1. Introduction

1. Introduction

This document describes the Locator/Identifier Separation Protocol (LISP), which provides a set of functions for routers to exchange information used to map from Endpoint Identifiers (EIDs) that are not globally routable to routable Routing Locators (RLOCs). It also defines a mechanism for these LISP routers to encapsulate IP packets addressed with EIDs for transmission across a network infrastructure that uses RLOCs for routing and forwarding.

Creation of LISP was initially motivated by discussions during the IAB-sponsored Routing and Addressing Workshop held in Amsterdam in October 2006 (see [RFC4984]). A key conclusion of the workshop was that the Internet routing and addressing system was not scaling well in the face of the explosive growth of new sites; one reason for this poor scaling is the increasing number of multihomed sites and other sites that cannot be addressed as part of topology-based or provider-based aggregated prefixes. Additional work that more completely describes the problem statement may be found in [RADIR].

A basic observation, made many years ago in early networking research such as that documented in [CHIAPPA] and [RFC4984], is that using a single address field for both identifying a device and for determining where it is topologically located in the network requires optimization along two conflicting axes: for routing to be efficient, the address must be assigned topologically; for collections of devices to be easily and effectively managed, without the need for renumbering in response to topological change (such as that caused by adding or removing attachment points to the network or by mobility events), the address must explicitly not be tied to the topology.

The approach that LISP takes to solving the routing scalability problem is to replace IP addresses with two new types of numbers: Routing Locators (RLOCs), which are topologically assigned to network attachment points (and are therefore amenable to aggregation) and used for routing and forwarding of packets through the network; and Endpoint Identifiers (EIDs), which are assigned independently from the network topology, are used for numbering devices, and are aggregated along administrative boundaries. LISP then defines functions for mapping between the two numbering spaces and for encapsulating traffic originated by devices using non-routable EIDs for transport across a network infrastructure that routes and forwards using RLOCs. Both RLOCs and EIDs are syntactically identical to IP addresses; it is the semantics of how they are used that differs.

This document describes the protocol that implements these functions. The database that stores the mappings between EIDs and RLOCs is explicitly a separate "module" to facilitate experimentation with a variety of approaches. One database design that is being developed for experimentation as part of the LISP working group work is [RFC6836]. Others that have been described include [CONS], [EMACS], and [RFC6837]. Finally, [RFC6833] documents a general-purpose service interface for accessing a mapping database; this interface is intended to make the mapping database modular so that different approaches can be tried without the need to modify installed LISP-capable devices in LISP sites.

This experimental specification has areas that require additional experience and measurement. It is NOT RECOMMENDED for deployment beyond experimental situations. Results of experimentation may lead to modifications and enhancements of protocol mechanisms defined in this document. See Section 15 for specific, known issues that are in need of further work during development, implementation, and experimentation.

An examination of the implications of LISP on Internet traffic, applications, routers, and security is for future study. This analysis will explain what role LISP can play in scalable routing and will also look at scalability and levels of state required for encapsulation, decapsulation, liveness, and so on.