Subject: RE: [dhcwg] thought you might know...

From: "Bernie Volz (EUD)" <[email-masked]>
Date: Wed, 24 Jul 2002 16:55:19 -0500

Dan:

DHCP servers don't generally have a mechanism for you to ask this kind of question of them. There is a work in progress to provide this support, but it is generally for use by other network equipment and would not be available to just anyone. See http://www.ietf.org/internet-drafts/draft-ietf-dhc-leasequery-03.txt.

However, there is another way you could obtain this information. Please see the Reverse ARP RFC (RFC 903). Of course, for this to work the device has to support this protocol and also has to be on the same link.

Likely your best best is to speak to the DHCP operator (ISP) to see whether you can be assigned a fixed address (via DHCP) for the wireless bridge.

I also don't fully understand your network configuration and why you have this problem. Perhaps more details regarding this would help to provide suggestions.

- Bernie

-----Original Message-----
From: Dan Clemens [mailto:[email-masked]]
Sent: Thursday, July 18, 2002 11:42 PM
To: [email-masked]
Subject: [dhcwg] thought you might know...

From what I see on your web page you are the folks how establish the
standards for DHCP.  Sorry to bother you with what I am sure is a basic
question but I have been searching for days now and can not find the
information I need.

What I would like to know is if there is a way to find out what IP addresses
DHCP has assigned to each of the clients on a network.  I know I can go to
each of the individual stations an get the info via IPCONFIG but several of
the devices on my network do not have a user interface.  One of these
devices on my network is a wireless bridge. It's configuration can be
managed via it's IP and a web browser.  But since it is dynamically assigned
I do not know it's IP (without attaching a laptop to it) and can not access
the configuration page via my browser.

I have thought of writing a script using ping to poll each address in the
range of the subnet mask but this seems kind of cumbersome and I do not want
to upset my ISP by accidentally doing something that may be illegal.

I am frustrated after the years of training I have had an the certifications
I still don't have the information I need!

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dhcwg mailing list
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https://www1.ietf.org/mailman/listinfo/dhcwg

---

From: "Raymond Jayaraj" <[email-masked]>
Date: Thu, 25 Jul 2002 10:14:34 +0800

RE: [dhcwg] thought you might know...Hi Dan,

This may not be the right list to be discussing this, but
there's a 'dirty' way of doing this, and it involves using
a sniffer such as ethereal (www.ethereal.com).

0. Run the sniffer on the same link as the machine whose IP
   address you'd like to know. Set filter (sniffer dependent)
   to capture only dhcp messages, or messages with the dhcp
   server's IP address.

1. Restart the machine.

2. You should see the DHCP messages on the sniffer, from 
   which you can obtain the IP address. You may also want to
   note its MAC address.

To go a step further, you can automate this for all machines,
for everytime you restart your system. But this requires some 
Linux C programming, and using either the libpcap library or 
netfilter. Also you have to keep track of the MAC addresses 
of each machine.

- Raymond

  ----- Original Message ----- 
  From: Bernie Volz (EUD) 
  To: 'Dan Clemens' ; [email-masked] 
  Sent: Thursday, July 25, 2002 5:55 AM
  Subject: RE: [dhcwg] thought you might know...

  Dan: 

  - Bernie