On Wed, 2006-08-02 at 15:10 -0400, Kenneth Lumia wrote:
> 1. Is the MAC address returned with ARP the actual 
>     server, or is it a computer between the router and the server?

Depends on how your network is set up. But off hand, an ARP of an IP
outside of your local segment will correctly return the MAC of the
gateway to that external network.

> 2. Which MAC should I use, and why?

You should use the MAC returned to ARP. If it's wrong then the device
giving you the wrong MAC is at fault. You shouldn't have to "check" if
the MACs are correct.

> 3. How often should I use ARP to get a new address?  I 
> imagine that unless the internet breaks, the server computer 
> is replaced or similar, that the MAC will remain the same.  
> Should I just ARP once and store it in eeprom, or when 
> the server stops talking for a period of time, or at every 
> power cycle, or once/day...?  What is "standard"?

I don't know about "standard". For "easiest" I would do it every time,
it doesn't take much time to do.

> 4. Does using the MAC not associated with the router 
> "bypass" or in anyway open me up to virus/hacking issues?

No.

> 5.Is it "normal" to have to ARP for a MAC to send a UDP 
> packet ( it appears to be required in the microchip stack)?
> In my limited past network forays, I used a class 
> library that encapsulated all this, I just needed to send in 
> the port numbers and the domain name (yes, I still need 
> to figure out how to access a DNS server for IP resolution).

Yes. Remember, you are dealing with multiple layers here. IP addresses
are good for the whole internet (ignoring private addresses). MACs are
addresses specific only to your local segment, they have no meaning
outside of your local segment. There are transports that IP ride on that
don't even use MACs. TTYL

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