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Middlebox Communication

Document Charter Middlebox Communication WG (midcom)
Title Middlebox Communication
Last updated 2008-03-26
State Approved
WG State Concluded
IESG Responsible AD David Harrington
Charter edit AD (None)
Send notices to (None)


As trusted third parties are increasingly being asked to make policy
decisions on behalf of the various entities participating in an
application's operation, a need has developed for applications to be
able to communicate their needs to the devices in the network that
provide transport policy enforcement. Examples of these devices
include firewalls, network address translators (both within and
address families), signature management for intrusion detection
systems, and multimedia buffer management. These devices are a subset
of what can be referred to as 'middleboxes.'

This working group will focus its attention on communication with
firewalls and network address translators (including translation
between IPv6 and IPv4). Work will not preclude extensibility to other
categories of middle box.

Decomposing applications requiring policy decisions by removing
application logic from the middle box and instead providing a
generalized communications interface provides a number of benefits,
including improved performance, lower software development and
maintenance costs, improved ability to support traversal of packet
filters by complex protocols, easier deployment of new applications,
and the ability to consolidate management functions. For example, by
moving stateful inspection of protocols such as H.323 and SIP out
of firewalls, it is possible to improve performance and scalability
reduce development and costs.

This working group will concern itself with an environment that
consists of:

  • one or more middle boxes in the data path

  • an external requesting entity

  • a policy entity for consultation purposes when the
    requesting entity is untrusted.

The requesting entity may be trusted or untrusted. In the case where
is trusted, the middle box will treat the request from the entity as
authoritative. In the case where it is not trusted, the intermediate
device will have to verify that it is authorized to complete the
request. That authorization could come from a separate or a built in
policy server.

The primary focus of the working group will be the application of this
architecture to communicating requests between applications and
firewalls or NATs. This will not preclude other uses, and care will be
taken to ensure that the protocol is extensible.

The working group will evaluate existing IETF protocols for their
applicability to this problem, using the framework and requirements
documents developed during the working group's first phase as criteria
for the evaluation. If a protocol is found to be suitable it will be
used as the basis for the development of a middlebox communication
protocol. In the unlikely case that one is not found to be suitable,
the working group will undertake development of a new protocol.

Discovery of middle boxes is out of scope.

The deliverables will be

o a document evaluating existing IETF protocols for their

o a document specifying a middlebox communication protocol
or profile based on the results of the protocol evaluation.

This working group will only deal with firewalls and network
address translators.

Ubiquitous deployment of midcom in all middleboxes could take many
years. In the interim, a solution is needed that allows applications
operate in the presence of midcom-unaware middleboxes. To support
the midcom group will develop or document a protocol or approach that
allows clients to indirectly obtain address bindings from midcom-
unaware middleboxes, through communications with server elements on
public side of the middlebox. The key goals for this effort are rapid
delivery of a simple solution (since it is an interim solution),
consistency with the midcom framework, and security. In particular,
proposed interim approaches will address (and document) the
architectural and pragmatic concerns described in [UNSAF].