MIDCOM Working Group C.Aoun
Internet Draft S.Sen
Category: Informational Nortel Networks
Expires on February 2001 August 2001
Required Information in Midcom Agents
<draft-aoun-midcom-agent-information-00.txt>
Status of this Memo
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Abstract
This draft is part of a gladiator contest within the MIDCOM WG to
determine what network topology information is needed at the Midcom agent.
By taking out application awareness from Middle Boxes in the
networks, and keeping this application knowledge in the application
devices (the Midcom Agents); sufficient information needs to be put
in the Midcom Agent to allow them to fulfill their responsibility.
Table of Contents
Abstract...........................................................1
1 Introduction.....................................................2
2 Conventions used in this document................................2
3 Used Terminology in the draft....................................2
4 Middle Box examples and Midcom requirements......................2
4.1 Middle Boxes connected to two address realms...................3
Internet Draft Required information in Midcom Agents August 2001
4.2 Middle Boxes connected networks having overlapped addresses....5
4.3 Multi-homed Middleboxes acting as media proxies...............6
5 Summary..........................................................6
6 References.......................................................6
7 Acknowledgments..................................................7
8 Author's Address.................................................7
9 Intellectual Property Statement..................................7
10 Full Copyright Statement........................................8
1 Introduction
The Midcom Agent (MA) should have sufficient information to request
the Middle Box to open pinholes or perform NAT binds or other
specific actions on packet flows.
This draft presents several types of Middle Boxes that could be
deployed in networks and the type of information that a MA needs
to have to perform it's tasks properly.
2 Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC-2119.
3 Used Terminology in the draft
If : an interface, it could be logical (ATM VC, FR DLCI, PPP
variants, IPSEC tunnel...) or physical.
Overlapped address networks: Networks having overlapping addresses
Loopback address: Address that is not linked to an interface
4 Middle Box examples and Midcom requirements
This section describes several Middle Boxes (MB) that are deployed
in networks:
- Middle Box connected to two address realms (that don't have
overlapped addresses).
- Middle Box connected to networks having overlapped addresses.
- Multi-homed Middle Box acting as a media proxy.
The first category include the residential and enterprise Middle
Boxes, the second includes the Provider Provisioned Middle Boxes or
other Middle Boxes interfacing networks that have overlapped
addresses and the third includes, for example, RTP Proxies that are
commonly used to allow VoIP media to pass through a firewall which
does not have application awareness nor supporting Midcom
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4.1 Middle Boxes connected to two address realms
++++++++++++++++++++
+ Customer If1 +
+ network +++++---+ o o o o o o +++++++++++++++++++
+ +MB1+If2+-------o o +Telephony Service+
+ If5----+++++ + oThe Internet o------+ Provider +
+ If4-----/ + + o o o o o o o + ++++ +
+ If3---+ + + +MA+ +
++++++++++++++++++ + ++++ +
+++++++++++++++++++
This example covers Middle Boxes that can have two (or more)
interfaces and connected to 2 address realms (the
enterprise realm and the public realm).
The example MB has 5 interfaces. 3 of the interfaces (could be
one in case of a 2 interfaces MB)are used to connect internal hosts
(if3,4,5) and 2 interfaces (could just be one in case of 2 interface
Middle Box)are used to connect to the customer's ISP (if1,2).
This MB is similar to all existing MB implementations, in that MB
packet filtering profiles are bounded to interfaces.
In the case of the NAT function, the profile is unique to the MB.
For packet filters, 2 profiles may exist: one for the egress and one for
ingress.
We shall not consider other networks (the model will still be
unchanged) since the purpose of the draft is to determine what
information the Midcom Agent requires to allow particular flows to
traverse a Middle Box.
Primary things the Midcom Agent needs to know when it needs to ask a
particular MB to apply certain tasks on a flow:
-Which MB the application flows will be traversing, this is
currently out of scope of the MIDCOM WG
-How to address the MB (loopback address or another reachable
address)
-Provide a matching or filter expression to enable the MB to
identify the flow
-Which tasks or queries to execute (Open a pinhole, get a BIND ...)
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What about the interface and the direction?
The direction information is relevant to the direction of the
packets on the interfaces (coming in or going out of the interface).
When the MA will send the Midcom message, it will contain a flow
matching expression and the action to apply to the flow. The MB will
know which profile to update (i.e. which interface is traversed and
which direction).
The direction is implied by the source and destination contained in
the flow matching expression.
The routing software could determine based on the routing table,
which interface the packets may traverse; the rule will then be
added to the proper MB function profile.
If the packet might traverse several interfaces the rule will be set
on all the related profiles.
There is a potential ambiguity when the source of the flow is not
known.
Typically this is the case of VoIP applications where the receiver
is known but not the sender (initially since not included in the
SDP).
In this case, all packet filter profiles need to be appended with
the new rule (including packet filters that are bounded to if3,4
&5).
Alternatively an optional parameter within the matching expression
could be used to express the directionality of the flow.
As an example:
-WAN could mean that the flow is from devices external to the
network (i.e. limiting the packet filter profiles to the ingress
ones of If1 & If2)
-LAN could mean that the flow is from devices internal to the
network (i.e. limiting the packet filter profiles to the ones of
if3,4,5)
The usage of "LAN" could address certain enterprise networks where
packet filters are introduced between certain departments (case
where packet filter profiles on internal interfaces require to be
updated with new rule set).
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4.2 Middle Boxes connected networks having overlapped addresses
Provider provisioned middle boxes addresses subscribers that have
outsourced their Middle Box services to their Internet Service
Providers (ISP).
This example shows 2 customer networks that are provided:
- The Internet connectivity service by the same ISP
- Their telephony service by either the same or different
Telephony Service Provider (TSP)
+++++++++++++ +++++++++++++
+ + If1 +ISP +
+Cust A +--------------+--++++++ +
+ 10/8 + If2 + + MB1+ + If3 o o o o
+++++++++++++ ----+--+ +---+----o o
/ + ++++++ +\
/ +++++++++++++ \ o Internet o
/ If4 \- o
/ o o o o o
++++++++++ / +
+ + / +
+Cust B +------- +
+ 10/8 + +++++++++++++
++++++++++ +TSP +
+ ++++ +
+ +MA+ +
+ ++++ +
+++++++++++++
The main difference between the previous example and this one is
that the physical MB, is subdivided into several logical MBs.
Each logical MB has it's own interfaces and MB function profiles.
The logical MBs need to be addressed with separate identifiers.
This is separate from the loop address which was discussed previously.
To communicate with the logical MB, the MA will require to use the logical
MB's identifier within the Midcom protocol.
There is potentially another variant in which even the logical
Middle Box could be connected to "overlapped addresses" networks.
In this case, the Midcom Agent will need to inform the Middle Box
about the address's realm (either source or destination)of the
specified flow.
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Both Middle Box identifier and the realm identifier should be
optional parameters in the Midcom protocol.
Apart from the previous, the information required for the MA and
provided to the MB via the Midcom protocol is similar to 3.1
4.3 Multi-homed Middleboxes acting as media proxies
+++++++++++++ +++++++++++++
+ + If1 +ISP +
+ A +--------------+--++++++ +
+ private + If2 + + MB1+ + If3 o o o o
+++++++++++++ ----+--+ +---+----o o
/ + ++++++ +\
/ +++++++++++++ \ o Internet o
/ /If5 If4 \- o
/
/ o o o o o
++++++++++ / /
+ B + / ++++++++++
+private +------- + C +
++++++++++ +private +
++++++++++
This case can be considered a special case of the scenario depicted
in Section 4.2. The MB1 in the above figure is a multi-homed RTP
Proxy (which terminates an RTP session in one interface and
initiates a new one from the other interface). Assume that networks
A, B and C contain private IP addresses, which overlap. To allow a
VoIP session through the Proxy, we need allocation of either two
private IP addresses (if a call is made between networks A, B or C),
or a private IP address and a public IP address (if a call is made
between an endpoint in networks A/B/C and an endpoint in the public
Internet). In this case the Agent needs to specify the interface (or
realm) through which the media will traverse the MB in order to make
the MB assign IP addresses and perform proper binding of the RTP
media with the interface.
5 Summary
The main issue to resolve while deploying Midcom enabled Middle
Boxes will be on providing the MB presence on the path of the flows
to the MAs.
Manual configuration will be a BIG operational burden on the
application service providers, and will not be the most common
solution (ref [DSCVRYCA]).
Extending the syntax to allow the MA to address properly a MB
(logical or physical) or to provide a proper flow filtering
expression is not a complicated issue.
The Middle Box discovery is still a key piece of the puzzle.
6 References
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[MDCMFRWK]P.Srisuresh,J.Kuthan, J.Rosenberg," MIDCOM Architecture
& Framework",
Internet draft, draft-ietf-midcom-framework-03.txt
[MDCMREQ] R.Swale, P.Mart, P.Sijben, " Middlebox Control (MIDCOM)
Protocol Architecture and Requirements",
Internet draft, draft-ietf-midcom- requirements-02.txt
[DSCVRYCA] C.Aoun, " Network topology considerations in
the MIDCOM Architectural framework",
Internet draft, draft-aoun-midcom-network-00.txt
7 Acknowledgments
The author would like to thank the following people for their useful
comments and suggestions related to this draft: Louis-Nicolas Hamer,
Julian Mitchell, Mick O'Doherty and others in Nortel Networks.
8 Author's Address
Cedric Aoun
Nortel Networks
33 Quai Paul Doumer
Paris La Defense
92415 Courbevoie Cedex
France
Email: cedric.aoun@nortelnetworks.com
Sanjoy Sen
Nortel Networks
2375 N. Glenville Drive, Building B,
Richardson, TX-75082
USA
E-mail: sanjoy@nortelnetworks.com
9 Intellectual Property Statement
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The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
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rights which may cover technology that may be required to practice
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10 Full Copyright Statement
Copyright (C) The Internet Society (2000). All Rights Reserved.
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