As wise monks have already stated above:
- arp only works for IP address from your local (segment|subnet|broadcast domain)
- if you try to arp-resolve an IP address from a different subnet, the resulting MAC address will be that of the router interface nearest you.
- MAC addresses are an Ethernet (not PPP) thang
Token-Ring and FDDI devices also have MAC addresses but, IIRC, you get into (big|little)-endian stuff there.
Arcnet and Appletalk used their own funkomatic hardware addressing schemes.
If you are indeed looking for the MAC address of a local-to-your-LAN-segment device, (code) MAC n' IP cheese includes code of OWTDI.
bumbling toward Perl Adept
(it's pronounced "why-bick")
Update: I was thinking of IPv4 only.
As lhoward points out, IPv6 is substantially different.
Update 2: Working from riffraff's Re: Re: Re: How can I find a MAC address from aremote IP ? post above, I found that (code) MAC n' IP cheese can work for remote segments just by replacing the "Querying ARP table..." section with
snmpwalk <router_name_or_address> <community_string> IpnetToMediaPhysAddress
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