Internet Draft M. Barnes
Document: draft-ietf-midcom-protocol-eval-02.txt Editor
Category: Informational Nortel Networks
Expires: December, 2002 June 28, 2002
Middlebox Communications (MIDCOM) Protocol Evaluation
Status of this Memo
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Abstract
This document provides an evaluation of the applicability of SNMP,
RSIP, MEGACO, DIAMETER and COPS as the MIDCOM protocol. A summary
of each of the proposed protocols against the MIDCOM requirements
and the MIDCOM framework is provided. Compliancy of each of the
protocols against each requirement is detailed. A conclusion
summarizes how each of the protocols fares in the evaluation.
Table of Contents
1 Protocol Proposals.............................................2
1.1 SNMP......................................................2
1.2 RSIP......................................................3
1.3 MEGACO....................................................5
1.4 DIAMETER..................................................6
1.5 COPS......................................................7
2 Item Level Compliance Evaluation...............................8
2.1 Protocol machinery........................................8
2.2 Protocol semantics.......................................14
2.3 General Security Requirements............................20
3 Conclusions...................................................22
Security Considerations.........................................23
Normative References............................................23
Appendix A - SNMP Overview......................................26
Appendix B - RSIP with tunneling................................27
Appendix C - MEGACO Modeling Approach...........................28
Appendix D - DIAMETER IPFilter Rule.............................29
Intellectual Property Statements................................32
Full Copyright Statement........................................32
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Overview
This document provides an evaluation of the applicability of SNMP,
RSIP, MEGACO, DIAMETER and COPS as the MIDCOM protocol. This
evaluation provides overviews of the protocols and general
statements of applicability based upon the MIDCOM framework [2] and
requirements [1] documents.
The process for the protocol evaluation was fairly straightforward
as individuals volunteered to provide an individual draft
evaluating a specific protocol. Thus, some protocols that might be
considered as reasonably applicable as the MIDCOM protocol are not
evaluated in this document since there were no volunteers to
champion the work. The individual protocol documents for which
there were volunteers were submitted for discussion on the list
with feedback being incorporated into an updated draft. The
updated versions of these drafts formed the basis for the content
of this WG document.
Section 1 contains a list of the proposed protocols submitted for
the purposes of the protocol evaluation with some background
information on the protocols and similarities and differences with
regards to the applicability to the framework [2] provided.
Section 2 provides the item level evaluation of the proposed
protocols against the Requirements [1].
In order for this document to serve as a complete evaluation of the
protocols, some of the background information and more detailed
aspects of the proposals documenting enhancements and applications
of the protocols to comply with the MIDCOM framework and
requirements are included in Appendices.
1 Protocol Proposals
The following protocols were submitted to the MIDCOM WG for
consideration:
o SNMP
o RSIP
o MEGACO
o DIAMETER
o COPS
The following provides an overview of each of the protocols and the
applicability of each protocol to the MIDCOM framework [2].
1.1 SNMP
A general overview of SNMP is provided in Appendix A. The
following provides a general statement with regards to the
applicability of SNMP as the MIDCOM protocol and some specifics
with regards to existing support for NAT and Firewall Control.
Section 1.1.3 addresses the differences between the SNMP framework
and the MIDCOM framework.
1.1.1 SNMP General Applicability
The primary advantages of SNMP compared to other protocols
evaluated are that it is a mature, well understood protocol
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currently deployed in various scenarios. In addition, mature
toolsets are available for SNMP managers and agents. SNMP is mainly
used for monitoring rather than for configuring network nodes,
however, thus reducing its applicability to MIDCOM.
1.1.2 SNMP Existing Support for NAT and Firewall Control
For configuring NATs, there is currently a NAT MIB module [NAT-MIB]
under development by the NAT WG. The NAT MIB module meets all of
the Midcom requirements concerning NAT control with the exception
of grouping of policy rules (requirement 2.2.3.). In order to
support this an additional grouping table in the NAT MIB module is
required.
Existing work for firewall control with SNMP only considered the
monitoring of firewalls and not the configuration. Further work is
required towards the development of MIBs for configuring firewalls.
1.1.3 Architectural Differences between SNMP and MIDCOM
The SNMP management framework provides functions equivalent to
those defined by the Midcom framework, although there are a few
architectural differences.
The roles of entities participating in SNMP communication are
called Manager and Agent. The SNMP use of the term agent is
different from its use in the Midcom framework: The SNMP Manager
corresponds to the Midcom agent and the SNMP Agent corresponds to
the Middlebox.
Although the SNMP management framework does not have the concept of
a session, session-like associations can be established through the
use of managed objects. In order to implement the Midcom protocol
based on SNMP, a Midcom MIB module is required. All requests from
the Midcom agent to the Middlebox would be performed using write
access to managed objects defined in the Midcom MIB module. Replies
to requests are signaled by the Middlebox (SNMP agent), by
modifying the managed objects. The Midcom agent (SNMP manager) can
receive this information by reading or polling, if required, the
corresponding managed object.
1.2 RSIP
1.2.1 Framework elements in common to MIDCOM and RSIP
The following framework elements are common to MIDCOM and RSIP
listed by their MIDCOM names, with the RSIP name indicated in
parenthesis:
o Hosts
o Applications
o Middleboxes (RSIP gateways)
o Private domain (private realm)
o External domain (public realm)
o Middlebox communication protocol (RSIP)
o MIDCOM agent registration (host registration)
o MIDCOM session (RSIP session)
o MIDCOM Filter (local / remote address and port number(s) pairs)
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1.2.2 MIDCOM Framework elements not supported by RSIP
The following MIDCOM framework elements are not supported by RSIP:
o Policy actions and rules. RSIP always implicitly assumes a
permit_action. To support MIDCOM, a more general and explicit
action parameter would have to be defined. RSIP requests
specifying local / remote address and port number(s) pairs would
have to be extended to include an action parameter, in MIDCOM
rules.
o Applications/MIDCOM agents. RSIP makes no distinction between
applications and agents; address assignment operations can be
performed equally by applications and agents.
o Policy Decision Points. RSIP assumes that middleboxes grant or
deny requests with reference to a policy known to them; the
policy could be determined jointly by the middlebox and a policy
decision point; such joint determination is not addressed by the
RSIP framework but not precluded by it.
1.2.3 RSIP Framework elements not supported by MIDCOM
The following elements are unique to the RSIP framework. If RSIP
were adopted as the basis for the MIDCOM protocol, they could be
added to the MIDCOM framework:
o RSIP client: that portion of the application (or agent) that
talks to the RSIP gateway using RSIP.
o RSIP server: that portion of an RSIP gateway that talks to
applications using RSIP.
o RSA-IP (Realm Specific Address IP) and RSAP-IP (Realm Specific
Address and Port IP): RSIP distinguishes between filters that
include all ports on an IP address and those that do not.
o Demultiplexing Fields: Any set of packet header or payload fields
that an RSIP gateway uses to route an incoming packet to an RSIP
host. RSIP allows a gateway to perform, and an application to
control, packet routing to hosts in the private domain based on
more than just IP header fields.
o Host-to-middlebox tunnels: RSIP assumes that data communicated
between a private realm host and a public realm host is
transferred through the private realm by a tunnel between the
inner host and the middle box, where it is converted to and from
native IP based communications to the public realm host.
1.2.4. Comparison of MIDCOM and RSIP frameworks
RSIP with tunneling, has the advantage that the public realm IP
addresses and port numbers are known to the private realm host
application, and therefore no translation if needed for protocols
such as SDP, the FTP control protocol, RTSP, SMIL, etc.. However,
this does require that an RSIP server and a tunneling protocol be
implemented in the middlebox and an RSIP client and the tunneling
protocol be implemented in the private realm host. The host
modifications can generally be made without modification to the
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host application or requiring the implementation of a host
application agent. This is viewed as a significant advantage over
NAT (Network Address Translation).
Further details on the evaluation of RSIP with regards to tunneling
in the context of NAT support are available in Appendix B of this
document.
1.3 MEGACO
1.3.1 Megaco Architectural Model
Megaco [25] is a master-slave, transaction-oriented protocol in
which Media Gateway Controllers (MGC) control the operation of
Media Gateways (MG). Originally designed to control IP Telephony
gateways, it is used between an application-unaware device (the
Media Gateway) and an intelligent entity (the Media Gateway
Controller) having application awareness.
The Megaco model includes the following key concepts:
1. Terminations: Logical entities on the MG that act as sources or
sink of packet streams. Can be physical or ephemeral. A Termination
is associated with a single MGC.
2. Context: An association between Terminations for sharing media
between the Terminations. Terminations can be added, subtracted
from a Context and can be moved from one Context to another. A
Context and all of the Terminations it contains are associated with
a single MGC.
3. Virtual Media Gateways: A physical MG can be partitioned into
multiple virtual MG's allowing multiple Controllers to interact
with disjoint sets of Contexts/Terminations within a single
physical device.
4. Transactions/Messages: Each Megaco command applies to one
Termination within a Context and generates a unique response.
Commands may be replicated implicitly so that they act on all
Terminations of a given Context through wildcarding of Termination
identifiers. Multiple commands addressed to different Contexts can
be grouped in a Transaction structure. Similarly, multiple
Transactions can be concatenated into a Message.
5. Descriptors/Properties: A Termination is described by a number
of characterizing parameters or Properties, which are grouped in a
set of Descriptors that are included in commands and responses.
6. Events and signals: A Termination can be programmed to perform
certain actions or to detect certain events and notify the Agent.
7. Packages: Packages are groups of properties, events, etc.
associated with a Termination. Packages are simple means of
extending the protocol to serve various types of devices or
Middleboxes.
1.3.2 Comparison of the Megaco and Midcom Architectural Frameworks
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In the Midcom architecture, the Middlebox plays the role of an
application-unaware device being controlled by the application-
aware Agent. In the Megaco architecture, the Media Gateway
controller serves a role similar to the the Midcom Agent (MA) and
the Media Gateway serves a role similar to the Middlebox (MB).
1.4 DIAMETER
1.4.1 Diameter Architecture
Diameter is designed to support AAA for network access. It is
meant to operate through networks of Diameter nodes, which both act
upon and route messages toward their final destinations. Endpoints
are characterized as either clients, which perform network access
control, or servers, which handle authentication, authorization and
accounting requests for a particular realm. Intermediate nodes
perform relay, proxy, redirect, and translation services. Design
requirements for the protocol [29] include robustness in the face
of bursty message loads and server failures, resistance to specific
DOS attacks and protection of message contents, and extensibility
including support for vendor-specific attributes and message types.
The protocol is designed as a base protocol to be supported by all
implementations, plus extensions devoted to specific applications.
Messages consist of a header and an aggregation of "Attribute-Value
Pairs (AVPs)", each of which is a tag-length-value construct. The
header includes a command code, which determines the processing of
the message and what other AVP types must or may be present. AVPs
are strongly typed. Some basic and compound types are provided by
the base protocol specification, while others may be added by
application extensions. One of the types provided in the base is
the IPFilterRule, which may be sufficient to express the Policy
Rules that Midcom deals with.
Messaging takes the form of request-answer exchanges. Some
exchanges may take multiple round-trips to complete. The protocol
is connection-oriented at both the transport and application
levels. In addition, the protocol is tied closely to the idea of
sessions, which relate sequences of message exchanges through use
of a common session identifier. Each application provides its own
definition of the semantics of a session. Multiple sessions may be
open simultaneously.
1.4.2 Comparison of DIAMETER With MIDCOM Architectural Requirements
The Midcom Agent does not perform the functions of a Diameter
client, nor does the Middlebox support the functions of a Diameter
server. Thus the Midcom application would introduce two new types
of endpoints into the Diameter architecture. Moreover, the Midcom
requirements do not at this time imply any type of intermediate
node.
A general assessment might be that Diameter meets and exceeds
Midcom architectural requirements. The connection orientation may
be too heavy for the number of relationships the Middlebox must
support. Certainly the focus on extensibility, request-response
messaging orientation, and treatment of the session, are all well-
matched to what Midcom needs. At this point, MIDCOM is focused on
simple point-to-point relationships, so the proxying and forwarding
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capabilities provided by Diameter are not needed. Most of the
commands and AVPs defined in the base protocol are also surplus to
MIDCOM requirements.
1.5 COPS
Within the context of this document, COPS and COPS-PR have similar
compliancy with regards to the MIDCOM protocol requirements, with
the only major difference being how MIDCOM policy rules attributes
are described with COPS MIDCOM client specific objects or with
COPS-PR MIDCOM PIB attributes. Thus, the evaluation takes into
account both COPS and COPS-PR. If COPS is deemed the most suitable
protocol for MIDCOM, the feasibility and complexity of the creation
and usage of COPS MIDCOM client specific objects versus the COPS-PR
MIDCOM specific PIBs should be compared. Thus, references to COPS
are applicable to both COPS and COPS-PR.
1.5.1 COPS protocol architecture
COPS is a simple query and response protocol that can be used to
exchange policy information between a policy server (Policy
Decision Point or PDP) and its clients (Policy Enforcement Points
or PEPs). COPS was defined to be a simple and extensible protocol.
The main characteristics of the COPS includes the following:
1. The protocol employs a client/server model. The PEP sends
requests, updates, and deletions to the remote PDP and the PDP
returns decisions back to the PEP.
2. The protocol uses TCP as its transport protocol for reliable
exchange of messages between policy clients and a server.
3. The protocol is extensible in that it is designed to leverage
self-identifying objects and can support diverse client specific
information without requiring modification to the COPS protocol
itself. The protocol was created for the general administration,
configuration, and enforcement of policies.
4. COPS provides message level security for authentication, replay
protection, and message integrity. COPS can make use of existing
protocols for security such as IPSEC [IPSEC] or TLS to authenticate
and secure the channel between the PEP and the PDP.
5. The protocol is stateful in two main aspects:
(1) Request/Decision state is shared and kept synchronized in a
transactional manner between client and server. Requests from the
client PEP are installed or remembered by the remote PDP until they
are explicitly deleted by the PEP. At the same time, Decisions from
the remote PDP can be generated asynchronously at any time for a
currently installed request state.
(2) State from various events (Request/Decision pairs) may be
inter-associated. The server may respond to new queries differently
because of previously installed, related Request/Decision state(s).
6. The protocol is stateful in that it allows the server to push
configuration information to the client, and then allows the server
to remove such state from the client when it is no longer
applicable.
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1.5.2 Comparison of COPS and the MIDCOM Framework
In the MIDCOM framework, the Middlebox enforces the policy
controlled by an application-aware Agent. Thus, when compared to
the COPS architecture, the Middlebox serves as the PEP (COPS
Client) and the Midcom Agent serves as the PDP (COPS Policy
Server).
2 Item Level Compliance Evaluation
This section contains a review of the protocol's level of
compliance to each of the MIDCOM Requirements [1]. The following
key will be used to identify the level of compliancy of each of the
individual protocols:
T = Total Compliance. Meets the requirement fully.
P+ = Partial Compliance+. Fundamentally meets the requirement
through the use of extensions (e.g. packages, additional
parameters, etc).
P = Partial Compliance. Meets some aspect of the requirement,
however, the necessary changes require more than an extension
and/or are inconsistent with the design intent of the
protocol.
F = Failed Compliance. Does not meet the requirement.
2.1 Protocol machinery
This section describes the compliancy of the proposed protocols
against the protocol machinery requirements from section 2.1 of the
requirements document [1]. A short description of each of the
protocols is provided to substantiate the evaluation.
2.1.1 Ability to establish association between Agent and Middlebox.
SNMP: T, RSIP: P+, MEGACO: F, DIAMETER: T, COPS: F
SNMP: With the SNMP management framework, associations are
established through the use of managed objects for session
identification and control. In SNMPv3, an association is
established between the SNMP manager and the SNMP agent to provided
secure data transfer. This association could serve as the
association between the MIDCOM Agent and Middlebox.
RSIP: RSIP allows sessions to be established between middleboxes
and applications and MIDCOM agents. Authorization credentials would
have to be added to the session establishment request to allow the
middlebox to authorize the session requestor.
MEGACO: There is a directionality component implicit in this
requirement in that the MA should initiate the establishment
of the authorized session. Megaco defines this association to
be established in the opposite direction, i.e., the Middlebox(MG)
initiates the establishment. If this restriction not considered,
then Megaco makes the syntax and semantics available for the
endpoint to initiate the connection.
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DIAMETER: Although this is out of scope, the Diameter specification
describes several ways to discover a peer. Having done so, a
Diameter node establishes a transport connection (TCP, TLS, or
SCTP) to the peer. The two peers then exchange Capability Exchange
Request/Answer messages to identify each other and determine the
Diameter applications each supports.
If the connection between two peers is lost, Diameter prescribes
procedures whereby it may be re-established. To ensure that loss
of connectivity is detected quickly, Diameter provides the Device-
Watchdog Request/Answer messages, to be used when traffic between
the two peers is low.
Diameter provides an extensive state machine to govern the
relationship between two peers.
COPS: COPS does not meet the directionality part of the
requirement. The definition of COPS allows a PEP (Middlebox) to
establish communication with a PDP (MIDCOM Agent). However, nothing
explicitly prohibits a PDP from establishing communication with a
PEP. The PEP could have local policies dictating what action to
take when it is contacted by an unknown PDP. These actions, defined
in the local policies, would ensure the proper establishment of an
authorized association.
2.1.2 Agent can relate to multiple Middleboxes
SNMP: T, RSIP: P, MEGACO: T, DIAMETER: T, COPS: T
SNMP: An SNMP manager can communicate simultaneously with several
Middleboxes.
RSIP: RSIP sessions are identified by their IP source and
destination addresses and their TCP / UDP port numbers. Thus each
RSIP client can communicate with multiple servers, and each server
can communicate with multiple clients. However, RSIP did not
explicitly include agents in its design, thus the applicability of
RSIP as the MIDCOM protocol is limited. The architecture and
semantics of RSIP messages do not preclude agents, thus the RSIP
architecture could certainly be extended to explicitly include
agents; therefore RSIP is deemed partially compliant to this
requirement.
MEGACO: MEGACO allows an MA to control several Middle Boxes. Each
message carries an identifier of the endpoint that transmitted the
message allowing the recipient to determine the source.
DIAMETER: Diameter allows connection to more than one peer (and
encourages this for improved reliability). Whether the Diameter
connection state machine is too heavy to support the number of
connections needed is a matter for discussion.
COPS: COPS PDPs are designed to communicate with several PEPs.
2.1.3 Middlebox can relate to multiple Agents
SNMP: T, RSIP: T, MEGACO: T, DIAMETER: T, COPS: T
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SNMP: An SNMP agent can communicate with several SNMP managers
Simultaneously.
RSIP: Refer to 2.1.2.
MEGACO: Megaco has the concept of Virtual Media Gateways (VMG),
allowing multiple MGCs to communicate simultaneously with the same
MG. Applying this model to MIDCOM would allow the same middlebox
(MG) to have associations with multiple MIDCOM Agents (MGCs).
DIAMETER: Diameter allows connection to more than one peer and
encourages this for improved reliability. Whether the Diameter
connection state machine is too heavy to support the number of
connections needed is a matter for discussion. The Middlebox and
Agent play symmetric roles as far as Diameter peering is concerned.
COPS: The COPS-PR framework specifies that a PEP should have a
unique PDP in order to achieve effective policy control. The COPS-
PR protocol would allow the scenario whereby a PEP establishes
communication with multiple PDPs by creating a COPS client instance
per PDP.
2.1.4 Deterministic outcome when multiple requests are presented to
the Middlebox simultaneously
SNMP: T, RSIP: T, MEGACO: T, DIAMETER: T, COPS: T
SNMP: Deterministic behavior of SNMP agents when being accessed by
multiple managers is important for several management applications
and supported by SNMP.
RSIP: All RSIP requests are defined to be atomic. Near simultaneous
requests are executed as is they were sequential.
MEGACO: Megaco supports the concept of VMG's to make these
interactions deterministic and to avoid resource access conflicts.
Each VMG has a single owner, in a MGC, and there can be no overlap
between the sets of Terminations belonging to multiple VMGs. The
Megaco protocol messages also include the identifier of the sending
entity, so that the MG can easily determine to whom to send the
response or asynchronously report certain events.
DIAMETER: Diameter depends partly upon the transport protocol to
provide flow control when the server becomes heavily loaded. It
also has application-layer messaging to indicate that it is too
busy or out of space (DIAMETER_TOO_BUSY and DIAMETER_OUT_OF_SPACE
result codes).
COPS: COPS has built-in support for clear state and policy
instances. This would allow the creation of well-behaved Midcom
state machines.
2.1.5 Known and stable state
SNMP: T, RSIP: T, MEGACO: T, DIAMETER: P, COPS: T
SNMP: A known and stable state of the SNMP agent is important for
several management applications and supported by SNMP.
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RSIP: RSIP assumes that on middlebox start-up no sessions are
defined, and thus no allocations have been made. In effect, all
resources are released upon restart after failure.
MEGACO: Megaco has extensive audit capabilities to synchronize
states between the MG and the MGC. Megaco also provides the
MGC with the ability to do mass resets, as well as individual
resets. MGC can always release resources in MG. The MG can also
initiate the release of resources by the MGC.
DIAMETER: Diameter documentation does not discuss the degree of
atomicity of message processing, so this would have to be specified
in the Midcom extension.
COPS: The COPS protocol maintains synchronized states between
Middleboxes and MA hence all the states are known on both sides.
2.1.6 Middlebox status report
SNMP: T, RSIP: T, MEGACO: T, DIAMETER: T, COPS: T
SNMP: SNMP meets this requirement with the Status report initiated
by the SNMP manager polling status objects at the SNMP agent.
RSIP: All RSIP client requests have explicit server responses.
Additionally, a client may explicitly request server status using
a QUERY request.
MEGACO: Megaco has extensive audit capabilities for the MG to
report status information to the MGC. It can also report some
status updates using the ServiceChange command.
DIAMETER: Diameter provides a number of response codes by means of
which a server can indicate error conditions reflecting status of
the server as a whole. The Disconnect-Peer-Request provides a
means in the extreme case to terminate a connection with a peer
gracefully, informing the other end about the reason for the
disconnection.
COPS: The COPS Report message is designed to indicate any
asynchronous conditions/events.
2.1.7 Middlebox can generate unsolicited messages
SNMP: T, RSIP: T, MEGACO: T, DIAMETER: T, COPS: T
SNMP: SNMP agents may send asynchronous notifications to SNMP
Managers. In SNMP v1 and v2, the only mechanism to support this is
through TRAPs. In SNMP v3, INFORMs could also be used and are
perhaps more desirable.
RSIP: An RSIP server will send an unsolicited DE_REGISTER_RESPONSE
to force an RSIP host to relinquish all of its bindings and
terminate its relationship with the RSIP gateway. An RSIP server
can send an asynchronous ERROR_RESPONSE to indicate less severe
conditions.
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MEGACO: MEGACO supports the asynchronous notification of events
using the Notify command.
DIAMETER: The Diameter protocol permits either peer in a connection
to originate transactions. Thus the protocol supports Middlebox-
originated messages.
COPS: The COPS Report message is designed to indicate any
asynchronous conditions/events.
2.1.8 Mutual authentication
SNMP: T, RSIP: F, MEGACO: T, DIAMETER: T, COPS: T
SNMP: SNMPv3 meets this requirement. SNMPv3 explicitly supports
symmetric secret key encryption between Midcom agent (SNMP manager)
and Middlebox (SNMP agent), thus supporting implicit mutual
authentication. The encryption method is specified in RFC 2574.
Beyond this SNMPv3 supports user authentication. Different users at
the same management application (Midcom agent) can authenticate
themselves with one of two authentication methods, also specified
in RFC 2574.
RSIP: The RSIP framework recommends all communication between an
RSIP host and gateway be authenticated. Authentication, in the form
of a message hash appended to the end of each RSIP protocol packet,
can serve to authenticate the RSIP host and gateway to one another,
provide message integrity, and avoid replay attacks with an anti-
replay counter_. However, the message hash and replay counter
parameters would need to be defined for the RSIP protocol.
MEGACO: MEGACO provides for the use of IPSec for all security
mechanisms including mutual authentication, integrity check and
encryption. Use of IKE is recommended with support of RSA
signatures and public key encryption.
DIAMETER: The Diameter base protocol assumes that messages are
secured by using either IP Security or TLS. Diameter requires that
when using the latter, peers must mutually authenticate themselves.
COPS: COPS has built-in message level security for authentication,
replay protection, and message integrity. COPS can also use TLS or
IPSec.
2.1.9 Termination of session by either party
SNMP: T, RSIP: T, MEGACO: T, DIAMETER: T, COPS: T
SNMP: As described in 2.1.1, a straight forward way of realizing
sessions within the SNMP management framework would be by using
managed objects for session identification and control. In SNMPv3
there is an association established between SNMP manager and SNMP
agent related to providing secure data transfer. This association
could serve as the basis for terminating a Midcom session.
RSIP: An RSIP client may terminate a session with a
DE_REGISTER_REQUEST. An RSIP server may terminate a session with an
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unsolicited DE_REGISTER_RESPONSE, and then respond to subsequent
requests on the session with a REGISTER_FIRST error.
MEGACO: The MEGACO protocol allows both peers to terminate the
association with proper reason code.
DIAMETER: Either peer in a connection may issue a Disconnect-Peer-
Request to end the connection gracefully.
COPS: COPS allows both the PEP and PDP to terminate a session.
2.1.10 Indication of success or failure
SNMP: T, RSIP: T, MEGACO: T, DIAMETER: T, COPS: T
SNMP: The SNMP Status report is typically initiated by the SNMP
manager's polling of status objects at the SNMP agent. This Status
Report is used for determining whether or not a previous request
was successful.
RSIP: All RSIP requests result in a paired RSIP response if the
request was successful or an ERROR_RESPONSE if the request was not
successful.
MEGACO: Megaco defines a special descriptor called an Error
descriptor that contains error code and an optional explanatory
string.
DIAMETER: Every Diameter request is matched by a response, and this
response contains a result code as well as other information.
COPS: The COPS Report message directly fulfills this requirement.
2.1.11 Version interworking
SNMP: T, RSIP: T, MEGACO: T, DIAMETER: T, COPS: T
SNMP: Capability exchange in SNMP is usually uni-directional.
Managed objects at the Middlebox (SNMP agent) keep information
about the capabilities of the Middlebox. They are read by the
Midcom agent (SNMP manager), which allows the Midcom agent to
utilize the capabilities accordingly. This capability exchange
along with the extensibility provided as a basic feature of the
SNMP management framework provide the basis for version
interworking.
RSIP: Each RSIP message contains a version parameter.
MEGACO: Version interworking and negotiation are supported both for
the protocol and any extension Packages.
DIAMETER: The Capabilities Exchange Request/Answer allows two peers
to determine information about what each supports, including
protocol version and specific applications.
COPS: The COPS protocol can carry a MIDCOM version number and
capability negotiation between the COPS client and the COPS server.
This capability negotiation mechanism allows the COPS client and
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server to communicate the supported features/capabilities. This
would allow seamless version interworking.
2.1.12 Deterministic behaviour in the presence of overlapping
rules
SNMP: T, RSIP: T, MEGACO: P, DIAMETER: T, COPS: T
SNMP: A Middlebox (SNMP agent) implementation achieves
deterministic behaviour in the presence of overlapping rules by
applying the atomic operations supported by the SNMP framework.
RSIP: All requests for allocation of IP addresses, or ports or both
resulting in rule overlap are rejected by an RSIP server with a
LOCAL_ADDR_INUSE error.
MEGACO: This is met with the help of a model that separates Megaco
protocol elements from the overlapping Policy rules (see
Appendix C). However, new behavior for the Megaco protocol elements
needs to be specified as part of a new MIDCOM specific Package.
DIAMETER: The IPFilterRule type specification, which would probably
be used as the type of a Policy Rule AVP, comes with an extensive
semantic description providing a deterministic outcome, which the
individual Agent cannot know unless it knows all of the Policy
Rules installed on the Middlebox. Rules for the appropriate
direction are evaluated in order, with the first matched rule
terminating the evaluation. Each packet is evaluated once. If no
rule matches, the packet is dropped if the last rule evaluated was
a permit, and passed if the last rule was a deny. The IPFilterRule
format and further details on its applicability to this requirement
are provided in Appendix D.
COPS: The COPS protocol provides transactional-based communication
between the PEP and PDP, hence the behavior is totally
deterministic provided the middlebox state machine is designed
correctly. The COPS protocol features encourage and support good
state machine design.
2.2 Protocol semantics
This section contains the individual protocols as evaluated against
the protocol semantic requirements from section 2.2 of the
requirements document [1]. A short description of each of the
protocols is provided to substantiate the evaluation.
2.2.1 Extensibility
SNMP: T, RSIP: P+, MEGACO: T, DIAMETER: T, COPS: T
SNMP: Extensibility is a basic feature of the SNMP management
Framework.
RSIP: All RSIP messages consist of three mandatory fields (protocol
version, message type, and message length) and a sequence of
parameterType / length / value 3-tuples. New messages may be
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defined by defining new values for the message type field. New
parameter types may be defined, and existing messages may be
extended, by defining new parameterType values. If new messages or
parameters or both are added in a non-backward compatible way, a
new value of the protocol version field may be defined. This may
be desirable even of the additions are backward compatible.
MEGACO: Megaco is easily extensible through new Packages, which
allow definition of new attributes and behavior of a Termination.
DIAMETER: Diameter provides a great deal of flexibility for
extensions, including allowance for vendor-defined commands and
AVPs and the ability to flag each AVP as must-understand or
ignorable if not understood.
COPS: The COPS protocol is extensible, since it was designed to
separate the Protocol from the Policy Control Information.
2.2.2 Support of multiple Middlebox types
SNMP: T, RSIP: P, MEGACO: T, DIAMETER: P, COPS: T
SNMP: SNMP explicitly supports managing different device types with
different capabilities. First the managed object called sysObjectID
from basic MIB-II [3] identifies the type of box. For boxes with
varying capabilites, SNMP can check the availability of
corresponding MIBs.
RSIP: All types of middleboxes are supported so long as the ruleset
action is _permit. Other actions would require the definition of a
new RSIP message parameter with values for permit and the other
desired actions.
MEGACO: Megaco can support multiple Middlebox types on the same
interface either by designing the properties representing the
Policy Rules to provide this support, or by using multiple
terminations in the same session, each representing one type of
action. In the latter case, the Megaco Context can be used as a
convenient means of managing the related terminations as a group.
However, the inherent idea of flow between terminations of a
context is irrelevant and would have to be discarded.
DIAMETER: Any necessary additional AVPs or values must be specified
as part of the Midcom application extension (see <2.2.8> below).
COPS: COPS allows a PDP to provide filters and actions to multiple
PEP functions through a single COPS session.
2.2.3 Ruleset groups
SNMP: P+, RSIP: F, MEGACO: T, DIAMETER: T, COPS: T
SNMP: This requirement can be realized via the SNMP management
framework by an appropriate definition of a Midcom MIB module. SMI,
the language used for defining MIB modules, is flexible enough to
allow the implementor of a MIB module to meet the semantics of this
requirement.
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RSIP: RSIP currently only allows one IP address or address and port
range to be assigned to a so-called _bind-ID_. RSIP could
implement rulesets as required by adding an optional bind-ID
parameter to ASSIGN_REQUESTs to extend an existing ruleset rather
than creating a new one. Similarly, the FREE_REQUESTs would have to
be extended by adding optional local and remote address and port
parameters.
MEGACO: The Megaco context can be used to group terminations which
are to be managed together. For example, all of the terminations
(each representing an instantiation of a Policy Rule) can be
deleted in one command by doing a wildcarded Subtract from the
context. However, the inherent idea of media flows between
terminations of a context would be irrelevant in this application
of the protocol.
DIAMETER: Diameter allows message syntax definitions where multiple
instances of the same AVP (for example, a Policy Rule AVP whose
syntax and low-level semantics are defined by the IPFilterRule type
definition) may be present. If a tighter grouping is required, the
set of Diameter base types includes the Grouped type. Midcom can
choose how to make use of these capabilities to meet the ruleset
group requirement when defining its application extension to the
Diameter protocol.
COPS: The COPS-PR Handle State may be used to associate the set of
closely related policy objects. As the Middlebox learns additional
requirements, the Middlebox adds these resource requirements under
the same handle ID, which constitutes the required aggregation.
2.2.4 Lifetime extension
SNMP: P+, RSIP: T, MEGACO: T, DIAMETER: T, COPS: P+
SNMP: This requirement can be realized via the SNMP management
framework by an appropriate definition of a Midcom MIB module. SMI,
the language used for defining MIB modules, is flexible enough to
allow the implementor of a MIB module to meet the semantics of this
requirement.
RSIP: A client may request an explicit lease time when a request is
made to assign one or more IP addresses or ports or both. The
server may grant the requested lease time, or assign one if none
was requested. Subsequently, the lease time may be extended if a
client's EXTEND_REQUEST is granted by the server.
MEGACO: The MG can report the imminent expiry of a policy rule to
the MGC that can then extend or delete the corresponding
Termination.
DIAMETER: The Diameter concept of a session includes the session
lifetime, grace period, and lifetime extension. It may make sense
to associate the Diameter session with the lifetime of a Midcom
Policy Rule, in which case support for lifetime extension comes
ready-made.
COPS: COPS allows a PDP to send unsolicited decisions to the PEP.
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However the unsolicited events will be relevant to the COPS MIDCOM
specific client or the MIDCOM specific PIB that will need to be
defined. This would allow the PDP to extend the lifetime of an
existing ruleset.
2.2.5 Handling of Mandatory/optional nature of unknown attributes
SNMP: P+, RSIP: T, MEGACO: P+, DIAMETER: P+, COPS: T
SNMP: This requirement can be met by an appropriate definition of a
Midcom MIB module. SMI, the language used for defining MIB modules,
is flexible enough to allow the implementor of a MIB module to meet
the semantics of this requirement.
RSIP: All options of all requests are fully specified. Not
understood parameters must be reported by an ERROR_RESPONSE with an
EXTRA_PARM error value, with the entire request otherwise ignored.
MEGACO: Megaco entities provide Error codes in response messages.
If a command marked "Optional" in a transaction fails, the
remaining commands will continue. However, the specified
requirement deals with rules of processing properties that need
definition in new Package.
DIAMETER: Indication of the mandatory or optional status of AVPs is
fully supported, provided it is enabled in the AVP definition. No
guidance is imposed regarding the return of diagnostic information
for optional AVPs.
COPS: COPS provides for the exchange of capabilities and
limitations between the PEP and PDP to ensure well-known outcomes
are understood for scenarios with unknown attributes. There is also
clear error handling for situations when the request is rejected.
2.2.6 Actionable failure reasons
SNMP: P+, RSIP: P+, MEGACO: T, DIAMETER: T, COPS: T
SNMP: This requirement can be met by an appropriate definition of a
Midcom MIB module. SMI, the language used for defining MIB modules,
is flexible enough to allow the implementer of a MIB module to meet
the semantics of this requirement.
RSIP: RSIP defines a fairly large number of very specific error
values. It is anticipated that additional error values will also
have to be defined along with the new messages and parameters
required for MIDCOM.
MEGACO: The MG can provide Error codes in response messages
allowing the MGC to modify its behavior. Megaco uses transaction
identifiers for correlation between a response and a command; in
case the same transaction id is received more than once, the
receiving entity silently discards the message. This provides some
protection against replay attacks.
DIAMETER: Diameter provides an extensive set of failure reasons in
the base protocol.
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COPS: COPS uses an error object that is used to identify a
particular COPS protocol error. The error sub-code field may
contain additional detailed client (i.e. the MIDCOM COPS client)
specific error codes.
2.2.7 Multiple Agents operating on the same ruleset.
SNMP: T, RSIP: F, MEGACO: P, DIAMETER: T, COPS: P
SNMP: The SNMP framework supports multiple managers working on the
same managed objects. The View-based Access Control Model (VACM,
[RFC2575]) even offers means to customize the access rights of
different managers in a fine-grained way.
RSIP: To simultaneously satisfy this requirement and the MIDCOM
security and deterministic behavior requirements may be impossible
for RSIP. The splitting of a ruleset and the passing of ownership
of a ruleset from one client to another should be possible
consistent with security and deterministic behavior.
MEGACO: If the Megaco state machine on the Middle Box is decoupled
from the Middle Box policy rule management, this requirement is met
with local policies on the Middle Box. However, this violates the
spirit of the Megaco protocol, thus Megaco is considered partially
compliant to this requirement.
DIAMETER: The Diameter protocol as currently defined offers no
impediment such an operation.
COPS: It is possible to use COPS to operate the same resource with
multiple agents. An underlying resource management function,
separate from the COPS state machine, on the Middlebox will handle
the arbitration when resource conflicts happen.
2.2.8 Transport of filtering rules
SNMP: P+, RSIP: P, MEGACO: T, DIAMETER: P+, COPS: P+
SNMP: This requirement can be met by an appropriate definition of a
Midcom MIB module. SMI, the language used for defining MIB modules,
is flexible enough to allow the implementation of a MIB module to
meet the semantics of this requirement.
RSIP: RSIP only supports a 4-tuple consisting of local and remote
IP addresses and port numbers. The addition of transport protocol
identification is straightforward.
MEGACO: Megaco protocol can carry descriptors and properties
defining all types of filters and associated actions.
DIAMETER: While Diameter defines the promising IPFilterRule data
type (see 2.1.12 above), there is no existing message, which would
convey this to a Middlebox along with other Midcom-required
attributes. A new Midcom application extension of Diameter would
have to be defined.
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COPS: The COPS protocol has all the flexibility to meet this
requirement by using a COPS MIDCOM specific client or a MIDCOM
specific PIB.
2.2.9 Mapped port parity
SNMP: P+, RSIP: F, MEGACO: P+, DIAMETER: P+, COPS: P+
SNMP: This requirement can be met by an appropriate definition of a
Midcom MIB module. SMI, the language used for defining MIB modules,
is flexible enough to allow the implementation of a MIB module to
meet the semantics of this requirement.
RSIP: This would be a very easy addition to RSIP.
MEGACO: Megaco can be easily extended using a MIDCOM specific
Package to support this feature.
DIAMETER: This capability is not part of the current IPFilterRule
type definition. Rather than modify the IPFilterRule type, Midcom
could group it with other AVPs which add the missing information.
COPS: The COPS protocol has all the flexibility to meet this
requirement by using a COPS MIDCOM specific client or a MIDCOM
specific PIB.
2.2.10 Consecutive range of port numbers
SNMP: P+, RSIP: T, MEGACO: P+, DIAMETER: P+, COPS: P+
SNMP: This requirement can be met by an appropriate definition of a
Midcom MIB module. SMI, the language used for defining MIB modules,
is flexible enough to allow the implementation of a MIB module to
meet the semantics of this requirement.
RSIP: The ports parameter of the RSIP ASSIGN_REQUESTs specifically
allows multiple, consecutive port numbers to be specified.
MEGACO: Megaco can be easily extended using a MIDCOM specific
Package to support this feature.
DIAMETER: This capability is not part of the current IPFilterRule
type definition. Rather than modify the IPFilterRule type, Midcom
could group it with other AVPs which add the missing information.
COPS: The COPS protocol has all the flexibility to meet this
requirement by using a COPS MIDCOM specific client or a MIDCOM
specific PIB.
2.2.11 More precise rulesets contradicting overlapping rulesets
SNMP: P+, RSIP: F, MEGACO: P+, DIAMETER: T, COPS: P+
SNMP: This requirement can be met by an appropriate definition of a
Midcom MIB module. SMI, the language used for defining MIB modules,
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is flexible enough to allow the implementation of a MIB module to
meet the semantics of this requirement.
RSIP: This capability can be added to RSIP, but the authors are not
convinced at this time of its desirability, especially if the
rulesets do not belong to the same RSIP client.
MEGACO: This requirement would be met if the policy in the
Middlebox allows contradictory, overlapping policy rules to be
installed.
DIAMETER: Allowed by the IPFilterRule semantics described in
Appendix D.
COPS: The COPS protocol has all the flexibility to meet this
requirement by using a COPS MIDCOM specific client or a MIDCOM
specific PIB.
2.3 General Security Requirements
This section the individual protocols as evaluated against the
General Security requirements from section 2.3 of the requirements
document [1]. A short description of each of the protocols is
provided to substantiate the evaluation.
2.3.1 Message Authentication, confidentiality and Integrity
SNMP: T, RSIP: F, MEGACO: T, DIAMETER: T, COPS: T
SNMP: SNMPv3 includes the User-based Security Model (USM,
[RFC2574]), which defines three standardized methods for providing
authentication, confidentiality, and integrity. Additionally, USM
has specific built-in mechanisms for preventing replay attacks
including unique protocol engine IDs, timers and counters per
engine and time windows for the validity of messages.
RSIP: The RSIP framework recommends all communication between an
RSIP host and gateway be authenticated. Authentication, in the form
of a message hash appended to the end of each RSIP protocol packet,
can serve to authenticate the RSIP host and gateway to one another,
provide message integrity, and avoid replay attacks with an anti-
replay counter_. However, the message hash and replay counter
parameters would need to be defined for the RSIP protocol.
MEGACO: Megaco provides for these functions with the combined usage
of IPSEC or TLS.
DIAMETER: Diameter relies on either IPSEC or TLS for these
functions.
COPS: COPS has built-in message level security for authentication,
replay protection, and message integrity. COPS can also use TLS or
IPSec, thus reusing existing security mechanisms that have
interoperated in the markets.
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2.3.2 Optional Confidentiality Protection
SNMP: T, RSIP: F, MEGACO: T, DIAMETER: T, COPS: T
SNMP: SNMPv3 includes the User-based Security Model, which defines
three standardized methods for providing authentication,
confidentiality, and integrity, and is open to add further methods.
The method to use can be optionally chosen.
RSIP: Refer to 2.3.1.
MEGACO: Refer to 2.3.1
DIAMETER: Implementation support of IPSEC ESP in Diameter
applications is not optional. Deployment of either IPSEC or TLS is
optional.
COPS: Refer to 2.3.1.
2.3.3 Operate Across Untrusted Domains
SNMP: T, RSIP: F, MEGACO: T, DIAMETER: T, COPS: T
SNMP: The User-based Security Model of SNMPv3 defines three
standardized methods for providing authentication, confidentiality,
and integrity, and it is open to add further methods. These methods
operate securely across untrusted domains.
RSIP: Refer to 2.3.1.
MEGACO: Refer to 2.3.1.
DIAMETER: The Diameter specification [28] recommends the use of TLS
across untrusted domains.
COPS: Refer to 2.3.1
2.3.4 Mitigates Replay Attacks on Control Messages
SNMP: T, RSIP: F, MEGACO: T, DIAMETER: T, COPS: T
SNMP: The User-based Security Model for SNMPv3 has specific built-
in mechanisms for preventing replay attacks including unique
protocol engine IDs, timers and counters per engine and time
windows for the validity of messages.
RSIP: Refer to 2.3.1
MEGACO: Megaco commands and responses include matching transaction
identifiers. The recipient receiving the same transaction id
multiple times would discard the message, thus providing some
protection against replay attacks. If even stronger protection
against replay attack is needed, Megaco provides for the use of
IPSec or TLS.
DIAMETER: Diameter requires that implementations support the replay
protection mechanisms of IPSEC.
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COPS: Refer to 2.3.1
3 Conclusions
The overall statistics with regards to the number of Fully
Compliant, Partially Compliant (P+ and P) and Failing Compliancy
requirements for each of the protocols is summarized in table 1.
T P+ P F
-----------------------------------------------------------------
SNMP 19 8 0 0
RSIP 12 3 3 9
MEGACO 20 4 2 1
DIAMETER 21 4 2 0
COPS 20 5 1 1
Table 1: Totals across all Requirements
The SNMP management framework meets all the specified MIDCOM
protocol requirements with the appropriate design of a MIDCOM MIB
module. SNMP is a proven technology with stable and proven
development tools, which already provides support for NAT
configuration. For matching the security requirements and for the
support of requirement 2.1.7, only the most recent version, SNMPv3,
is suited. Although, SNMPv3 is not as proven of a technology as
SNMPv1 and SNMPv2, the protocol specifications are more mature and
have undergone more validation than the other protocols in the
evaluation.
RSIP fails to meet several of the MIDCOM requirements, in
particular none of the security related requirements are met. In
addition, RSIP requires additions/extensions to meet several of the
requirements. RSIP would also require several framework elements to
be added to the MIDCOM framework as identified in section 1.2.3.
Megaco meets most of the key requirements for the Midcom
Protocol with the exception of 2.1.1, which has an implicit
directionality component, that can't be met with Megaco as defined.
Modeling the underlying Middlebox resources (e.g., filters, policy
rules) as separate elements from the Megaco entities might allow
the usage of the protocol as-is, satisfying some of the resource
access control requirements. Additional extensions in the form of
new Termination / Package definition (without impacting the base
protocol) would be required for Midcom.
The DIAMETER evaluation indicated a good overall fit with no
requirements failing to be met. Some partially met requirements
were identified that could be addressed by a new application
extension. However, the Diameter architecture may be too heavy for
the Midcom application and clearly much of the Diameter base is not
needed. In addition, DIAMETER is the only protocol in the
evaluation for which the RFCs are not yet published. Other than
these reservations, the protocol is a good fit to Midcom
requirements.
The COPS evaluation indicates that the protocol meets the majority
of the MIDCOM protocol requirements by using the protocol's native
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extension techniques, with COPS-PR being explicitly required to
meet requirements 2.1.3 and 2.2.3. However, as with the Megaco
evaluation, COPS also fails to meet requirement 2.1.1 due to the
implied directionality aspect.
Security Considerations
Security considerations for the MIDCOM protocol are covered by the
comparison against the specific Security requirements in the MIDCOM
requirements document [1] and are specifically addressed by section
2.1.8 and section 2.3.
Normative References
[1] R. Swale, P. Mart, P. Sijben, S. Brim, M. Shore, "Middlebox
Communications (MIDCOM) Protocol Requirements", draft-ietf-midcom-
requirements-05.txt, November, 2001.
[2] P. Srisuresh, J. Kuthan, J. Rosenberg, A. Molitor, A. Rayhan,
"Middlebox Communications Architecture and Framework", draft-ietf-
midcom-framework-07.txt, February, 2002.
[3] Rose, M., and K. McCloghrie, "Management Information Base for
Network Management of TCP/IP-based internets: MIB-II", RFC 1213,
March, 1991.
[4] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
[5] Harrington, D., Presuhn, R., and B. Wijnen, "An Architecture
for Describing SNMP Management Frameworks", RFC 2571, April 1999.
[6] Rose, M., and K. McCloghrie, "Structure and Identification of
Management Information for TCP/IP-based Internets", STD 16, RFC
1155, May 1990.
[7] Rose, M., and K. McCloghrie, "Concise MIB Definitions", STD 16,
RFC 1212, March 1991.
[8] M. Rose, "A Convention for Defining Traps for use with the
SNMP", RFC 1215, March 1991.
[9] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose,
M., and S. Waldbusser, "Structure of Management Information Version
2 (SMIv2)", STD 58, RFC 2578, April 1999.
[10] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
Rose, M., and S. Waldbusser, "Textual Conventions for SMIv2", STD
58, RFC 2579, April 1999.
[11] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
Rose, M., and S. Waldbusser, "Conformance Statements for SMIv2",
STD 58, RFC 2580, April 1999.
[12] Case, J., Fedor, M., Schoffstall, M., and J. Davin, "Simple
Network Management Protocol", STD 15, RFC 1157, May 1990.
[13] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
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"Introduction to Community-based SNMPv2", RFC 1901, January 1996.
[14] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
"Transport Mappings for Version 2 of the Simple Network
Management Protocol (SNMPv2)", RFC 1906, January 1996.
[15] Case, J., Harrington D., Presuhn R., and B. Wijnen, "Message
Processing and Dispatching for the Simple Network Management
Protocol (SNMP)", RFC 2572, April 1999.
[16] Blumenthal, U., and B. Wijnen, "User-based Security Model(USM)
for version 3 of the Simple Network Management Protocol (SNMPv3)",
RFC 2574, April 1999.
[17] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
"Protocol Operations for Version 2 of the Simple Network Management
Protocol (SNMPv2)", RFC 1905, January 1996.
[18] Levi, D., Meyer, P., and B. Stewart, "SNMPv3 Applications",
RFC 2573, April 1999.
[19] Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based Access
Control Model (VACM) for the Simple Network Management Protocol
(SNMP)", RFC 2575, April 1999.
[20] Case, J., Mundy, R., Partain, D., and B. Stewart,
"Introduction to Version 3 of the Internet-standard Network
Management Framework", RFC 2570, April 1999
[21] M. Borella, J. Lo, D. Grabelsky, G. Montenegro, "Realm
Specific IP: Framework", RFC 3102, October, 2001.
[22] M. Borella, D. Grabelsky, J. Lo, K. Taniguchi, "Realm Specific
IP: Protocol Specification",_RFC 3103, October 2001.
[23] G. Montenegro, M. Borella, "RSIP Support for End-to-end
Ipsec", RFC 3104, October 2001.
[24] J. Kempf, G. Montenegro, "Finding an RSIP Server with SLP",
RFC 3105, October 2001.
[25] F. Cuervo, N. Greene, A. Rayhan, C. Huitema, B. Rosen, J.
Segers, "MEGACO Protocol Version 1.0", RFC 3015, November, 2000.
[26] S. Kent, R. Atkinson, "IP Authentication Header", RFC 2402,
November 1998.
[27] S. Kent, R. Atkinson, "IP Encapsulating Security Payload",
RFC 2406, November 1998.
[28] P. Calhoun, J. Arkko, E. Guttman, G. Zorn, J. Loughney,
"Diameter Base Protocol", draft-ietf-aaa-diameter-10.txt, IETF
work in progress, April 2002.
[29] P. Calhoun, G. Zorn, P. Pan, H. Akhtar, "Diameter Framework
Document", draft-ietf-aaa-diameter-framework-01.txt, IETF work in
progress, March 2001.
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[30] P. Calhoun, W. Bulley, A. Rubens, J. Haag, G. Zorn, D.
Spence, "Diameter NASREQ Application", draft-ietf-aaa-diameter-
nasreq-09.txt, IETF work in progress, March 2002.
[31] D.Durham et al, "The COPS (Common Open Policy Service)
Protocol", RFC 2748, January 2000.
[32] K. Chan, D. Durham, S. Gai, S. Herzog, K. McCloghrie, F.
Reichmeyer, J. Seligson, A. Smith, R. Yavatkar, "COPS Usage
for Policy Provisioning", RFC 3084, March 2001.
Contributors
The following identifies the key contributors who provided the primary
content for this document in the form of individual drafts for each
protocol:
RSIP
Jim Renkel
The CommWorks Corp., a 3Com company
3800 Golf Rd. Phone: +1.847.262.2539
Rolling Meadows, IL, USA Email:james_renkel@commworks.com
SNMP
Juergen Quittek
NEC Europe Ltd.
Network Laboratories
Adenauerplatz 6
69115 Heidelberg Phone: +49 6221 90511-15
Germany Email: quittek@ccrle.nec.de
MEGACO
Sanjoy Sen
Nortel Networks Email: sanjoy@nortelnetworks.com
Cedric Aoun
Nortel Networks Email: cedric.aoun@nortelnetworks.com
Tom Taylor
Nortel Networks Email: taylor@nortelnetworks.com
DIAMETER
Tom Taylor
Nortel Networks
1852 Lorraine Ave.
Ottawa, Ontario Phone: +1 613 736 0961
Canada K1H 6Z8 Email: taylor@nortelnetworks.com
COPS
Cedric Aoun
Nortel Networks
FRANCE Email: cedric.aoun@nortelnetworks.com
Kwok-Ho Chan
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Nortel Networks
600 Technology Park Drive
Billerica, MA 01821 Email: khchan@nortelnetworks.com
Louis-Nicolas Hamer
Nortel Networks
PO Box 3511 Station C
Ottawa, Ontario Phone: +1 613.768.3409
Canada K1Y 4H7 Email: nhamer@nortelnetworks.com
Reinaldo Penno
Nortel Networks
2305 Mission College Boulevard
Building SC9
Santa Clara, CA 95054 Email: rpenno@nortelnetworks.com
Sanjoy Sen
Nortel Networks
2380 Performance Drive
Richardson, TX-75082 Email: sanjoy@nortelnetworks.com
Acknowledgements
The editor would like to acknowledge the constructive feedback
provided by Joel M. Halpern on the individual protocol evaluation
contributions. In addition, a thanks to Elwyn Davies, Christopher
Martin, Bob Penfield, Scott Brim and Martin Stiemerling for
contributing to the mailing list discussion on the draft content.
Author's Address
Mary Barnes
Nortel Networks
2380 Performance Drive Phone: 1-972-684-5432
Richardson, TX USA Email: mbarnes@nortelnetworks.com
Appendix A - SNMP Overview
The SNMP Management Framework presently consists of five major
components:
o An overall architecture, described in RFC 2571 [5].
o Mechanisms for describing and naming objects and events for
the purpose of management. The first version of this
Structure of Management Information (SMI) is called SMIv1 and
described in STD 16, RFC 1155 [6], STD 16, RFC 1212 [7] and
RFC 1215 [8]. The second version, called SMIv2, is described
in STD 58, RFC 2578 [9], STD 58, RFC 2579 [10] and STD 58, RFC
2580 [11].
o Message protocols for transferring management information.
The first version of the SNMP message protocol is called
SNMPv1 and described in STD 15, RFC 1157 [12]. A second
version of the SNMP message protocol, which is not an Internet
standards track protocol, is called SNMPv2c and described in
RFC 1901 [13] and RFC 1906 [14]. The third version of the
message protocol is called SNMPv3 and described in RFC 1906
[14], RFC 2572 [15] and RFC 2574 [16].
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o Protocol operations for accessing management information. The
first set of protocol operations and associated PDU formats is
described in STD 15, RFC 1157 [12]. A second set of protocol
operations and associated PDU formats is described in RFC 1905
[17].
o A set of fundamental applications described in RFC 2573 [18]
and the view-based access control mechanism described in RFC
2575 [19].
A more detailed introduction to the current SNMP Management
Framework can be found in RFC 2570 [20].
Managed objects are accessed via a virtual information store,
termed the Management Information Base or MIB. Objects in the MIB
are defined using the mechanisms defined in the SMI.
Appendix B - RSIP with tunneling
NAT requires ALGs (Application Layer Gateways) in middleboxes
without MIDCOM, and application modifications or agents for
middleboxes with MIDCOM.
Support for NAT without tunneling could easily be added to the RSIP
control protocol (NAT would be defined as a new, null_tunnel
type.). Support for the NAT _null_ tunnels could be implemented in
hosts, or in applications or application agents.
If support for NAT _null_ tunnels were implemented in hosts, no
modifications to applications would be required, and no application
agents or ALGs would be required. This has obvious advantages. In
addition to the NAT _null_ tunnel, the host would have to implement
an RSIP / MIDCOM client (or a STUN client) and the middlebox would
have to implement an RSIP / MIDCOM server (or a STUN server would
have to be available _beyond_ the middlebox. Note that the STUN
client / server approach may not work with all types of
middleboxes.).
If support for NAT _null_ tunnels were NOT implemented in hosts,
then applications would have to be modified, or application agents
or ALGs would have to be implemented. This has the advantage over
tunnels (whether _null_ or not) of not requiring modification to
hosts, but would require the modification of host applications or
the implementation of application agents, both of which would
include an RSIP / MIDCOM client, and the implementation of an
RSIP/MIDCOM server in the middlebox. (Again, in some situations,
STUN could be used instead of RSIP / MIDCOM.)
Tunneled or not, an RSIP / MIDCOM server is needed in the
middlebox. Tunneled, the host needs to be modified, but not the
application. Untunneled, an agent must be added or the application
must be modified, but there would be no host modifications. The
advantages/disadvantages of tunneling would need to be evaluated in
considering RSIP.
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Appendix C - MEGACO Modeling Approach
To model the Middlebox functions such as firewall, NAT etc., a new
Middlebox Termination type needs to be defined within Megaco. If
policy-rule overlap or modification by multiple Agents is NOT
required, then a policy rule is equivalent to a Termination (see
Figure 1). The various components of a Policy rule such as filter,
action, life-time, creator etc. are described as various properties
of a Termination. Use of the Virtual Media Gateway (VMG) concept
allows for conflict-free interaction of multiple MA's with the same
MB.
+-------+ +-------+
| MA-1 | | MA-2 |
| | | |
+-------+ |IF2 +-------+
| | |
+-------------|---------|----------|-----------+
| +---------+ | +-------------+ |
IF1 |VMG1 | +--+ | | | +--+ +--+ |VMG2 |IF3
----------| |Tx|-------+ +---|Ty|--|Tz|----------------
| | +--+ | | | +--+ +--+ | |
| ....| | | +-------------+ |
| +---------+ | |
| +---------------------------------
| Middlebox | IF4
+----------------------------------------------+
Tx: Termination x = Policy rule x
Ty: Termination y = Policy rule y
Tz: Termination z = Policy rule z
MA: Midcom Agent
IF: Interface
Figure 1.
If it is required to allow multiple agents manipulate the same
Middlebox resource (e.g., a Policy rule or a filter), the latter
needs to be kept separate from the Termination (the Policy rule is
manipulated by the MA by manipulating the properties of the
associated Termination). For example, if overlapping policy rule
manipulation is required, then a Termination shall be associated
with a single policy rule, but a policy rule may be associated with
more than one Termination. Thus, a Termination can share a policy
rule with another Termination, or have a policy rule partially
overlapping with that of another Termination. This model allows two
MAËs, controlling two distinct Terminations (see Figure 2),
manipulate the same or overlapping policy rules. In Figure 2,
policy rules 1 and 2 are overlapping and they are shared by MA-1
and MA-2.
+-------+ +-------+
| MA-1 | | MA-2 |
| | | |
+-------+ |IF2 +-------+
| | | MB
+-------------|---------|----------|-----------+
| +-----------+ | +-------------+ |
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IF1 |VMG1 | +--+ | | | +--+ +--+ |VMG2 |IF3
------------------|Ty|----+ +---|Tx|--|Tz|----------------
| | +--+ | | | +--+ +--+ | |
| .... | | | | +--/------\---+ |
| +-------|---+ | / \ |
| | +----/----------\------------------
| +------+----+------+ +------+ |IF4
| |Policy1 Policy2 | |Policy| |
| | | | | | 3 | |
| +----+------+------+ +------+ |
+----------------------------------------------+
Tx: Termination x
Ty: Termination y
Tz: Termination z
MA: Midcom Agent
IF: Interface
MB: Middlebox
Figure 2.
This requires that the Agent and the Middlebox adhere to the
following principles:
(1) Only one Termination has read/write access to a filter at any
time.
(2) When the policy rule is being modified by a new agent (i.e.
not the one that created the policy) the Middlebox makes a policy
decision and decides whether to accept the requested modification
or not. In the case the modification is accepted the initial Midcom
agent may be notified.
Appendix D - DIAMETER IPFilter Rule
The IPFilterRule format is derived from the OctetString AVP Base
Format. It uses the UTF-8 encoding and has the same requirements
as the UTF8String. Packets may be filtered based on the following
information that is associated with it:
Direction (in or out)
Source and destination IP address (possibly masked)
Protocol
Source and destination port (lists or ranges)
TCP flags
IP fragment flag
IP options
ICMP types
Rules for the appropriate direction are evaluated in order, with
the first matched rule terminating the evaluation. Each packet is
evaluated once. If no rule matches, the packet is dropped if the
last rule evaluated was a permit, and passed if the last rule was a
deny.
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IPFilterRule filters MUST follow the format:
action dir proto from src to dst [options]
action permit - Allow packets that match the rule.
deny - Drop packets that match the rule.
dir "in" is from the terminal, "out" is to the
terminal.
proto An IP protocol specified by number. The "ip"
keyword means any protocol will match.
src and dst <address/mask> [ports]
The <address/mask> may be specified as:
ipno An IPv4 or IPv6 number in dotted-
quad or canonical IPv6 form. Only
this exact IP number will match the
rule.
ipno/bits An IP number as above with a mask
width of the form 1.2.3.4/24. In
this case, all IP numbers from
1.2.3.0 to 1.2.3.255 will match.
The bit width MUST be valid for the
IP version and the IP number MUST
NOT have bits set beyond the mask.
For a match to occur, the same IP
version must be present in the
packet that was used in describing
the IP address. To test for a
particular IP version, the bits part
can be set to zero. The keyword
"any" is 0.0.0.0/0 or the IPv6
equivalent. The keyword "assigned"
is the address or set of addresses
assigned to the terminal. For IPv4,
a typical first rule is often
"deny in ip! assigned"
The sense of the match can be inverted by
preceding an address with the not modifier (!),
causing all other addresses to be matched
instead. This does not affect the selection of
port numbers.
With the TCP, UDP and SCTP protocols, optional
ports may be specified as:
{port|port-port}[,ports[,...]]
The '-' notation specifies a range of ports
(including boundaries).
Fragmented packets that have a non-zero offset
(i.e. not the first fragment) will never match
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a rule that has one or more port
specifications. See the frag option for
details on matching fragmented packets.
options:
frag Match if the packet is a fragment and this is not
the first fragment of the datagram. frag may not
be used in conjunction with either tcpflags or
TCP/UDP port specifications.
ipoptions spec
Match if the IP header contains the comma
separated list of options specified in spec. The
supported IP options are:
ssrr (strict source route), lsrr (loose source
route), rr (record packet route) and ts
(timestamp). The absence of a particular option
may be denoted with a '!'.
tcpoptions spec
Match if the TCP header contains the comma
separated list of options specified in spec. The
supported TCP options are:
mss (maximum segment size), window (tcp window
advertisement), sack (selective ack), ts (rfc1323
timestamp) and cc (rfc1644 t/tcp connection
count). The absence of a particular option may
be denoted with a '!'.
established
TCP packets only. Match packets that have the RST
or ACK bits set.
setup TCP packets only. Match packets that have the SYN
bit set but no ACK bit.
tcpflags spec
TCP packets only. Match if the TCP header
contains the comma separated list of flags
specified in spec. The supported TCP flags are:
fin, syn, rst, psh, ack and urg. The absence of a
particular flag may be denoted with a '!'. A rule
that contains a tcpflags specification can never
match a fragmented packet that has a non-zero
offset. See the frag option for details on
matching fragmented packets.
icmptypes types
ICMP packets only. Match if the ICMP type is in
the list types. The list may be specified as any
combination of ranges or individual types
separated by commas. Both the numeric values and
the symbolic values listed below can be used. The
supported ICMP types are:
echo reply (0), destination unreachable (3),
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source quench (4), redirect (5), echo request
(8), router advertisement (9), router
solicitation (10), time-to-live exceeded (11), IP
header bad (12), timestamp request (13),
timestamp reply (14), information request (15),
information reply (16), address mask request (17)
and address mask reply (18).
There is one kind of packet that the access device MUST always
discard, that is an IP fragment with a fragment offset of one. This
is a valid packet, but it only has one use, to try to circumvent
firewalls.
An access device that is unable to interpret or apply a deny rule
MUST terminate the session. An access device that is unable to
interpret or apply a permit rule MAY apply a more restrictive rule.
An access device MAY apply deny rules of its own before the
supplied rules, for example to protect the access device owner's
infrastructure.
The rule syntax is a modified subset of ipfw(8) from FreeBSD, and
the ipfw.c code may provide a useful base for implementations.
Intellectual Property Statements
It should be noted that two of the individual protocol evaluation
documents included IPR statements: COPS and MEGACO, thus
those statements are referenced below with the specific protocol to
which they apply being explicitly identified by replacing the word
"in this draft" and "described in this draft" with the phrase "with
regards to the applicability of "protocol x" as the MIDCOM protocol
as described in this draft" to explicitly identify the scope of the
potential for IPR.
Nortel Networks may have Intellectual Property Rights for
technologies described with regards to the applicability of COPS
as the MIDCOM protocol as described in this draft. The authors
would like to refer to the general Nortel Networks IPR statement
on the IETF IPR repository.
Nortel Networks may be pursuing Intellectual Property Rights for
concepts with regards to the applicability of MEGACO as the
MIDCOM protocol as described in this draft. The IPR statement
http://www.ietf.org/ietf/IPR/NORTEL-GENERAL is applicable to this
draft.
Full Copyright Statement
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or assist in its implementation may be prepared, copied, published
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document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
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Internet organizations, except as needed for the purpose of
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