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

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

On Sun, Apr 30, 2000 at 09:28:08AM -0500, Jeff Dike wrote:
> gbr...@mi... said:
> > You can send much more arbitrary network data, more protocols, etc.
> 
> I'm just taking arbitrary bits, coding them up a bit, and sending them down 
> the slip line.  I think what happens in the kernel is that those bits get 
> reconstituted and passed into the network code.  I don't see any generality 
> problems there.

This doesn't actually work for protocols other than IP.  You can't send such
things as AppleTalk over the SLIP link.

> > Also, it allows you to setup bridging fairly trivially on the host
> > such that eth0 is bridged to tap0 which would let you have the uml
> > hosts appearing on the same outer network as the host
> 
> How is this different from having umn bridged to sl0, and putting the uml 
> hosts on the outer net?

You cannot bridge ethernet traffic onto a SLIP link.  The point is raw
ethernet frames are reproduced onto the other side of the bridge, which is
impossible over SLIP because you are limited to IP traffic and lose the lower
layer of information.  Also, SLIP is a point-to-point link which is not
particularly useful for communication to multiple UMLs running on a single
machine.  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.  With the solution I'm talking about,
you would simply need to setup uml-net with the ethertap device on the host
machine, and setup a bridge between eth0 and tap0.  Now every UML which is
using uml-net can simply configure its eth0 as if it were on the host's
ethernet directly.

				-- Gerald