Point-to-Point Operation over LAN in Link State Routing Protocols
RFC 5309
Document | Type | RFC - Informational (October 2008; No errata) | |
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Authors | Alex Zinin , Naiming Shen | ||
Last updated | 2020-07-29 | ||
Stream | Internent Engineering Task Force (IETF) | ||
Formats | plain text html pdf htmlized (tools) htmlized bibtex | ||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 5309 (Informational) | |
Action Holders |
(None)
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Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Bill Fenner | ||
Send notices to | (None) |
Network Working Group N. Shen, Ed. Request for Comments: 5309 Cisco Systems Category: Informational A. Zinin, Ed. Alcatel-Lucent October 2008 Point-to-Point Operation over LAN in Link State Routing Protocols Status of This Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Abstract The two predominant circuit types used by link state routing protocols are point-to-point and broadcast. It is important to identify the correct circuit type when forming adjacencies, flooding link state database packets, and representing the circuit topologically. This document describes a simple mechanism to treat the broadcast network as a point-to-point connection from the standpoint of IP routing. 1. Introduction Point-to-point and broadcast are the two predominant circuit types used by link state routing protocols such as IS-IS [ISO10589] [RFC1195] and OSPF [RFC2328] [RFC5340]. They are treated differently with respect to establishing neighbor adjacencies, flooding link state information, representing the topology, and calculating the Shortest Path First (SPF) and protocol packets. The most important differences are that broadcast circuits utilize the concept of a designated router and are represented topologically as virtual nodes in the network topology graph. Compared with broadcast circuits, point-to-point circuits afford more straightforward IGP operation. There is no designated router involved, and there is no representation of the pseudonode or network Link State Advertisement (LSA) in the link state database. For IS- IS, there also is no periodic database synchronization. Conversely, if there are more than two routers on the LAN media, the traditional view of the broadcast circuit will reduce the routing information in the network. Shen & Zinin Informational [Page 1] RFC 5309 P2P over LAN October 2008 When there are only two routers on the LAN, it makes more sense to treat the connection between the two routers as a point-to-point circuit. This document describes the mechanism to allow link state routing protocols to operate using point-to-point connections over a LAN under this condition. Some implications related to forwarding IP packets on this type of circuit are also discussed. We will refer to this as a p2p-over-lan circuit in this document. 1.1. Terminology 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 RFC 2119 [RFC2119]. 2. Motivation Even though a broadcast circuit is meant to handle more than two devices, there are cases where only two routers are connected over either the physical or logical LAN segment: 1. The media itself is being used for point-to-point operation between two routers. This is mainly for long-haul operation. 2. There are only two routers on the physical LAN. 3. There are only two routers on a virtual LAN (vLAN). In any of the above cases, the link state routing protocols will normally still treat the media as a broadcast circuit. Hence, they will have the overhead involved with protocol LAN operation without the benefits of reducing routing information and optimized flooding. Being able to treat a LAN as a point-to-point circuit provides the benefit of reduction in the amount of information routing protocols must carry and manage. DR/DIS (Designated Router / Designated Intermediate System) election can be omitted. Flooding can be done as in p2p links without the need for using "LSA reflection" by the DR in OSPF or periodic Complete Sequence Number Packets (CSNPs) in IS- IS. Also, if a broadcast segment wired as a point-to-point link can be treated as a point-to-point link, only the connection between the two routers would need to be advertised as a topological entity. Even when there are multiple routers on the LAN, an ISP may want to sub-group the routers into multiple vLANs, since this allows them to assign different costs to IGP neighbors. When there are only two routers in some of the vLANs, this LAN can be viewed by the IGP as a mesh of point-to-point connections. Shen & Zinin Informational [Page 2] RFC 5309 P2P over LAN October 2008 The IP unnumbered configuration is widely used in networks. ItShow full document text