Eric,
For a thorough explaination, you might want to go to
http://www.ietf.org/ and read RFC's 1058 and 2453.  For a very brief
explaination, they define a relatively simple way of routers sharing
information about what networks they have attached.  See also OSPF,
IGRP and EIGRP (the latter two being proprietary Cisco protocols).
-Erik

On 5/4/06, Eric Shubes <plug@shubes.net> wrote:
> Darrin Chandler wrote:
> > On Wed, May 03, 2006 at 10:20:51PM -0700, Dazed_75 wrote:
>
> > Hmm. Does the router doing dhcp support RIP? Some do, some don't.
>
> Can you explain what RIP is/does?
>
> >> BTW, a reminder that both interfaces get the same DNS IPs from the one
> >> router acting as a DHCP server.  So the issue may be with the dhclient
> >> effects but somehow the effect seems to change which interface traffic
> >> is going to.
> >
> > The dhcp client (dhclient) gets its info and sets up the ip address,
> > subnet, and *routing*. Normally you only do this on one interface, and
> > it's your only link, and it works great. Add a second interface and one
> > of the dhclients stomps on the routing of the other. Both dhclients
> > remain active and periodically check in with the dhcp server, and will
> > renew their info, including *routing*. So, with multiple dhcp interfaces
> > it's anyone's guess how things will route at any particular moment.
>
> That's a very good description of what's going on here. Thanks, Darrin.
> I have two interfaces on my notebook, and have been meaning to do a bit
> of testing, which I've now done. I have an IPCop box and a wireless
> router configured on a *different subnet*. Whichever interface is
> brought up last 'wins' the routing war (is used as the external
> gateway). If the interface which came up last is brought down, network
> access is lost, because the gateway route is removed. If the interface
> which came up first is brought down, network access persists. I'm
> guessing that as DHCP leases are renewed, the connection(s) would remain
> working, and the most recently renewed lease would become the default route.
>
> I'm wondering why anyone would want more than one network interface on
> the same subnet active at the same. I can't think of any reason to do so.
>
> I've also been wondering why Mark is using the same IP address for his
> wired and wireless interfaces. Seems to me that each interface should
> have a unique IP address, like the MAC address. I suppose that it might
> make things easier resolving host names. If that's the case, why not
> spoof the MAC address(es) to be the same on both cards, and let DHCP
> handle setting things up? Of course, I think you'd still want to be
> careful to have only one interface active at a time due to leases being
> renewed.
>
> --
> -Eric 'shubes'
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