Type of Service in the Internet Protocol Suite
RFC 1349
Document | Type |
RFC - Proposed Standard
(July 1992; Errata)
Obsoleted by RFC 2474
Was draft-almquist-tos (rreq WG)
|
|
---|---|---|---|
Author | Philip Almquist | ||
Last updated | 2020-01-21 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized with errata bibtex | ||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 1349 (Proposed Standard) | |
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | (None) | ||
Send notices to | (None) |
Network Working Group P. Almquist Request for Comments: 1349 Consultant Updates: RFCs 1248, 1247, 1195, July 1992 1123, 1122, 1060, 791 Type of Service in the Internet Protocol Suite Status of This Memo This document specifies an IAB standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "IAB Official Protocol Standards" for the standardization state and status of this protocol. Distribution of this memo is unlimited. Summary This memo changes and clarifies some aspects of the semantics of the Type of Service octet in the Internet Protocol (IP) header. The handling of IP Type of Service by both hosts and routers is specified in some detail. This memo defines a new TOS value for requesting that the network minimize the monetary cost of transmitting a datagram. A number of additional new TOS values are reserved for future experimentation and standardization. The ability to request that transmission be optimized along multiple axes (previously accomplished by setting multiple TOS bits simultaneously) is removed. Thus, for example, a single datagram can no longer request that the network simultaneously minimize delay and maximize throughput. In addition, there is a minor conflict between the Host Requirements (RFC-1122 and RFC-1123) and a number of other standards concerning the sizes of the fields in the Type of Service octet. This memo resolves that conflict. Table of Contents 1. Introduction ............................................... 3 2. Goals and Philosophy ....................................... 3 3. Specification of the Type of Service Octet ................. 4 4. Specification of the TOS Field ............................. 5 Almquist [Page 1] RFC 1349 Type of Service July 1992 5. Use of the TOS Field in the Internet Protocols ............. 6 5.1 Internet Control Message Protocol (ICMP) ............... 6 5.2 Transport Protocols .................................... 7 5.3 Application Protocols .................................. 7 6. ICMP and the TOS Facility .................................. 8 6.1 Destination Unreachable ................................ 8 6.2 Redirect ............................................... 9 7. Use of the TOS Field in Routing ............................ 9 7.1 Host Routing ........................................... 10 7.2 Forwarding ............................................. 12 8. Other consequences of TOS .................................. 13 APPENDIX A. Updates to Other Specifications ................... 14 A.1 RFC-792 (ICMP) ......................................... 14 A.2 RFC-1060 (Assigned Numbers) ............................ 14 A.3 RFC-1122 and RFC-1123 (Host Requirements) .............. 16 A.4 RFC-1195 (Integrated IS-IS) ............................ 16 A.5 RFC-1247 (OSPF) and RFC-1248 (OSPF MIB) ................ 17 APPENDIX B. Rationale ......................................... 18 B.1 The Minimize Monetary Cost TOS Value ................... 18 B.2 The Specification of the TOS Field ..................... 19 B.3 The Choice of Weak TOS Routing ......................... 21 B.4 The Retention of Longest Match Routing ................. 22 B.5 The Use of Destination Unreachable ..................... 23 APPENDIX C. Limitations of the TOS Mechanism .................. 24 C.1 Inherent Limitations ................................... 24 C.2 Limitations of this Specification ...................... 25 References ..................................................... 27 Acknowledgements ............................................... 28 Security Considerations ........................................ 28 Author's Address ............................................... 28 Almquist [Page 2] RFC 1349 Type of Service July 1992 1. Introduction Paths through the Internet vary widely in the quality of service they provide. Some paths are more reliable than others. Some impose high call setup or per-packet charges, while others do not do usage-based charging. Throughput and delay also vary widely. Often there are tradeoffs: the path that provides the highest throughput may well not be the one that provides the lowest delay or the lowest monetary cost. Therefore, the "optimal" path for a packet to follow throughShow full document text