Grant Edwards <[EMAIL PROTECTED]> writes:
> On 2006-09-15, Diez B. Roggisch <[EMAIL PROTECTED]> wrote:
>
>>>>> Is it possible to specify which port to use as the outbound port on a
>>>>> connection?
>>> [...]
>>>>> Specifically, I'm trying to write an FTP host, and I'm trying to
>>>>> implement the PORT command.
>>>>
>>>> AFAIK you neither can't do that nor need it.
>>>
>>> It's not the issue here, but to specify the outgoing port
>>> call bind(('', portnum)) before connect().
>>
>> I wasn't aware of that. Cool.
>
> It's an interesting thing to know, but I've been doing TCP
> stuff for many years and never run across a situation where
> it's something I needed to do. If somebody in this thread
> actually does need to do it, I'd be curious bout why...
Well, one of ftpd implementations I have here (C code from RTEMS) does
this:
/* anchor socket to avoid multi-homing problems */
data_source = info->ctrl_addr;
data_source.sin_port = htons(20); /* ftp-data port */
if(bind(s, (struct sockaddr *)&data_source, sizeof(data_source)) < 0)
ERROR;
...
if(connect(s,
(struct sockaddr *)&info->def_addr,
sizeof(struct sockaddr_in)) < 0
)
ERROR;
I've no idea what "multi-homing problems" are, but maybe it gives you
some hint?
-- Sergei.
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