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Date:      Wed, 09 Oct 2002 15:17:37 -0700
From:      Andy Sparrow <spadger@best.com>
To:        thomas@cuivre.fr.eu.org
Cc:        freebsd-stable@FreeBSD.ORG
Subject:   Re: Setup routing entry for host with a non-local IP address 
Message-ID:  <20021009221737.0A7AA2A7@CRWdog.demon.co.uk>
In-Reply-To: Message from Thomas Quinot <thomas@cuivre.fr.eu.org>  of "Wed, 09 Oct 2002 17:17:33 %2B0200." <20021009151733.GA15162@melusine.cuivre.fr.eu.org> 

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> Suppose that on a 4.6.2 machine (hostA), I have an interface xl0
> with address 10.10.1.2, netmask 255.255.255.0.
> =

> On that ethernet, I have a host (hostB) that is set up as 10.10.0.1,
> netmask 255.255.255.0. I need to send a packet from hostA to hostB,
> and to that effect I would like to set up a static route on hostA
> indicating that 10.10.0.1 lives on its xl0 interface.

This can't work, not as described.

> Am I trying to do something impossible, or am I just clueless enough
> that I did not find the proper way of cajoling the kernel into
> cooperation?

Layer 3 routing only cares about networks, not hosts.

You need to use a router, as these hosts are in different networks (the =

fact that they're sharing the same physical network segment =

notwithstanding).

You can use a multi-homed host (e.g. one with a network interface in =

both networks) that will forward packets.

You could add a NIC to one of the hosts and number it so that it is in =

the "other" network.

You could use a "real" router. =


You could add an alias[0] to either one of the hosts on the shared =

network segment so that they "understand" that they have two interfaces =

on the same network and can thus talk to each other.

You could also subnet the Class A network you're using with a /16 =

netmask, so that the 10.10 portion would be the network identifier, and =

the 1.2 & 0.1 portion of the IP address(es) would be the host identifier 
=

- thus, both hosts would be on the same network, and can communicate =

directly. This will have other implications for your network, however[1]

HTH.

Rgards,

AS

[0] From this list, I believe that the alias needs a /32 netmask (e.g. =

255.255.255.255) on recent -STABLEs to work correctly.

[1] Broadcast address will change, for one. You should probably adjust =

the netmask on every node on that new network.




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