| I don't believe we supply a "proxy arp daemon" with Digital UNIX. At least
I haven't heard of it...
As the name implies, a "proxy arp" is a response to an ARP request made on
the behalf of another machine. Usually this other machine is one that cannot
respond directly to the ARP.
This comes up in PPP: you have a machine at home who's only network connection
is a dial-up PPP link. There's no Ethernet adaptor involved, hence no
hardware address. But if that remote PPP connection has an IP address which
appears to belong to the office LAN that it's dialed into, then other hosts
on that LAN segment will expect to be able to resolve the remote machine's
hardware address.
This is where proxy arp comes into play: the thing that you dial in to,
whether it be another computer or terminal server or whatever, will offer
to answer ARP requests for that remote machine. In this specific case, the
result is that network traffic which originates somewhere on the office LAN
and is directed to the IP address of the machine at home, will instead get
sent to the thing that maintains the office-side of the PPP link. That box
is reponsible for forwarding those packets over the PPP link to the home
machine.
The trick in the above case is that when something tries to ARP the machine
at home, the answer it gets back is the hardware address of the box that
maintains the other side of the PPP connection (since effectively the
machine at home has no hardware address of its own.)
This is just one example of proxy arp and why you might want to use it.
Another thing I can think of doing with this is to help broken BOOTP clients
which are struggling to boot across different IP subnets.
Check out the manual page for arp(8). You can use this to install entries
into the arp cache manually. Note that you have to explicitly tell arp
to "publish" an IP address/hardware address pair if you want to proxy arp
for that host.
-- Farrell
[Posted by WWW Notes gateway]
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| We don't supply a proxy arp daemon, however, Digital UNIX supports
the use of proxy arp, as Farrell outlined, and other than having to
know the addresses in advance so you can load them by hand, it handles
all of the functions which a proxy arp daemon would handle, if one
existed.
John
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