science

Locator/Identifier Separation Protocol

Locator/Identifier Separation Protocol is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Locator/Identifier Separation Protocol rather than just read about it. In short: Locator/ID Separation Protocol (LISP) is a "map-and-encapsulate" protocol which is developed by the Internet Engineering Task Force LISP Working Group. The basic idea behind the separation is that the Internet architecture combines two functions, routing locators (where a client is attached to the network) and identifiers (who the client is) in one number space: the IP address.

Locator/Identifier Separation Protocol — illustration

Key takeaways

Locator/Identifier Separation Protocol belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Locator/Identifier Separation Protocol to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Locator/Identifier Separation Protocol from memory before moving on to harder problems.

Reference excerpt

Locator/ID Separation Protocol (LISP) is a "map-and-encapsulate" protocol which is developed by the Internet Engineering Task Force LISP Working Group. The basic idea behind the separation is that the Internet architecture combines two functions, routing locators (where a client is attached to the network) and identifiers (who the client is) in one number space: the IP address. LISP supports the separation of the IPv4 and IPv6 address space following a network-based map-and-encapsulate scheme (RFC 1955). In LISP, both identifiers and locators can be IP addresses or arbitrary elements like a set of GPS coordinates or a MAC address. The protocol is currently an IETF Proposed Standard, specified in RFC 9300.

History The Internet Architecture Board's October 2006 Routing and Addressing Workshop renewed interest in the design of a scalable routing and addressing architecture for the Internet. Key issues driving this renewed interest include concerns about the scalability of the routing system and the impending exhaustion of IPv4 address space. Since the IAB workshop, several proposals have emerged that attempted to address the concerns expressed at the workshop. All of these proposals are based on a common concept: the separation of Locator and Identifier in the numbering of Internet devices, often termed the "Loc/ID split".

Characteristics The current namespace architecture used by the Internet Protocol uses IP addresses for two separate functions:

as an end-point identifier to uniquely identify a network interface within its local network addressing context as a locator for routing purposes, to identify where a network interface is located within a larger routing context There are several advantages to decoupling Location and Identifier, and to LISP specifically.

Improved routing scalability BGP-free multihoming in active-active configuration Address family traversal: IPv4 over IPv4, IPv4 over IPv6, IPv6 over IPv6, IPv6 over IPv4 Inbound traffic engineering Mobility Simple deployability No host changes are needed Customer driven VPN provisioning replacing MPLS-VPN Network virtualization Customer operated encrypted VPN based on LISP/GETVPN replacing IPsec scalability problems High availability for seamless communication sessions through (constraint-based) multihoming A recent discussion of several LISP use cases may be found in IETF has an active workgroup establishing standards for LISP. As of 2016, the LISP specifications are on the experimental track. The LISP workgroup started to move the core specifications onto the standards track in 2017 - as of June 2021 three revisions (for RFC 6830, RFC 6833, and 8113) are ready for publication as RFCs, but they await completion of work on a revision of RFC 6834 and the LISP Security Framework.

Terminology Routing Locator (RLOC): A RLOC is an IPv4 or IPv6 address of an egress tunnel router (ETR). A RLOC is the output of an EID-to-RLOC mapping lookup. Endpoint ID (EID): An EID is an IPv4 or IPv6 address used in the source and destination address fields of the first (most inner) LISP header of a packet. Egress Tunnel Router (ETR): An ETR is a device that is the tunnel endpoint; it accepts an IP packet where the destination address in the "outer" IP header is one of its own RLOCs. ETR functionality does not have to be limited to a router device; server host can be the endpoint of a LISP tunnel as well. Ingress Tunnel Router (ITR): An ITR is a device that is the tunnel start point; it receives IP packets from site end-systems on one side and sends LISP-encapsulated IP packets, across the Internet to an ETR, on the other side. Proxy ETR (PETR): A LISP PETR implements ETR functions on behalf of non-LISP sites. A PETR is typically used when a LISP site needs to send traffic to non-LISP sites but the LISP site is connected through a service provider that does not accept nonroutable EIDs as packet sources. Proxy ITR (PITR): A PITR is used for inter-networking between Non-LISP and LISP sites, a PITR acts like an ITR but does so on behalf of non-LISP sites which send packets to destinations at LISP sites. xTR: A xTR refers to a device which functions both as an ITR and an ETR (which is typical), when the direction of data flow is not part of the context description. Re-encapsulating Tunnel Router (RTR): An RTR is used for connecting LISP-to-LISP communications within environments where direct connectivity is not supported. Examples include: 1) joining LISP sites connected to "disjointed locator spaces"—for example a LISP site with IPv4-only RLOC connectivity and a LISP site with IPv6-only RLOC connectivity; and 2) creating a data plane 'anchor point' by a LISP-speaking device behind a NAT box to send and receive traffic through the NAT device.

Mapping system In the Locator/Identifier Separation Protocol the network elements (routers) are responsible for looking up the mapping between end-point-identifiers (EID) and route locators (RLOC) and this process is invisible to the Internet end-hosts. The mappings are stored in a distributed database called the mapping system, which responds to the lookup queries. The LISP beta network initially used a BGP-based mapping system called LISP ALternative Topology (LISP+ALT), but this has now been replaced by a DNS-like indexing system called DDT inspired from LISP-TREE. The protocol design made it easy to plug in a new mapping system, when a different design proved to have benefits. Some proposals have already emerged and have been compared.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Locator/Identifier Separation Protocol

Start with the simplest possible case. Write down what Locator/Identifier Separation Protocol claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Locator/Identifier Separation Protocol before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Locator/Identifier Separation Protocol ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Locator/Identifier Separation Protocol

In research: Locator/Identifier Separation Protocol appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Locator/Identifier Separation Protocol in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Locator/Identifier Separation Protocol is common in secondary-school and first-year university syllabi. It links to neighbouring topics Internet Protocol, Internet architecture, Internet layer protocols, so understanding it makes those chapters shorter.
In everyday life: Look for Locator/Identifier Separation Protocol outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Locator/Identifier Separation Protocol in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Locator/Identifier Separation Protocol means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Locator/Identifier Separation Protocol out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Locator/Identifier Separation Protocol in simple terms?

Why does Locator/Identifier Separation Protocol matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Locator/Identifier Separation Protocol?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Locator/Identifier Separation Protocol.