Freebsd 5.1 <-> Win XP Networking problems

[Chuck Swiger]

Danny MacMillan wrote:
[ ... ]
> I'm pretty sure I understand subnet masks.  The information I
> was looking for was how my machine determines which MAC address
> to put on the ethernet packet when sending to a machine off
> my network.

The packet will contain the MAC address of the router.

Your machine will lookup the MAC address by doing an ARPOP_REQUEST for the IP 
address mentioned in the routing table which matches the destination IP 
address of the packet being sent (typically, using your "default" route).

> First it has to know the machine is off my network,
> and the network address (as determined by the IP address ANDed
> with the subnet mask) is the only way I can figure that would
> tell my computer that.  In fact, if I understand correctly,
> that is the raison d'etre of subnet masks.  But nothing I read
> about subnet masks comes out and says that directly.

Your description is right.  A good primer of TCP networking ought to discuss 
why people use subnetting, perhaps check 'TCP/IP Network Admin' from O'Reilly.

-- 
-Chuck