Re: [User-mode-linux-devel] uml ethernet interface - code

[Gerald B. <gbr...@mi...>]

On Sun, Apr 30, 2000 at 01:36:53PM -0500, Jeff Dike wrote:
> That's a real good reason to switch to ethertap, but I'd still like to know 
> what about slip makes it impossible to encapsulate things like appletalk.

SLIP was designed to only carry IP over the serial link, this is one of the
major reasons PPP came about as it can carry mostly arbitrary protocols.

> > If there are say 4 UML sessions running on a single machine, you would
> > need 4 separate SLIP connections and individual routes for each of
> > them to get them visible to the outside world.
> 
> You'd make one uml the gateway to the outside world, give it a connection to 
> the host, and set up routes on the others to it.

Yes, that's pretty much what you'd have to do, and it would require setting
up routing and subnetting which potentially wouldn't be possible on the
network.

> I agree that that's pretty slick.  Would all the packets on the ethernet flow 
> through the bridge?  If so, I think that would make it look like all the umls 
> really were on the physical ethernet.

Yes, it would.  It's also possible to make the bridge filter so that it acts
more like switched ethernet and would only pass broadcasts and packets
destined for the other side of the bridge.

> The problem I have is the combining of virtually networking umls and 
> connecting them to the host.  Those seem to me to belong in separate drivers.
> 
> On a physical machine, if you have a local ethernet and a connection to an 
> outside network, those are different devices and probably different drivers.

My ethernet is my connection to the outside world, and has been for years.

> Without a good reason to put them in the same driver, I'd like to mimic the 
> physical world as much as possible.

It isn't going to endup being any changes to the virtual ethernet driver to
make my idea work, the userland daemon acting as the virtual network would
simply have another connection to it connected to the ethertap.  I haven't
taken a look at the uml-net program, but if it works as I suspect it does,
it wouldn't actually require modification to it, just a separate program to
connect between it and the ethertap (or an interface to an AF_PACKET system
for doing bridging).

				-- Gerald