RFCs in HTML Format


RFC 1716

                  Towards Requirements for IP Routers
























Almquist & Kastenholz                                           [Page i]

RFC 1716 Towards Requirements for IP Routers November 1994 Table of Contents 0. PREFACE ....................................................... 1 1. INTRODUCTION .................................................. 2 1.1 Reading this Document ........................................ 4 1.1.1 Organization ............................................... 4 1.1.2 Requirements ............................................... 5 1.1.3 Compliance ................................................. 6 1.2 Relationships to Other Standards ............................. 7 1.3 General Considerations ....................................... 8 1.3.1 Continuing Internet Evolution .............................. 8 1.3.2 Robustness Principle ....................................... 9 1.3.3 Error Logging .............................................. 9 1.3.4 Configuration .............................................. 10 1.4 Algorithms ................................................... 11 2. INTERNET ARCHITECTURE ......................................... 13 2.1 Introduction ................................................. 13 2.2 Elements of the Architecture ................................. 14 2.2.1 Protocol Layering .......................................... 14 2.2.2 Networks ................................................... 16 2.2.3 Routers .................................................... 17 2.2.4 Autonomous Systems ......................................... 18 2.2.5 Addresses and Subnets ...................................... 18 2.2.6 IP Multicasting ............................................ 20 2.2.7 Unnumbered Lines and Networks and Subnets .................. 20 2.2.8 Notable Oddities ........................................... 22 2.2.8.1 Embedded Routers ......................................... 22 2.2.8.2 Transparent Routers ...................................... 23 2.3 Router Characteristics ....................................... 24 2.4 Architectural Assumptions .................................... 27 3. LINK LAYER .................................................... 29 3.1 INTRODUCTION ................................................. 29 3.2 LINK/INTERNET LAYER INTERFACE ................................ 29 3.3 SPECIFIC ISSUES .............................................. 30 3.3.1 Trailer Encapsulation ...................................... 30 3.3.2 Address Resolution Protocol - ARP .......................... 31 3.3.3 Ethernet and 802.3 Coexistence ............................. 31 3.3.4 Maximum Transmission Unit - MTU ............................ 31 3.3.5 Point-to-Point Protocol - PPP .............................. 32 3.3.5.1 Introduction ............................................. 32 3.3.5.2 Link Control Protocol (LCP) Options ...................... 33 3.3.5.3 IP Control Protocol (ICP) Options ........................ 34 3.3.6 Interface Testing .......................................... 35 4. INTERNET LAYER - PROTOCOLS .................................... 36 4.1 INTRODUCTION ................................................. 36 4.2 INTERNET PROTOCOL - IP ....................................... 36 Almquist & Kastenholz [Page ii]
RFC 1716 Towards Requirements for IP Routers November 1994 4.2.1 INTRODUCTION ............................................... 36 4.2.2 PROTOCOL WALK-THROUGH ...................................... 37 4.2.2.1 Options: RFC 791 Section 3.2 ............................. 37 4.2.2.2 Addresses in Options: RFC 791 Section 3.1 ................ 40 4.2.2.3 Unused IP Header Bits: RFC 791 Section 3.1 ............... 40 4.2.2.4 Type of Service: RFC 791 Section 3.1 ..................... 41 4.2.2.5 Header Checksum: RFC 791 Section 3.1 ..................... 41 4.2.2.6 Unrecognized Header Options: RFC 791 Section 3.1 ......... 41 4.2.2.7 Fragmentation: RFC 791 Section 3.2 ....................... 42 4.2.2.8 Reassembly: RFC 791 Section 3.2 .......................... 43 4.2.2.9 Time to Live: RFC 791 Section 3.2 ........................ 43 4.2.2.10 Multi-subnet Broadcasts: RFC 922 ........................ 43 4.2.2.11 Addressing: RFC 791 Section 3.2 ......................... 43 4.2.3 SPECIFIC ISSUES ............................................ 47 4.2.3.1 IP Broadcast Addresses ................................... 47 4.2.3.2 IP Multicasting .......................................... 48 4.2.3.3 Path MTU Discovery ....................................... 48 4.2.3.4 Subnetting ............................................... 49 4.3 INTERNET CONTROL MESSAGE PROTOCOL - ICMP ..................... 50 4.3.1 INTRODUCTION ............................................... 50 4.3.2 GENERAL ISSUES ............................................. 50 4.3.2.1 Unknown Message Types .................................... 50 4.3.2.2 ICMP Message TTL ......................................... 51 4.3.2.3 Original Message Header .................................. 51 4.3.2.4 ICMP Message Source Address .............................. 51 4.3.2.5 TOS and Precedence ....................................... 51 4.3.2.6 Source Route ............................................. 52 4.3.2.7 When Not to Send ICMP Errors ............................. 53 4.3.2.8 Rate Limiting ............................................ 54 4.3.3 SPECIFIC ISSUES ............................................ 55 4.3.3.1 Destination Unreachable .................................. 55 4.3.3.2 Redirect ................................................. 55 4.3.3.3 Source Quench ............................................ 56 4.3.3.4 Time Exceeded ............................................ 56 4.3.3.5 Parameter Problem ........................................ 57 4.3.3.6 Echo Request/Reply ....................................... 57 4.3.3.7 Information Request/Reply ................................ 58 4.3.3.8 Timestamp and Timestamp Reply ............................ 58 4.3.3.9 Address Mask Request/Reply ............................... 59 4.3.3.10 Router Advertisement and Solicitations .................. 61 4.4 INTERNET GROUP MANAGEMENT PROTOCOL - IGMP .................... 61 5. INTERNET LAYER - FORWARDING ................................... 62 5.1 INTRODUCTION ................................................. 62 5.2 FORWARDING WALK-THROUGH ...................................... 62 5.2.1 Forwarding Algorithm ....................................... 62 5.2.1.1 General .................................................. 63 5.2.1.2 Unicast .................................................. 64 Almquist & Kastenholz [Page iii]
RFC 1716 Towards Requirements for IP Routers November 1994 5.2.1.3 Multicast ................................................ 65 5.2.2 IP Header Validation ....................................... 66 5.2.3 Local Delivery Decision .................................... 68 5.2.4 Determining the Next Hop Address ........................... 70 5.2.4.1 Immediate Destination Address ............................ 71 5.2.4.2 Local/Remote Decision .................................... 71 5.2.4.3 Next Hop Address ......................................... 72 5.2.4.4 Administrative Preference ................................ 77 5.2.4.6 Load Splitting ........................................... 78 5.2.5 Unused IP Header Bits: RFC 791 Section 3.1 ................. 79 5.2.6 Fragmentation and Reassembly: RFC 791 Section 3.2 .......... 79 5.2.7 Internet Control Message Protocol - ICMP ................... 80 5.2.7.1 Destination Unreachable .................................. 80 5.2.7.2 Redirect ................................................. 82 5.2.7.3 Time Exceeded ............................................ 84 5.2.8 INTERNET GROUP MANAGEMENT PROTOCOL - IGMP .................. 84 5.3 SPECIFIC ISSUES .............................................. 84 5.3.1 Time to Live (TTL) ......................................... 84 5.3.2 Type of Service (TOS) ...................................... 85 5.3.3 IP Precedence .............................................. 87 5.3.3.1 Precedence-Ordered Queue Service ......................... 88 5.3.3.2 Lower Layer Precedence Mappings .......................... 88 5.3.3.3 Precedence Handling For All Routers ...................... 89 5.3.4 Forwarding of Link Layer Broadcasts ........................ 92 5.3.5 Forwarding of Internet Layer Broadcasts .................... 92 5.3.5.1 Limited Broadcasts ....................................... 94 5.3.5.2 Net-directed Broadcasts .................................. 94 5.3.5.3 All-subnets-directed Broadcasts .......................... 95 5.3.5.4 Subnet-directed Broadcasts ............................... 97 5.3.6 Congestion Control ......................................... 97 5.3.7 Martian Address Filtering .................................. 99 5.3.8 Source Address Validation .................................. 99 5.3.9 Packet Filtering and Access Lists .......................... 100 5.3.10 Multicast Routing ......................................... 101 5.3.11 Controls on Forwarding .................................... 101 5.3.12 State Changes ............................................. 101 5.3.12.1 When a Router Ceases Forwarding ......................... 102 5.3.12.2 When a Router Starts Forwarding ......................... 102 5.3.12.3 When an Interface Fails or is Disabled .................. 103 5.3.12.4 When an Interface is Enabled ............................ 103 5.3.13 IP Options ................................................ 103 5.3.13.1 Unrecognized Options .................................... 103 5.3.13.2 Security Option ......................................... 104 5.3.13.3 Stream Identifier Option ................................ 104 5.3.13.4 Source Route Options .................................... 104 5.3.13.5 Record Route Option ..................................... 104 5.3.13.6 Timestamp Option ........................................ 105 Almquist & Kastenholz [Page iv]
RFC 1716 Towards Requirements for IP Routers November 1994 6. TRANSPORT LAYER ............................................... 106 6.1 USER DATAGRAM PROTOCOL - UDP ................................. 106 6.2 TRANSMISSION CONTROL PROTOCOL - TCP .......................... 106 7. APPLICATION LAYER - ROUTING PROTOCOLS ......................... 109 7.1 INTRODUCTION ................................................. 109 7.1.1 Routing Security Considerations ............................ 109 7.1.2 Precedence ................................................. 110 7.2 INTERIOR GATEWAY PROTOCOLS ................................... 110 7.2.1 INTRODUCTION ............................................... 110 7.2.2 OPEN SHORTEST PATH FIRST - OSPF ............................ 111 7.2.2.1 Introduction ............................................. 111 7.2.2.2 Specific Issues .......................................... 111 7.2.2.3 New Version of OSPF ...................................... 112 7.2.3 INTERMEDIATE SYSTEM TO INTERMEDIATE SYSTEM - DUAL IS-IS .............................................................. 112 7.2.4 ROUTING INFORMATION PROTOCOL - RIP ......................... 113 7.2.4.1 Introduction ............................................. 113 7.2.4.2 Protocol Walk-Through .................................... 113 7.2.4.3 Specific Issues .......................................... 118 7.2.5 GATEWAY TO GATEWAY PROTOCOL - GGP .......................... 119 7.3 EXTERIOR GATEWAY PROTOCOLS ................................... 119 7.3.1 INTRODUCTION ............................................... 119 7.3.2 BORDER GATEWAY PROTOCOL - BGP .............................. 120 7.3.2.1 Introduction ............................................. 120 7.3.2.2 Protocol Walk-through .................................... 120 7.3.3 EXTERIOR GATEWAY PROTOCOL - EGP ............................ 121 7.3.3.1 Introduction ............................................. 121 7.3.3.2 Protocol Walk-through .................................... 122 7.3.4 INTER-AS ROUTING WITHOUT AN EXTERIOR PROTOCOL .............. 124 7.4 STATIC ROUTING ............................................... 125 7.5 FILTERING OF ROUTING INFORMATION ............................. 127 7.5.1 Route Validation ........................................... 127 7.5.2 Basic Route Filtering ...................................... 127 7.5.3 Advanced Route Filtering ................................... 128 7.6 INTER-ROUTING-PROTOCOL INFORMATION EXCHANGE .................. 129 8. APPLICATION LAYER - NETWORK MANAGEMENT PROTOCOLS .............. 131 8.1 The Simple Network Management Protocol - SNMP ................ 131 8.1.1 SNMP Protocol Elements ..................................... 131 8.2 Community Table .............................................. 132 8.3 Standard MIBS ................................................ 133 8.4 Vendor Specific MIBS ......................................... 134 8.5 Saving Changes ............................................... 135 9. APPLICATION LAYER - MISCELLANEOUS PROTOCOLS ................... 137 9.1 BOOTP ........................................................ 137 9.1.1 Introduction ............................................... 137 9.1.2 BOOTP Relay Agents ......................................... 137 10. OPERATIONS AND MAINTENANCE ................................... 139 Almquist & Kastenholz [Page v]
RFC 1716 Towards Requirements for IP Routers November 1994 10.1 Introduction ................................................ 139 10.2 Router Initialization ....................................... 140 10.2.1 Minimum Router Configuration .............................. 140 10.2.2 Address and Address Mask Initialization ................... 141 10.2.3 Network Booting using BOOTP and TFTP ...................... 142 10.3 Operation and Maintenance ................................... 143 10.3.1 Introduction .............................................. 143 10.3.2 Out Of Band Access ........................................ 144 10.3.2 Router O&M Functions ...................................... 144 10.3.2.1 Maintenance - Hardware Diagnosis ........................ 144 10.3.2.2 Control - Dumping and Rebooting ......................... 145 10.3.2.3 Control - Configuring the Router ........................ 145 10.3.2.4 Netbooting of System Software ........................... 146 10.3.2.5 Detecting and responding to misconfiguration ............ 146 10.3.2.6 Minimizing Disruption ................................... 147 10.3.2.7 Control - Troubleshooting Problems ...................... 148 10.4 Security Considerations ..................................... 149 10.4.1 Auditing and Audit Trails ................................. 149 10.4.2 Configuration Control ..................................... 150 11. REFERENCES ................................................... 152 APPENDIX A. REQUIREMENTS FOR SOURCE-ROUTING HOSTS ................ 162 APPENDIX B. GLOSSARY ............................................. 164 APPENDIX C. FUTURE DIRECTIONS .................................... 169 APPENDIX D. Multicast Routing Protocols .......................... 172 D.1 Introduction ................................................. 172 D.2 Distance Vector Multicast Routing Protocol - DVMRP ........... 172 D.3 Multicast Extensions to OSPF - MOSPF ......................... 173 APPENDIX E Additional Next-Hop Selection Algorithms .............. 174 E.1. Some Historical Perspective .................................. 174 E.2. Additional Pruning Rules ..................................... 176 E.3 Some Route Lookup Algorithms ................................. 177 E.3.1 The Revised Classic Algorithm ............................... 178 E.3.2 The Variant Router Requirements Algorithm ................... 179 E.3.3 The OSPF Algorithm .......................................... 179 E.3.4 The Integrated IS-IS Algorithm .............................. 180 Security Considerations ........................................... 182 Acknowledgments ................................................... 183 Editor's Address .................................................. 186 Almquist & Kastenholz [Page vi]
RFC 1716 Towards Requirements for IP Routers November 1994 0. PREFACE This document is a snapshot of the work of the Router Requirements working group as of November 1991. At that time, the working group had essentially finished its task. There were some final technical matters to be nailed down, and a great deal of editing needed to be done in order to get the document ready for publication. Unfortunately, these tasks were never completed. At the request of the Internet Area Director, the current editor took the last draft of the document and, after consulting the mailing list archives, meeting minutes, notes, and other members of the working group, edited the document to its current form. This effort included the following tasks: 1) Deleting all the parenthetical material (such as editor's comments). Useful information was turned into DISCUSSION sections, the rest was deleted. 2) Completing the tasks listed in the last draft's To be Done sections. As a part of this task, a new "to be done" list was developed and included as an appendix to the current document. 3) Rolling Philip Almquist's "Ruminations on the Next Hop" and "Ruminations on Route Leaking" into this document. These represent significant work and should be kept. 4) Fulfilling the last intents of the working group as determined from the archival material. The intent of this effort was to get the document into a form suitable for publication as an Historical RFC so that the significant work which went into the creation of this document would be preserved. The content and form of this document are due, in large part, to the working group's chair, and document's original editor and author: Philip Almquist. Without his efforts, this document would not exist. Almquist & Kastenholz [Page 1]
RFC 1716 Towards Requirements for IP Routers November 1994 1. INTRODUCTION The goal of this work is to replace RFC 1009, Requirements for Internet Gateways ([INTRO:1]) with a new document. This memo is an intermediate step toward that goal. It defines and discusses requirements for devices which perform the network layer forwarding function of the Internet protocol suite. The Internet community usually refers to such devices as IP routers or simply routers; The OSI community refers to such devices as intermediate systems. Many older Internet documents refer to these devices as gateways, a name which more recently has largely passed out of favor to avoid confusion with application gateways. An IP router can be distinguished from other sorts of packet switching devices in that a router examines the IP protocol header as part of the switching process. It generally has to modify the IP header and to strip off and replace the Link Layer framing. The authors of this memo recognize, as should its readers, that many routers support multiple protocol suites, and that support for multiple protocol suites will be required in increasingly large parts of the Internet in the future. This memo, however, does not attempt to specify Internet requirements for protocol suites other than TCP/IP. This document enumerates standard protocols that a router connected to the Internet must use, and it incorporates by reference the RFCs and other documents describing the current specifications for these protocols. It corrects errors in the referenced documents and adds additional discussion and guidance for an implementor. For each protocol, this final version of this memo also contains an explicit set of requirements, recommendations, and options. The reader must understand that the list of requirements in this memo is incomplete by itself; the complete set of requirements for an Internet protocol router is primarily defined in the standard protocol specification documents, with the corrections, amendments, and supplements contained in this memo. This memo should be read in conjunction with the Requirements for Internet Hosts RFCs ([INTRO:2] and [INTRO:3]). Internet hosts and routers must both be capable of originating IP datagrams and receiving IP datagrams destined for them. The major distinction between Internet hosts and routers is that routers are required to implement forwarding algorithms and Internet hosts do not require forwarding capabilities. Any Internet host acting as a router must adhere to the requirements contained in the final version of this memo. Almquist & Kastenholz [Page 2]
RFC 1716 Towards Requirements for IP Routers November 1994 The goal of open system interconnection dictates that routers must function correctly as Internet hosts when necessary. To achieve this, this memo provides guidelines for such instances. For simplification and ease of document updates, this memo tries to avoid overlapping discussions of host requirements with [INTRO:2] and [INTRO:3] and incorporates the relevant requirements of those documents by reference. In some cases the requirements stated in [INTRO:2] and [INTRO:3] are superseded by the final version of this document. A good-faith implementation of the protocols produced after careful reading of the RFCs, with some interaction with the Internet technical community, and that follows good communications software engineering practices, should differ from the requirements of this memo in only minor ways. Thus, in many cases, the requirements in this document are already stated or implied in the standard protocol documents, so that their inclusion here is, in a sense, redundant. However, they were included because some past implementation has made the wrong choice, causing problems of interoperability, performance, and/or robustness. This memo includes discussion and explanation of many of the requirements and recommendations. A simple list of requirements would be dangerous, because: o Some required features are more important than others, and some features are optional. o Some features are critical in some applications of routers but irrelevant in others. o There may be valid reasons why particular vendor products that are designed for restricted contexts might choose to use different specifications. However, the specifications of this memo must be followed to meet the general goal of arbitrary router interoperation across the diversity and complexity of the Internet. Although most current implementations fail to meet these requirements in various ways, some minor and some major, this specification is the ideal towards which we need to move. These requirements are based on the current level of Internet architecture. This memo will be updated as required to provide additional clarifications or to include additional information in those areas in which specifications are still evolving. Almquist & Kastenholz [Page 3]
RFC 1716 Towards Requirements for IP Routers November 1994 1.1 Reading this Document 1.1.1 Organization This memo emulates the layered organization used by [INTRO:2] and [INTRO:3]. Thus, Chapter 2 describes the layers found in the Internet architecture. Chapter 3 covers the Link Layer. Chapters 4 and 5 are concerned with the Internet Layer protocols and forwarding algorithms. Chapter 6 covers the Transport Layer. Upper layer protocols are divided between Chapter 7, which discusses the protocols which routers use to exchange routing information with each other, Chapter 8, which discusses network management, and Chapter 9, which discusses other upper layer protocols. The final chapter covers operations and maintenance features. This organization was chosen for simplicity, clarity, and consistency with the Host Requirements RFCs. Appendices to this memo include a bibliography, a glossary, and some conjectures about future directions of router standards. In describing the requirements, we assume that an implementation strictly mirrors the layering of the protocols. However, strict layering is an imperfect model, both for the protocol suite and for recommended implementation approaches. Protocols in different layers interact in complex and sometimes subtle ways, and particular functions often involve multiple layers. There are many design choices in an implementation, many of which involve creative breaking of strict layering. Every implementor is urged to read [INTRO:4] and [INTRO:5]. In general, each major section of this memo is organized into the following subsections: (1) Introduction (2) Protocol Walk-Through - considers the protocol specification documents section-by-section, correcting errors, stating requirements that may be ambiguous or ill-defined, and providing further clarification or explanation. (3) Specific Issues - discusses protocol design and implementation issues that were not included in the walk- through. Under many of the individual topics in this memo, there is parenthetical material labeled DISCUSSION or IMPLEMENTATION. This material is intended to give a justification, clarification or Almquist & Kastenholz [Page 4]
RFC 1716 Towards Requirements for IP Routers November 1994 explanation to the preceding requirements text. The implementation material contains suggested approaches that an implementor may want to consider. The DISCUSSION and IMPLEMENTATION sections are not part of the standard. 1.1.2 Requirements In this memo, the words that are used to define the significance of each particular requirement are capitalized. These words are: o MUST This word means that the item is an absolute requirement of the specification. o MUST IMPLEMENT This phrase means that this specification requires that the item be implemented, but does not require that it be enabled by default. o MUST NOT This phrase means that the item is an absolute prohibition of the specification. o SHOULD This word means that there may exist valid reasons in particular circumstances to ignore this item, but the full implications should be understood and the case carefully weighed before choosing a different course. o SHOULD IMPLEMENT This phrase is similar in meaning to SHOULD, but is used when we recommend that a particular feature be provided but does not necessarily recommend that it be enabled by default. o SHOULD NOT This phrase means that there may exist valid reasons in particular circumstances when the described behavior is acceptable or even useful, but the full implications should be understood and the case carefully weighed before implementing any behavior described with this label. o MAY This word means that this item is truly optional. One vendor may choose to include the item because a particular marketplace requires it or because it enhances the product, for example; another vendor may omit the same item. Almquist & Kastenholz [Page 5]
RFC 1716 Towards Requirements for IP Routers November 1994 1.1.3 Compliance Some requirements are applicable to all routers. Other requirements are applicable only to those which implement particular features or protocols. In the following paragraphs, Relevant refers to the union of the requirements applicable to all routers and the set of requirements applicable to a particular router because of the set of features and protocols it has implemented. Note that not all Relevant requirements are stated directly in this memo. Various parts of this memo incorporate by reference sections of the Host Requirements specification, [INTRO:2] and [INTRO:3]. For purposes of determining compliance with this memo, it does not matter whether a Relevant requirement is stated directly in this memo or merely incorporated by reference from one of those documents. An implementation is said to be conditionally compliant if it satisfies all of the Relevant MUST, MUST IMPLEMENT, and MUST NOT requirements. An implementation is said to be unconditionally compliant if it is conditionally compliant and also satisfies all of the Relevant SHOULD, SHOULD IMPLEMENT, and SHOULD NOT requirements. An implementation is not compliant if it is not conditionally compliant (i.e., it fails to satisfy one or more of the Relevant MUST, MUST IMPLEMENT, or MUST NOT requirements). For any of the SHOULD and SHOULD NOT requirements, a router may provide a configuration option that will cause the router to act other than as specified by the requirement. Having such a configuration option does not void a router's claim to unconditional compliance as long as the option has a default setting, and that leaving the option at its default setting causes the router to operate in a manner which conforms to the requirement. Likewise, routers may provide, except where explicitly prohibited by this memo, options which cause them to violate MUST or MUST NOT requirements. A router which provides such options is compliant (either fully or conditionally) if and only if each such option has a default setting which causes the router to conform to the requirements of this memo. Please note that the authors of this memo, although aware of market realities, strongly recommend against provision of such options. Requirements are labeled MUST or MUST NOT because experts in the field have judged them to be particularly important to interoperability or proper functioning in the Internet. Vendors should weigh carefully the customer Almquist & Kastenholz [Page 6]
RFC 1716 Towards Requirements for IP Routers November 1994 support costs of providing options which violate those rules. Of course, this memo is not a complete specification of an IP router, but rather is closer to what in the OSI world is called a profile. For example, this memo requires that a number of protocols be implemented. Although most of the contents of their protocol specifications are not repeated in this memo, implementors are nonetheless required to implement the protocols according to those specifications. 1.2 Relationships to Other Standards There are several reference documents of interest in checking the current status of protocol specifications and standardization: o INTERNET OFFICIAL PROTOCOL STANDARDS This document describes the Internet standards process and lists the standards status of the protocols. As of this writing, the current version of this document is STD 1, RFC 1610, [ARCH:7]. This document is periodically re-issued. You should always consult an RFC repository and use the latest version of this document. o Assigned Numbers This document lists the assigned values of the parameters used in the various protocols. For example, IP protocol codes, TCP port numbers, Telnet Option Codes, ARP hardware types, and Terminal Type names. As of this writing, the current version of this document is STD 2, RFC 1700, [INTRO:7]. This document is periodically re-issued. You should always consult an RFC repository and use the latest version of this document. o Host Requirements This pair of documents reviews the specifications that apply to hosts and supplies guidance and clarification for any ambiguities. Note that these requirements also apply to routers, except where otherwise specified in this memo. As of this writing (December, 1993) the current versions of these documents are RFC 1122 and RFC 1123, (STD 3) [INTRO:2], and [INTRO:3] respectively. o Router Requirements (formerly Gateway Requirements) This memo. Note that these documents are revised and updated at different times; in case of differences between these documents, the most recent must prevail. Almquist & Kastenholz [Page 7]
RFC 1716 Towards Requirements for IP Routers November 1994 These and other Internet protocol documents may be obtained from the: The InterNIC DS.INTERNIC.NET InterNIC Directory and Database Service +1 (800) 444-4345 or +1 (619) 445-4600 info@internic.net 1.3 General Considerations There are several important lessons that vendors of Internet software have learned and which a new vendor should consider seriously. 1.3.1 Continuing Internet Evolution The enormous growth of the Internet has revealed problems of management and scaling in a large datagram-based packet communication system. These problems are being addressed, and as a result there will be continuing evolution of the specifications described in this memo. New routing protocols, algorithms, and architectures are constantly being developed. New and additional internet-layer protocols are also constantly being devised. Because routers play such a crucial role in the Internet, and because the number of routers deployed in the Internet is much smaller than the number of hosts, vendors should expect that router standards will continue to evolve much more quickly than host standards. These changes will be carefully planned and controlled since there is extensive participation in this planning by the vendors and by the organizations responsible for operation of the networks. Development, evolution, and revision are characteristic of computer network protocols today, and this situation will persist for some years. A vendor who develops computer communications software for the Internet protocol suite (or any other protocol suite!) and then fails to maintain and update that software for changing specifications is going to leave a trail of unhappy customers. The Internet is a large communication network, and the users are in constant contact through it. Experience has shown that knowledge of deficiencies in vendor software propagates quickly through the Internet technical community. Almquist & Kastenholz [Page 8]
RFC 1716 Towards Requirements for IP Routers November 1994 1.3.2 Robustness Principle At every layer of the protocols, there is a general rule (from [TRANS:2] by Jon Postel) whose application can lead to enormous benefits in robustness and interoperability: Be conservative in what you do, be liberal in what you accept from others. Software should be written to deal with every conceivable error, no matter how unlikely; sooner or later a packet will come in with that particular combination of errors and attributes, and unless the software is prepared, chaos can ensue. In general, it is best to assume that the network is filled with malevolent entities that will send packets designed to have the worst possible effect. This assumption will lead to suitably protective design. The most serious problems in the Internet have been caused by unforeseen mechanisms triggered by low probability events; mere human malice would never have taken so devious a course! Adaptability to change must be designed into all levels of router software. As a simple example, consider a protocol specification that contains an enumeration of values for a particular header field - e.g., a type field, a port number, or an error code; this enumeration must be assumed to be incomplete. If the protocol specification defines four possible error codes, the software must not break when a fifth code shows up. An undefined code might be logged, but it must not cause a failure. The second part of the principle is almost as important: software on hosts or other routers may contain deficiencies that make it unwise to exploit legal but obscure protocol features. It is unwise to stray far from the obvious and simple, lest untoward effects result elsewhere. A corollary of this is watch out for misbehaving hosts; router software should be prepared to survive in the presence of misbehaving hosts. An important function of routers in the Internet is to limit the amount of disruption such hosts can inflict on the shared communication facility. 1.3.3 Error Logging The Internet includes a great variety of systems, each implementing many protocols and protocol layers, and some of these contain bugs and misfeatures in their Internet protocol software. As a result of complexity, diversity, and distribution of function, the diagnosis of problems is often very difficult. Almquist & Kastenholz [Page 9]
RFC 1716 Towards Requirements for IP Routers November 1994 Problem diagnosis will be aided if routers include a carefully designed facility for logging erroneous or strange events. It is important to include as much diagnostic information as possible when an error is logged. In particular, it is often useful to record the header(s) of a packet that caused an error. However, care must be taken to ensure that error logging does not consume prohibitive amounts of resources or otherwise interfere with the operation of the router. There is a tendency for abnormal but harmless protocol events to overflow error logging files; this can be avoided by using a circular log, or by enabling logging only while diagnosing a known failure. It may be useful to filter and count duplicate successive messages. One strategy that seems to work well is to both: o Always count abnormalities and make such counts accessible through the management protocol (see Chapter 8); and o Allow the logging of a great variety of events to be selectively enabled. For example, it might useful to be able to log everything or to log everything for host X. This topic is further discussed in [MGT:5]. 1.3.4 Configuration In an ideal world, routers would be easy to configure, and perhaps even entirely self-configuring. However, practical experience in the real world suggests that this is an impossible goal, and that in fact many attempts by vendors to make configuration easy actually cause customers more grief than they prevent. As an extreme example, a router designed to come up and start routing packets without requiring any configuration information at all would almost certainly choose some incorrect parameter, possibly causing serious problems on any networks unfortunate enough to be connected to it. Often this memo requires that a parameter be a configurable option. There are several reasons for this. In a few cases there currently is some uncertainty or disagreement about the best value and it may be necessary to update the recommended value in the future. In other cases, the value really depends on external factors - e.g., the distribution of its communication load, or the speeds and topology of nearby networks - and self-tuning algorithms are unavailable and may be insufficient. In some cases, configurability is needed because of administrative requirements. Almquist & Kastenholz [Page 10]
RFC 1716 Towards Requirements for IP Routers November 1994 Finally, some configuration options are required to communicate with obsolete or incorrect implementations of the protocols, distributed without sources, that persist in many parts of the Internet. To make correct systems coexist with these faulty systems, administrators must occasionally misconfigure the correct systems. This problem will correct itself gradually as the faulty systems are retired, but cannot be ignored by vendors. When we say that a parameter must be configurable, we do not intend to require that its value be explicitly read from a configuration file at every boot time. For many parameters, there is one value that is appropriate for all but the most unusual situations. In such cases, it is quite reasonable that the parameter default to that value if not explicitly set. This memo requires a particular value for such defaults in some cases. The choice of default is a sensitive issue when the configuration item controls accommodation of existing, faulty, systems. If the Internet is to converge successfully to complete interoperability, the default values built into implementations must implement the official protocol, not misconfigurations to accommodate faulty implementations. Although marketing considerations have led some vendors to choose misconfiguration defaults, we urge vendors to choose defaults that will conform to the standard. Finally, we note that a vendor needs to provide adequate documentation on all configuration parameters, their limits and effects. 1.4 Algorithms In several places in this memo, specific algorithms that a router ought to follow are specified. These algorithms are not, per se, required of the router. A router need not implement each algorithm as it is written in this document. Rather, an implementation must present a behavior to the external world that is the same as a strict, literal, implementation of the specified algorithm. Algorithms are described in a manner that differs from the way a good implementor would implement them. For expository purposes, a style that emphasizes conciseness, clarity, and independence from implementation details has been chosen. A good implementor will choose algorithms and implementation methods which produce the same results as these algorithms, but may be more efficient or less general. Almquist & Kastenholz [Page 11]
RFC 1716 Towards Requirements for IP Routers November 1994 We note that the art of efficient router implementation is outside of the scope of this memo. Almquist & Kastenholz [Page 12]
RFC 1716 Towards Requirements for IP Routers November 1994 2. INTERNET ARCHITECTURE This chapter does not contain any requirements. However, it does contain useful background information on the general architecture of the Internet and of routers. General background and discussion on the Internet architecture and supporting protocol suite can be found in the DDN Protocol Handbook [ARCH:1]; for background see for example [ARCH:2], [ARCH:3], and [ARCH:4]. The Internet architecture and protocols are also covered in an ever-growing number of textbooks, such as [ARCH:5] and [ARCH:6]. 2.1 Introduction The Internet system consists of a number of interconnected packet networks supporting communication among host computers using the Internet protocols. These protocols include the Internet Protocol (IP), the Internet Control Message Protocol (ICMP), the Internet Group Management Protocol (IGMP), and a variety transport and application protocols that depend upon them. As was described in Section [1.2], the Internet Engineering Steering Group periodically releases an Official Protocols memo listing all of the Internet protocols. All Internet protocols use IP as the basic data transport mechanism. IP is a datagram, or connectionless, internetwork service and includes provision for addressing, type-of-service specification, fragmentation and reassembly, and security. ICMP and IGMP are considered integral parts of IP, although they are architecturally layered upon IP. ICMP provides error reporting, flow control, first-hop router redirection, and other maintenance and control functions. IGMP provides the mechanisms by which hosts and routers can join and leave IP multicast groups. Reliable data delivery is provided in the Internet protocol suite by Transport Layer protocols such as the Transmission Control Protocol (TCP), which provides end-end retransmission, resequencing and connection control. Transport Layer connectionless service is provided by the User Datagram Protocol (UDP). Almquist & Kastenholz [Page 13]
RFC 1716 Towards Requirements for IP Routers November 1994 2.2 Elements of the Architecture 2.2.1 Protocol Layering To communicate using the Internet system, a host must implement the layered set of protocols comprising the Internet protocol suite. A host typically must implement at least one protocol from each layer. The protocol layers used in the Internet architecture are as follows [ARCH:7]: o Application Layer The Application Layer is the top layer of the Internet protocol suite. The Internet suite does not further subdivide the Application Layer, although some application layer protocols do contain some internal sub-layering. The application layer of the Internet suite essentially combines the functions of the top two layers - Presentation and Application - of the OSI Reference Model [ARCH:8]. The Application Layer in the Internet protocol suite also includes some of the function relegated to the Session Layer in the OSI Reference Model. We distinguish two categories of application layer protocols: user protocols that provide service directly to users, and support protocols that provide common system functions. The most common Internet user protocols are: - Telnet (remote login) - FTP (file transfer) - SMTP (electronic mail delivery) There are a number of other standardized user protocols and many private user protocols. Support protocols, used for host name mapping, booting, and management, include SNMP, BOOTP, TFTP, the Domain Name System (DNS) protocol, and a variety of routing protocols. Application Layer protocols relevant to routers are discussed in chapters 7, 8, and 9 of this memo. o Transport Layer The Transport Layer provides end-to-end communication services. This layer is roughly equivalent to the Transport Layer in the OSI Reference Model, except that it also incorporates some of OSI's Session Layer establishment and destruction functions. Almquist & Kastenholz [Page 14]
RFC 1716 Towards Requirements for IP Routers November 1994 There are two primary Transport Layer protocols at present: - Transmission Control Protocol (TCP) - User Datagram Protocol (UDP) TCP is a reliable connection-oriented transport service that provides end-to-end reliability, resequencing, and flow control. UDP is a connectionless (datagram) transport service. Other transport protocols have been developed by the research community, and the set of official Internet transport protocols may be expanded in the future. Transport Layer protocols relevant to routers are discussed in Chapter 6. o Internet Layer All Internet transport protocols use the Internet Protocol (IP) to carry data from source host to destination host. IP is a connectionless or datagram internetwork service, providing no end-to-end delivery guarantees. IP datagrams may arrive at the destination host damaged, duplicated, out of order, or not at all. The layers above IP are responsible for reliable delivery service when it is required. The IP protocol includes provision for addressing, type-of-service specification, fragmentation and reassembly, and security. The datagram or connectionless nature of IP is a fundamental and characteristic feature of the Internet architecture. The Internet Control Message Protocol (ICMP) is a control protocol that is considered to be an integral part of IP, although it is architecturally layered upon IP, i.e., it uses IP to carry its data end-to-end. ICMP provides error reporting, congestion reporting, and first-hop router redirection. The Internet Group Management Protocol (IGMP) is an Internet layer protocol used for establishing dynamic host groups for IP multicasting. The Internet layer protocols IP, ICMP, and IGMP are discussed in chapter 4. o Link Layer To communicate on its directly-connected network, a host must implement the communication protocol used to interface to that network. We call this a Link Layer layer protocol. Almquist & Kastenholz [Page 15]
RFC 1716 Towards Requirements for IP Routers November 1994 Some older Internet documents refer to this layer as the Network Layer, but it is not the same as the Network Layer in the OSI Reference Model. This layer contains everything below the Internet Layer. Protocols in this Layer are generally outside the scope of Internet standardization; the Internet (intentionally) uses existing standards whenever possible. Thus, Internet Link Layer standards usually address only address resolution and rules for transmitting IP packets over specific Link Layer protocols. Internet Link Layer standards are discussed in chapter 3. 2.2.2 Networks The constituent networks of the Internet system are required to provide only packet (connectionless) transport. According to the IP service specification, datagrams can be delivered out of order, be lost or duplicated, and/or contain errors. For reasonable performance of the protocols that use IP (e.g., TCP), the loss rate of the network should be very low. In networks providing connection-oriented service, the extra reliability provided by virtual circuits enhances the end-end robustness of the system, but is not necessary for Internet operation. Constituent networks may generally be divided into two classes: o Local-Area Networks (LANs) LANs may have a variety of designs. In general, a LAN will cover a small geographical area (e.g., a single building or plant site) and provide high bandwidth with low delays. LANs may be passive (similar to Ethernet) or they may be active (such as ATM). o Wide-Area Networks (WANs) Geographically-dispersed hosts and LANs are interconnected by wide-area networks, also called long-haul networks. These networks may have a complex internal structure of lines and packet-switches, or they may be as simple as point-to-point lines. Almquist & Kastenholz [Page 16]
RFC 1716 Towards Requirements for IP Routers November 1994 2.2.3 Routers In the Internet model, constituent networks are connected together by IP datagram forwarders which are called routers or IP routers. In this document, every use of the term router is equivalent to IP router. Many older Internet documents refer to routers as gateways. Historically, routers have been realized with packet-switching software executing on a general-purpose CPU. However, as custom hardware development becomes cheaper and as higher throughput is required, but special-purpose hardware is becoming increasingly common. This specification applies to routers regardless of how they are implemented. A router is connected to two or more networks, appearing to each of these networks as a connected host. Thus, it has (at least) one physical interface and (at least) one IP address on each of the connected networks (this ignores the concept of un-numbered links, which is discussed in section [2.2.7]). Forwarding an IP datagram generally requires the router to choose the address of the next-hop router or (for the final hop) the destination host. This choice, called routing, depends upon a routing database within the router. The routing database is also sometimes known as a routing table or forwarding table. The routing database should be maintained dynamically to reflect the current topology of the Internet system. A router normally accomplishes this by participating in distributed routing and reachability algorithms with other routers. Routers provide datagram transport only, and they seek to minimize the state information necessary to sustain this service in the interest of routing flexibility and robustness. Packet switching devices may also operate at the Link Layer; such devices are usually called bridges. Network segments which are connected by bridges share the same IP network number, i.e., they logically form a single IP network. These other devices are outside of the scope of this document. Another variation on the simple model of networks connected with routers sometimes occurs: a set of routers may be interconnected with only serial lines, to form a network in which the packet switching is performed at the Internetwork (IP) Layer rather than the Link Layer. Almquist & Kastenholz [Page 17]
RFC 1716 Towards Requirements for IP Routers November 1994 2.2.4 Autonomous Systems For technical, managerial, and sometimes political reasons, the routers of the Internet system are grouped into collections called autonomous systems. The routers included in a single autonomous system (AS) are expected to: o Be under the control of a single operations and maintenance (O&M) organization; o Employ common routing protocols among themselves, to dynamically maintain their routing databases. A number of different dynamic routing protocols have been developed (see Section [7.2]); the routing protocol within a single AS is generically called an interior gateway protocol or IGP. An IP datagram may have to traverse the routers of two or more ASs to reach its destination, and the ASs must provide each other with topology information to allow such forwarding. An exterior gateway protocol (generally BGP or EGP) is used for this purpose. 2.2.5 Addresses and Subnets An IP datagram carries 32-bit source and destination addresses, each of which is partitioned into two parts - a constituent network number and a host number on that network. Symbolically: IP-address ::= { <Network-number>, <Host-number> } To finally deliver the datagram, the last router in its path must map the Host-number (or rest) part of an IP address into the physical address of a host connection to the constituent network. This simple notion has been extended by the concept of subnets, which were introduced in order to allow arbitrary complexity of interconnected LAN structures within an organization, while insulating the Internet system against explosive growth in network numbers and routing complexity. Subnets essentially provide a multi-level hierarchical routing structure for the Internet system. The subnet extension, described in [INTERNET:2], is now a required part of the Internet architecture. The basic idea is to partition the <Host-number> field into two parts: a subnet number, and a true host number on that subnet: IP-address ::= Almquist & Kastenholz [Page 18]
RFC 1716 Towards Requirements for IP Routers November 1994 { <Network-number>, <Subnet-number>, <Host-number> } The interconnected physical networks within an organization will be given the same network number but different subnet numbers. The distinction between the subnets of such a subnetted network is normally not visible outside of that network. Thus, routing in the rest of the Internet will be based only upon the <Network- number> part of the IP destination address; routers outside the network will combine <Subnet-number> and <Host-number> together to form an uninterpreted rest part of the 32-bit IP address. Within the subnetted network, the routers must route on the basis of an extended network number: { <Network-number>, <Subnet-number> } Under certain circumstances, it may be desirable to support subnets of a particular network being interconnected only via a path which is not part of the subnetted network. Even though many IGP's and no EGP's currently support this configuration effectively, routers need to be able to support this configuration of subnetting (see Section [4.2.3.4]). In general, routers should not make assumptions about what are subnets and what are not, but simply ignore the concept of Class in networks, and treat each route as a { network, mask }-tuple. DISCUSSION: It is becoming clear that as the Internet grows larger and larger, the traditional uses of Class A, B, and C networks will be modified in order to achieve better use of IP's 32-bit address space. Classless Interdomain Routing (CIDR) [INTERNET:15] is a method currently being deployed in the Internet backbones to achieve this added efficiency. CIDR depends on the ability of assigning and routing to networks that are not based on Class A, B, or C networks. Thus, routers should always treat a route as a network with a mask. Furthermore, for similar reasons, a subnetted network need not have a consistent subnet mask through all parts of the network. For example, one subnet may use an 8 bit subnet mask, another 10 bit, and another 6 bit. Routers need to be able to support this type of configuration (see Section [4.2.3.4]). The bit positions containing this extended network number are indicated by a 32-bit mask called the subnet mask; it is recommended but not required that the <Subnet-number> bits be contiguous and fall between the <Network-number> and the <Host- number> fields. No subnet should be assigned the value zero or -1 Almquist & Kastenholz [Page 19]
RFC 1716 Towards Requirements for IP Routers November 1994 (all one bits). Although the inventors of the subnet mechanism probably expected that each piece of an organization's network would have only a single subnet number, in practice it has often proven necessary or useful to have several subnets share a single physical cable. There are special considerations for the router when a connected network provides a broadcast or multicast capability; these will be discussed later. 2.2.6 IP Multicasting IP multicasting is an extension of Link Layer multicast to IP internets. Using IP multicasts, a single datagram can be addressed to multiple hosts. This collection of hosts is called a multicast group. Each multicast group is represented as a Class D IP address. An IP datagram sent to the group is to be delivered to each group member with the same best-effort delivery as that provided for unicast IP traffic. The sender of the datagram does not itself need to be a member of the destination group. The semantics of IP multicast group membership are defined in [INTERNET:4]. That document describes how hosts and routers join and leave multicast groups. It also defines a protocol, the Internet Group Management Protocol (IGMP), that monitors IP multicast group membership. Forwarding of IP multicast datagrams is accomplished either through static routing information or via a multicast routing protocol. Devices that forward IP multicast datagrams are called multicast routers. They may or may not also forward IP unicasts. In general, multicast datagrams are forwarded on the basis of both their source and destination addresses. Forwarding of IP multicast packets is described in more detail in Section [5.2.1]. Appendix D discusses multicast routing protocols. 2.2.7 Unnumbered Lines and Networks and Subnets Traditionally, each network interface on an IP host or router has its own IP address. Over the years, people have observed that this can cause inefficient use of the scarce IP address space, since it forces allocation of an IP network number, or at least a subnet number, to every point-to-point link. To solve this problem, a number of people have proposed and implemented the concept of unnumbered serial lines. An unnumbered Almquist & Kastenholz [Page 20]
RFC 1716 Towards Requirements for IP Routers November 1994 serial line does not have any IP network or subnet number associated with it. As a consequence, the network interfaces connected to an unnumbered serial line do not have IP addresses. Because the IP architecture has traditionally assumed that all interfaces had IP addresses, these unnumbered interfaces cause some interesting dilemmas. For example, some IP options (e.g. Record Route) specify that a router must insert the interface address into the option, but an unnumbered interface has no IP address. Even more fundamental (as we shall see in chapter 5) is that routes contain the IP address of the next hop router. A router expects that that IP address will be on an IP (sub)net that the router is connected to. That assumption is of course violated if the only connection is an unnumbered serial line. To get around these difficulties, two schemes have been invented. The first scheme says that two routers connected by an unnumbered serial line aren't really two routers at all, but rather two half-routers which together make up a single (virtual) router. The unnumbered serial line is essentially considered to be an internal bus in the virtual router. The two halves of the virtual router must coordinate their activities in such a way that they act exactly like a single router. This scheme fits in well with the IP architecture, but suffers from two important drawbacks. The first is that, although it handles the common case of a single unnumbered serial line, it is not readily extensible to handle the case of a mesh of routers and unnumbered serial lines. The second drawback is that the interactions between the half routers are necessarily complex and are not standardized, effectively precluding the connection of equipment from different vendors using unnumbered serial lines. Because of these drawbacks, this memo has adopted an alternative scheme, which has been invented multiple times but which is probably originally attributable to Phil Karn. In this scheme, a router which has unnumbered serial lines also has a special IP address, called a router-id in this memo. The router-id is one of the router's IP addresses (a router is required to have at least one IP address). This router-id is used as if it is the IP address of all unnumbered interfaces. Almquist & Kastenholz [Page 21]
RFC 1716 Towards Requirements for IP Routers November 1994
RFC 1716 Towards Requirements for IP Routers November 1994 Algorithm: (1) It supports type of service routing. (2) Its rules are written down, rather than merely being a part of the Internet folklore. (3) It (obviously) works with OSPF. However, this algorithm also retains some of the disadvantages of the Revised Classic Algorithm: (1) Path properties other than type of service (e.g. MTU) are ignored. (2) As in the Revised Classic Algorithm, the details (or even the existence) of the Policy step are left to the discretion of the implementor. The OSPF Algorithm also has a further disadvantage (which is not shared by the Revised Classic Algorithm). OSPF internal (intra- area or inter-area) routes are always considered to be superior to routes learned from other routing protocols, even in cases where the OSPF route matches fewer bits of the destination address. This is a policy decision that is inappropriate in some networks. Finally, it is worth noting that the OSPF Algorithm's TOS support suffers from a deficiency in that routing protocols which support TOS are implicitly preferred when forwarding packets which have non-zero TOS values. This may not be appropriate in some cases. E.3.4 The Integrated IS-IS Algorithm Integrated IS-IS uses an algorithm which is similar to but not quite identical to the OSPF Algorithm. Integrated IS-IS uses a different set of route classes, and also differs slightly in its handling of type of service. The algorithm is: 1. Basic Match 2. IS-IS Route Classes 3. Longest Match 4. Weak TOS 5. Best Metric 6. Policy Although Integrated IS-IS uses Weak TOS, the protocol is only capable of carrying routes for a small specific subset of the possible values for the TOS field in the IP header. Packets Almquist & Kastenholz [Page 180]
RFC 1716 Towards Requirements for IP Routers November 1994 containing other values in the TOS field are routed using the default TOS. Type of service support is optional; if disabled, the fourth step would be omitted. As in OSPF, the specification does not include the Policy step. This algorithm has some advantages over the Revised Classic Algorithm: (1) It supports type of service routing. (2) Its rules are written down, rather than merely being a part of the Internet folklore. (3) It (obviously) works with Integrated IS-IS. However, this algorithm also retains some of the disadvantages of the Revised Classic Algorithm: (1) Path properties other than type of service (e.g. MTU) are ignored. (2) As in the Revised Classic Algorithm, the details (or even the existence) of the Policy step are left to the discretion of the implementor. (3) It doesn't work with OSPF because of the differences between IS-IS route classes and OSPF route classes. Also, because IS-IS supports only a subset of the possible TOS values, some obvious implementations of the Integrated IS-IS algorithm would not support OSPF's interpretation of TOS. The Integrated IS-IS Algorithm also has a further disadvantage (which is not shared by the Revised Classic Algorithm): IS-IS internal (intra-area or inter-area) routes are always considered to be superior to routes learned from other routing protocols, even in cases where the IS-IS route matches fewer bits of the destination address and doesn't provide the requested type of service. This is a policy decision that may not be appropriate in all cases. Finally, it is worth noting that the Integrated IS-IS Algorithm's TOS support suffers from the same deficiency noted for the OSPF Algorithm. Almquist & Kastenholz [Page 181]
RFC 1716 Towards Requirements for IP Routers November 1994 Security Considerations Although the focus of this document is interoperability rather than security, there are obviously many sections of this document which have some ramifications on network security. Security means different things to different people. Security from a router's point of view is anything that helps to keep its own networks operational and in addition helps to keep the Internet as a whole healthy. For the purposes of this document, the security services we are concerned with are denial of service, integrity, and authentication as it applies to the first two. Privacy as a security service is important, but only peripherally a concern of a router - at least as of the date of this document. In several places in this document there are sections entitled ... Security Considerations. These sections discuss specific considerations that apply to the general topic under discussion. Rarely does this document say do this and your router/network will be secure. More likely, it says this is a good idea and if you do it, it *may* improve the security of the Internet and your local system in general. Unfortunately, this is the state-of-the-art AT THIS TIME. Few if any of the network protocols a router is concerned with have reasonable, built-in security features. Industry and the protocol designers have been and are continuing to struggle with these issues. There is progress, but only small baby steps such as the peer-to-peer authentication available in the BGP and OSPF routing protocols. In particular, this document notes the current research into developing and enhancing network security. Specific areas of research, development, and engineering that are underway as of this writing (December 1993) are in IP Security, SNMP Security, and common authentication technologies. Notwithstanding all of the above, there are things both vendors and users can do to improve the security of their router. Vendors should get a copy of Trusted Computer System Interpretation [INTRO:8]. Even if a vendor decides not to submit their device for formal verification under these guidelines, the publication provides excellent guidance on general security design and practices for computing devices. Almquist & Kastenholz [Page 182]
RFC 1716 Towards Requirements for IP Routers November 1994 Acknowledgments O that we now had here But one ten thousand of those men in England That do no work to-day! What's he that wishes so? My cousin Westmoreland? No, my fair cousin: If we are mark'd to die, we are enow To do our country loss; and if to live, The fewer men, the greater share of honour. God's will! I pray thee, wish not one man more. By Jove, I am not covetous for gold, Nor care I who doth feed upon my cost; It yearns me not if men my garments wear; Such outward things dwell not in my desires: But if it be a sin to covet honour, I am the most offending soul alive. No, faith, my coz, wish not a man from England: God's peace! I would not lose so great an honour As one man more, methinks, would share from me For the best hope I have. O, do not wish one more! Rather proclaim it, Westmoreland, through my host, That he which hath no stomach to this fight, Let him depart; his passport shall be made And crowns for convoy put into his purse: We would not die in that man's company That fears his fellowship to die with us. This day is called the feast of Crispian: He that outlives this day, and comes safe home, Will stand a tip-toe when the day is named, And rouse him at the name of Crispian. He that shall live this day, and see old age, Will yearly on the vigil feast his neighbours, And say 'To-morrow is Saint Crispian:' Then will he strip his sleeve and show his scars. And say 'These wounds I had on Crispin's day.' Old men forget: yet all shall be forgot, But he'll remember with advantages What feats he did that day: then shall our names. Familiar in his mouth as household words Harry the king, Bedford and Exeter, Warwick and Talbot, Salisbury and Gloucester, Be in their flowing cups freshly remember'd. This story shall the good man teach his son; And Crispin Crispian shall ne'er go by, Almquist & Kastenholz [Page 183]
RFC 1716 Towards Requirements for IP Routers November 1994 From this day to the ending of the world, But we in it shall be remember'd; We few, we happy few, we band of brothers; For he to-day that sheds his blood with me Shall be my brother; be he ne'er so vile, This day shall gentle his condition: And gentlemen in England now a-bed Shall think themselves accursed they were not here, And hold their manhoods cheap whiles any speaks That fought with us upon Saint Crispin's day. This memo is a product of the IETF's Router Requirements Working Group. A memo such as this one is of necessity the work of many more people than could be listed here. A wide variety of vendors, network managers, and other experts from the Internet community graciously contributed their time and wisdom to improve the quality of this memo. The editor wishes to extend sincere thanks to all of them. The current editor also wishes to single out and extend his heartfelt gratitude and appreciation to the original editor of this document; Philip Almquist. Without Philip's work, both as the original editor and as the Chair of the working group, this document would not have been produced. Philip Almquist, Jeffrey Burgan, Frank Kastenholz, and Cathy Wittbrodt each wrote major chapters of this memo. Others who made major contributions to the document included Bill Barns, Steve Deering, Kent England, Jim Forster, Martin Gross, Jeff Honig, Steve Knowles, Yoni Malachi, Michael Reilly, and Walt Wimer. Additional text came from Art Berggreen, John Cavanaugh, Ross Callon, John Lekashman, Brian Lloyd, Gary Malkin, Milo Medin, John Moy, Craig Partridge, Stephanie Price, Yakov Rekhter, Steve Senum, Richard Smith, Frank Solensky, Rich Woundy, and others who have been inadvertently overlooked. Some of the text in this memo has been (shamelessly) plagiarized from earlier documents, most notably RFC 1122 by Bob Braden and the Host Requirements Working Group, and RFC 1009 by Bob Braden and Jon Postel. The work of these earlier authors is gratefully acknowledged. Jim Forster was a co-chair of the Router Requirements Working Group during its early meetings, and was instrumental in getting the group off to a good start. Jon Postel, Bob Braden, and Walt Prue also contributed to the success by providing a wealth of good advice prior to the group's first meeting. Later on, Phill Gross, Vint Cerf, and Noel Chiappa all provided valuable advice and support. Almquist & Kastenholz [Page 184]
RFC 1716 Towards Requirements for IP Routers November 1994 Mike St. Johns coordinated the Working Group's interactions with the security community, and Frank Kastenholz coordinated the Working Group's interactions with the network management area. Allison Mankin and K.K. Ramakrishnan provided expertise on the issues of congestion control and resource allocation. Many more people than could possibly be listed or credited here participated in the deliberations of the Router Requirements Working Group, either through electronic mail or by attending meetings. However, the efforts of Ross Callon and Vince Fuller in sorting out the difficult issues of route choice and route leaking are especially acknowledged. The previous editor, Philip Almquist, wishes to extend his thanks and appreciation to his former employers, Stanford University and BARRNet, for allowing him to spend a large fraction (probably far more than they ever imagined when he started on this) of his time working on this project. The current editor wishes to thank his employer, FTP Software, for allowing him to spend the time necessary to finish this document. Almquist & Kastenholz [Page 185]
RFC 1716 Towards Requirements for IP Routers November 1994 Editor's Address The address of the current editor of this document is Frank J. Kastenholz FTP Software 2 High Street North Andover, MA, 01845-2620 USA Phone: +1 508-685-4000 EMail: kasten@ftp.com



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