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Date:      20 Mar 1998 09:29:20 -0600
From:      GLEN.W.MANN@monsanto.com
To:        fullermd@futuresouth.com, freebsd-questions@FreeBSD.ORG
Subject:   Re[2]: arp/IP to ethernet addresses
Message-ID:  <"0320144044-Re2: arp/IP to ethernet addresses"@MHS>

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(Pardon my cc:Mail!)

The purpose is asset control verification.  Basically an on-demand thing.  
If ifconfig -a gives

lp0: flags=8810<POINTOPOINT,SIMPLEX,MULTICAST> mtu 1500
ep0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        inet 123.456.6.80 netmask 0xfffffe00 broadcast 123.456.7.255
        inet 123.456.6.81 netmask 0xffffffff broadcast 123.456.6.81
        ether 00:a0:24:25:e4:59
tun0: flags=8010<POINTOPOINT,MULTICAST> mtu 1500
sl0: flags=c010<POINTOPOINT,LINK2,MULTICAST> mtu 552
ppp0: flags=8010<POINTOPOINT,MULTICAST> mtu 1500
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
        inet 127.0.0.1 netmask 0xff000000

then I use 123.456.7.255 as broadcast?  This will cross a (rather slow) WAN 
link (modem bank or something) to subnet 123.456.7.  If I ping 
123.456.6.255 will I be restricted to the local subnet (123.456.6)?

The ping manpage talks about pinging a multicast address.  Is this the same 
thing?

Thanks again...
-Glen Mann

______________________________ Reply Separator 
Subject: Re: arp/IP to ethernet addresses
Author:  fullermd@futuresouth.com at INTERNET
Date:    3/19/98 4:19 PM


On 19 Mar 1998 GLEN.W.MANN@monsanto.com wrote:

>      Hello!
>      
>      On the network at work, we would like the ability to match ethernet 
>      addresses (e.g., 00:a0:24:12:34:56) to IP addresses.

Dynamically?
Or once-over?
For what purpose, if I may ask?
     
>      The output for `arp -a' is confusing.  It shows more IP addresses than 
>      there are hosts in our DNS namedb tables, but not a full listing of 
>      all the machines on the network.  What other than explicit action, 
>      updates the arp tables?  Some time ago, `arp -a' showed me many more 
>      entries, perhaps all the machines on the network.  Is there a way to 
>      cause the translation tables to be more complete?
     
I'm not sure exactly what you're saying here.  The arp tables should hold 
every MAC address that the host has talked to (fairly recently) on the 
local network, with no routers in between.  If they haven't talked, 
there's no MAC address stored.
     
>      If I build a script to send pings (one per) to each possible IP 
>      address on the net, the arp table is built.  Is this a good idea?
     
Might be better to ping the broadcast address once.
Unless is breaks your network with the load, I can't imagine it's 
necessarily a *bad* idea.  Doesn't mean it's *good*, but...
     
>      The man pages say the arp stuff works with 10Mbit ethernet, though it 
>      seems to work with 100Mbit as well.  I guess the man pages are 
>      outdated?
     
Never thought of it that way.  I always thought of arp as a function of 
Ethernet, regardless of speed.  *shrug*
     
     
     
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