Subject: Re: [netatalk-admins] how do you restrict netatalk by ip address?

From: Michael Egan <[email-masked]>
Date: Wed, 29 Jul 1998 13:06:35 -0700 (PDT)

On Wed, 29 Jul 1998, Wes Brown wrote:
> > It would take either writing a new utility or re-writing arp, but if you
> > could grab the given computer's hardware ethernet address (which *MUST* be
> > transmitted with *EVERY* packet), and then compare that to a list
> > generated by arp (esp. after pinging the broadcast address), then you
> > might be able to discover the correct IP address. 
> 
> Two problems with that.  Your arp table size must be the size of your local
> address space.
> 
> Secondly, this would be VERY BAD if you have a network with 256x256
> machines like some locations I know of.

Somehow a (256x256) 65K node LAN without subnetting, and routing seems a 
bit silly to me. The network congestion would probably be unbearable. 
Even with switches and partitioning/segmentation without subnetting, 
without a router to better segment your network, and keep total traffic 
down to a useable level, I would suspect serious problems would emerge.

In Linux with a kernel that has /proc file system enabled in the kernel:
cat /proc/net/arp

That should show you the MAC addresses associated with IP addresses on 
your LAN. If you know the MAC address of the Mac, then you may be able to 
find it here, or the IP address of the Mac can give you the MAC address of 
the Mac. (Please note that this only lists *recent* IP/MAC address pairs 
from connections that have taken place. If the AppleShare is over IP, I 
suspect that it should appear here just as all other LAN connection on 
the subnet appear in this list. IP addresses *not* on my subnet do not 
appear here, but my gateway is listed.

I found it useful to make a webpage that takes the IP address of the 
connecting session, and takes the entry from /proc/net/arp to show me the 
MAC address and IP addrss of a machine that connect from (assuming it is 
on the same subnet) and return it in an HTML page. So, it is simple, but 
I find it useful.

-M

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Systems Department Operating Systems Analyst for the Ruben Salazar Library
              of California State University at Sonoma.
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From: Tony Stuckey <[email-masked]>
Date: Wed, 29 Jul 1998 15:10:48 -0500 (CDT)

> appear here, but my gateway is listed.

	These correlations are commonly available in network management
software.  We use Cabletron's VLAN manager at work, and it will happily
show the MAC address and any (including multiple/historical) Appletalk or IP
addresses accumulated by the machine.
-- 
Anthony J. Stuckey                              [email-masked]
"When I was young, the sky was full of stars.
 I watched them burn out one by one."  -Warren Zevon