linux sockets - connect()

Hi,

When a client wants to connect to a server, the connect() call takes
the argument to specify where to connect to, but is there a way to
specify, which interface on the client to use, to connect to the remote
machine?

I'm asking because I have a multi-home client and want it to use a
specific IP to make connections from.

Thanks,
Bahadir

<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...

> When a client wants to connect to a server, the connect() call takes
> the argument to specify where to connect to, but is there a way to
> specify, which interface on the client to use, to connect to the remote
> machine?

When you say "which interface" do you mean the source IP address? Or do
you mean what interface the packets go out of? There is a *huge* difference.

> I'm asking because I have a multi-home client and want it to use a
> specific IP to make connections from.

You can specify the source IP address with a 'bind' call before the
'connect'. But that has no affect on which interface is used to transmit
packets or which interface the return packets will wind up at.

DS

i guess both the interface and the ip address are one and the same
thing. Isn't that why a machine having two ip addresses is having two
interfaces.

corrections are welcome.

"manish" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ps.com...

>i guess both the interface and the ip address are one and the same
> thing. Isn't that why a machine having two ip addresses is having two
> interfaces.

No. A machine can have two interfaces with the same IP address or two IP
addresses assigned to one interface. While IP addresses are assigned to
interfaces, not machines, an interface can have zero, one, or any number of
IP addresses.

DS

what do you mean by interface...? is the network card an interface or
some logical opening of the system?

David Schwartz wrote:
> No. A machine can have two interfaces with the same IP address or two IP
> addresses assigned to one interface. While IP addresses are assigned to
> interfaces, not machines, an interface can have zero, one, or any number of
> IP addresses.
>
> DS

Hi,

I didn't know this. If I have two ethernet interfaces with distinct MAC
addresses, how could I have a single IP address for both? How would
R/ARP and DHCP work then?

In reply to your bind() suggestion, so you mean I should first bind()
my client socket on a particular local IP address, and then connect to
the remote machine?

Thanks,
Bahadir

"manish" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...

> what do you mean by interface...? is the network card an interface or
> some logical opening of the system?

It can be either. Generally, there is one interface for each network
card, whether or not it has any IP addresses assigned to it. There may also
be additional interface generated logically by the system, for example, the
loopback interface or a 'bridge interface' to assign an IP address to
several bridged physical interfaces.

DS

<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...

> I didn't know this. If I have two ethernet interfaces with distinct MAC
> addresses, how could I have a single IP address for both? How would
> R/ARP and DHCP work then?

It's not easy to do this with ethernet interfaces, it's much more common
with point-to-point interfaces.

> In reply to your bind() suggestion, so you mean I should first bind()
> my client socket on a particular local IP address, and then connect to
> the remote machine?

Yes, that's correct.

DS