How can I verify which machines are turn on in single LAN from a websever?

Hello,

we have around 25 machiens in two floors, all are on single LAN with
single subnet, one Router provides all network related services, but we
have inernal web server for internal web site purpose. All LAN machines
gets ip address from Router using DHCP. from this web server, how can I
know which machines are on and which are off. I can ping by based on ip
addr?. the reason is, I need to backup some directories from other
Linux nachines, then I need to store all that on different external
disk. Thanks.

On 29 Oct 2005 08:32:05 -0700, GS
<(E-Mail Removed)> wrote:
> Hello,
>
> we have around 25 machiens in two floors, all are on single LAN with
> single subnet, one Router provides all network related services, but we
> have inernal web server for internal web site purpose. All LAN machines
> gets ip address from Router using DHCP. from this web server, how can I
> know which machines are on and which are off. I can ping by based on ip
> addr?. the reason is, I need to backup some directories from other
> Linux nachines, then I need to store all that on different external
> disk. Thanks.
>
If you ping the broadcast address, you should get replies from every
active machine on the subnet.


--
Go placidly amid the noise and waste, and remember what value there may
be in owning a piece thereof.
-- National Lampoon, "Deteriorata"

Well, I tried broadcast ping, I get reply form Linux machines only, the
windows machines not replying at all. Is this is common?. Thanks.

GS wrote:

> Hello,
>
> we have around 25 machiens in two floors, all are on single LAN with
> single subnet, one Router provides all network related services, but we
> have inernal web server for internal web site purpose. All LAN machines
> gets ip address from Router using DHCP. from this web server, how can I
> know which machines are on and which are off. I can ping by based on ip
> addr?. the reason is, I need to backup some directories from other
> Linux nachines, then I need to store all that on different external
> disk. Thanks.

Assuming the computers are configured to respond to ping, that will work.

GS wrote:

> Well, I tried broadcast ping, I get reply form Linux machines only, the
> windows machines not replying at all. Is this is common?. Thanks.

I'd stick with individual pings for each computer, as you're ready to begin
the backup. Otherwise, there might be significant time between the
broadcast ping and when you get around to copying files. You might also
want to send a message to the computers, to alert users to the backup in
progress, so that they don't kill the machine. Also, it's a simple
matter, to power up computers remotely, using "magic packets" which trigger
wake on lan. And in Linux it's very easy to turn off the computer again,
when done.

GS wrote:
> Well, I tried broadcast ping, I get reply form Linux machines only, the
> windows machines not replying at all. Is this is common?. Thanks.

Yes. The Windows machines have broadcast ping
response turned off.

There is a tool, arping, that can be used to
ping anti-social hosts in a local network,
but even this must be done on a single host
at a time basis.

You have the leases granted by the DHCP
server at /var/lib/dhcp/dhcpd.leases (or
/var/lib/dhcp3/dhcpd.leases) but it needs
a fair amout of parsing to find the currently
active ones.

--

Tauno Voipio
tauno voipio (at) iki fi