Date: Thu, 15 Jul 2004 14:55:19 -0400 From: Chuck Swiger <cswiger@mac.com> To: Danny MacMillan <flowers@users.sourceforge.net> Cc: freebsd-questions@freebsd.org Subject: Re: Freebsd 5.1 <-> Win XP Networking problems Message-ID: <40F6D317.1030406@mac.com> In-Reply-To: <20040715180514.GB1473@procyon.nekulturny.org> References: <20040713200422.36735.qmail@web52502.mail.yahoo.com> <001001c46920$f347b790$152a15ac@spud> <20040714094104.GA71531@happy-idiot-talk.infracaninophile.co.uk> <20040714224010.GA1520@procyon.nekulturny.org> <20040714230638.0667d90c@localhost> <20040714232113.6bfba8e8@localhost> <20040715180514.GB1473@procyon.nekulturny.org>
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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
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