[c-nsp] unusual arp behavior

[sthaug at nethelp.no]

> I have noticed that some (all?) cisco routers don't respond to ARP 
> requests if the requestor IP address is not in the subnet of that router. 

That is the expected behavior.

> RFC826 doesn't specify this behavior, and I haven't seen any other devices 
> do this.

There are plenty of other devices that do the same, fortunately.

> It also breaks duplicate address detection on DHCP clients, which 
> uses 0.0.0.0 as the requestor IP address.

Um, a DCHP client is supposed to ask for an IP address, and *then* it can
start using ARP. In the DHCP request it is common to see 0.0.0.0 as the
requestor address. Not in the ARP reqest, that would be very strange.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no