Machines on LAN

Is there an easy way to determine all the machines
(or other devices) on a LAN?

On 2007-10-31, Timothy Murphy <(E-Mail Removed)> wrote:
> Is there an easy way to determine all the machines
> (or other devices) on a LAN?

Define "determine", "machines (or other devices)", and "LAN".

Let's start backwards: officially, the LAN is anything on ethernet that
doesn't go through a router. But some sites have more than one router,
and some people want to know about all the machines at their site.

Do you want to know about machines with a MAC or IP, or *all* devices?
It might not be so easy to determine whether (or where) there are hubs
or switches, nor to determine whether there's a machine connected but
it's not powered on (or its interface is down).

What do you want to know about these machines? IP, MAC, hostname, OS,
other?

Modulo the answers to the above questions, one easy way to report some
machine information is by using nmap on your subnet (if you have
permission to do so). You can nmap anything with an IP address, so you
can cross a router if needed; it's real-time, so if a machine is off at
the time you nmap, you won't find it.

--keith


--
kkeller-(E-Mail Removed)
(try just my userid to email me)
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Timothy Murphy <(E-Mail Removed)> writes:

>Is there an easy way to determine all the machines
>(or other devices) on a LAN?

No, not for sure.
arp -a
will list the ip and mac for all the machines yours has talked to recently.

If the machine does not respond to any requests on any port or go out, then
it can sit there silently listening with non-the-wiser.

Unruh wrote:

>>Is there an easy way to determine all the machines
>>(or other devices) on a LAN?
>
> No, not for sure.
> arp -a
> will list the ip and mac for all the machines yours has talked to
> recently.

OK, thanks.
Actually, this is what "arp -a" gives on my desktop:
-------------------------------------
[root@alfred ~]# arp -a
blanche (192.168.2.7) at 00:0E:A6:AF:0B:11 [ether] on eth1
? (192.168.2.11) at 00:02:2D:27:218 [ether] on eth1
? (192.168.1.254) at 00:00:C5:C3:96:50 [ether] on eth0
-------------------------------------
The first of these is another desktop,
and the second is a laptop,
while the third is my ADSL modem.

But I also have a Linksys WRT54GL access point on 192.168.2.12;
I wonder why this is not listed?
Especially as it is the link (via ethernet) to 192.168.2.7
and (via WiFi) to 192.168.11.

The WRT54GL actually runs Linux, and "arp -a" on that device
gives
-------------------------------------
~ # arp -a
? (192.168.2.1) at 00:40:F4:6E:07:A1 [ether] on br0
-------------------------------------
which is the desktop.

So it seems to me that "arp -a" gives a very partial account
of the devices on my LANs.

I found nmap (suggested by someone else) more or less useless
for this purpose, as "man nmap" says far too much in an unreadable way ...

Timothy Murphy wrote:
> Is there an easy way to determine all the machines
> (or other devices) on a LAN?
>
>

This AMD 64 machine is running Mepis 6.5 and in the toolbar is Synaptic.

It grabs programs from Ubuntu, Debian, and Mepis repositories.

Better, I can select a Search box, type in nmap, and hit enter, and it
will come back with the synaptic results for all things that have nmap
in their description, name...

I got 40 things back, like amap, knmap, nmap. There are GUIs for most.

checked the boxes, and it was done in a jiffy.

Now, they are in my toolbar mainmenu.

Though over a hundred machines here, run on about 30 different OSes,
Mepis really fills the bill for most needs for most of my needs and
those of the parents, teachers, students, and businesses I encounter.

Others are for expermentation, familiarization, training. Some are:
PC-BSD, Vixta, DamnSmallLinux, FreeBSD, FrieBSIE, Frenzy, Puppy, Fedora
7, PCLinuxOS, FreeBSD6.2, Sabayon, Knoppix, miniKnoppix, SLAMPP,
VectorLinux, Quaintain, YellowDog.

Just about anything on http://livecdlist.com or http://distrowatch.com
is ripe for testing on my Acers, Dells, Compaqs, HPs, and generic
sytems, with X86, X86-64, Alpha, PPro, PPC, Motorola, AMD, Intel, IBM ,
platforms /support chip boards from over 49 makers.

Donated hardware is fun to run, and the performance is surprising!

Timothy Murphy wrote:
> But I also have a Linksys WRT54GL access point on 192.168.2.12;
> I wonder why this is not listed?

Ping it first, then try again?

> I found nmap (suggested by someone else) more or less useless
> for this purpose, as "man nmap" says far too much in an unreadable way ...

Unreadable, really? Is English your second language? Welcome, noob
You meant readable, but indecipherable. Try this:
map -sP 192.168.2.0/24


--
As we enjoy great advantages from inventions of others, we should be
glad of an opportunity to serve others by any invention of ours;
and this we should do freely and generously.
--Benjamin Franklin

johnny bobby bee wrote:
> You meant readable, but indecipherable. Try this:
> map -sP 192.168.2.0/24

Sorry, meant: nmap -sP 192.168.2.0/24


--
As we enjoy great advantages from inventions of others, we should be
glad of an opportunity to serve others by any invention of ours;
and this we should do freely and generously.
--Benjamin Franklin

johnny bobby bee wrote:

> johnny bobby bee wrote:
>> You meant readable, but indecipherable. Try this:

> Sorry, meant: nmap -sP 192.168.2.0/24

Thanks, that gets all the information:
----------------------------
[root@alfred tim]# nmap -sP 192.168.2.0/24

Starting Nmap 4.20 ( http://insecure.org ) at 2007-11-01 13:57 GMT
Host alfred (192.168.2.1) appears to be up.
Host carrie (192.168.2.4) appears to be up.
MAC Address: 00:15:00:16:2A:EA (Intel Corporate)
Host blanche (192.168.2.7) appears to be up.
MAC Address: 00:0E:A6:AF:0B:11 (Asustek Computer)
Host 192.168.2.11 appears to be up.
MAC Address: 00:02:2D:27:218 (Agere Systems)
Host wrt (192.168.2.12) appears to be up.
MAC Address: 00:16:B6A:56:B2 (Cisco-Linksys)
Nmap finished: 256 IP addresses (5 hosts up) scanned in 8.002 seconds
----------------------------

On Wed, 31 Oct 2007 20:47:13 +0000, Timothy Murphy wrote:

> Is there an easy way to determine all the machines
> (or other devices) on a LAN?

Try nmap

Dan

Dan N wrote:

>> Is there an easy way to determine all the machines
>> (or other devices) on a LAN?
>
> Try nmap

The trouble with nmap is that there are a billion options,
and it is not at all clear which to choose.
But someone pointed out to me

nmap -sP 192.168.2.0/24

which did the trick.