Subject: Re: illegal network routes and a ponderance
To: <>
From: David Laight <>
List: tech-net
Date: 02/19/2003 08:43:52
> > > *Many* ethernet segments are shared by multiple networks.

yes - typically happens when a large company has so many small networks
that the subnet size is reduced to 64 hosts, but some segments have
rather more than 60 systems connected to them.

In order to stop packete appearing on the cable twice, it is necessary
to add a route that indicates that systems in that subnet should be
arped.  (ICMP redirects can't fix this one.)

> > Certainly.  And as far as I can see this fact is totally irrelevant to
> > the discussion at hand.
> Not at all. It currently seems impossible (unless perhaps I'm missing 
> something, which itself is certainly possible) to set the default route to be 
> an IP on one of those other networks.

It is easy....

1) Allocate an address out of your own subnet to the router,
2) Set that address as the target of the default route
3) Add a local arp table entry for the address you allocated to the
   router with the routers actual ethernet address.

Note that the configuration of the router doesn't ned to be changed.


David Laight: