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Date:      Tue, 20 Feb 2001 23:37:44 -0800 (PST)
From:      Ken Lui <klui@cup.hp.com>
To:        Lowell Gilbert <lowell@world.std.com>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: Question about arp for wakeonlan
Message-ID:  <Pine.HPX.4.10.10102202318420.6164-100000@hpcuhe.cup.hp.com>
In-Reply-To: <rd6elwuvyin.fsf@world.std.com>

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On 19 Feb 2001, Lowell Gilbert wrote:
> > So do I specify my local router's IP but my home PC's ethernet
> > address? OK, I did this but I lost connection with my work machine.
> > I'm unsure of how to set up a "proxy" entry in arp.
> 
> Proxy arp is a terrible hack, and breaks the IP layering model
> something fierce.  Nonetheless, there are occasions when people find
> it useful; however, those situations involve a router (which does the
> proxying) which is directly connected to both the host for which the
> router is proxying and the hosts receiving the proxy packets.  It
> doesn't sound like that's what's happening in your case, unless the
> default router for your home machine is somehow the same machine as
> the default router for your work machine.
> 
> You indicated that you want to do wake-on-LAN, but that this only
> works if the router has a current ARP entry for the machine you're
> waking.  This makes sense; the machine won't wake up on broadcasts, or
> wake-on-LAN would never work at all, so the router has to be able to
> do a unicast for the wake packet.  This is only possible if the router
> has an ARP mapping, so you're depending on the router keeping a valid
> ARP entry for the host; if the host is sleeping, this is only possible
> with a static entry in the router's ARP table.  So you need to do the
> ARP command on the router, not either of the end machines.
> Alternatively, you could get another machine on the same link to send
> the "wake" packet for you, and make sure that *it* has the static ARP
> entry for the sleeping machine.
> 
> I hope that this explanation is sufficient to get you going.  If not,
> it's likely that you simply don't have the access to be able to do
> what you want.

Lowell,

Thanks for taking the time to explain arp to a network newbie
like myself. Although your reply indicated that it will not work,
I did get wake on LAN to work over the WAN even after the arp
entry has expired on the (in my case Cisco) router. My two
machines--both FreeBSD--are on different subnets connected by
different routers using different netmasks. Once the arp entry
expired, I could no longer wake my work machine (for example)
from home via wakeonlan
<URL:http://gsd.di.uminho.pt/jpo/software/wakeonlan/>. I then
tried to add a proxy on my home system via the command:
   arp -s <home.router.internet.name> <work.pc.ethernet.address> pub
I had to do this twice because the first time, I got the error of
"cannot intuit interface index and type for
<router.internet.address.com>". But when I issued the command a
second time, the command was successful and I could use wakeonlan
to wake up my work machine. I would speculate that issuing
   arp -s <work.router.internet.name> <home.pc.ethernet.address> pub
followed by a wakeonlan command would wake my home PC from work.


Regards,
Ken


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