Network Working Group J. Hadi Salim
Internet-Draft Mojatatu Networks
Expires: August 2, 2009 K. Ogawa
NTT Corporation
January 29, 2009
SCTP based TML (Transport Mapping Layer) for ForCES protocol
draft-ietf-forces-sctptml-02
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Abstract
This document defines the SCTP based TML (Transport Mapping Layer)
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for the ForCES protocol. It explains the rationale for choosing the
SCTP (Stream Control Transmission Protocol) [RFC2960] and also
describes how this TML addresses all the requirements described in
[RFC3654] and the ForCES protocol [FE-PROTO] draft.
Table of Contents
1. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Protocol Framework Overview . . . . . . . . . . . . . . . . . 3
3.1. The PL . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. The TML . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2.1. TML and PL Interfaces . . . . . . . . . . . . . . . . 5
3.2.2. TML Parameterization . . . . . . . . . . . . . . . . . 6
4. SCTP TML overview . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Rationale for using SCTP for TML . . . . . . . . . . . . . 8
4.2. Meeting TML requirements . . . . . . . . . . . . . . . . . 9
4.2.1. SCTP TML Channels . . . . . . . . . . . . . . . . . . 10
4.2.2. Satisfying TML Requirements . . . . . . . . . . . . . 14
5. Channel work scheduling . . . . . . . . . . . . . . . . . . . 15
5.1. FE Channel work scheduling . . . . . . . . . . . . . . . . 16
5.2. CE Channel work scheduling . . . . . . . . . . . . . . . . 17
6. Service Interface . . . . . . . . . . . . . . . . . . . . . . 17
6.1. TML Boot-strapping . . . . . . . . . . . . . . . . . . . . 18
6.2. TML Shutdown . . . . . . . . . . . . . . . . . . . . . . . 19
6.3. TML Sending and Receiving . . . . . . . . . . . . . . . . 20
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
8. Security Considerations . . . . . . . . . . . . . . . . . . . 22
8.1. TML Security Services using TLS and DTLS . . . . . . . . . 22
8.1.1. TLS Usage . . . . . . . . . . . . . . . . . . . . . . 22
8.2. TML Security Services using IPsec . . . . . . . . . . . . 23
8.2.1. IPsec Usage . . . . . . . . . . . . . . . . . . . . . 23
9. Manageability Considerations . . . . . . . . . . . . . . . . . 23
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 24
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
11.1. Normative References . . . . . . . . . . . . . . . . . . . 24
11.2. Informative References . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
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1. Definitions
The following definitions are taken from [RFC3654]and [RFC3746]:
ForCES Protocol -- The protocol used at the Fp reference point in the
ForCES Framework in [RFC3746].
ForCES Protocol Layer (ForCES PL) -- A layer in ForCES protocol
architecture that defines the ForCES protocol architecture and the
state transfer mechanisms as defined in [FE-PROTO].
ForCES Protocol Transport Mapping Layer (ForCES TML) -- A layer in
ForCES protocol architecture that specifically addresses the protocol
message transportation issues, such as how the protocol messages are
mapped to different transport media (like SCTP, IP, ATM, Ethernet,
etc), and how to achieve and implement reliability, security, etc.
2. Introduction
The ForCES (Forwarding and Control Element Separation) working group
in the IETF defines the architecture and protocol for separation of
Control Elements(CE) and Forwarding Elements(FE) in Network
Elements(NE) such as routers. [RFC3654] and [RFC3746] respectively
define architectural and protocol requirements for the communication
between CE and FE. The ForCES protocol layer specification
[FE-PROTO] describes the protocol semantics and workings. The ForCES
protocol layer operates on top of an inter-connect hiding layer known
as the TML. The relationship is illustrated in Figure 1.
This document defines the SCTP based TML for the ForCES protocol
layer. It also addresses all the requirements for the TML including
security, reliability, etc as defined in [FE-PROTO].
3. Protocol Framework Overview
The reader is referred to the Framework document [RFC3746], and in
particular sections 3 and 4, for an architectural overview and
explanation of where and how the ForCES protocol fits in.
There is some content overlap between the ForCES protocol draft
[FE-PROTO] and this section (Section 3) in order to provide basic
context to the reader of this document.
The ForCES protocol layering constitutes two pieces: the PL and TML
layer. This is depicted in Figure 1.
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+----------------------------------------------+
| CE PL |
+----------------------------------------------+
| CE TML |
+----------------------------------------------+
^
|
ForCES PL | messages
|
v
+-----------------------------------------------+
| FE TML |
+-----------------------------------------------+
| FE PL |
+-----------------------------------------------+
Figure 1: Message exchange between CE and FE to establish an NE
association
The PL is in charge of the ForCES protocol. Its semantics and
message layout are defined in [FE-PROTO]. The TML is necessary to
connect two ForCES end-points as shown in Figure 1.
Both the PL and TML are standardized by the IETF. While only one PL
is defined, different TMLs are expected to be standardized. The TML
at each of the nodes (CE and FE) is expected to be of the same
definition in order to inter-operate.
When transmitting from a ForCES end-point, the PL delivers its
messages to the TML. The TML then delivers the PL message to the
destination TML(s).
On reception of a message, the TML delivers the message to its
destination PL level (as described in the ForCES header).
3.1. The PL
The PL is common to all implementations of ForCES and is standardized
by the IETF [FE-PROTO]. The PL level is responsible for associating
an FE or CE to an NE. It is also responsible for tearing down such
associations.
An FE may use the PL level to asynchronously send packets to the CE.
The FE may redirect via the PL (from outside the NE) various control
protocol packets (e.g. OSPF, etc) to the CE. Additionally, the FE
delivers various events that CE has subscribed-to via PL [FE-MODEL].
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The CE and FE may interact synchronously via the PL. The CE issues
status requests to the FE and receives responses via the PL. The CE
also configures the associated FE's LFBs' components using the PL
[FE-MODEL].
3.2. The TML
The TML level is responsible for transport of the PL level messages.
[FE-PROTO] section 5 defines the requirements that need to be met by
a TML specification. The SCTP TML specified in this document meets
all the requirements specified in [FE-PROTO] section 5.
Section 4.2.2 describes how the TML requirements are met.
3.2.1. TML and PL Interfaces
There are two interfaces to the PL and TML, both of which are out of
scope for ForCES. The first one is the interface between the PL and
TML and the other is the CE Manager (CEM)/FE Manager (FEM)[RFC3746]
interface to both the PL and TML. Both interfaces are shown in
Figure 2.
[TML-API] defines an interface between the PL and the TML layers.
The end goal of [TML-API] is to provide a consistent top edge
semantics for all TMLs to adhere to. Conforming to such an interface
makes it easy to plug in different TMLs over time for a singular PL.
+----------------------------+
| +----------------------+ |
| | | |
+---------+ | | PL Layer | |
| | | +----------------------+ |
|FEM/CEM |<---->| ^ |
| | | | |
+---------+ | |TML API |
| | |
| V |
| +----------------------+ |
| | | |
| | TML Layer | |
| | | |
| +----------------------+ |
+----------------------------+
Figure 2: The TML-PL interface
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XXX - Editorial Note: There is some concern (and confusion) about
defining APIs in ForCES. So at the moment the future of [TML-API] is
unknown and we will remove references to it in future revisions of
this document.
Figure 2 also shows an interface referred to as CEM/FEM[RFC3746]
which is responsible for bootstrapping and parameterization of the
TML. In its most basic form the CEM/FEM interface takes the form of
a simple static config file which is read on startup in the pre-
association phase.
Section 6 discusses in more details the service interfaces.
3.2.2. TML Parameterization
It is expected that it should be possible to use a configuration
reference point, such as the FEM or the CEM, to configure the TML.
Some of the configured parameters may include:
o PL ID
o Connection Type and associated data. For example if a TML uses
IP/SCTP then parameters such as SCTP ports and IP addresses need
to be configured.
o Number of transport connections
o Connection Capability, such as bandwidth, etc.
o Allowed/Supported Connection QoS policy (or Congestion Control
Policy)
4. SCTP TML overview
SCTP [RFC2960] is an end-to-end transport protocol that is equivalent
to TCP, UDP, or DCCP in many aspects. With a few exceptions, SCTP
can do most of what UDP, TCP, or DCCP can achieve. SCTP as well can
do most of what a combination of the other transport protocols can
achieve (eg TCP and DCCP or TCP and UDP).
Like TCP, it provides ordered, reliable, connection-oriented, flow-
controlled, congestion controlled data exchange. Unlike TCP, it does
not provide byte streaming and instead provides message boundaries.
Like UDP, it can provide unreliable, unordered data exchange. Unlike
UDP, it does not provide multicast support
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Like DCCP, it can provide unreliable, ordered, congestion controlled,
connection-oriented data exchange.
SCTP also provides other services that none of the 3 transport
protocols mentioned above provide. These include:
o Multi-homing
An SCTP connection can make use of multiple destination IP
addresses to communicate with its peer.
o Runtime IP address binding
With the SCTP Dynamic Address Reconfiguration ([RFC5061]) feature,
a new IP address can be bound at runtime. This allows for
migration of endpoints without restarting the association
(valuable for high availability).
o A range of reliability shades with congestion control
SCTP offers a range of services from full reliability to none, and
from full ordering to none. With SCTP, on a per message basis,
the application can specify a message's time-to-live. When the
expressed time expires, the message can be "skipped".
o Built-in heartbeats
SCTP has built-in heartbeat mechanism that validate the
reachability of peer addresses.
o Multi-streaming
A known problem with TCP is head of line (HOL) blocking. If you
have independent messages, TCP enforces ordering of such messages.
Loss at the head of the messages implies delays of delivery of
subsequent packets. SCTP allows for defining up to 64K
independent streams over the same socket connection, which are
ordered independently.
o Message boundaries with reliability
SCTP allows for easier message parsing (just like UDP but with
reliability built in) because it establishes boundaries on a PL
message basis. On a TCP stream, one would have to use techniques
such peeking into the message to figure the boundaries.
o Improved SYN DOS protection
Unlike TCP, which does a 3 way connection setup handshake, SCTP
does a 4 way handshake. This improves against SYN-flood attacks
because listening sockets do not set up state until a connection
is validated.
o Simpler transport events
An application (such as the TML) can subscribe to be notified of
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both local and remote transport events. Events that can be
subscribed-to include indication of association changes,
addressing changes, remote errors, expiry of timed messages, etc.
These events are off by default and require explicit subscription.
o Simplified replicasting
Although SCTP does not allow for multicasting it allows for a
single message from an application to be sent to multiple peers.
This reduces the messaging that typically crosses different memory
domains within a host (example in a kernel to user space domain of
an operating system).
4.1. Rationale for using SCTP for TML
SCTP has all the features required to provide a robust TML. As a
transport that is all-encompassing, it negates the need for having
multiple transport protocols in order to satisfy the TML requirements
([FE-PROTO] section 5). As a result it allows for simpler coding and
therefore reduces a lot of the interoperability concerns.
SCTP is also very mature and widely used making it a good choice for
ubiquitous deployment.
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4.2. Meeting TML requirements
PL
+----------------------+
| |
+-----------+----------+
| TML API
TML |
+-----------+----------+
| | |
| +------+------+ |
| | TML core | |
| +-+----+----+-+ |
| | | | |
| SCTP socket API |
| | | | |
| | | | |
| +-+----+----+-+ |
| | SCTP | |
| +------+------+ |
| | |
| | |
| +------+------+ |
| | IP | |
| +-------------+ |
+----------------------+
Figure 3: The TML-SCTP interface
Figure 3 details the interfacing between the PL and SCTP TML and the
internals of the SCTP TML. The core of the TML interacts on its
north-bound interface to the PL (utilizing the TML API). On the
south-bound interface, the TML core interfaces to the SCTP layer
utilizing the standard socket interface [XXX Editorial: add here a
reference to SCTP Sockets API doc]. There are three SCTP socket
connections opened between any two PL endpoints (whether FE or CE).
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4.2.1. SCTP TML Channels
+--------------------+
| |
| TML core |
| |
+-+-------+--------+-+
| | |
| Med prio, |
| Semi-reliable |
| channel |
| | Low prio,
| | Unreliable
| | channel
| | |
^ ^ ^
| | |
Y Y Y
High prio,| | |
reliable | | |
channel | | |
Y Y Y
+-+--------+--------+-+
| |
| SCTP |
| |
+---------------------+
Figure 4: The TML-SCTP channels
Figure 4 details further the interfacing between the TML core and
SCTP layers. There are 3 channels used to separate and prioritize
the different types of ForCES traffic. Each channel constitutes a
socket interface. It should be noted that all SCTP channels are
congestion aware (and for that reason that detail is left out of the
description of the 3 channels). SCTP port 6700, 6701, 6702 are used
for the higher, medium and lower priority channels respectively.
4.2.1.1. Justifying Choice of 3 Sockets
SCTP allows up to 64K streams to be sent over a single socket
interface. The authors initially envisioned using a single socket
for all three channels (mapping a channel to an SCTP stream). This
simplifies programming of the TML as well as conserves use of SCTP
ports.
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Further analysis revealed head of line blocking issues with this
initial approach. Lower priority packets not needing reliable
delivery could block higher priority packets (needing reliable
delivery) under congestion situation. For this reason, we elected to
go with mapping each of the three channels to a different SCTP socket
(instead of a different stream within a single socket).
4.2.1.2. Higher Priority, Reliable channel
The higher priority (HP) channel uses a standard SCTP reliable socket
on port 6700. It is used for CE solicited messages and their
responses:
1. ForCES configuration messages flowing from CE to FE and responses
from the FE to CE.
2. ForCES query messages flowing from CE to FE and responses from
the FE to the CE.
It is recommended that the following PL messages use the HP channel
for transport:
o Association Setup
o Association Setup Response
o Association Teardown
o Config
o Config Response
o Query
o Query Response
4.2.1.3. Medium Priority, Semi-Reliable channel
The medium priority (MP) channel uses SCTP-PR on port 6701. Time
limits on how long a message is valid are set on each outgoing
message. This channel is used for events from the FE to the CE that
are obsoleted over time. Events that are accumulative in nature and
are recoverable by the CE (by issuing a query to the FE) can tolerate
lost events and therefore should use this channel. For example, a
generated event which carries the value of a counter that is
monotonically incrementing fits to use this channel.
It is recommended that the following PL messages use the MP channel
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for transport:
o Event Notification
4.2.1.4. Lower Priority, Unreliable channel
The lower priority (LP) channel uses SCTP port 6702. This channel
also uses SCTP-PR with lower timeout values than the MP channel. The
reason an unreliable channel is used for redirect messages is to
allow the control protocol at both the CE and its peer-endpoint to
take charge of how the end-to-end semantics of the said control
protocol's operations. For example:
1. Some control protocols are reliable in nature, therefore making
this channel reliable introduces an extra layer of reliability
which could be harmful. So any end-to-end retransmits will
happen from remote.
2. Some control protocols may desire to have obsolescence of
messages over retransmissions; making this channel reliable
contradicts that desire.
Given ForCES PL level heartbeats are traffic sensitive, sending them
over the LP channel also makes sense. If the other end is not
processing other channels it will eventually get heartbeats; and if
it is busy processing other channels heartbeats will be obsoleted
locally over time (and it does not matter if they did not make it).
It is recommended that the following PL messages use the MP channel
for transport:
o Packet Redirect
o Heartbeats
4.2.1.5. Scheduling of The 3 Channels
Strict priority work-conserving scheduling is used to process both on
sending and receiving (of the PL messages) by the TML Core as shown
in Figure 5.
This means that the HP messages are always processed first until
there are no more left. The LP channel is processed only if a
channel that is higher priority than itself has no more messages left
to process. This means that under congestion situation, a higher
priority channel with sufficient messages that occupy the available
bandwidth would starve lower priority channel(s).
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The design intent of the SCTP TML is to tie prioritization as
described in Section 4.2.1.1 and transport congestion control to
provide implicit node congestion control. This is further detailed
in Section 5.
SCTP channel +----------+
Work available | DONE +---<--<--+
| +---+------+ |
Y ^
| +-->--+ +-->---+ |
+-->-->-+ | | | | |
| | | | | | ^
| ^ ^ Y ^ Y |
^ / \ | | | | |
| / \ | ^ | ^ ^
| / Is \ | / \ | / \ |
| / there \ | /Is \ | /Is \ |
^ / HP work \ ^ /there\ ^ /there\ ^
| \ ? / | /MP work\ | /LP work\ |
| \ / | \ ? / | \ ? / |
| \ / | \ / | \ / ^
| \ / ^ \ / ^ \ / |
| \ / | \ / | \ / |
^ Y-->-->-->+ Y-->-->-->+ Y->->->-+
| | NO | NO | NO
| | | |
| Y Y Y
| | YES | YES |
^ | | |
| Y Y Y
| +----+------+ +---|-------+ +----|------+
| |- process | |- process | |- process |
| | HP work | | MP work | | LP work |
| +------+----+ +-----+-----+ +-----+-----+
| | | |
^ Y Y Y
| | | |
| Y Y Y
+--<--<---+--<--<----<----+-----<---<-----+
Figure 5: SCTP TML Strict Priority Scheduling
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4.2.1.6. SCTP TML Parameterization
The following is a list of parameters needed for booting the TML. It
is expected these parameters will be extracted via the FEM/CEM
interface for each PL ID.
1. The IP address or a resolvable DNS/hostname of the CE/FE.
2. The HP SCTP port, as discussed in Section 4.2.1.2. The default
HP port value is 6700 (Section 7).
3. The MP SCTP port, as discussed in Section 4.2.1.3. default MP
port value is 6701 (Section 7).
4. The LP SCTP port, as discussed in Section 4.2.1.4. default LP
port value is 6702 (Section 7).
4.2.2. Satisfying TML Requirements
[FE-PROTO] section 5 lists requirements that a TML needs to meet.
This section describes how the SCTP TML satisfies those requirements.
4.2.2.1. Satisfying Reliability Requirement
As mentioned earlier, a shade of reliability ranges is possible in
SCTP. Therefore this requirement is met.
4.2.2.2. Satisfying Congestion Control Requirement
Congestion control is built into SCTP. Therefore, this requirement
is met.
4.2.2.3. Satisfying Timeliness and Prioritization Requirement
By using 3 sockets in conjunction with the partial-reliability
feature, both timeliness and prioritization can be achieved.
4.2.2.4. Satisfying Addressing Requirement
There are no extra headers required for SCTP to fulfil this
requirement. SCTP can be told to replicast packets to multiple
destinations. The TML implementation will need to translate PL level
addresses, to a variety of unicast IP addresses in order to emulate
multicast and broadcast PL addresses.
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4.2.2.5. Satisfying HA Requirement
Transport link resiliency is one of SCTP's strongest point. Failure
detection and recovery is built in, as mentioned earlier.
o The SCTP multi-homing feature is used to provide path diversity.
Should one of the peer IP addresses become unreachable, the
other(s) are used without needing lower layer convergence
(routing, for example) or even the TML becoming aware.
o SCTP heartbeats and data transmission thresholds are used on a per
peer IP address to detect reachability faults. The faults could
be a result of an unreachable address or peer, which may be caused
by a variety of reasons, like interface, network, or endpoint
failures. The cause of the fault is noted.
o With the ADDIP feature, one can migrate IP addresses to other
nodes at runtime. This is not unlike the VRRP[RFC3768] protocol
use. This feature is used in addition to multi-homing in a
planned migration of activity from one FE/CE to another. In such
a case, part of the provisioning recipe at the CE for replacing an
FE involves migrating activity of one FE to another.
4.2.2.6. Satisfying DOS Prevention Requirement
Three separate channels, one per socket, are used within any FE-CE
setup. The scheduling design for processing channels
(Section 4.2.1.5) is strict priority and ties transport and node
overload implicitly together. The HP channel work gets prioritized
at the expense of the MP and LP channels in the presence of low
processing and bandwidth resource conditions. I.e., if redirected
packets (from outside the NE) attempt to overload the NE, they get
assigned very low priority and obsoleted in short periods if either
the CE or FE is busy processing more important work or the CE-FE path
is congested. Refer to Section 5 for details.
4.2.2.7. Satisfying Encapsulation Requirement
There is no extra encapsulation added by the SCTP TML.
In the future, should the need arise, a new SCTP extension/chunk can
be defined to meet newer ForCES requirements [XXX: Editorial note:
provide reference to SCTP extensibility].
5. Channel work scheduling
This section provides high level details of the scheduling view of
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the SCTP TML core (Section 4.2.1). A practical scheduler
implementation takes care of many little details (such as timers,
work quanta, etc) not described in this document. The implementor is
left to take care of those details.
The CE(s) and FE(s) are coupled together in the principles of the
scheduling scheme described here to tie together node overload with
transport congestion. The design intent is to provide the highest
possible robust work throughput for the NE under any network or
processing congestion.
XXX (Editorial note): We need to solicit feedback whether it would
help implementors if we publish algorithm for the CE/FE scheduling in
the form of pseudo-code.
5.1. FE Channel work scheduling
The FE scheduling, in priority order, needs to I/O process:
1. The HP channel I/O in the following priority order:
1. Transmitting back to the CE any outstanding result of
executed work via the HP channel transmit path.
2. Taking new incoming work from the CE which creates ForCES
work to be executed by the FE.
2. ForCES events which result in transmission of unsolicited ForCES
packets to the CE via the MP channel.
3. Incoming Redirect work in the form of control packets that come
from the CE via LP channel. After redirect processing, these
packets get sent out on external (to the NE) interface.
4. Incoming Redirect work in the form of control packets that come
from other NEs via external (to the NE) interfaces. After some
processing, such packets are sent to the CE.
It is worth emphasizing at this point again that the SCTP TML
processes the channel work in strict priority. For example, as long
as there are messages to send to the CE on the HP channel, they will
be processed first until there are no more left before processing the
next priority work (which is to read new messages on the HP channel
incoming from the CE).
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5.2. CE Channel work scheduling
The CE scheduling, in priority order, needs to deal with:
1. The HP channel I/O in the following priority order:
1. Process incoming responses to requests of work it made to the
FE(s).
2. Transmitting any outstanding HP work it needs for the FE(s)
to complete.
2. Incoming ForCES events from the FE(s) via the MP channel.
3. Outgoing Redirect work in the form of control packets that get
sent from the CE via LP channel destined to external (to the NE)
interface on FE(s).
4. Incoming Redirect work in the form of control packets that come
from other NEs via external (to the NE) interfaces on the FE(s).
It is worth to repeat for emphasis again that the SCTP TML processes
the channel work in strict priority. For example, if there are
messages incoming from an FE on the HP channel, they will be
processed first until there are no more left before processing the
next priority work which is to transmit any outstanding HP channel
messages going to the FE.
6. Service Interface
XXX - Editorial Note and repeated emphasis: There is some concern
(and confusion) about defining APIs in ForCES. So at the moment the
future of [TML-API] is unknown and we will remove references to it in
future revisions of this document.
This section provides high level service interface between FEM/CEM
and TML, the PL and TML, and between local and remote TMLs. The
intent of this interface discussion is to provide general guidelines.
The implementer is expected to worry about details and even follow a
different approach if needed.
The theory of operation for the PL-TML service is as follows:
1. The PL starts up and bootstraps the TML. The end result of a
successful TML bootstrap is that the CE TML and the FE TML
connect to each other at the transport level.
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2. Sending and reception of the PL level messages commences after a
successful TML bootstrap. The PL uses send and receive PL-TML
interfaces to communicate to its peers. The TML is agnostic to
the nature of the messages being sent or received. The first
message exchanges that happen are to establish ForCES
association. Subsequent messages maybe either unsolicited events
from the FE PL, control message redirects from/to the CE to/from
FE, and configuration from the CE to the FE and their responses
flowing from the FE to the CE.
3. The PL does a shutdown of the TML after terminating ForCES
association.
6.1. TML Boot-strapping
Figure 6 illustrates a flow for the TML bootstrapped by the PL.
When the PL starts up (possibly after some internal initialization),
it boots up the TML. The TML first interacts with the FEM/CEM and
acquires the necessary TML parameterization (Section 4.2.1.6). Next
the TML uses the information it retrieved from the FEM/CEM interface
to initialize itself.
The TML on the FE proceeds to connect the 3 channels to the CE. The
socket interface is used for each of the channels. The TML continues
to re-try the connections to the CE until all 3 channels are
connected. It is advisable that the number of connection retry
attempts and the time between each retry is also configurable via the
FEM. On failure to connect one or more channels, and after the
configured number of retry thresholds is exceeded, the TML will
return an appropriate failure indicator to the PL. On success (as
shown in Figure 6), a success indication is presented to the TML.
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FE PL FE TML FEM CEM CE TML CE PL
| | | | | |
| | | | | Bootup |
| | | | |<-------------------|
| Bootup | | | | |
|----------->| | |get CEM info| |
| |get FEM info | |<-----------| |
| |------------>| ~ ~ |
| ~ ~ |----------->| |
| |<------------| | |
| | |-initialize TML |
| | |-create the 3 chans.|
| | | to listen to FEs |
| | | |
| |-initialize TML |Bootup success |
| |-create the 3 chans. locally |------------------->|
| |-connect 3 chans. remotely | |
| |------------------------------>| |
| ~ ~ - FE TML connected ~
| ~ ~ - FE TML info init ~
| | channels connected | |
| |<------------------------------| |
| Bootup | | |
| succeeded | | |
|<-----------| | |
| | | |
Figure 6: SCTP TML Bootstrapping
On the CE things are slightly different. After initializing from the
CEM, the TML on the CE side proceeds to initialize the 3 channels to
listen to remote connections from the FEs. The success or failure
indication is passed on to the CE PL level (in the same manner as was
done in the FE).
Post boot-up, the CE TML waits for connections from the FEs. Upon a
successful connection by an FE, the CE TML level keeps track of the
transport level details of the FE. Note, at this stage only
transport level connection has been established; ForCES level
association follows using send/receive PL-TML interfaces (refer to
Section 6.3 and Figure 8).
6.2. TML Shutdown
Figure 7 shows an example of an FE shutting down the TML. It is
assumed at this point that the ForCES Association Teardown has been
issued by the CE.
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When the FE PL issues a shutdown to its TML for a specific PL ID, the
TML releases all the channel connections to the CE. This is achieved
by closing the sockets used to communicate to the CE.
FE PL FE TML CE TML CE PL
| | | |
| Shutdown | | |
|----------->| | |
| |-disconnect 3 chans. | |
| |------------------------>| |
| | | |
| | |-FE TML info cleanup|
| | |-optionally tell PL |
| | |------------------->|
| |- clean up any state of | |
| | channels disconnected | |
| | | |
| |<------------------------| |
| Shutdown | | |
| succeeded | | |
|<-----------| | |
| | | |
Figure 7: FE Shutting down
On the CE side, a TML level disconnection would result in possible
cleanup of the FE state. Optionally, depending on the
implementation, there may be need to inform the PL about the TML
disconnection.
6.3. TML Sending and Receiving
The TML is agnostic to the nature of the PL message it delivers to
the remote TML (which subsequently delivers the message to its PL).
Figure 8 shows an example of a message exchange originated at the FE
and sent to the CE (such as a ForCES association message) which
illustrates all the necessary service interfaces for sending and
receiving.
When the FE PL sends a message to the TML, the TML is expected to
pick one of HP/MP/LP channels and send out the ForCES message.
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FE PL FE TML CE TML CE PL
| | | |
|PL send | | |
|----------->| | |
| | | |
| |-Format msg. | |
| |-pick channel | |
| |-TML Send | |
| |------------->| |
| | |-TML Receive on chan. |
| | |-decapsulate |
| | |- mux to PL/PL recv |
| | |--------------------->|
| | | ~
| | | ~ PL Process
| | | ~
| | | PL send |
| | |<---------------------|
| | |-Format msg. for send |
| | |-pick chan to send on |
| | |-TML send |
| |<-------------| |
| |-TML Receive | |
| |-decapsulate | |
| |-mux to PL | |
| PL Recv | | |
|<---------- | | |
| | | |
Figure 8: Send and Recv Flow
When the CE TML receives the ForCES message on the channel it was
sent on, it demultiplexes the message to the CE PL.
The CE PL, after some processing (in this example dealing with the
FE's association), sends to the TML the response. And as in the case
of FE PL, the CE TML picks the channel to send on before sending.
The processing of the ForCES message upon arriving at the FE TML and
delivery to the FE PL is similar to the CE side equivalent as shown
above in Section 6.3.
7. IANA Considerations
This document makes request of IANA to reserve SCTP ports 6700, 6701,
and 6702.
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8. Security Considerations
The SCTP TML provides the following security services to the PL
level:
o A mechanism to authenticate ForCES CEs and FEs at transport level
in order to prevent the participation of unauthorized CEs and
unauthorized FEs in the control and data path processing of a
ForCES NE.
o A mechanism to ensure message authentication of PL data and
headers transferred from the CE to FE (and vice-versa) in order to
prevent the injection of incorrect data into PL messages.
o A mechanism to ensure the confidentiality of PL data and headers
transferred from the CE to FE (and vice-versa), in order to
prevent disclosure of PL level information transported via the
TML.
Security choices provided by the TML are made by the operator and
take effect during the pre-association phase of the ForCES protocol.
An operator may choose to use all, some or none of the security
services provided by the TML in a CE-FE connection.
When operating under a secured environment, or for other operational
concerns (in some cases performance issues) the operator may turn off
all the security functions between CE and FE.
The operator has the choice of configuring either a combination of
Transport Layer Security(TLS) [RFC4346] and Datagram Transport Layer
Security(DTLS) [RFC4347], or IP Security Protocol (IPsec) [RFC4301]
to provide needed security. It is recommended that the TLS/DTLS
combination is used and only in its absence should IPsec be
considered.
XXXX: Editors note: we should take note of RFC 3554 and 3436
8.1. TML Security Services using TLS and DTLS
TLS and DTLS were designed to provide the mutual authentication,
message integrity and message confidentiality outlined in the TML
security requirements ([FE-PROTO]).
8.1.1. TLS Usage
Since in the ForCES architecture, the CE is master and FEs are
slaves, the FEs are D/TLS clients and CEs are D/TLS server. The FE
HP channel opens a TLS connection on SCTP port 6700. The FE MP and
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LP channels open DTLS connections on SCTP ports 6701 and 6702
respectively.
The endpoints that implement D/TLS MUST perform mutual authentication
during D/TLS session establishment process. Certificates are used to
achieve mutual authentication.
We recommend TLS-RSA-with-AES-128-CBC-SHA cipher suite. Although
consistency is expected it is possible for the CE or FE to negotiate
other D/TLS cipher suites.
8.2. TML Security Services using IPsec
XXXX: Editors note: We should review what RFCs to list as references
(eg IKEv2, ESP etc).
IPsec is an IP level security scheme transparent to the higher-layer
applications and therefore can provide security for any transport
layer protocol. This gives IPsec the advantage that it can be used
to secure everything between the CE and FE without expecting the TML
implementation to be aware of the details.
The IPsec architecture is designed to provide message integrity and
message confidentiality outlined in the TML security requirements
([FE-PROTO]). Mutual authentication and key exchange protocol
Internet Key Exchange (IKE)[RFC4109].
8.2.1. IPsec Usage
It is recommended that the following options be used for consistency
(although it is expected to be possible for the CE or FE to negotiate
other cipher suites):
o Internet Key Exchange (IKE)[RFC4109] with certificates for
endpoint authentication.
o Transport Mode Encapsulating Security Payload (ESP)
o HMAC-SHA1-96 [RFC2404] for message integrity protection
o AES-CBC with 128-bit keys [RFC3602] for message confidentiality.
9. Manageability Considerations
TBA
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10. Acknowledgements
The authors would like to thank Joel Halpern, Michael Tuxen and Randy
Stewart for engaging us in discussions that have made this draft
better.
11. References
11.1. Normative References
[RFC2404] Madson, C. and R. Glenn, "The Use of HMAC-SHA-1-96 within
ESP and AH", RFC 2404, November 1998.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC2960] Stewart, R., Xie, Q., Morneault, K., Sharp, C.,
Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M.,
Zhang, L., and V. Paxson, "Stream Control Transmission
Protocol", RFC 2960, October 2000.
[RFC3602] Frankel, S., Glenn, R., and S. Kelly, "The AES-CBC Cipher
Algorithm and Its Use with IPsec", RFC 3602,
September 2003.
[RFC3654] Khosravi, H. and T. Anderson, "Requirements for Separation
of IP Control and Forwarding", RFC 3654, November 2003.
[RFC3746] Yang, L., Dantu, R., Anderson, T., and R. Gopal,
"Forwarding and Control Element Separation (ForCES)
Framework", RFC 3746, April 2004.
[RFC4109] Hoffman, P., "Algorithms for Internet Key Exchange version
1 (IKEv1)", RFC 4109, May 2005.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006.
[RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security", RFC 4347, April 2006.
[RFC5061] Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M.
Kozuka, "Stream Control Transmission Protocol (SCTP)
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Dynamic Address Reconfiguration", RFC 5061,
September 2007.
11.2. Informative References
[FE-MODEL]
Halpern, J. and J. Hadi Salim, "ForCES Forwarding Element
Model", October 2008.
[FE-PROTO]
Doria (Ed.), A., Haas (Ed.), R., Hadi Salim (Ed.), J.,
Khosravi (Ed.), H., M. Wang (Ed.), W., Dong, L., and R.
Gopal, "ForCES Protocol Specification", November 2008.
[TML-API] M. Wang, W., Hadi Salim, J., and A. Audu, "ForCES
Transport Mapping Layer (TML) Service Primitives",
Feb. 2007.
Authors' Addresses
Jamal Hadi Salim
Mojatatu Networks
Ottawa, Ontario
Canada
Email: hadi@mojatatu.com
Kentaro Ogawa
NTT Corporation
3-9-11 Midori-cho
Musashino-shi, Tokyo 180-8585
Japan
Email: ogawa.kentaro@lab.ntt.co.jp
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