Routing R. Perlman Internet Draft Sun microsystems Intended status: Internet Draft February 18, 2008 A. Roy Expires: August 2008 Cisco Systems M. Thomas University of Essex Automatic Method for Minimization of Extraneous Pseudonodes draft-rtgwg-pseudo-perlman-roy-thomas-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. This document may not be modified, and derivative works of it may not be created. This document may only be posted in an Internet-Draft. 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 August 10, 2008. Copyright Notice Perlman et al Expires August 2008 [Page 1] Internet-Draft Automatic Method for the Minimization February 2008 of Extraneous Pseudonodes Copyright (C) The IETF Trust (2008). Abstract An automatic method is recommended for a link state protocol to automatically decide whether an Ethernet link should be represented by a pseudonode or not. Conventions used in this document In examples, "C:" and "S:" indicate lines sent by the client and server respectively. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119 Table of Contents 1. Introduction...................................................2 2. Method.........................................................3 3. Goals:.........................................................4 4. Generic changes................................................4 5. Security Considerations........................................5 6. IANA Considerations............................................5 7. Acknowledgments................................................5 8. References.....................................................5 8.1. Normative References......................................6 8.2. Informative References....................................6 Author's Addresses................................................6 Intellectual Property Statement...................................7 Disclaimer of Validity............................................7 1. Introduction When Ethernets were originally introduced as a type of link, the assumption was that an "Ethernet" was assumed to be a large cloud with many directly connected nodes. Given that the overhead of a link state protocol (such as IS-IS or OSPF) is proportional to the number of links in the topology, a cloud with a lot of neighbors, represented in the most straightforward way, as having all nodes on the cloud being fully connected, would represent n^2 links. Thus to make large shared links scalable, the concept of a "pseudonode" was introduced. If there are n neighbors on an Ethernet, rather than representing the connectivity between the neighbors as n^2 links, one router on the Ethernet is elected Designated Router, and that router Perlman et al Expires August 2008 [Page 2] Internet-Draft Automatic Method for the Minimization February 2008 of Extraneous Pseudonodes impersonates the cloud itself, issuing link state information on behalf of the cloud, and each router on the cloud (in addition to the Designated Router) claims only the pseudonode as a neighbor. The "pseudonode" is the cloud itself. In this way the pseudonode will have n router neighbors, but each router will only report a single neighbor (the pseudonode). However, Ethernet has evolved into "switched Ethernet", where instead of Ethernet being a large cloud, it is often as small as a single pt- to-pt link connecting exactly two neighbors. An Ethernet might even be a pt-to-pt link between a router and an endnode. It would be wasteful to represent such a link as a pseudonode. 2. Method This paper presents a method that allows a router in a link state protocol (IS-IS or OSPF) to decide when it is appropriate to represent an Ethernet as a pseudonode, and when it is appropriate instead to represent the topology as direct connections between all the nodes on the cloud. Goals are not to require configuration, and not to be disruptive to the rest of the network if routers on the cloud fail and reappear. The basic idea is that in the Hello message on a broadcast link, routers advertise their ability to do the functionality in this internet draft. If every router on the link claims the ability to represent the broadcast link without a pseudonode, then the Designated Router specifies to the routers on the link whether the link will be represented by a pseudonode or not. The actual algorithm chosen by the DR need not be the same for all routers. A router MAY be configured with a different algorithm, or experience may show that a different algorithm might be more optimal. Since the DR decides on behalf of the link, whether it will be represented with a pseudonode, or as fully connected direct links between each pair of routers, there is no need for all routers to have the same algorithm. The only requirement is that a router follow the mandate of the DR. The algorithm in this document is that the DR mandates use of a pseudonode if there are at least 4 routers on the link (including the DR), and mandates no pseudonode if there are only 2 routers on the link (including the DR). If there are 3 routers on the link (including the DR), the DR does not change the state of the link. So if there are 4 routers on the link, the link will be represented by a pseudonode. If one of those routers go down, the link will remain represented by a pseudonode. Only when two of the four routers go Perlman et al Expires August 2008 [Page 3] Internet-Draft Automatic Method for the Minimization February 2008 of Extraneous Pseudonodes down, so that the DR has only one neighbor, will the DR revert to "no pseudonode". When the DR has specified that the link is not to be represented by a pseuonode, the link will remain as "no pseudonode" until there are again 4 or more routers on the link. 3. Goals: o Work well with no configuration o Optionally allow configuration o Allow incremental deployment (i.e., not require all routers to be simultaneously upgraded). It is possible that while a router that does not implement this feature is connected to a link, the link will have to be represented by a pseudonode; however, it is essential that a mixture of routers that support this feature and those that don't will interoperate o Only routers on a link need support the feature; e.g., routers that are not connected to the link will not be confused, even if they do not support the feature o Represent large links with a pseudonode. Represent small links without using a pseudonode. 4. Generic changes Generic changes to a link State protocol 1. The Hello message on a broadcast link must contain a flag specifying the ability of the transmitting router to do pseudonode minimization 2. The Hello message on a broadcast link must contain a flag set by the DR to indicate that the link is not to be represented by a pseudonode. If the link is not to be represented by a pseudonode, then there is no need to give a name to the pseudonode. 3. The DR must check the "pseudonode minimization capable" flag of all routers on the link. If any router does not advertise this ability, the DR MUST represent the link with a pseudonode. 4. If the link is not to be represented by a pseudonode, then all routers on the link will report direct pt-to-pt links to each other router on the link. Perlman et al Expires August 2008 [Page 4] Internet-Draft Automatic Method for the Minimization February 2008 of Extraneous Pseudonodes 5. If all routers on the link are "pseudonode minimization capable", then the DR specifies that the link will not use a pseudonode if the number of routers on the link is 2 or fewer (i.e., the DR has at most one router neighbor). 6. If there are at least 4 routers on the link (i.e., the DR has at least 3 router neighbors), then the DR specifies use of a pseudonode for the link. 7. If there are 3 routers on the link, then the DR does not change the state of the link. 8. If a non compatible router appears on the link then the DR signals to the other routers to no longer perform pseudonode minimization 5. Security Considerations A group of 3 routers could maliciously come up and down as a group, or a single router could pretend to be 3 routers, and cause the pseudonode state of the link to oscillate. Also, a malicious DR can oscillate the state of the link. A single router could oscillate the state of the link by advertising first that it is capable of pseudonode minimization, and then advertising that it is not capable. However, any disruption to routing by a router using any of these strategies can already be done trivially by, for instance, pretending to be highest priority and taking over as DR, and then changing identity and the pseudonode name. So the capability in this document does not make it any easier for a malicious router on a link to cause disruption. 6. IANA Considerations None 7. Acknowledgments We thank Mike Shand for doing the math to show that the link state database in IS-IS becomes smaller with use of a pseudonode on a link with at least 4 routers. 8. References Perlman et al Expires August 2008 [Page 5] Internet-Draft Automatic Method for the Minimization February 2008 of Extraneous Pseudonodes 8.1. Normative References [RFC2234] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 2334, October 1998. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC2119, March 1997. 8.2. Informative References [OSPFV2] Moy, J., "OSPF Version 2", RFC2328, April 1998. [OSPFV3] Coltun, R., Ferguson, D., and J. Moy, "OSPF for IPv6", RFC2740, December 1999. [IS-IS] "Intermediate System to Intermediate System Intra-Domain Routing Exchange Protocol for use in Conjunction with the Protocol for Providing the Connectionless-mode Network Service (ISO 8473)", ISO 10589. [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and dual environments", RFC 1195, December 1990. Author's Addresses Radia Perlman Sun Microsystems Email: radia.perlman@sun.com Abhay Roy Cisco Systems E-mail: akr@cisco.com Matthew Thomas University of Essex Email: mrthom@essex.ac.uk Perlman et al Expires August 2008 [Page 6] Internet-Draft Automatic Method for the Minimization February 2008 of Extraneous Pseudonodes Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Perlman et al Expires August 2008 [Page 7] Internet-Draft Automatic Method for the Minimization February 2008 of Extraneous Pseudonodes Perlman et al Expires August 2008 [Page 8]