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    <p>Everything Joe says is correct.</p> <p>Having just finished teaching this to a class myself. Let me put this in the terms I used in that class.</p> <p>Your question says you have two hosts on two subnets. Let's call the remote host, a server and your local host, well let's stick with local host.</p> <p>You local host has an IP address, a subnet mask and a default gateway.</p> <p>When you ping the server, your local host uses it's IP address and subnet mask to see if the address being pinged is local or remote. In this case, your server's remote. Knowing this, it knows it has to send the ping to the default gateway. To do that, it has to arp for the default gateway's address. This leaves the entry in the arp table for your default gateway and it's mac address.</p> <p>You're correct in thinking that the packet that then leaves your local host to your server has the mac address of the default gateway, but the IP address of the server, but this doesn't effect what's in the arp table.</p> <p>Remember, an arp packet asks "Who has?" and provides an IP address. In the network you've described, your default gateway will only respond for it's own IP, not all the IP addresses it can route to.</p> <p>Now I could really confuse you here by telling you about the network configurations where this would work differently, but I don't think that would be helpful.</p> <p>However it's worth knowing that there are times in the real world when you find things don't work this way. (I'm looking at you NAT and proxy arp).</p> <p>I'm not sure this is any clearer than what Joe wrote, but sometimes just hearing a few different explanations help things to click.</p> <p>Hope this helps,</p> <p>Alex</p>
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    1. COYes, it does. So I think the confusion was mostly between that: the arp table and the way the L2 addresses change. So, to make sure i understand: when the local host sends a message destined to the server on the remote network it first resolves the arp (associating the L2 address with the L3 address of the server in its arp table), and then it sends the packets with L2 dest address of the router and L3 dest address of the server, right? Yes, it does make sense now that i think about it. If that weren't the case, the arp table would have to have associations of many L3 addresses to the same L2.
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