Re: [LARTC] Proxy Arp with same left/right IP address.

[Adrian Chung <adrian@enfusion-group.com>]

On Wed, Feb 13, 2002 at 04:52:09PM +0100, Ard van Breemen wrote:
> On Wed, Feb 13, 2002 at 10:35:15AM -0500, Adrian Chung wrote:
[...]
> > Except that I'm confused as to how the kernel deals with the fact that
> > both interfaces have the same IP address.
> The kernel sees one IP address, and two nics, with each having some part
> of a network directly attached to it.
> 
> > I guess logically it doesn't matter to the kernel, because the routes
> > clearly delineate which interface to send packets to, proxy-arp
> > connects the two LANs, and both interfaces have different MAC
> > addresses.
> Yep.
> > It just seems wrong. :)
> Nope.
> If you think about it: it is CLEAN!

You're definitely right about that.  It's a *very* cool solution, I'd
been looking for a way to do this.

[...]
> Another thing I am now busy to find out (I am not sure if this also
> works on 2.2, but I have no reason to believe it does not work):
> 
> ip link set up dev eth0
> ip addr add 127.0.0.1/32 dev eth0
> echo 1 > /proc/sys/net/ipv4/conf/eth0/proxy_arp
> ip link set up dev eth1
> ip addr add 127.0.0.1/32 dev eth1
> echo 1 > /proc/sys/net/ipv4/conf/eth1/proxy_arp
> ip route add x.x.x.96/28 dev eth0
> ip route add x.x.x.97/32 dev eth1
> 
> The theory behind it: the IP protocol driver needs to be bound to the
> device. This is done by giving any (bogus) ip address to an interface.
> Only after the IP protocol driver is bound to the interface you can use
> it for IP.
> /proc/sys/net/ipv4/conf will only show interfaces bound to the IP
> protocol... :)
> 
> Of course: you cannot reach the firewall, and the firewall can't reach
> you. You need a non-bogus ip address for that... (Hmmmm: ssh 127.0.0.1
> .. Hah! I hacked the firewall.... shutdown -h now ... Uh? ;) )

Is this for real?  So you bind 127.0.0.1 to both eth0 and eth1, not
using an ISP assigned IP at all on the bridging box, and you'd still
be able to route from the ISP's network through to machines on the ISP
assigned network?

That's way too neat. :)

Have you tried this under 2.4?

--
Adrian Chung (adrian at enfusion-group dot com)
http://www.enfusion-group.com/~adrian
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