Subject: RE: [midcom] draft-brim-midcom-inandout-00.txt

From: "Christian Huitema" <[email-masked]>
Date: Wed, 19 Sep 2001 09:21:15 -0700

> >          10.0.0.7    Realm A !
> >            +----+            !               Realm SP
> >       .....|AP-A|......      !
> >      /     +----+      \    +------+A=192.168.20.241
> >  +----+                 \...|.....A|.................+-----+
> >  |EP-A+->-------------------|-->Y  |                 |     |
> >  +----+<--------------------|<+ |  |Y=192.168.20.243 |AP-SP|
> > 10.0.0.2                    | | |  |                 |     |
> >                             | | |  |                 |     |
> > - - - - - - - - - - - - - - | | |  |=================|MA   |
> >                             | | |  |                 |     |
> > 10.0.0.2                    | | |  |X=192.168.20.244 |     |
> >  +----+->-------------------|>X |  |                 |     |
> >  |EP-B+<--------------------|<--+  |        .........+-----+
> >  +----+               ......|.....B|......./           192.168.20.1
> >      \     +----+    /      +------+B=192.168.20.242
> >       \....|AP-B|.../        !
> >            +----+            !
> >            10.0.0.9  Realm B !
> >
> > .../ represents the signaling messages flowing between application
> end
> > points (EPs) and application proxies (APs).
> >
> > ==== represents the midcom messages from the midcom agent (MA) co-
> located
> > with AP-SP.
> >
> > ---- represents the media/data flows between the application end-
> points
> > (EP).
> 
> That really is an awesome diagram.

What the diagram shows is that if we handle scoped addresses, any
mention of addresses should be qualified with a mention of the scope.
The simplest solution is to consider the declaration of the interface as
part of the filter specification. For example, using a diagram, and
assuming that the interface serving "realm A" is called A, a filter
would be:
	Interface = A, Interior=10.0.0.2, Exterior=192.168.20.244
This has the advantage of being unambiguous: we refer to the packet as
in crosses the interface.

Note that there are two ways to provide the interface information. We
can repeat it in every filter specification, or we can consider that a
specific MIDCOM association is between a MIDCOM agent and a specific
interface. The latter would be less verbose in the case of minimal
implementations, e.g. a home gateway serving a single home. In fact, a
compromise could be to assume that there is a default interface
specified as part of the association, but that the default can be
overridden on a command by command basis.

-- Christian Huitema

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---

From: Scott Brim <[email-masked]>
Date: Wed, 19 Sep 2001 13:48:40 -0400

> mention of addresses should be qualified with a mention of the scope.

Yes.

> in crosses the interface.

I thought we already determined that it would be hard for agents to know
which interface to use and how to name them.  But anyway ...

> overridden on a command by command basis.

Interesting idea.  

Small devices like your two-interface home network box are easily
handled by the inandout informant address scheme.  Set the informant
address to all ones and set the "outside okay" flag or not, depending on
what you want to do.  

In order to associate a default interface with a middlebox (or an only
interface), the middlebox still needs a way to specify that interface.
How would the middlebox get the information it needs to do that?

..Scott