Subject: Re: [midcom] Topology considerations documents

From: "Bob Penfield" <[email-masked]>
Date: Fri, 7 Sep 2001 10:02:30 -0400

OK, let's try an example.

   +---------+                  MB
   | Realm A +---\             +---+     +----------+
   +---------+   +---+ VLAN1   |  (2)----+          |
                 |L2X+========(1)  | WAN | Realm SP |
   +---------+   +---+ VLAN2   |  (3)----+          |
   | Realm B +---/             +---+     +----------+
   +---------+

Here's a middlebox connected to 3 networks (realms). It has 3 physical
interface (1), (2), and (3). Realms A and B are connected to a Layer 2
switch (L2X) which aggregates/multiplexes the 2 LANs over a single ethernet
connection to (1) using VLAN tags. Interfaces (2) and (3) both connect to
the SP network for redundancy. There are 3 "logical" interfaces: VLAN1 and
VLAN2 on physical interface (1) and WAN on physical interfaces (2)&(3).
These logical interfaces are equivalent to the realm they connect to. The
realm is at the other end of the logical pipe. Thus VLAN1=Realm A,
VLAN2=Realm B, and WAN=Realm SP.

I basically agree with Andrew that what were are trying to communicate to
the middlebox is which interfaces the flow goes in/out of the middlebox.
What I'm trying to illustrate above is that it is not physical interface,
but logical interface that needs to be communicated in MIDCOM. Now if we
want to call this logical interface (or even interface for short), that's
fine with me.

The middlebox owns the namespace for these logical interfaces. There is no
need for a global or universal namespace. Only the midcom agents that talk
to the middlebox need to be aware of the names/identifiers to use. Agents
that need to differentiate the identifiers of multiple middleboxes COULD use
the IP address or FQDN of the middlebox.

(-:bob

Robert F. Penfield
Chief Software Architect
Acme Packet, Inc.
130 New Boston Street
Woburn, MA 01801
[email-masked]

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---

From: Scott Brim <[email-masked]>
Date: Thu, 13 Sep 2001 13:23:48 -0400

>    | Realm B +---/             +---+     +----------+

OK, so the middlebox that you are trying to control owns the naming of
the realms it is attached to.

- How is that naming communicated to agents so they know which realm
  they are in?  What if it changes?

- Since not all application proxies will be agents, how does an existing
  application proxy find out the naming, so that it can know which realm
  it is in and communicate it to your agent+proxy?  What if it changes?
  Note you need a scheme that works for all current and future
  application proxies that do session control, not just SIP.

- If you have more than one middlebox connecting two realms, how do you
  get them to agree on the naming?  If they don't, then how does an
  application proxy know which naming scheme to use when talking to your
  agent?

I'm not after nicely engineered solutions, but I want an existence proof
that something robust, scalable, and securable is possible.

The method Adina and I proposed requires none of this.

..Scott