Users' IPs of a modem/router

Hi.

Is it possible to know the IP addresses of all clients using the
modem/router where I am on? How?

Thanks

"Paulo da Silva" <(E-Mail Removed)> wrote in message
news:4e55e374$0$13785$(E-Mail Removed)...
> Is it possible to know the IP addresses of all clients using the
> modem/router where I am on? How?

Only on the same interface that you connect to.
IPv4: Listen for the ARP requests and answers.
IPv6: Listen for the ICMP messages that replaced ARP.
However, if a client remains silent and never transmits a packet, you won't
find out about it until it does....

Em 25-08-2011 07:25, D. Stussy escreveu:
> "Paulo da Silva" <(E-Mail Removed)> wrote in message
> news:4e55e374$0$13785$(E-Mail Removed)...
>> Is it possible to know the IP addresses of all clients using the
>> modem/router where I am on? How?
>
> Only on the same interface that you connect to.
> IPv4: Listen for the ARP requests and answers.
> IPv6: Listen for the ICMP messages that replaced ARP.
> However, if a client remains silent and never transmits a packet, you won't
> find out about it until it does....
>
>
Thanks

On Thu, 25 Aug 2011, in the Usenet newsgroup comp.os.linux.networking, in
article <4e55e374$0$13785$(E-Mail Removed)>, Paulo da Silva wrote:

>Is it possible to know the IP addresses of all clients using the
>modem/router where I am on? How?

Ambiguous question. What is it you are trying to ask?

>NNTP-Posting-Host: a95-92-69-2.cpe.netcabo.pt

Using a DNS query tool (dig, dnsquery, host or nslookup), that hostname
translates to 95.92.69.2.

Asking the RIPE whois server, I am told:

0.0.0.0 - 255.255.255.255 IANA-BLK The whole IPv4 address space
77.0.0.0 - 95.255.255.255 EU-ZZ-80-93 Administered by RIPE
95.92.0.0 - 95.95.255.255 PT-TVCABO-20081215 TVCABO Portugal, S.A.
95.92.0.0 - 95.93.255.255 TVCABO-Portugal Cable Modem Network
95.92.64.0 - 95.92.127.255 TVCABO-Portugal

and they don't _publish_ any data on smaller segments. Depending on
your router, you may be able to find a web page on it that gives the
equivalent of the output of the UNIX command /sbin/route and that
will give a clue about what might be a smaller sized allocation. It
will also identify the TVCabo router from your segment to "the world"
(identified as the default route). The last range listed above is
about 16380 hosts - a bit larger than I'd expect. Learning more than
that about the TVCabo side of your router depends on how that router
is configured and whether or not you have "root" (or "administrator")
access to the router - probably not.

On the other hand, if you are trying to learn all of the clients on
your side of the router, that may likewise depend on the router and
what access you have to it. Look on your system, and see what
'/sbin/ifconfig -a' tells you about the address range in use. Look
also at output of '/sbin/route -n'. A simple check there is to look
at 'ARP' packets (which would be broadcast from a hosts to all hosts
on the local wire) and see who is there. Run a packet sniffer such as
ethereal, tcpdump or wireshark. For tcpdump, the command would be

/usr/sbin/tcpdump -ni eth0 arp

Which would produce output like

12:25:18.62 arp who-has 192.168.1.25 tell 192.168.1.1
12:25:30.27 arp who-has 192.168.1.9 tell 192.168.1.1
12:25:30.27 arp reply 192.168.1.9 is-at 00:26:18:06:8a:dc
12:25:31.27 arp who-has 192.168.1.1 tell 192.168.1.9
12:25:31.27 arp reply 192.168.1.1 is-at 00:c0:d1:57:00:f0
12:25:54.68 arp who-has 192.168.1.2 tell 192.168.1.1
12:25:54.68 arp reply 192.168.1.2 is-at 08:00:20:cd:1b:22

It may take several minutes to see all of the ARP packets. You may
not see the "arp reply" packets unless you are on the calling or
called host.

Old guy

On Thu, 25 Aug 2011 06:53:58 +0100, Paulo da Silva wrote:

> Hi.
>
> Is it possible to know the IP addresses of all clients using the
> modem/router where I am on? How?
>
> Thanks

Often the modem/router will have that information available if you have
the authorization to log in and check. Elsewise, you could do a 'ping
all' type of utility to find out what machines are on your local net - I
recall writing a little utility like that a few years back.

Em 25-08-2011 06:53, Paulo da Silva escreveu:
> Hi.
>
> Is it possible to know the IP addresses of all clients using the
> modem/router where I am on? How?
>
> Thanks

Thank you all who responded.
I have access to the router using a browser.
But what I need is a console tool that perodically "sees" who is using
the router. The idea of capturing arp seems fine.
tcpdump can help on this. Later I'll perhaps write some code to do the
job the way I need.

Thank you very much.
Paulo

On Fri, 26 Aug 2011 07:01:45 +0100, Paulo da Silva wrote:
> Em 25-08-2011 06:53, Paulo da Silva escreveu:
>>
>> Is it possible to know the IP addresses of all clients using the
>> modem/router where I am on? How?
>
> Thank you all who responded.
> I have access to the router using a browser.
> But what I need is a console tool that perodically "sees" who is using
> the router. The idea of capturing arp seems fine.
> tcpdump can help on this. Later I'll perhaps write some code to do the
> job the way I need.

Look at
`lynx --dump --nolist [router_page.URL]`
and/or
`wget -qO- [router_page.URL]`

from the command line. Pipe into `grep` to prune down to
_just_ the lines of interest. Further formatting at that point is an
exercise left to the student.

Jonesy
--
Marvin L Jones | jonz | W3DHJ | linux
38.24N 104.55W | @ config.com | Jonesy | OS/2
* Killfiling google & XXXXbanter.com: jonz.net/ng.htm

On Fri, 2011-08-26, Paulo da Silva wrote:
> Em 25-08-2011 06:53, Paulo da Silva escreveu:
>> Hi.
>>
>> Is it possible to know the IP addresses of all clients using the
>> modem/router where I am on? How?

....
> But what I need is a console tool that perodically "sees" who is using
> the router. The idea of capturing arp seems fine.
> tcpdump can help on this.

Tcpdump is a fine utility, but perhaps arpwatch(8) is what you need.

/Jorgen

--
// Jorgen Grahn <grahn@ Oo o. . .
\X/ snipabacken.se> O o .