.
yes, but not for broadcast or multicast packets, see the kernel code
udp_rcv() in net/ip4/udp.c

>
> > with SO_REUSEADDR set,
>
> You misunderstand the purpose of SO_REUSEADDR. It is intended for TCP
> servers doing active close only. Read man ip(7).

it is also intended for UDP with broadcasting or multicasting.

Zhang Huan wrote:
> Maxim Yegorushkin wrote:
> > Zhang Huan wrote:
> > > i have a server, which broadcast data to a client. in the client,
> > > there're two processes waiting on the same port,
> >
> > Port identifies a process. Only one process is ever likely to receive
> > data for the same port.
> yes, but not for broadcast or multicast packets, see the kernel code
> udp_rcv() in net/ip4/udp.c

Sorry, my mistake.

> > > with SO_REUSEADDR set,
> >
> > You misunderstand the purpose of SO_REUSEADDR. It is intended for TCP
> > servers doing active close only. Read man ip(7).
>
> it is also intended for UDP with broadcasting or multicasting.

Could you point me to the source of this information?

see UNIX.Network.Programming.Volume1 3rd edition

chapter 7.5 generic socket options

Zhang Huan wrote:
> see UNIX.Network.Programming.Volume1 3rd edition
>
> chapter 7.5 generic socket options

Thank you, it describes it indeed.