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Date:      Fri, 20 Mar 1998 08:56:56 -0600 (CST)
From:      "Matthew D. Fuller" <fullermd@futuresouth.com>
To:        GLEN.W.MANN@monsanto.com
Cc:        freebsd-questions@FreeBSD.ORG
Subject:   Re: Re[2]: arp/IP to ethernet addresses
Message-ID:  <Pine.BSF.3.96.980320084444.20071a-100000@shell.futuresouth.com>
In-Reply-To: <"0320144044-Re2: arp/IP to ethernet addresses"@MHS>

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On 20 Mar 1998 GLEN.W.MANN@monsanto.com wrote:

>      
> (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)? 

Well, if the interfaces are setup to see 123.456.7.255 as the broadcast
address, they won't say a darn thing back if they get 123.456.6.255. 
I'm not sure how that would work, with the subnet divided over multiple
local networks; with parts of it on different sides of a router, I'm not
sure how the broadcast address will get routed.  However, you won't get
arp entries for systems on the other side of the router; you'd have to
have a system on each (physical) network to catalog the MAC addresses.

> The ping manpage talks about pinging a multicast address.  Is this the same 
> thing?
No, that's an experimental technology, having to do with referencing a
given set of hosts with a single address.  It might, theoretically, solve
your problem, but implementing it would be a lot of trouble.  But I'm not
too knowledgeable about multicasting; I'll let someone else handle that
one.  It MIGHT be a solution, but probably a whole lot more work that it's
worth.


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|       FreeBSD; the way computers were meant to be       |
* "The only reason I'm burning my candle at both ends, is *
| that I haven't figured out how to light the middle yet."|
*    fullermd@futuresouth.com      :-}  MAtthew Fuller    *
|      http://keystone.westminster.edu/~fullermd          |
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