Internet Engineering Task Force Phill Gross ed. INTERNET-DRAFT ANS July, 1991 IESG Recommendation for Interior Gateway Protocols 1 Status of this Memo This document will be submitted to the RFC Editor as a policy statement. Comments on this document should be sent to the IESG at the IESG-TECH@nri.reston.va.us mailing list. 2 Background There is an urgent need for a high functionality non-proprietary ``common'' Interior Gateway Protocol (IGP) for the TCP/IP protocol family. An IGP is the routing protocol used within a single administrative domain (commonly referred to as an ``Autonomous System'' AS). By ``common'', we simply mean a protocol that is ubiquitously available from all router vendors (as in `in common'). Users and network operators have expressed a strong need for routers from different vendors to have the capablity to interoperate within an AS through use of a common IGP. Note: Routing between AS's is handled by a different type of routing protocol, called an "Exterior Gateway Protocol" ("an EGP", of which the Border Gateway Protocol [RFC1163] and "The Exterior Gateway Protocol" [RFC904] are examples.) The issues of routing between AS's using ``an'' EGP is not considered in this memo. There are two IGPs in the Internet standards track capable of routing IP traffic -- Open Shortest Path First [OSPF] and Integrated IS-IS [RFC1195] (based on the OSI IS-IS). These two protocols are both modern ``link state'' routing protocols, based on the Dijkstra algorithm. There has been substantial cooperation among the engineers involved in each effort, and the protocols share some similar features. However, there are a number of technical design differences. Most noteably, OSPF has been designed solely for support of the Internet Protocol (IP), while Integrated IS-IS has been designed to support both IP and the OSI Connectionless Network Layer Protocol (CLNP) INTERNET-DRAFT IESG Recommendation for IGP's July, 1991 simultaneously. In February 1990, the IESG recommended that the question of designating a ``common'' IGP be postponed until more information was available from each protocol. More than a year has now passed since the IESG's recommendation. There have been significant advancements in specification, implementation, and operational experience with each protocol. It is now reasonable to re-open the consideration of designating a ``common IGP''. 3 Recent Developments At the March 1991 meeting of the IETF, the IETF Routing Area Director, Robert Hinden, presented a set of criteria for the advancement of routing protocols through the Internet standards process. This document is available as an Internet-Draft [ROUTING], and will ultimately be available as an RFC. More information regarding the IAB Internet Standards process can be found in [RFC1200]. Also at the March 1991 meeting of the IETF, the OSPF Working Group requested that OSPF be considered for advancement to Draft Internet Standard. The OSPF WG submitted four documents to the IETF to support its request: o a revised protocol specification to update RFC 1131 o an SNMP Management Information Base (MIB) [OSPF MIB] o 2 technical reports giving a technical analysis and operational experience with OSPF. [EXPERIENCE, ANALYSIS] These reports follow the format recommended in the routing protocol ``standardscriteria'' document mentioned above. These four documents are currently available as Internet-Drafts, and are expected to be available soon as RFCs. 4 In summary for OSPF o all features of OSPF have tested (although not all features have been used in operation), o OSPF has been shown to operate well in several operational networks containing between 10 and 20 routers, o interoperation among routers from at least six vendors has been demonstrated at organized ``bakeoffs''. Phill Gross ed. [Page 2] INTERNET-DRAFT IESG Recommendation for IGP's July, 1991 In May 1991, the IAB approved the IETF/IESG recommendation to advance OSPF to Draft Internet Standard. Integrated IS-IS, as specified in RFC 1195, is currently a Proposed Internet Standard. In July 1991, the status of Integrated IS-IS is as follows: o There are at least four separate implementations of integrated IS-IS under development, o Integrated IS-IS has worked well in one multi-area operational network containing between 20 and 30 routers, as well as in several smaller operational networks, o These recent operational results have not yet been fully documented. Documentation, showing satisfaction of the criteria for advancing routing protocols, will be submitted when Integrated IS-IS is submitted for Draft Internet Standard status. o The IS-IS Working Group currently plans to submit Integrated IS-IS for Draft Internet Standard status at the November 1991 IETF meeting. 5 Multiple Internet Standard Routing Protocols Possible The Internet architecture makes a distinction between ``Interior Gateway Protocols (IGPs)'' that is routing protocols used within an Autonomous System (AS), and ``Exterior Gateway Protocols (EGPs)'' that is, routing protocols used between different AS's. Therefore, the Internet architecture supports the use and standardization of multiple IGP routing protocols. For example, it is perfectly reasonable for one routing protocol to be used within one AS, while a second routing protocol is used within a second AS, at the same time that a proprietary routing protocol is used within a third AS. The primary purpose of making standards is to allow interoperability, that is, ``if you wish to use this protocol, you should do it as specified in the standard so that you can interoperate with others who also follow this standard.'' It is important to understand that simply specifying a standard does not, by itself, designate a requirement to use the standard. It is merely meant to allow interoperability among those who choose to follow the standard. Therefore, it is reasonable for both OSPF and Integrated IS-IS to be progressed through the Internet Standards process as appropriate (based on the criteria specified in [ROUTING]). In addition, it is possible that other IGPs may be developed and standardized in the future. Phill Gross ed. [Page 3] INTERNET-DRAFT IESG Recommendation for IGP's July, 1991 6 A Common IGP Although the Internet architecture allows for multiple standard IGP routing protocols, interoperability of router products from different vendors within a single AS would be greatly facilitated if a single ``common'' IGP were available from all router vendors. Designating a common IGP would have the goal of enabling multi-vendor router interoperation with a modern high functionality routing protocol. However, designating a common IGP would not be meant to discourage the use of other IGPs in situations where there may be sound technical reasons to do so. The Internet standards process makes allowance for defining an ``Applicability Statement'' on any Internet standard [ref TBA]. It is the ``Applicability Statement'' which would assign any requirement to use a specific protocol. This memo is meant to be an ``Applicability Statement'' for Internet routing protocols, in which a ``common'' IGP is designated. 7 Future Internet topology considerations There are topology considerations which will affect the designation of a ``common'' Internet IGP. The Internet requires support for a wide variety of protocol suites. If we consider only IP and OSI CLNP, then the Internet is expected to contain: 1. Pure IP AS's (in which IP is used but OSI CLNP is not used); 2. Pure CLNP AS's (in which CLNP is used but IP is not used); 3. Dual IP/CLNP ASs, with a common topology (i.e., all links and routers in the AS support IP and CLNP, and a single common topology is used for both protocol suites); 4. Dual, overlapping IP/CLNP ASs with differing topologies (i.e., some links are dual, while some are IP-only and some are CLNP-only, resulting in different topologies for IP routing and CLNP routing). For (1), (i.e., a pure IP environment) any IGP capable of routing IP traffic could be used (e.g., OSPF or Integrated IS-IS). For (2), (i.e., a pure CLNP environment) any IGP capbale of routing CLNP traffic could be used (e.g., OSI IS-IS or Integrated IS-IS). Phill Gross ed. [Page 4] INTERNET-DRAFT IESG Recommendation for IGP's July, 1991 For (3), (i.e., routing environments in which both IP and CLNP are present in a common topology) there are two possibilities for managing routing: 1. Separate routing protocols could be used for each supported protocol suite. For example, OSPF may be used for calculating routes for IP traffic and OSI IS-IS may be used for calculating routes for OSI traffic. This approach of using separate routing protocols and management for each supported protocol family has come to be known as ``Ships in the Night'' because the two routing protocols share the hardware/software resources of the router without ever actually interacting on a protocol level. 2. ``Integrated routing'' could be used, in which a single routing protocol is used for both IP and CLNP. For (4), (i.e., routing environments in which both IP and CLNP are present but in an overlapping different topology) separate routing protocols are required for the IP and CLNP environments (i.e., ``Ships in the Night''). This is equivalent to two separates cases of (1) and (2), but it is pointed out here as a separate case for completeness. 8 Commitment to both IP and CLNP The IAB/IETF is commited to a timely introduction of OSI into the Internet and compliance with U.S. GOSIP. However, while this introduction is taking place, it is essential that existing services based on IP be continued. The IESG also feels that even after more widespread introduction of CLNP, coexistence of IP and CLNP will continue for quite some time. This view is consistent with the IAB goal of a multi-protocol Internet. Therefore, the IESG has a strong commitment to the continued support for IP throughout the Internet. Maintenance of this IP support requires selection of a common IGP suitable for support of IP, and requires that this selection be based on operational experience. 9 Recommendation Based on the available operational experience and the pressing need for a high functionality IGP for the IP protocol family, the IESG recommends that OSPF be designated as the common IGP for the IP portions of the Internet. To help ensure that this IGP is available to all users, the IESG recommends that the ``Requirements for Internet IP Routers'' specify OSPF as ``MUST IMPLEMENT''. As mentioned above, the IESG is also interested in multiprotocol Phill Gross ed. [Page 5] INTERNET-DRAFT IESG Recommendation for IGP's July, 1991 environments, and expects usage of OSI CLNP to increase in the Internet over time. At this time, the IESG is not prepared to take a position regarding the preference of either ``Ships in the Night'' or Integrated routing for such mixed routing environments. At this time, the ``Ships in the Night'' approach is most widely used in the Internet. Integrated routing has the potential advantage of reducing resource utilization. However, additional operational experience is needed before any potential advantages can be fully evaluated. Therefore, the IESG wishes to encourage implementation of Integrated IS-IS so that a reasonable position can be determined based on operational experience. All implementers of Integrated IS-IS are encouraged to coordinate their activity with the IETF IS-IS Working Group, which is actively collecting information on such experience. It is useful to recognize the limits of this recommendation. This recommendation does not take a position on any of the following issues: 1. What IGP (if any) users should run inside an AS. Users are free to run any IGP they wish inside an AS. 2. What IGP is technically superior, or has greater operational utility. 3. What IGP any vendor should recommend to its users for any specific environment. 4. What IGP should be used within a CLNP-only environment. Again, this recommendation is meant to designate one modern high functionality IGP that should be implemented by all routing vendors. This will enable routers from vendors who follow this recommendation to interoperate within a single AS. It is not our intent to discourage the use of other routing protocols in situations where there may be sound technical reasons to do so. Therefore, developers of Internet routers are free to implement, and network operators are free to use, other Internet standard routing protocols, or proprietary non-Internet-standard routing protocols, as they wish. 10 References ROUTING Hinden, R., ``Internet Routing Protocol Standardization Criteria'' Internet Draft: , April 1991. Phill Gross ed. [Page 6] INTERNET-DRAFT IESG Recommendation for IGP's July, 1991 OSPF Moy, J., ``OSPF Version 2.0, Internet Draft: , January 1991. ANALYSIS Moy, J., ``OSPF Protocol Analysis, Internet Draft: , April 1991. EXPERIENCE Moy, J., ``Experience with the OSPF Protocol'' Internet Draft: , April 1991. OSPF MIB Baker, F. and Coltun, R., ``OSPF Version 2 Management Information Base'', Internet Draft: , March 1991. RFC1195 Callon, R., ``Use of OSI IS-IS for Routing in TCP/IP and Dual Environments'', RFC 1195, December 1990. RFC 1200 Postel, J,. ``IAB Official Protocol Standards'', RFC 1200, April 1991. ISO10589 ``Intermediate System to Intermediate System Intra-Domain Routeing Exchange Protocol for use in Conjunction with the Protocol for Providing the Connectionless-mode Network Service (ISO 8473)'', ISO DP 10589, February 1990. RFC1163 Lougheed, K., and Rekhter, Y., ``A Border Gateway Protocol (BGP)'', RFC 1163, June 1990. RFC904 Mills, D., ``Exterior Gateway Protocol formal specification'', RFC 904, April 1984 Phill Gross ed. [Page 7]