On Sun, 22 Apr 2001, Andreas Meyer wrote:
> Am Sam, 21 Apr 2001 schrieb Fred Wright:
>
> > Proxy ARP is a kludge alternative to proper subnet routing. Let's say you
> > have a system connected via a serial link to another system that's also on
> > your LAN. There are two ways to make this work:
> >
> > 1) Put the serial IPs in a different subnet from the LAN, and make sure
> > that other systems on the LAN are aware that the LAN<->serial machine is
> > the gateway to the serial machine's IP. If the LAN<->serial machine is
> > also the default gateway, this is pretty much automatic, but otherwise it
> > requires some manual routing, at least on the default gateway, and perhaps
> > elsewhere.
>
> My LAN is on 192.168.0.0 eth0. Now I want to make it possible for a caller
I presume that's just the network number, not the IP address of any
machine, since "host number" 0 is supposed to be avoided.
> from outside to connect to the router on 192.168.2.3. Therefore the router
> has also the IP 192.168.2.3 listening on the modemport.
> A caller from outside logs in using ppp and gets the IP 192.168.2.41.
> Now to make it possible to him to see the LAN, I must do some routing?
Actually, *him* seeing the *LAN* isn't an issue, since he has a
point-to-point link with the peer as the default gateway for everything.
The problem is getting the *LAN* to see *him*.
> The routingtable looks like this:
> Kernel IP routing table
> Destination Gateway Genmask Flags Metric Ref Use Iface
> 192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
> 127.0.0.0 0.0.0.0 255.0.0.0 U 0 0 0 lo
> 0.0.0.0 192.168.2.3 0.0.0.0 UG 0 0 0 ppp0
>
> Should this be ok and I don�t have to use proxyarp?
Yes, although you don't even need the extra IP for the router if you don't
want it. The router's end of the PPP link can have the same IP as the
LAN, which doesn't confuse it because the link is P2P. The imporatnt
thing is that the *remote* IP be in a different subnet, so that the
*other* machines on the LAN know that it's not on the Ethernet. As long
as the router is also the default gateway in general, no additional
routing setup is needed.
> > 2) Put the serial IPs in the same subnet as the LAN, and configure the
> > LAN<->serial machine to answer ARP requests for the serial IP, supplying
> > its own Ethernet address. Then it appears to other machines on the LAN to
> > be directly connected to the LAN. This is called Proxy ARP, and has some
> > disadvantages with respect to broadcast handling and things like
> > traceroute, but it's an alternative if #1 doesn't work.
>
> So you say proxyarp is only needed, if the router and the LAN are on the
> same subnet and I don� t want to do manual routing?
Correct.
Fred Wright
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