[1064] in linux-net channel archive
Re: ProxyArp parameterized on interface?
daemon@ATHENA.MIT.EDU (Rob Janssen reading Linux mailingl)
Wed Sep 6 17:19:34 1995
From: linux@pe1chl.ampr.org (Rob Janssen reading Linux mailinglist)
To: almesber@lrc.epfl.ch (Werner Almesberger)
Date: Wed, 6 Sep 1995 08:45:07 +0200 (MET DST)
Cc: linux-net@vger.rutgers.edu
In-Reply-To: <199509050607.IAA09992@lrc.epfl.ch> from "Werner Almesberger" at Sep 5, 95 08:07:44 am
Reply-To: linux-vger@wab-tis.rabobank.nl
According to Werner Almesberger:
> Ove Ewerlid wrote:
> > Has anyone ever heard of proxyarp that is interface specific.
>
> Actually, I never quite understood why ARP actually doesn't use a
> separate table for each interface in the first place, apart from
> historical reasons (i.e. BSD).
>
> There shouldn't be many cases where the same ARP entry would appear in
> more than one table and it's probably always undesirable to use an ARP
> entry obtained at interface A on interface B.
Yes, I think there should be separate ARP tables per interface. The
IP->hwaddr mapping is something specific to a subnet, and the mapping
can be different on each subnet even when proxy ARP is not in use, e.g.
when you setup a redundant network using 2 cards in each machine.
> Except for proxy ARP and related hacks, it should actually be possible
> to use the existing tools/APIs without changes, because the interface
> could be determined from the IP address. (We don't allow interfaces
> with !((A.local_addr ^ B.local_addr) & A.netmask & B.netmask) &&
> (A.netmask & B.netmask) != ~0 (network parts of non-p2p interfaces
> overlap), right ?)
It would be best when it is allowed to run parallel networks with the
same IP address but different hardware addressing.
In amateur packet radio (at least here locally) it is customary to use
only a single IP address for a station even when it is present on
multiple frequencies (i.e. the different interfaces use the same IP
address).
The hardware address (callsign+ssid) can be different on each interface.
Before I changed my version of NET to have a separate ARP table per
interface, certain situations caused trouble. Amongst them were stations
that heard eachother on two different frequencies, and stations that
wanted to setup a proxy ARP on one frequency and not on the other.
Rob
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