Network Working Group F. Baker Internet-Draft Cisco Systems Intended status: Informational September 28, 2009 Expires: April 1, 2010 Core Protocols in the Internet Protocol Suite draft-baker-ietf-core-02 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and 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 April 1, 2010. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract This note attempts to identify the core of the Internet Protocol Suite. The target audience is NIST, in the Smart Grid discussion, as they have requested guidance on how to profile the Internet Protocol Baker Expires April 1, 2010 [Page 1] Internet-Draft Core Protocols September 2009 Suite. In general, that would mean selecting what they need from the picture presented here. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. The Internet Protocol Suite . . . . . . . . . . . . . . . . . 5 2.1. Internet Protocol Layers . . . . . . . . . . . . . . . . . 5 2.1.1. Application . . . . . . . . . . . . . . . . . . . . . 5 2.1.2. Transport . . . . . . . . . . . . . . . . . . . . . . 6 2.1.3. Network . . . . . . . . . . . . . . . . . . . . . . . 6 2.1.3.1. Internet Layer . . . . . . . . . . . . . . . . . . 6 2.1.3.2. Lower layer networks . . . . . . . . . . . . . . . 7 2.1.4. Physical and Link layers . . . . . . . . . . . . . . . 7 2.2. Security issues . . . . . . . . . . . . . . . . . . . . . 7 2.2.1. Physical security . . . . . . . . . . . . . . . . . . 7 2.2.2. Session identification, authentication, authorization, and accounting . . . . . . . . . . . . 8 2.2.3. Confidentiality . . . . . . . . . . . . . . . . . . . 9 2.3. Network Infrastructure . . . . . . . . . . . . . . . . . . 9 2.3.1. Domain Name System (DNS) . . . . . . . . . . . . . . . 9 2.3.2. Network Management Issues . . . . . . . . . . . . . . 10 3. Specific protocols . . . . . . . . . . . . . . . . . . . . . . 10 3.1. Security solutions . . . . . . . . . . . . . . . . . . . . 10 3.1.1. Session identification, authentication, authorization, and accounting . . . . . . . . . . . . 10 3.1.2. IP Security Architecture (IPsec) . . . . . . . . . . . 11 3.1.3. Transport Layer Security (TLS) . . . . . . . . . . . . 11 3.1.4. Secure/Multipurpose Internet Mail Extensions (S/MIME) . . . . . . . . . . . . . . . . . . . . . . . 11 3.2. Network Layer . . . . . . . . . . . . . . . . . . . . . . 12 3.2.1. Internet Protocol Version 4 . . . . . . . . . . . . . 12 3.2.1.1. IPv4 Address Allocation and Assignment . . . . . . 12 3.2.1.2. IPv4 Unicast Routing . . . . . . . . . . . . . . . 12 3.2.1.3. IPv4 Multicast Forwarding and Routing . . . . . . 13 3.2.2. Internet Protocol Version 6 . . . . . . . . . . . . . 13 3.2.2.1. IPv6 Address Allocation and Assignment . . . . . . 13 3.2.2.2. IPv6 Routing . . . . . . . . . . . . . . . . . . . 14 3.2.2.3. IPv6 Multicast Forwarding and Routing . . . . . . 14 3.2.3. Adaptation to lower layer networks and link layer protocols . . . . . . . . . . . . . . . . . . . . . . 14 3.3. Transport Layer . . . . . . . . . . . . . . . . . . . . . 15 3.3.1. User Datagram Protocol (UDP) . . . . . . . . . . . . . 15 3.3.2. Transmission Control Protocol (TCP) . . . . . . . . . 16 3.3.3. Stream Control Transmission Protocol (SCTP) . . . . . 16 3.3.4. Datagram Congestion Control Protocol (DCCP) . . . . . 17 3.4. Infrastructure . . . . . . . . . . . . . . . . . . . . . . 17 Baker Expires April 1, 2010 [Page 2] Internet-Draft Core Protocols September 2009 3.4.1. Domain Name System . . . . . . . . . . . . . . . . . . 17 3.4.2. Dynamic Host Configuration . . . . . . . . . . . . . . 18 3.4.3. Network Time . . . . . . . . . . . . . . . . . . . . . 18 3.4.4. Session Initiation Protocol . . . . . . . . . . . . . 18 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 5. Security Considerations . . . . . . . . . . . . . . . . . . . 19 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19 7.1. Normative References . . . . . . . . . . . . . . . . . . . 19 7.2. Informative References . . . . . . . . . . . . . . . . . . 19 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 26 Baker Expires April 1, 2010 [Page 3] Internet-Draft Core Protocols September 2009 1. Introduction In the discussion of the Smart Grid, a question has arisen as to what the "core" protocols of the Internet Protocol Suite are. In this note, I will attempt to identify the structure of the Internet Protocol Suite and the key protocols that should be considered as critical in integrating Smart Grid devices into an IP-based infrastructure. In many cases, the protocols are options - one might choose, for example, TCP, SCTP, DCCP, or some other transport, or use UDP as a label and build the transport into the application itself. In the Transport layer, therefore, one is not limited to exactly one of those, nor is one required to implement them all. One should, however, pick the right one for the purpose one intends. This kind of discussion will be had at every layer. The set of protocols defined in this document focus on the use of the IP Protocol Suite in end systems, also known as hosts. In the Smart Grid, these end systems will be various devices such as power meters, sensors and actuators. These end systems can leverage infrastructure built on networking components using the IP Protocol Suite, which have well-proven implementations and deployments in the Internet. IETF participants in the Smart Grid discussion have been wary of the desire to write a "profile", repeatedly expressed. The IETF is all about interoperability, and in our experience attempts to "profile" protocols and architectures has resulted in a failure to interoperate. Examples of such failures abound. In IETF experience, writing a conforming and interoperable implementation of the right set of protocols works. Selecting some options and deselecting others within a defined protocol, however, is a dangerous course of action. So while this document is clearly a step in the direction of writing a "Smart Grid Profile", such a profile should in our opinion be a selected set of protocols, not of protocol subsets. For its own purposes, the IETF has written several documents that describe its expectations regarding implementations of the Internet Protocol Suite. These include: o Requirements for Internet Hosts - Communication Layers [RFC1122], o Requirements for Internet Hosts - Application and Support [RFC1123], o Requirements for IP Version 4 Routers [RFC1812], and o IPv6 Node Requirements [RFC4294], At this writing, RFC 4294 is in the process of being updated, in Baker Expires April 1, 2010 [Page 4] Internet-Draft Core Protocols September 2009 [I-D.ietf-6man-node-req-bis]. This document will read like an annotated list of RFCs. That is because that is what it is. 2. The Internet Protocol Suite Before listing a list of protocols, it would be well to lay out how they relate to each other. In this section, we will discuss the layered architecture of the Internet Protocol Suite and the jobs of the various layers and their protocols. 2.1. Internet Protocol Layers The Internet Architecture uses the definitions and language of the ISO Open System Interconnect Reference Model, as shown in Figure 1. It actually predates that model, and as a result uses some different words - an "end system" is generally called a "host", and an "intermediate system" is more generally called an "internet gateway" or "router". But the fundamental concepts are essentially the same. +--------------------+ | Application Layer | +--------------------+ | Presentation Layer | +--------------------+ | Session Layer | +--------------------+ | Transport layer | +--------------------+ | Network Layer | +--------------------+ | Data Link Layer | +--------------------+ | Physical Layer | +--------------------+ Figure 1: The ISO OSI Reference Model 2.1.1. Application In implementation, the Application, Presentation, and Session layers are generally compressed into a single entity, which the IETF calls "the application". The SNMP protocol, for example, describes an application (a management application or a client that it communicates with) that encodes its data in a profile of ASN.1 (a presentation layer) and engages in a session to manage a network Baker Expires April 1, 2010 [Page 5] Internet-Draft Core Protocols September 2009 element. In the Internet, therefore, the distinction between these layers exists but is not generally highlighted. 2.1.2. Transport The term "transport" is perhaps among the most confusing words in the communication architecture, because people with various backgrounds use it to refer to "the layer below that which I am interested in, which gets my data to my peer". In these contexts, optical fiber and other physical layers, the Internet Protocol or other networked protocols, and in some cases application layer protocols like HTTP are referred to as "the transport". In the Internet context, the "transport" is the lowest layer that travels end-to-end unmodified, and is responsible for end-to-end data delivery services. At minimum these include the ability to multiplex several applications on one IP address, and may also include the delivery of data (either as a stream of messages or a stream of bytes) in a stated sequence with stated expectations regarding delivery rate and loss. TCP, for example, will reduce rate to avoid loss, while DCCP accepts some level of loss if necessary to maintain timeliness. 2.1.3. Network The network layer is nominally that which identifies a remote destination and gets data to it. In connection-oriented networking, such as MPLS or ATM, a path (one of many "little tubes") is set up once, and data is delivered through it. In connectionless ("datagram") networks, which include Ethernet and IP among others, each datagram contains the addresses of both the source and destination devices, and the network is responsible to deliver it. 2.1.3.1. Internet Layer IPv4 and IPv6, each of which is called the Internet Protocol, are connectionless ("datagram") architectures. They are designed as common elements that interconnect network elements across a network of lower layer networks. In addition to the basic service of identifying a datagram's source and destination, they offer services to fragment and reassemble datagrams when necessary, assist in diagnosis of network failures, and carry additional information necessary in special cases. The Internet Layer provides a uniform network abstraction or virtual network that hides the differences between different network technologies. This is the layer that allows diverse networks such as Ethernet, 802.15.4, etc. to be combined into a uniform IP network. Baker Expires April 1, 2010 [Page 6] Internet-Draft Core Protocols September 2009 New network technologies can be introduced into the IP Protocol Suite by defining how IP is carried over those technologies, leaving the other layers of the IP Protocol Suite and applications that use those protocol unchanged. 2.1.3.2. Lower layer networks The network layer is recursively subdivided as needed. For various reasons, IP may be carried in virtual private networks across more public networks using tunneling technologies like IP-in-IP or GRE, traffic engineered in circuit networks such as MPLS, GMPLS, or ATM, and distributed across local wireless (IEEE 802.11, 802.15.4, or 802.16) and switched Ethernet (IEEE 802.3). 2.1.4. Physical and Link layers At the lowest layer of the architecture, we encode digital data in messages onto appropriate physical media. While the IETF specifies algorithms for carrying IPv4 and IPv6 on such media, it rarely actually defines the media - it happily uses specifications from IEEE, ITU, and other sources. 2.2. Security issues It is popular to complain about the security of the Internet; that said, solutions exist but are often left unused. As with automobile seat belts, they are of more value when actively used. Security designs attempt to mitigate a set of known threats at a specified cost; addressing security issues requires first a threat analysis and assessment and a set of mitigations appropriate to the threats. Since we have threats at every layer, we should expect to find mitigations at every layer. 2.2.1. Physical security At the physical and data link layers, threats involve physical attacks on the network - the effects of backhoes, deterioration of physical media, and various kinds of environmental noise. Radio- based networks are subject to signal fade due to distance, interference, and environmental factors; it is widely noted that IEEE 802.15.4 networks frequently place a metal ground plate between the meter and the device that manages it. Fiber was at one time deployed because it was believed to be untappable; we have since learned to tap it by bending the fiber and collecting incidental light, and we have learned about backhoes. So now some installations encase fiber optic cable in a pressurized sheath, both to quickly identify the location of a cut and to make it more difficult to tap. Baker Expires April 1, 2010 [Page 7] Internet-Draft Core Protocols September 2009 While there are protocol behaviors that can detect certain classes of physical faults, such as keep-alive exchanges, physical security is generally not a protocol problem. 2.2.2. Session identification, authentication, authorization, and accounting At the transport and application layers, and in lower layer networks where dynamic connectivity like ATM SVCs or "dial" connectivity is in use, there tend to be several different classes of authentication/ authorization requirements. One must 1. Verify that the peers one exchanges data with are appropriate partners; this generally means knowing "who" they are and that they have a "need to know" or are trusted sources. 2. Verify that information that appears to be from a trusted peer is in fact from that peer. 3. Validate the content of the data exchanged; it must conform to the rules of the exchange. 4. One must also defend the channel against denial of service attacks. In other words, there is a need to secure the channel that carries a message, and there is a need to secure the exchanges, both by knowing the source of the information and to have proof of its validity. Three examples suffice to illustrate the challenges. One common attack is to bombard a transport session (an application's channel) with reset messages. If the attacker is lucky, he might cause the session to fail. Including information in the transport header or a related protocol like IPsec or TLS that identifies the right messages and facilitates speedy discard of the rest can mitigate this. Another common attack involves unauthorized communication with a router or a service. For example, an unauthorized party might try to join the routing system. One wants the ISP's router, before accepting routing information from a new peer, to o demand identification from the new peer, o verify that the peer is in fact who it claims to be, and o verify that it is authorized to carry on the exchange. Baker Expires April 1, 2010 [Page 8] Internet-Draft Core Protocols September 2009 More generally, in securing the channel, one wants to verify that messages putatively received from a peer were in fact received from the peer, and given that they are, to only carry on transactions with peers that one trusts. This is analogous to how one responds to a salesman at the front door - one asks who the salesman represents, seeks a credential as proof, and then asks one self whether one wants to deal with that company. Only if all indications are positive does one carry on a transaction. Unfortunately, even trusted peers can be the purveyors of incorrect or malicious content; having secured the channel, one also wants to secure the information exchanged through the channel. In electronic mail and other database exchanges, it may be necessary to be able to verify the identity of the sender and the correctness of the content long after the information exchange has occurred - for example, if a contract is exchanged that is secured by digital signatures, one will wish to be able to verify those signatures at least throughout the lifetime of the contract, and probably a long time after that. The third "A" in "AAA" is Accounting. This service is especially important for Internet Service Providers; the related service of auditing is important for enterprises. RADIUS and DIAMETER are commonly used to realize these services. 2.2.3. Confidentiality At several layers, there is a question of confidentiality. If one is putting one's credit card in a transaction, one wants application layer privacy, which might be supplied by an encrypting application or transport layer protocol. If one is trying to hide one's network structure, one might additionally want to encrypt the network layer header. 2.3. Network Infrastructure While these are not critical to the design of a specific system, they are important to running a network. We therefore bring them up. 2.3.1. Domain Name System (DNS) While not critical to running a network, certain functions are made a lot easier if numeric addresses can be replaced with mnemonic names. This facilitates renumbering of networks, which happens, and generally improves the manageability and serviceability of the network. DNS has a set of security extensions called DNSSEC, which can be used to provide strong cryptographic authentication to that protocol. Baker Expires April 1, 2010 [Page 9] Internet-Draft Core Protocols September 2009 2.3.2. Network Management Issues Network management has proven to be a difficult problem; there are many solutions, and each has proponents with solid arguments for their viewpoint. In the IETF, we have two major network management solutions for device operation: SNMP, which is ASN.1-encoded and is primarily used for monitoring of system variables in a polled architecture, and NetConf, which is XML-encoded and primarily used for device configuration. Another aspect of network management is the initial provisioning and configuration of hosts. Address assignment and other configuration is discussed in Section 3.4.2. Smart Grid deployments will require additional identity authentication and authorization as well as other provisioning and configuration that may not be within the scope of DHCP and Neighbor Discovery. While the IP Protocol Suite does not have specific solutions for secure provisioning and configuration, these problems have been solved using IP protocols in specifications such as DOCSIS 3.0 [SP-MULPIv3.0]. 3. Specific protocols In this section, having briefly laid out the architecture and some of the problems that the architecture tries to address, we introduce specific protocols that might be appropriate to various use cases. In each place, the options are in the protocols used - one wants to select the right privacy, AAA, transport, and network solutions in each case. 3.1. Security solutions As noted, a key consideration in security solutions is a good threat analysis coupled with appropriate mitigations at each layer. 3.1.1. Session identification, authentication, authorization, and accounting In the Internet Protocol Suite there are several approaches to AAA issues; generally, one chooses one of them for a purpose. As they have different attack surfaces and protection domains, they require some thought in application. Two important ones are the IP Security Architecture, which protects IP datagrams, and Transport Layer Security, which protects the information that the Transport delivers. Baker Expires April 1, 2010 [Page 10] Internet-Draft Core Protocols September 2009 3.1.2. IP Security Architecture (IPsec) The Security Architecture for the Internet Protocol [RFC4301] is a set of control and data protocols that are implemented between IPv4 and its Transport layer, or in IPv6's Security extension header. It allows transport layer sessions (which underlie applications) to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. The architecture is spelled out in a number of additional specifications for specific components: the Encapsulating Security Payload (ESP) [RFC4303], the Internet Security Association and Key Management Protocol (ISAKMP) [RFC4304], Internet Key Exchange (IKEv2) [RFC4306], Cryptographic Algorithms [RFC4307], and the use of Advanced Encryption Standard (AES) [RFC4309]. In the transport mode, IPsec ESP encrypts the transport layer and the application data. In the tunnel mode, which is frequently used for Virtual Private Networks, one also encrypts the Internet Protocol, and encapsulates the encrypted data inside a second IP header directed to the intended decryptor. 3.1.3. Transport Layer Security (TLS) Transport Layer Security [RFC5246] and Datagram Transport Layer Security [RFC4347][I-D.ietf-tls-rfc4347-bis] are mechanisms that travel within the transport layer PDU, meaning that they readily traverse network address translators and secure the information exchanges without securing the datagrams exchanged or the transport layer itself. Each allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. 3.1.4. Secure/Multipurpose Internet Mail Extensions (S/MIME) The S/MIME [RFC2045] [RFC2046] [RFC2047] [RFC4289] [RFC2049] [RFC3850] [RFC3853] [RFC4262] specification was originally specified as an extension to SMTP Mail to provide evidence that the putative sender of an email message in fact sent it, and that the content received was in fact the content that was sent. As its name suggests, by extension this is a way of securing any object that can be exchanged, by any means, and has become one of the most common ways to secure an object. Other approaches also exist, such as the use of digital signatures on XML-encoded files, as jointly standardized by W3C and the IETF [RFC3275]. Baker Expires April 1, 2010 [Page 11] Internet-Draft Core Protocols September 2009 3.2. Network Layer Here we mention both IPv4 and IPv6. The reader is warned: IPv4 is running out of address space, and IPv6 has positive reasons that one might choose it apart from the IPv6 space such as the address autoconfiguration facility and its ability to support an arbitrarily large number of hosts in a subnet. As such, the IETF recommends that one always choose IPv6 support, and additionally choose IPv4 support in the near term. 3.2.1. Internet Protocol Version 4 IPv4 [RFC0791], with the Internet Control Message Protocol [RFC0792], constitutes the traditional protocol implemented throughout the Internet. IPv4 provides for transmission of datagrams from source to destination hosts, which are identified by fixed length addresses. IPv4 also provides for fragmentation and reassembly of long datagrams, if necessary, for transmission through "small packet" networks. ICMP, which is a separate protocol implemented along with IPv4, enables the network to report errors and other issues to hosts that originate problematic datagrams. 3.2.1.1. IPv4 Address Allocation and Assignment IPv4 addresses are administratively assigned, usually using automated methods, and assigned using the Dynamic Host Configuration Protocol (DHCP) [RFC2131]. On most interface types, neighboring equipment identify each other's addresses using Address Resolution Protocol (ARP) [RFC0826]. 3.2.1.2. IPv4 Unicast Routing Routing for the IPv4 Internet is done by routing applications that exchange connectivity information and build semi-static destination routing databases. If a datagram is directed to a given destination address, the address is looked up in the routing database, and the most specific ("longest") prefix found that contains it is used to identify the next hop router, or the end system it will be delivered to. This is not generally implemented on hosts, although it can be; generally, a host sends datagrams to a router on its local network, and the router carries out the intent. IETF specified routing protocols include RIP Version 2 [RFC2453], OSI IS-IS for IPv4 [RFC1195], OSPF Version 2 [RFC2328], and BGP-4 [RFC4271]. Active research exists in mobile ad hoc routing and other routing paradigms; these result in new protocols and modified forwarding paradigms. Baker Expires April 1, 2010 [Page 12] Internet-Draft Core Protocols September 2009 3.2.1.3. IPv4 Multicast Forwarding and Routing IPv4 was originally specified as a unicast (point to point) protocol, and was extended to support multicast in [RFC1112]. This uses the Internet Group Management Protocol [RFC3376][RFC4604] to enable applications to join multicast groups, and for most applications uses Source-Specific Multicast [RFC4607] for routing and delivery of multicast messages. An experiment carried out in IPv4 that is not core to the architecture but may be of interest in the Smart Grid is the development of so-called "Reliable Multicast". This is "so-called" because it is not "reliable" in the strict sense of the word - it is perhaps better described as "enhanced reliability". A best effort network by definition can lose traffic, duplicate it, or reorder it, something as true for multicast as for unicast. Research in "Reliable Multicast" technology intends to improve the probability of delivery of multicast traffic. In that research, the IETF imposed guidelines [RFC2357] on the research community regarding what was desirable. Important results from that research include a number of papers and several proprietary protocols including some that have been used in support of business operations. RFCs in the area include The Use of Forward Error Correction (FEC) in Reliable Multicast [RFC3453], the Negative- acknowledgment (NACK)-Oriented Reliable Multicast (NORM) Protocol [RFC3940], and the Selectively Reliable Multicast Protocol (SRMP) [RFC4410]. These are considered experimental. 3.2.2. Internet Protocol Version 6 IPv6 [RFC2460], with the Internet Control Message Protocol "v6" [RFC4443], constitutes the next generation protocol for the Internet. IPv6 provides for transmission of datagrams from source to destination hosts, which are identified by fixed length addresses. IPv6 also provides for fragmentation and reassembly of long datagrams by the originating host, if necessary, for transmission through "small packet" networks. ICMPv6, which is a separate protocol implemented along with IPv6, enables the network to report errors and other issues to hosts that originate problematic datagrams. 3.2.2.1. IPv6 Address Allocation and Assignment An IPv6 Address [RFC4291] may be administratively assigned using DHCPv6 [RFC3315] in a manner similar to the way IPv4 addresses are, but may also be autoconfigured, facilitating network management. Autoconfiguration procedures are defined in [RFC4862] and [RFC4941]. Baker Expires April 1, 2010 [Page 13] Internet-Draft Core Protocols September 2009 IPv6 neighbors identify each other's addresses using either Neighbor Discovery (ND) [RFC4861] or SEcure Neighbor Discovery (SEND) [RFC3971]. 3.2.2.2. IPv6 Routing Routing for the IPv6 Internet is done by routing applications that exchange connectivity information and build semi-static destination routing databases. If a datagram is directed to a given destination address, the address is looked up in the routing database, and the most specific ("longest") prefix found that contains it is used to identify the next hop router, or the end system it will be delivered to. This is not generally implemented on hosts, although it can be; generally, a host sends datagrams to a router on its local network, and the router carries out the intent. IETF specified routing protocols include RIP for IPv6 [RFC2080], IS-IS for IPv6 [RFC5308], OSPF for IPv6 [RFC5340], and BGP-4 for IPv6 [RFC2545]. Active research exists in mobile ad hoc routing, routing in low power networks (sensors and smart grids) and other routing paradigms; these result in new protocols and modified forwarding paradigms. 3.2.2.3. IPv6 Multicast Forwarding and Routing From its initial design, IPv6 has specified both unicast and multicast datagram exchange. This uses the Multicast Listener Discovery Protocol (MLDv2) [RFC2710] [RFC3590] [RFC3810] [RFC4604] to enable applications to join multicast groups, and for most applications uses Source-Specific Multicast [RFC4607] for routing and delivery of multicast messages. The IPv6 over Low-Power Wireless Personal Area Networks [RFC4919] RFC addresses IPv6 header compression and subnet architecture in at least some sensor networks, and may be appropriate to the Smart Grid AMI or other sensor domains. The mechanisms experimentally developed for reliable multicast in IPv4, discussed in Section 3.2.1.3, can be used in IPv6 as well. 3.2.3. Adaptation to lower layer networks and link layer protocols In general, the layered architecture enables the Internet Protocol Suite to run over any appropriate layer 2 architecture; with tongue in cheek, specifications have been written and demonstrated to work for the carriage of IP by Carrier Pigeon [RFC1149][RFC2549] (perhaps the most common carrier known to man) and on barbed wire [Chapman]. The ability to change the link or physical layer without having to Baker Expires April 1, 2010 [Page 14] Internet-Draft Core Protocols September 2009 rethink the network layer, transports, or applications has been a great benefit in the Internet. Examples of link layer adaptation technology include: Ethernet/IEEE 802.3: IPv4 has run on each link layer environment that uses the Ethernet header (which is to say 10 and 100 MBPS wired Ethernet, 1 and 10 GBPS wired Ethernet, and the various versions of IEEE 802.11) using [RFC0894]. IPv6 does the same using [RFC2464]. PPP: The IETF has defined a serial line protocol, the Point-to-Point Protocol (PPP) [RFC1661], that uses HDLC (bit-synchronous or byte synchronous) framing. The IPv4 adaptation specification is [RFC1332], and the IPv6 adaptation specification is [RFC5072]. Current use of this protocol is in traditional serial lines, authentication exchanges in DSL networks using PPP Over Ethernet (PPPoE) [RFC2516], and in the Digital Signaling Hierarchy (generally referred to as Packet-on-SONET/SDH) using PPP over SONET/SDH [RFC2615]. IEEE 802.15.4: The adaptation specification for IPv6 transmission over IEEE 802.15.4 Networks is [RFC4944]. Numerous other adaptation specifications exist, including ATM, Frame Relay, X.25, other standardized and proprietary LAN technologies, and others. 3.3. Transport Layer In this we list several transports: UDP, TCP, SCTP, and DCCP. Of these, UDP and TCP are best known and most widely used, due to history. SCTP and DCCP were built for specific purposes more recently and bear consideration at least for those purposes. Note that if it is appropriate, other transports can also be built. This is largely a question of requirements. 3.3.1. User Datagram Protocol (UDP) The User Datagram Protocol [RFC0768] and the Lightweight User Datagram Protocol [RFC3828] are properly not "transport" protocols in the sense of "a set of rules governing the exchange or transmission of data electronically between devices". They are labels that provide for multiplexing of applications directly on the IP layer, with transport functionality embedded in the application. From a historical perspective, one should note that many simplistic Baker Expires April 1, 2010 [Page 15] Internet-Draft Core Protocols September 2009 exchange designs have been built using UDP, and many of them have not worked all that well. The use of UDP really should be treated as designing a new transport. More generally, advice on the use of UDP in new applications has been compiled in the Unicast UDP Usage Guidelines for Application Designers [RFC5405]. Datagram Transport Layer Security [RFC5238] can be used to prevent eavesdropping, tampering, or message forgery. Alternatively, UDP can run over IPsec. 3.3.2. Transmission Control Protocol (TCP) TCP [RFC0793] is the predominant transport protocol in use in the Internet, with a long history. It is "reliable", as the term is used in protocol design: it delivers data to its peer and provides acknowledgement to the sender, or it dies trying. It has extensions for Congestion Control [RFC2581] and Explicit Congestion Notification [RFC3168]. The user interface for TCP is a byte stream interface - an application using TCP might "write" to it several times only to have the data compacted into a common segment and delivered as such to its peer. For message-stream interfaces, we generally use the ISO Transport Service on TCP [RFC1006][RFC2126] in the application. Transport Layer Security [RFC5246] can be used to prevent eavesdropping, tampering, or message forgery. Alternatively, TCP can run over IPsec. Additionally, [RFC4987] discusses mechanisms similar to SCTP and DCCP's "cookie" approach that may be used to secure TCP sessions against flooding attacks. TCP has supported ongoing research since it was written. As a result, the End to End research group has published a Roadmap for TCP Specification Documents [RFC4614] which will guide expectations in that area. 3.3.3. Stream Control Transmission Protocol (SCTP) SCTP [RFC4960] is a more recent reliable transport protocol that can be imagined as a TCP-like context containing multiple separate and independent message streams (as opposed to TCP's byte streams). The design of SCTP includes appropriate congestion avoidance behavior and resistance to flooding and masquerade attacks. As it uses a message stream interface as opposed to TCP's byte stream interface, it may also be more appropriate for the ISO Transport Service than RFC 1006/ 2126. SCTP offers several delivery options. The basic service is Baker Expires April 1, 2010 [Page 16] Internet-Draft Core Protocols September 2009 sequential non-duplicated delivery of messages within a stream, for each stream in use. Since streams are independent, one stream may pause due to head of line blocking while another stream in the same session continues to deliver data. In addition, SCTP provides a mechanism for bypassing the sequenced delivery service. User messages sent using this mechanism are delivered to the SCTP user as soon as they are received. SCTP implements a simple "cookie" mechanism intended to limit the effectiveness of flooding attacks by mutual authentication. This demonstrates that the application is connected to the same peer, but does not identify the peer. Mechanisms also exist for Dynamic Address Reconfiguration [RFC5061], enabling peers to change addresses during the session and yet retain connectivity. Transport Layer Security [RFC3436] can be used to prevent eavesdropping, tampering, or message forgery. Alternatively, SCTP can run over IPsec. 3.3.4. Datagram Congestion Control Protocol (DCCP) DCCP [RFC4340] is an "unreliable" transport protocol (e.g., one that does not guarantee message delivery) that provides bidirectional unicast connections of congestion-controlled unreliable datagrams. DCCP is suitable for applications that transfer fairly large amounts of data and that can benefit from control over the tradeoff between timeliness and reliability. DCCP implements a simple "cookie" mechanism intended to limit the effectiveness of flooding attacks by mutual authentication. This demonstrates that the application is connected to the same peer, but does not identify the peer. Datagram Transport Layer Security [RFC5238] can be used to prevent eavesdropping, tampering, or message forgery. Alternatively, DCCP can run over IPsec. 3.4. Infrastructure 3.4.1. Domain Name System To facilitate network management and operations, the Internet Community has defined the Domain Name System (DNS) [RFC1034][RFC1035]. Names are hierarchical: a name like example.com is found registered with a .com registrar, and within the associated network other names like baldur.cincinatti.example.com can be defined, with obvious hierarchy. Security extensions, which all a registry to sign the records it contains and as a result demonstrate their authenticity, are defined by the DNS Security Extensions [RFC4033][RFC4034][RFC4035]. Similarly unrequired but useful is the ability for a device to update Baker Expires April 1, 2010 [Page 17] Internet-Draft Core Protocols September 2009 its own DNS record. One could imagine a sensor, for example, that is using Stateless Address Autoconfiguration [RFC4862] to create an address to associate it with a name using DNS Dynamic Update [RFC2136] or DNS Secure Dynamic Update [RFC3007]. 3.4.2. Dynamic Host Configuration As discussed in Section 3.2.1 and Section 3.2.2, IPv6 address assignment can be accomplished using autoconfiguration but can also be accomplished using DHCP [RFC2131] or DHCPv6 [RFC3315]. The best argument for the use of autoconfiguration is a large number of systems that require little more than a random number as an address; the argument for DHCP is administrative control. There are other parameters that may need to be allocated to hosts, and these do require administrative configuration; examples include the address of one's DNS server, keys if Secure DNS is in use, and others. 3.4.3. Network Time The Network Time Protocol was originally designed by Dave Mills of the University of Delaware and CSNET, for the purpose of implementing a temporal metric in the Fuzzball Routing Protocol and generally coordinating time experiments. The current versions of the time protocol are the Network Time Protocol [RFC1305], which is designed for synchronization to within a few microseconds, and the Simple Network Time Protocol [RFC4330] which is used to set real time clocks to within a few milliseconds. The former is more precise, but relies on frequent exchanges; the latter is less precise and lower overhead. NTP is currently being updated in [I-D.ietf-ntp-ntpv4-proto]. 3.4.4. Session Initiation Protocol The Session Initiation Protocol [RFC3261][RFC3265][RFC3853][RFC4320][RFC4916][RFC5393][RFC5621] was originally developed to manage Voice-on-IP and Video-on-IP sessions on the Internet, as an open source alternative to H.323. Via extensions, it is generally used for session setup for a variety of purposes and for very quick management exchanges. 4. IANA Considerations This memo asks the IANA for no new parameters. Note to RFC Editor: This section will have served its purpose if it Baker Expires April 1, 2010 [Page 18] Internet-Draft Core Protocols September 2009 correctly tells IANA that no new assignments or registries are required, or if those assignments or registries are created during the RFC publication process. From the author"s perspective, it may therefore be removed upon publication as an RFC at the RFC Editor's discretion. 5. Security Considerations Security is addressed in some detail in Section 2.2 and Section 3.1. 6. Acknowledgements Review comments were made by Andrew Yourtchenko, Ashok Narayanan, Bernie Volz, Chris Lonvick, Dave McGrew, Dave Oran, David Su, Hemant Singh, John Meylor, Joseph Salowey, Julien Abeille, Kerry Lynn, Murtaza Chiba, Paul Duffy, Ralph Droms, Russ White, and Toerless Eckert. Dave McGrew and Ralph Droms suggested text. 7. References 7.1. Normative References [RFC1122] Braden, R., "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, October 1989. [RFC1123] Braden, R., "Requirements for Internet Hosts - Application and Support", STD 3, RFC 1123, October 1989. [RFC1812] Baker, F., "Requirements for IP Version 4 Routers", RFC 1812, June 1995. [RFC4294] Loughney, J., "IPv6 Node Requirements", RFC 4294, April 2006. 7.2. Informative References [Chapman] Chapman, E., "Ethernet over Barbed Wire, Arcnet, 100MB Token Ring, 100Base-VGAnylan and iSCSI ...", 2007. [I-D.ietf-6man-node-req-bis] Loughney, J. and T. Narten, "IPv6 Node Requirements RFC 4294-bis", draft-ietf-6man-node-req-bis-03 (work in progress), July 2009. [I-D.ietf-ntp-ntpv4-proto] Baker Expires April 1, 2010 [Page 19] Internet-Draft Core Protocols September 2009 Burbank, J., "Network Time Protocol Version 4 Protocol And Algorithms Specification", draft-ietf-ntp-ntpv4-proto-11 (work in progress), September 2008. [I-D.ietf-tls-rfc4347-bis] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security version 1.2", draft-ietf-tls-rfc4347-bis-02 (work in progress), March 2009. [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August 1980. [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, RFC 792, September 1981. [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, September 1981. [RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or converting network protocol addresses to 48.bit Ethernet address for transmission on Ethernet hardware", STD 37, RFC 826, November 1982. [RFC0894] Hornig, C., "Standard for the transmission of IP datagrams over Ethernet networks", STD 41, RFC 894, April 1984. [RFC1006] Rose, M. and D. Cass, "ISO transport services on top of the TCP: Version 3", STD 35, RFC 1006, May 1987. [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, November 1987. [RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, November 1987. [RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5, RFC 1112, August 1989. [RFC1149] Waitzman, D., "Standard for the transmission of IP datagrams on avian carriers", RFC 1149, April 1990. [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and dual environments", RFC 1195, December 1990. [RFC1305] Mills, D., "Network Time Protocol (Version 3) Baker Expires April 1, 2010 [Page 20] Internet-Draft Core Protocols September 2009 Specification, Implementation", RFC 1305, March 1992. [RFC1332] McGregor, G., "The PPP Internet Protocol Control Protocol (IPCP)", RFC 1332, May 1992. [RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51, RFC 1661, July 1994. [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996. [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text", RFC 2047, November 1996. [RFC2049] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples", RFC 2049, November 1996. [RFC2080] Malkin, G. and R. Minnear, "RIPng for IPv6", RFC 2080, January 1997. [RFC2126] Pouffary, Y. and A. Young, "ISO Transport Service on top of TCP (ITOT)", RFC 2126, March 1997. [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997. [RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, "Dynamic Updates in the Domain Name System (DNS UPDATE)", RFC 2136, April 1997. [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. [RFC2357] Mankin, A., Romanov, A., Bradner, S., and V. Paxson, "IETF Criteria for Evaluating Reliable Multicast Transport and Application Protocols", RFC 2357, June 1998. [RFC2453] Malkin, G., "RIP Version 2", STD 56, RFC 2453, November 1998. [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. Baker Expires April 1, 2010 [Page 21] Internet-Draft Core Protocols September 2009 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet Networks", RFC 2464, December 1998. [RFC2516] Mamakos, L., Lidl, K., Evarts, J., Carrel, D., Simone, D., and R. Wheeler, "A Method for Transmitting PPP Over Ethernet (PPPoE)", RFC 2516, February 1999. [RFC2545] Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol Extensions for IPv6 Inter-Domain Routing", RFC 2545, March 1999. [RFC2549] Waitzman, D., "IP over Avian Carriers with Quality of Service", RFC 2549, April 1999. [RFC2581] Allman, M., Paxson, V., and W. Stevens, "TCP Congestion Control", RFC 2581, April 1999. [RFC2615] Malis, A. and W. Simpson, "PPP over SONET/SDH", RFC 2615, June 1999. [RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast Listener Discovery (MLD) for IPv6", RFC 2710, October 1999. [RFC3007] Wellington, B., "Secure Domain Name System (DNS) Dynamic Update", RFC 3007, November 2000. [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition of Explicit Congestion Notification (ECN) to IP", RFC 3168, September 2001. [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [RFC3265] Roach, A., "Session Initiation Protocol (SIP)-Specific Event Notification", RFC 3265, June 2002. [RFC3275] Eastlake, D., Reagle, J., and D. Solo, "(Extensible Markup Language) XML-Signature Syntax and Processing", RFC 3275, March 2002. [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003. [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. Baker Expires April 1, 2010 [Page 22] Internet-Draft Core Protocols September 2009 Thyagarajan, "Internet Group Management Protocol, Version 3", RFC 3376, October 2002. [RFC3436] Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport Layer Security over Stream Control Transmission Protocol", RFC 3436, December 2002. [RFC3453] Luby, M., Vicisano, L., Gemmell, J., Rizzo, L., Handley, M., and J. Crowcroft, "The Use of Forward Error Correction (FEC) in Reliable Multicast", RFC 3453, December 2002. [RFC3590] Haberman, B., "Source Address Selection for the Multicast Listener Discovery (MLD) Protocol", RFC 3590, September 2003. [RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery Version 2 (MLDv2) for IPv6", RFC 3810, June 2004. [RFC3828] Larzon, L-A., Degermark, M., Pink, S., Jonsson, L-E., and G. Fairhurst, "The Lightweight User Datagram Protocol (UDP-Lite)", RFC 3828, July 2004. [RFC3850] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.1 Certificate Handling", RFC 3850, July 2004. [RFC3853] Peterson, J., "S/MIME Advanced Encryption Standard (AES) Requirement for the Session Initiation Protocol (SIP)", RFC 3853, July 2004. [RFC3940] Adamson, B., Bormann, C., Handley, M., and J. Macker, "Negative-acknowledgment (NACK)-Oriented Reliable Multicast (NORM) Protocol", RFC 3940, November 2004. [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005. [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "DNS Security Introduction and Requirements", RFC 4033, March 2005. [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Resource Records for the DNS Security Extensions", RFC 4034, March 2005. [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Protocol Modifications for the DNS Security Extensions", RFC 4035, March 2005. Baker Expires April 1, 2010 [Page 23] Internet-Draft Core Protocols September 2009 [RFC4262] Santesson, S., "X.509 Certificate Extension for Secure/ Multipurpose Internet Mail Extensions (S/MIME) Capabilities", RFC 4262, December 2005. [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, January 2006. [RFC4289] Freed, N. and J. Klensin, "Multipurpose Internet Mail Extensions (MIME) Part Four: Registration Procedures", BCP 13, RFC 4289, December 2005. [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006. [RFC4301] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, December 2005. [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303, December 2005. [RFC4304] Kent, S., "Extended Sequence Number (ESN) Addendum to IPsec Domain of Interpretation (DOI) for Internet Security Association and Key Management Protocol (ISAKMP)", RFC 4304, December 2005. [RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC 4306, December 2005. [RFC4307] Schiller, J., "Cryptographic Algorithms for Use in the Internet Key Exchange Version 2 (IKEv2)", RFC 4307, December 2005. [RFC4309] Housley, R., "Using Advanced Encryption Standard (AES) CCM Mode with IPsec Encapsulating Security Payload (ESP)", RFC 4309, December 2005. [RFC4320] Sparks, R., "Actions Addressing Identified Issues with the Session Initiation Protocol's (SIP) Non-INVITE Transaction", RFC 4320, January 2006. [RFC4330] Mills, D., "Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI", RFC 4330, January 2006. [RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram Congestion Control Protocol (DCCP)", RFC 4340, March 2006. [RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security", RFC 4347, April 2006. Baker Expires April 1, 2010 [Page 24] Internet-Draft Core Protocols September 2009 [RFC4410] Pullen, M., Zhao, F., and D. Cohen, "Selectively Reliable Multicast Protocol (SRMP)", RFC 4410, February 2006. [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", RFC 4443, March 2006. [RFC4604] Holbrook, H., Cain, B., and B. Haberman, "Using Internet Group Management Protocol Version 3 (IGMPv3) and Multicast Listener Discovery Protocol Version 2 (MLDv2) for Source- Specific Multicast", RFC 4604, August 2006. [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for IP", RFC 4607, August 2006. [RFC4614] Duke, M., Braden, R., Eddy, W., and E. Blanton, "A Roadmap for Transmission Control Protocol (TCP) Specification Documents", RFC 4614, September 2006. [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, September 2007. [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, September 2007. [RFC4916] Elwell, J., "Connected Identity in the Session Initiation Protocol (SIP)", RFC 4916, June 2007. [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): Overview, Assumptions, Problem Statement, and Goals", RFC 4919, August 2007. [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 4941, September 2007. [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, "Transmission of IPv6 Packets over IEEE 802.15.4 Networks", RFC 4944, September 2007. [RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC 4960, September 2007. [RFC4987] Eddy, W., "TCP SYN Flooding Attacks and Common Mitigations", RFC 4987, August 2007. Baker Expires April 1, 2010 [Page 25] Internet-Draft Core Protocols September 2009 [RFC5061] Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M. Kozuka, "Stream Control Transmission Protocol (SCTP) Dynamic Address Reconfiguration", RFC 5061, September 2007. [RFC5072] S.Varada, Haskins, D., and E. Allen, "IP Version 6 over PPP", RFC 5072, September 2007. [RFC5238] Phelan, T., "Datagram Transport Layer Security (DTLS) over the Datagram Congestion Control Protocol (DCCP)", RFC 5238, May 2008. [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 2008. [RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308, October 2008. [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF for IPv6", RFC 5340, July 2008. [RFC5393] Sparks, R., Lawrence, S., Hawrylyshen, A., and B. Campen, "Addressing an Amplification Vulnerability in Session Initiation Protocol (SIP) Forking Proxies", RFC 5393, December 2008. [RFC5405] Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines for Application Designers", BCP 145, RFC 5405, November 2008. [RFC5621] Camarillo, G., "Message Body Handling in the Session Initiation Protocol (SIP)", RFC 5621, September 2009. [SP-MULPIv3.0] CableLabs, "DOCSIS 3.0 MAC and Upper Layer Protocols Interface Specification, CM-SP-MULPIv3.0-I10-090529", May 2009. Author's Address Fred Baker Cisco Systems Santa Barbara, California 93117 USA Email: fred@cisco.com Baker Expires April 1, 2010 [Page 26]