Trouble resolving hostnames with arp -a

Question

I'm trying to lookup hostnames of computers on the same network as me. Sometimes when I use arp -a I get a question mark (?) for the hostname. I've tried using nslookup xx.xx.xx.xx and host xx.xx.xx.xx but they can't resolve the hostname either:

** server can't find xx.xx.xx.xx.in-addr.arpa.: NXDOMAIN

I know that these other machines do have hostnames because I can see them on some wifi networks but not others.

Is there a way to resolve these hostnames and what is the reason that the hostname is sometimes not available with arp -a?

Thanks!

BTW if this is the wrong stack exchange group to post this in, just let me know which one it should go in and I'll move it.

Answer 1

arp uses the same name resolution functions as the other commands, so if the reverse DNS entries in your network aren't set for some IPs, then none of the tools will be able to resolve those IPs.

It's possible to try to resolve hostnames through nmblookup if the machines are Windows, but in general, the administrator of your DHCP/DNS systems should be able to resolve these questions.

(Moved from comment.)