On Sun, Nov 06, 2005 at 10:29:55PM -0500, Ian C. Blenke wrote:
> Paul M Foster wrote:
> >Anyone know of a command that will cause other machines on a subnet to
> >echo back their IPs and names? Obviously, this wouldn't work if you had
> >to know the names of the machines first. So it would have to be like a
> >broadcast command that used ICMP or something to cause others to answer.
> >Anyone know of such a beast? Seems like I should know this, but I don't.
> >
> The best command for this is really nmap:
>
> # nmap -sP 192.168.1.1-254
>
This works fine. Thanks.
> If you don't use "-n", the DNS for the IPs will be resolved back into
> their names (if the IPs have in-addr.arpa entries on your nameserver).
>
> On any box, you should be able to see the recently cached ARP entries:
>
> arp -a
>
Hmm. This appears to attempt random IPs, through all the subnet. It
works if done as:
arp -a | grep -v incomplete
Then it gives only the ones actually up and working.
> Again, if you don't include "-n", the DNS for the IPs will be resolved
> back into their names (if the IPs have in-addr.arpa entries on your
> nameserver).
>
> Finding the "names" of the machines on the segment requires something
> beyond ARP or any kind of ICMP or UDP echo query.
>
> On a "pure" IP segment, you can find machine names using:
> - SMB over IP Netbios naming requests (see below)
> - an authorative in-addr.arpa DNS nameserver for your network segment
> (via dynamic or static assignment)
> - sniffing DHCP leases.
> - a naming service like rwhod (not really used by anyone anymore)
> - watching SLP announcements and other zero-conf broadcasts (ala
> "bonjour", previously "rendezvous")
>
Most boxes on the LAN don't use SMB. I only use it when absolutely
necessary for Windows boxen. As it happens, all the machines on this
network are logged in /etc/hosts on each box. So this whole exercise is
sort of moot. But I've recently thought of changing this to have a DNS
server running. And it occurred to me to wonder what I'd do if I wanted
to know the name/IP of boxes on a LAN I wasn't familiar with, or which
weren't mapped in /etc/hosts.
Thanks.
Paul
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