Midcom Working Group R P Swale
Internet Draft BTexact Technologies
November 2001 P A Mart
Expires May 2002 Marconi Communications
P Sijben
Lucent Technologies
Scott Brim
Melinda Shore
Cisco Systems
Middlebox Communications (midcom) Protocol Requirements
<draft-ietf-midcom-requirements-03.txt>
Status of this Memo
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Abstract
This document specifies the requirements that the Middlebox Commu-
nication (midcom) protocol must satisfy in order to meet the needs
of applications wishing to influence middlebox function. These
requirements were developed with a specific focus on network
address translation and firewall middleboxes.
Swale et al. Internet Draft [Page 1]
Midcom Requirements October 2001
1. Introduction
This document is one of two developed by the Middlebox Communica-
tion (midcom) working group to address the requirements and frame-
work for a protocol between middleboxes and "midcom agents." This
document presents midcom requirements; [MCFW] presents the context
and framework. That document also presents terminology and defini-
tions and should be read in tandem with this one.
These requirements were developed by examining the midcom framework
and extracting requirements, both explicit and implicit, that
appeared there.
2. Requirements
Each requirement is presented as a statement, followed by brief
explanatory material as appropriate. Terminology is defined in
[MCFW]. There may be overlap between requirements.
2.1. Protocol machinery
2.1.1.
The Midcom protocol must enable a Midcom agent requiring the ser-
vices of a middlebox to establish an authorized association between
itself and the middlebox.
This states that the protocol must allow the middlebox to identify
an agent requesting services and make a determination as to whether
or not the agent will be permitted to do so.
2.1.2.
The Midcom protocol must allow a Midcom agent to communicate with
more than one middleboxe simultaneously.
In any but the most simple network, an agent is likely to want to
influence the behavior of more than one middlebox. The protocol
design must not preclude the ability to do this.
2.1.3.
The Midcom protocol must allow a middlebox to communicate with more
than one Midcom agent simultaneously.
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Midcom Requirements October 2001
There may be multiple instances of a single application or multiple
applications desiring service from a single middlebox. The proto-
col design must not preclude the ability to do so.
2.1.4.
Where a multiplicity of Midcom Agents are interacting with a given
middlebox, the Midcom protocol must provide mechanisms ensuring
that the overall behavior is deterministic.
The states that the protocol must include mechanisms for avoiding
race conditions or other situations in which the requests of one
agent may influence the results of the requests of other agents in
an unpredictable manner.
2.1.5.
The Midcom protocol must enable the middlebox and any associated
Midcom agents to establish known and stable state. This must
include the case of power failure, or other failure, where the pro-
tocol must ensure that any resources used by a failed element can
be released.
This states that the protocol must provide identifying clear iden-
tification for requests and results and that protocol operations
must be atomic with respect to the midcom protocol.
2.1.6.
The middlebox must be able to report its status to a Midcom agent
with which it is associated.
2.1.7.
The protocol must support unsolicited messages from middlebox to
agent, for reporting conditions detected asynchronously at the mid-
dlebox.
It may be the case that exceptional conditions at the middlebox
(resource shortages, intrusion mitigation) will cause the middlebox
to close pinholes or release resources without consulting the asso-
ciated Midcom agent. In that event the protocol must allow the
middlebox to notify the agent.
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Midcom Requirements October 2001
2.1.8.
The Midcom protocol must provide for the mutual authentication of
Midcom agent and middlebox to one another.
In addition for the more obvious need for the Midcom agent to
authenticate itself to the middlebox, there are some attacks
against the protocol which can be mitigated by having the middlebox
authenticate to the agent. See [MCFW].
2.1.9.
The Midcom protocol must allow either the Midcom agent or the mid-
dlebox to terminate the Midcom session between a Midcom Agent and a
middlebox. This allows either entity to close the session for
maintenance, security or other reasons.
2.1.10.
A Midcom agent must be able to determine whether or not a request
was successful.
This states that a middlebox must return a success or failure indi-
cation to a request made by an agent.
2.1.11.
The Midcom protocol must contain version interworking capabilities
to enable subsequent extensions to support different types of mid-
dlebox and future requirements of applications not considered at
this stage.
We assume that there will be later revisions of this protocol. The
initial version will focus on communication with firewalls and
NATs, and it is possible that the protocol will need to be modified
as support other middlebox types is added. These version inter-
working capabilities may include (but not be limited to) a protocol
version number.
2.1.12.
It must be possible to deterministically predict the behavior of
the middlebox in the presence of overlapping rules.
By "overlapping" we refer to rulesets that may be subsets or super-
sets of other rulesets. Rulesets that partially overlap other
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Midcom Requirements October 2001
rulesets can create nondeterministic behavior and must not be per-
mitted.
2.2. Midcom Protocol Semantics
2.2.1.
The syntax and semantics of the Midcom protocol must be extensible
to allow the requirements of future applications to be dopted.
This is related to, but different from, the requirement for ver-
sioning support. As support for additional middlebox types is
added there may be a need to add new message types.
2.2.2.
The Midcom protocol must support the ability of an agent to install
a ruleset that governs multiple types of middlebox actions (e.g.
firewall and NAT).
This states that a the protocol must support rules and actions for
a variety of types of middleboxes. A Midcom agent ought to be able
to have a single Midcom connection with a middlebox and use the
Midcom interface on the middlebox to interface with different mid-
dlebox functions on the same middlebox interface.
2.2.3.
The protocol must support the concept of a ruleset group comprising
a multiple of individual rulesets to be treated as an aggregate.
Applications using more than one data stream may find it more con-
venient and more efficient to be able to use single messages to
tear down, extend, and manipulate all middlebox rulesets being used
by one instance of the application.
2.2.4.
The protocol must allow the midcom agent to extend the lifetime of
an existing ruleset that otherwise would be deleted by the middle-
box.
2.2.5.
If a peer does not understand an option it must be clear whether
the action required is to proceed without the unknown attribute
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Midcom Requirements October 2001
being taken into account or the request is to be rejected. Where
attributes may be ignored if not understood, a means may be pro-
vided to inform the client about what has been ignored.
This states that failure modes must be robust, providing sufficient
information for the agent or middlebox to be able to accomodate the
failure or to retry with a new option that is more likely to suc-
ceed.
2.2.6.
To enable management systems to interact with the Midcom environ-
ment, the protocol must include failure reasons that allow the Mid-
com Agent behaviour to be modified as a result of the information
contained in the reason. Failure reasons need to be chosen such
that they do not make an attack on security easier.
2.2.7.
The Midcom protocol must not preclude multiple authorized agents
from working on the same ruleset.
2.2.8.
The Midcom protocol must be able to carry filtering rules, includ-
ing but not limited to the 5-tuple, from the midcom agent to the
middlebox.
By "5-tuple" we refer to the standard <source address, source port,
destination address, destination port, transport protocol> tuple.
Other filtering elements may be carried, as well.
2.2.9.
When the middlebox performs a port mapping function, the protocol
should allow the Midcom agent to request that the external port
number have the same oddity as the internal port.
This requirement is to support RTP and RTCP [RFC1889] "oddity"
requirements.
2.2.10.
When the middlebox performs a port mapping function, the protocol
should allow the Midcom agent to request that a consecutive range
of external port numbers be mapped to consecutive internal ports.
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Midcom Requirements October 2001
This requirement is to support RTP and RTCP "sequence requirements.
2.2.11.
It should be possible to define rulesets that contain a more spe-
cific filter spec than an overlapping ruleset. This should allow
agents to request actions for the subset that contradict those of
the overlapping set.
This should allow Midcom agent to request to a Midcom server con-
trolling a firewall function that a subset of the traffic that
would be allowed by the overlapping ruleset be specifically disal-
lowed.
2.3. General Security Requirements
2.3.1.
The Midcom protocol must provide for message authentication, confi-
dentiality, and integrity.
2.3.2.
The Midcom protocol must allow for optional confidentiality protec-
tion of control messages. If provided the mechanism should allow a
choice in the algorithm to be used.
2.3.3.
The Midcom protocol must operate across un-trusted domains between
the Midcom agent and middlebox in a secure fashion.
2.3.4.
The Midcom protocol must define mechanisms to mitigate replay
attacks on the control messages.
3. References
[MCFW] Srisuresh, S. et al. "Middlebox Communication Architecture and
framework," work in progress. October 2001.
[RFC1889] Schulzrinne, H. et al. "RTP: A Transport Protocol for Real-
Time Applications," RFC 1889. January 1996.
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Midcom Requirements October 2001
[RFC2026] Bradner, S. "The Internet Standards Process -- Revision 3,"
RFC 2026. October 1996.
Authors' Addresses
Richard Swale
BTexact Technologies
Callisto House
Adastral Park
Ipswich United Kingdom
Email: richard.swale@bt.com
Paul Sijben
Lucent Technologies EMEA BV
Huizen
Netherlands
Email: sijben@lucent.com
Philip Mart
Marconi Communications Ltd.
Edge Lane
Liverpool
United Kingdom
Email: philip.mart@marconi.com
Scott Brim
Cisco Systems
146 Honness Lane
Ithaca, NY 14850
Email: sbrim@cisco.com
Melinda Shore
Cisco Systems
809 Hayts Road
Ithaca, NY 14850
Email: mshore@cisco.com
Copyright
The following copyright notice is copied from RFC 2026 [RFC2026]
Section 10.4, and describes the applicable copyright for this docu-
ment.
Swale et al. Internet Draft [Page 8]
Midcom Requirements October 2001
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Swale et al. Internet Draft [Page 10]
