Network Working Group J. Hadi Salim Internet-Draft ZNYX Networks Expires:
May 12, 2008January 15, 2009 K. Ogawa NTT Network Service Systems Laboratories November 9, 2007Corporation July 14, 2008 SCTP based TML (Transport Mapping Layer) for ForCES protocol draft-ietf-forces-sctptml-00draft-ietf-forces-sctptml-01 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on May 12, 2008. Copyright Notice Copyright (C) The IETF Trust (2007).January 15, 2009. Abstract This document defines the SCTP based TML (Transport Mapping Layer) 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 . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.2. The TML layer . . . . . . . . . . . . . . . . . . . . . . 5 3.2.1. TML Parameterization . . . . . . . . . . . . . . . . . 6 3.3. The TML-PL interface . . . . . . . . . . . . . . . . . . . 6 4. SCTP TML overview . . . . . . . . . . . . . . . . . . . . . . 7 4.1. Introduction to SCTP . . . . . . . . . . . . . . . . . . . 7 4.2.Rationale for using SCTP for TML . . . . . . . . . . . . . 9 18.104.22.168. Meeting TML requirements . . . . . . . . . . . . . . . . . 9 4.3.1. Reliability . . . . .10 4.2.1. SCTP TML Channels . . . . . . . . . . . . . . . . 10 4.3.2. Congestion control. . 11 4.2.2. Satisfying Reliability Requirement . . . . . . . . . . 13 4.2.3. Satisfying Congestion Control Requirement . . . . . . 10 22.214.171.124 4.2.4. Satisfying Timeliness and prioritization . . .prioritizationi Requirement . . . . . . . . . 10 4.3.4. Addressing. . . . . . . . . . . . 13 4.2.5. Satisfying Addressing Requirement . . . . . . . . . . 10 126.96.36.199 4.2.6. Satisfying HA Requirement . . . . . . . . . . . . . . 14 4.2.7. Satisfying DOS Prevention Requirement . . . . . . . . . . . . 10 4.3.6. DOS prevention14 4.2.8. Satisfying Encapsulation Requirement . . . . . . . . . 14 5. IANA Considerations . . . . . . . . . . . 11 4.3.7. Encapsulation. . . . . . . . . . 15 6. Security Considerations . . . . . . . . . . 11 5. IANA Considerations. . . . . . . . . 15 6.1. TLS Usage for Securing TML . . . . . . . . . . . . 11 6. Security Considerations. . . . 15 6.2. IPSec Usage for securing TML . . . . . . . . . . . . . . . 1115 7. Manageability Considerations . . . . . . . . . . . . . . . . . 1116 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 1116 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 1216 9.1. Normative References . . . . . . . . . . . . . . . . . . . 1216 9.2. Informative References . . . . . . . . . . . . . . . . . . 1216 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 1217 Intellectual Property and Copyright Statements . . . . . . . . . . 1418 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 TCP, IP, ATM, Ethernet, etc), and how to achieve and implement reliability, multicast, ordering, etc. 2. Introduction The ForCES (Forwarding and Control Element Separation) working group in the IETF is defining the architecture and protocol for separation of controlControl Elements(CE) and forwarding elementsForwarding Elements(FE) in network elementsNetwork 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]. XXXX: TBD - a reference to the correct document for a more complete list of terminology. 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 in order to provide clarity.clarity to the reader of this document. The ForCES layout constitutes two pieces: the PL and TML layer. This is depicted in Figure 1. +----------------------------------------------+----------------------------------------------+ | CE PL | +----------------------------------------------+----------------------------------------------+ | CE TML | +----------------------------------------------+----------------------------------------------+ ^ | ForCES | (i.e. Forces data + control PL | packets ) messages | over | specific | TML | encaps |encapsulation| and | transport | | v +------------------------------------------------+-----------------------------------------------+ | FE TML | +------------------------------------------------+-----------------------------------------------+ | FE PL | +------------------------------------------------+-----------------------------------------------+ Figure 1: Message exchange between CE and FE to establish an NE association The PL layer is in charge of the ForCES protocol. Its semantics and message layout are defined in [FE-PROTO]. The TML Layer is necessary to connect two ForCES PL layers 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 peers (CE and FE) is expected to be of the same definition in order to inter-operate. When transmitting, the PL delivers its messages to the TML. The TML then delivers the PL message to the destination peer TML(s) as defined by the addressing in the PL message. On reception of a message, the TML delivers the message to its destination PL layer(s).layer(s) (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 layer is responsible for associating an FE or CE to an NE. It is also responsible for tearing down such associations. An FE uses the PL layer to throw various subscribed-to events to the CE PL layer as well as respond to various status requests issued from the CE PL. The CE configures both the FE and associated LFBs attributes using the PL layer. In addition the CE may send various requests to the FE to activate or deactivate it, reconfigure its HA parameterization, subscribe to specific events etc. 3.2. The TML layer The TML layer is responsible for transport of the PL layer messages. The TML provides the following services on behalf of the ForCES protocol: 1. Reliability As defined by RFC 3654, section 6 #6. 2. Security TML provides security services to the ForCES PL. The TML definition needs to define how the following are achieved: * Endpoint authentication of FE and CE * Message authentication * Confidentiality service 3. Congestion Control The congestion control mechanism defined by the TML should prevent the FE from being overloaded by the CE. Additionally, the circumstances under which notification is sent to the PL to notify it of congestion must be defined. 4. Uni/multi/broadcast addressing/delivery, if any If there is any mapping between PL and TML level uni/multi/ broadcast addressing it needs to be defined. 5. Transport High Availability It is expected that availability of transport links is the TML's responsibility. However, on config basis, the PL layer may wish to participate in link failover schemes and therefore the TML must allow for this. 6. Encapsulations used Different types of TMLs will encapsulate the PL messages on different types of headers. The TML needs to specify the encapsulation used. 7. Prioritization The TML SHOULD will be able to handle up to 8 priority levels needed by the PL and will provide preferential treatment. The TML needs to define how this is achieved. 8. Protection against DoS attacks As described in the Requirements RFC 3654, section 6 It is expected more than one TML will be standardized. The different TMLs each could implement things differently based on capabilities of underlying media and transport. However, since each TML is standardized, interoperability is guaranteed only as long as both endpoints support the same TML. 3.2.1. 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/TCP/UDP then parameters such as TCP and UDP 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) 3.3. The TML-PL interface [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. It also allows for simplified TML parameterization requirement stated in Section 3.2.1. ,''''''''''''''''''''''|+----------------------+ | | | PL Layer | | | |........ .............|+----------------------+ ^ | | TML API | | V ,''''''''''''''''''''''`.+----------------------+ | | | TML Layer | | | '`'''''''''''''''''''''''+----------------------+ Figure 2: The TML-PL interface We are going to assume the existence of such an interface and not discuss it further. The reader is encouraged to read [TML-API] as a background. Editorial Note: There is some concern (and confusion) about defining APIs in ForCES. So at the moment the future of [TML-API] is unknown (unless these concerns are cleared). 4. SCTP TML overview 4.1. Introduction to SCTPSCTP [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 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 ADDIP feature, a new 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 upto 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 peekuse 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 both local and remote transport events. Events such asthat can be subscribed-to include indication of association changes, addressing changes, remote errors, expiry of timed messages, etc,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 crosess different memory domains within a host. 188.8.131.52. 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, as has been suggested so far in the other proposals for TMLs. As a result it allows for simpler coding and therefore reduces a lot of the interoperability concerns. SCTP is also very mature and widely deployed completing the equation that makes it a superior choice in comparison with other proposed TMLs. 184.108.40.206. Meeting TML requirements ,''''''''''''''''''''|PL +---------------------+ | | +-----------+---------+ | PLTML API TML | +-----------+----------+ | | |........ .+.........|| + TML API| ,''''''''''+'''''''''`.+------+------+ | | | TML core | | | +-+----+----+-+ | | | | | | '`'''''''''+'''''''''''| +SCTP socket API | ,''''''''''+'''''''''`.| | | | | | | | | | | +-+----+----+-+ | | | SCTP | | (over IP)| +------+------+ | | | | | | | | +------+------+ | | | IP | | | +-------------+ | '`'''''''''''''''''''''+----------------------+ Figure 3: The TML-SCTP interface Figure 3 above showsdetails the interfacing between the TML and SCTP. There is only one socket connection open with two streams used. The first stream which is high priority will be dedicated for configuration dataSCTP and the second lower priority stream is used for data path redirect.internals of the SCTP TML. The TML will use information passed bycore of the TML APIinterfaces on its north bound interface to select which ofthe two streams to use when sending. ThePL (utilizing the TML will also subscribe toAPI). On the southbound interface, the TML core interfaces to the SCTP layer utilizing the standard socket interface [Editorial: add here a reference to SCTP Sockets API doc]. There are three SCTP socket connections opened between any two PL layers (whether FE or CE). 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. 220.127.116.11. Justifying Choice of 3 Sockets SCTP allows upto 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. 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. This proposal alleviates that problem by making the medium and low priority channels obsolete over a period of time, but that is still insufficient to resolve the outstanding HOL issue. XXX: Talk here about Michael Tuxen's approach which will allow for SCTP to prioritize streams within a single socket. Unfortunately, until that approach completes standardization effort we cannot recomend its use for ForCES TML. 18.104.22.168. Higher Priority, Reliable channel The higher priority 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. Some events which require guaranteed delivery could also optionally use this interface. An example of an event that would be prioritized and delivered on this channel would be a PL heartbeat (in a scenario when the first few HBs fail to make it to the destination). 22.214.171.124. Medium Priority, Mixed Reliable channel The medium priority 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 fromand therefore should this channel. Example a counter that is monotonically incrementing fits to use this channel. 126.96.36.199. Lower Priority, Unreliable channel The lower priority channel on SCTP associatedport 6702 is used for redirect messages between the CE and FE. This channel also uses SCTP-PR with lower timeout values than the two streams. 4.3.1.medium priority 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. 188.8.131.52. Scheduling of The 3 Channels Strict priority work-conserving scheduling is used to process both on sending and receving by the TML Core. This means that the higher priority messages are always processed first until there are no more left. The lower priority 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). The authors feel this is justified given the choice of the messaging prioritization as described above. 184.108.40.206. TML Parameterization TBA: This section will have a list of all parameters needed for booting the TML. 220.127.116.11. TML Bootstrapping TBA: This section will show how the FE and CE side of bootstrapping. 4.2.2. Satisfying Reliability Requirement As mentioned earlier, a shade of reliability ranges is possible in SCTP. Therefore this requirement is met. Redirected control traffic in ForCES is not expected to be reliably delivered but MUST at the same time be congestion aware. This requirement is also met by SCTP. 18.104.22.168.2.3. Satisfying Congestion controlControl Requirement Congestion control is built into SCTP. Therefore, this requirement is met. 22.214.171.124.2.4. Satisfying Timeliness and prioritizationprioritizationi Requirement By using multiple streams3 sockects in conjunction with the partial-reliability feature, both timeliness and prioritization can be achieved. 126.96.36.199.2.5. Satisfying Addressing Requirement SCTP can be told to replicast packets to multiple destinations. The TML will translate PL level addresses, to a variety of unicast IP addresses in order to emulate multicast and broadcast. Note, however, unlike other proposed TMLs,that there are no extra headers required for SCTP. 188.8.131.52.2.6. Satisfying HA Requirement Transport link resiliency is SCTP's strongest point (where it totally outclasses all other TML proposals). 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. 184.108.40.206.2.7. Satisfying DOS prevention TwoPrevention Requirement Three separate streams (one per socket) are used within any FE-CE setup: the higher priority one is for configuration and the lower priority one for data redirection.setup. The scheduling design isfor processing channels (Section 220.127.116.11)is strict priority to further guaranteepriority. This guarantees that lower priority ismessages are starved if lack of resources happen. 4.3.7.i.e under congestion (which is likely to occur under DOS attack), redirected packets (from outside the NE) get very low priority and obsoleted in short periods if the CE-FE path is congested without consuming resources on the CE-FE path. 4.2.8. Satisfying Encapsulation Requirement There is no extra encapsulation added by this TML. SCTP provides for extensions to be added to it by defining new chunks. In the future, should the need arise, a new SCTP extension can be defined to meet newer ForCES requirements. 5. IANA Considerations This document makes norequest of IANA. NoteIANA to RFC Editor: this section may be removed on publication as an RFC.reserve SCTP ports 6700, 6701, and 6702. 6. Security Considerations TBA: howWhen operating under a secured environment then the network administrator can turn off all the security functions. This feature is configured during the pre-association phase of the protocol. This mode is called "no security" mode of operation. When the CEs, FEs are running over IP networks or in an insecure environment, the operator has the choice of configuring either TLS [RFC2246] or IPSec [RFC2401] to provide needed security. For IPSec, The security association between the CEs and FEs MUST be established before any ForCES protocol messages are exchanged between the CEs and FEs. 6.1. TLS Usage for Securing TML This section is applicable for CE or FE endpoints that use the TML with TLS [RFC2246] to secure communication. Since CE is master and FEs are slaves, the FEs are TLS clients and CEs are TLS server. The endpoints that implement TLS MUST perform mutual authentication during TLS session establishment process. CE must request certificate from FE and FE needs to pass the requested information. 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 TLS cipher suites. 6.2. IPSec Usage for securing TML This section is applicable for CE or FE endpoints that use TLS,IPSECthe TML with IPSec [RFC2401] to secure their respective communication. IPSec is transparent to the higher-layer applications and can provide security for any transport layer protocol. This mechanism is can be used to secure just the control or both the control and the data channel simultaneously. Editorial Note: We need to flesh the security section with more details. 7. Manageability Considerations TBA 8. 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. 9. References 9.1. Normative References [RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC 2246, January 1999. [RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the Internet Protocol", RFC 2401, 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. [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. 9.2. Informative References [FE-MODEL] Halpern, J. and E.J., Deleganes, E., and J. Hadi Salim, "ForCES Forwarding Element Model", Oct. 2007.February 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", July 2007.March 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 ZNYX Networks Ottawa, Ontario Canada Email: firstname.lastname@example.org Kentaro Ogawa NTT Network Service Systems LaboratoriesCorporation 3-9-11 Midori-cho Musashino-shi, Tokyo 180-8585 Japan Email: email@example.com Full Copyright Statement Copyright (C) The IETF Trust (2007).(2008). 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