Re: Communicating on Specific Ethernet ports
Re: Communicating on Specific Ethernet ports
- Subject: Re: Communicating on Specific Ethernet ports
- From: Quinn <email@hidden>
- Date: Mon, 25 Oct 2004 10:06:05 +0100
At 12:29 +0100 21/10/04, Mark Thomas wrote:
I'm trying to work out whether its possible if I can send out some TCP/IP
traffic on a specific Ethernet device. I think this is possible using OT via
something like
OTOpenEndpointInContext(OTCreateConfiguration(PortRecord.fPortName), ...
This has never worked for TCP/IP endpoints in Open Transport. It
kinda works that way for AppleTalk on traditional Mac OS, but not for
TCP/IP.
I'm wondering what happens if this port isn't selected/checked in the list
of ports in the network configuration system preference's panel. Would it
still allow traffic through it ???.
For a start, there's no way to send and receive TCP/IP from a port
without enabling it via System Configuration framework (which is what
the Network preferences panel is implemented in terms of). The act
of enabling the port is what causes the IP configuration agent to run
against the port; that, in turn, is what causes the port to be
assigned an IP address. Without an IP address, you have no IP
configuration.
So, if you want to use TCP/IP to communicate over a port that the
user hasn't already enabled, you will have to write code to enable it.
Once the port is enabled you can bind to its specific IP address and
then all traffic you send will have that address as its source
address. However, it's not guaranteed to be sent via that port. The
traffic is still subject to the standard routine algorithm. In a
default Mac OS X install that algorithm is:
1. If we have a port whose subnet contains the destination address,
send it out that port.
2. Otherwise send it out the default port (which is the first active
port with an real IP address; the ordering is defined in System
Configuration).
It's possible to monkey with this algorithm, although it's not
something that I'd recommend.
S+E
--
Quinn "The Eskimo!" <http://www.apple.com/developer/>
Apple Developer Technical Support * Networking, Communications, Hardware
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