An Architectural Introduction to the Locator/ID Separation Protocol (LISP)
draft-ietf-lisp-introduction-13
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 9299.
|
|
|---|---|---|---|
| Authors | Albert Cabellos-Aparicio , Damien Saucez | ||
| Last updated | 2021-07-29 (Latest revision 2015-04-02) | ||
| Replaces | draft-chiappa-lisp-introduction | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Luigi Iannone | ||
| Shepherd write-up | Show Last changed 2014-12-31 | ||
| IESG | IESG state | Became RFC 9299 (Informational) | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | Alvaro Retana | ||
| Send notices to | aretana.ietf@gmail.com | ||
| IANA | IANA review state | Version Changed - Review Needed | |
| IANA action state | No IANA Actions | ||
| RFC Editor | RFC Editor state | MISSREF | |
| Details |
draft-ietf-lisp-introduction-13
Network Working Group A. Cabellos
Internet-Draft UPC-BarcelonaTech
Intended status: Informational D. Saucez (Ed.)
Expires: October 4, 2015 INRIA
April 02, 2015
An Architectural Introduction to the Locator/ID Separation Protocol
(LISP)
draft-ietf-lisp-introduction-13.txt
Abstract
This document describes the architecture of the Locator/ID Separation
Protocol (LISP), making it easier to read the rest of the LISP
specifications and providing a basis for discussion about the details
of the LISP protocols. This document is used for introductory
purposes, more details can be found in RFC6830, the protocol
specification.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on October 4, 2015.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 4
3. LISP Architecture . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Design Principles . . . . . . . . . . . . . . . . . . . . 5
3.2. Overview of the Architecture . . . . . . . . . . . . . . 5
3.3. Data-Plane . . . . . . . . . . . . . . . . . . . . . . . 8
3.3.1. LISP Encapsulation . . . . . . . . . . . . . . . . . 8
3.3.2. LISP Forwarding State . . . . . . . . . . . . . . . . 10
3.4. Control-Plane . . . . . . . . . . . . . . . . . . . . . . 10
3.4.1. LISP Mappings . . . . . . . . . . . . . . . . . . . . 10
3.4.2. Mapping System Interface . . . . . . . . . . . . . . 11
3.4.3. Mapping System . . . . . . . . . . . . . . . . . . . 11
3.5. Internetworking Mechanisms . . . . . . . . . . . . . . . 14
4. LISP Operational Mechanisms . . . . . . . . . . . . . . . . . 15
4.1. Cache Management . . . . . . . . . . . . . . . . . . . . 15
4.2. RLOC Reachability . . . . . . . . . . . . . . . . . . . . 16
4.3. ETR Synchronization . . . . . . . . . . . . . . . . . . . 17
4.4. MTU Handling . . . . . . . . . . . . . . . . . . . . . . 17
5. Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6. Multicast . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 19
7.1. Traffic Engineering . . . . . . . . . . . . . . . . . . . 19
7.2. LISP for IPv6 Co-existence . . . . . . . . . . . . . . . 20
7.3. LISP for Virtual Private Networks . . . . . . . . . . . . 20
7.4. LISP for Virtual Machine Mobility in Data Centers . . . . 21
8. Security Considerations . . . . . . . . . . . . . . . . . . . 21
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
11.1. Normative References . . . . . . . . . . . . . . . . . . 23
11.2. Informative References . . . . . . . . . . . . . . . . . 25
Appendix A. A Brief History of Location/Identity Separation . . 25
A.1. Old LISP Models . . . . . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
1. Introduction
This document introduces the Locator/ID Separation Protocol (LISP)
[RFC6830] architecture, its main operational mechanisms and its
design rationale. Fundamentally, LISP is built following a well-
known architectural idea: decoupling the IP address overloaded
semantics. Indeed and as pointed out by Noel Chiappa [RFC4984],
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currently IP addresses both identify the topological location of a
network attachment point as well as the node's identity. However,
nodes and routing have fundamentally different requirements, routing
systems require that addresses are aggregatable and have topological
meaning, while nodes require to be identified independently of their
current location [RFC4984].
LISP creates two separate namespaces, EIDs (End-host IDentifiers) and
RLOCs (Routing LOCators), both are syntactically identical to the
current IPv4 and IPv6 addresses. EIDs are used to uniquely identify
nodes irrespective of their topological location and are typically
routed intra-domain. RLOCs are assigned topologically to network
attachment points and are typically routed inter-domain. With LISP,
the edge of the Internet (where the nodes are connected) and the core
(where inter-domain routing occurs) can be logically separated and
interconnected by LISP-capable routers. LISP also introduces a
database, called the Mapping System, to store and retrieve mappings
between identity and location. LISP-capable routers exchange packets
over the Internet core by encapsulating them to the appropriate
location.
In summary:
o RLOCs have meaning only in the underlay network, that is the
underlying core routing system.
o EIDs have meaning only in the overlay network, which is the
encapsulation relationship between LISP-capable routers.
o The LISP edge maps EIDs to RLOCs
o Within the underlay network, RLOCs have both locator and
identifier semantics
o An EID within a LISP site carries both identifier and locator
semantics to other nodes within that site
o An EID within a LISP site carries identifier and limited locator
semantics to nodes at other LISP sites (i.e., enough locator
information to tell that the EID is external to the site)
The relationship described above is not unique to LISP but it is
common to other overlay technologies.
The initial motivation in the LISP effort is to be found in the
routing scalability problem [RFC4984], where, if LISP were to be
completely deployed, the Internet core is populated with RLOCs while
Traffic Engineering mechanisms are pushed to the Mapping System. In
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such scenario RLOCs are quasi-static (i.e., low churn), hence making
the routing system scalable [Quoitin], while EIDs can roam anywhere
with no churn to the underlying routing system. [RFC7215] discusses
the impact of LISP on the global routing system during the transition
period. However, the separation between location and identity that
LISP offers makes it suitable for use in additional scenarios such as
Traffic Engineering (TE), multihoming, and mobility among others.
This document describes the LISP architecture and its main
operational mechanisms as well as its design rationale. It is
important to note that this document does not specify or complement
the LISP protocol. The interested reader should refer to the main
LISP specifications [RFC6830] and the complementary documents
[RFC6831], [RFC6832], [RFC6833], [RFC6834], [RFC6835], [RFC6836],
[RFC7052] for the protocol specifications along with the LISP
deployment guidelines [RFC7215].
2. Definition of Terms
Endpoint IDentifier (EID): EIDs are addresses used to uniquely
identify nodes irrespective of their topological location and are
typically routed intra-domain.
Routing LOcator (RLOC): RLOCs are addresses assigned topologically
to network attachment points and typically routed inter-domain.
Ingress Tunnel Router (ITR): A LISP-capable router that encapsulates
packets from a LISP site towards the core network.
Egress Tunnel Router (ETR): A LISP-capable router that decapsulates
packets from the core of the network towards a LISP site.
xTR: A router that implements both ITR and ETR functionalities.
Map-Request: A LISP signaling message used to request an EID-to-RLOC
mapping.
Map-Reply: A LISP signaling message sent in response to a Map-
Request that contains a resolved EID-to-RLOC mapping.
Map-Register: A LISP signaling message used to register an EID-to-
RLOC mapping.
Map-Notify: A LISP signaling message sent in response of a Map-
Register to acknowledge the correct reception of an EID-to-RLOC
mapping.
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This document describes the LISP architecture and does not introduce
any new term. The reader is referred to [RFC6830], [RFC6831],
[RFC6832], [RFC6833], [RFC6834], [RFC6835], [RFC6836], [RFC7052],
[RFC7215] for the complete definition of terms.
3. LISP Architecture
This section presents the LISP architecture, it first details the
design principles of LISP and then it proceeds to describe its main
aspects: data-plane, control-plane, and internetworking mechanisms.
3.1. Design Principles
The LISP architecture is built on top of four basic design
principles:
o Locator/Identifier split: By decoupling the overloaded semantics
of the current IP addresses the Internet core can be assigned
identity meaningful addresses and hence, can use aggregation to
scale. Devices are assigned with relatively opaque topologically
meaningful addresses that are independent of their topological
location.
o Overlay architecture: Overlays route packets over the current
Internet, allowing deployment of new protocols without changing
the current infrastructure hence, resulting into a low deployment
cost.
o Decoupled data and control-plane: Separating the data-plane from
the control-plane allows them to scale independently and use
different architectural approaches. This is important given that
they typically have different requirements and allows for other
data-planes to be added. While decoupled, data and control-plane
are not completely isolated because the LISP data-plane may
trigger control-plane activity.
o Incremental deployability: This principle ensures that the
protocol interoperates with the legacy Internet while providing
some of the targeted benefits to early adopters.
3.2. Overview of the Architecture
LISP splits architecturally the core from the edge of the Internet by
creating two separate namespaces: Endpoint Identifiers (EIDs) and
Routing LOCators (RLOCs). The edge consists of LISP sites (e.g., an
Autonomous System) that use EID addresses. EIDs are IPv4 or IPv6
addresses that uniquely identify communication end-hosts and are
assigned and configured by the same mechanisms that exist at the time
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of this writing. EIDs do not contain inter-domain topological
information and because of this, EIDs are usually routable at the
edge (within LISP sites) or in the non-LISP Internet; see Section 3.5
for discussion of LISP site internetworking with non-LISP sites and
domains in the Internet.
LISP sites (at the edge of the Internet) are connected to the core of
the Internet by means of LISP-capable routers (e.g., border routers).
LISP sites are connected across the core of the Internet using
tunnels between the LISP-capable routers. When packets originated
from a LISP site are flowing towards the core network, they ingress
into an encapsulated tunnel via an Ingress Tunnel Router (ITR). When
packets flow from the core network to a LISP site, they egress from
an encapsulated tunnel to an Egress Tunnel Router (ETR). An xTR is a
router which can perform both ITR and ETR operations. In this
context ITRs encapsulate packets while ETRs decapsulate them, hence
LISP operates as an overlay on top of the current Internet core.
/-----------------\ ---
| Mapping | |
. System | | Control
-| |`, | Plane
,' \-----------------/ . |
/ | ---
,.., - _,....,, | ,.., |
/ ` ,' ,-` `', | / ` |
/ \ +-----+ ,' `, +-----+ / \ |
| EID |-| xTR |--/ RLOC ,--| xTR |-| EID | | Data
| Space |-| |--| Space |--| |-| Space | | Plane
\ / +-----+ . / +-----+ \ / |
`. .' `. ,' `. .' |
`'-` `., ,.' `'-` ---
``'''``
LISP Site (Edge) Core LISP Site (Edge)
Figure 1.- A schema of the LISP Architecture
With LISP, the core uses RLOCs, an RLOC is an IPv4 or IPv6 address
assigned to an Internet-facing network interface of an ITR or ETR.
Typically RLOCs are numbered from topologically aggregatable blocks
assigned to a site at each point to which it attaches to the global
Internet, the topology is defined by the connectivity of networks.
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A database which is typically distributed, called the Mapping System,
stores mappings between EIDs and RLOCs. Such mappings relate the
identity of the devices attached to LISP sites (EIDs) to the set of
RLOCs configured at the LISP-capable routers servicing the site.
Furthermore, the mappings also include traffic engineering policies
and can be configured to achieve multihoming and load balancing. The
LISP Mapping System is conceptually similar to the DNS where it is
organized as a distributed multi-organization network database. With
LISP, ETRs register mappings while ITRs retrieve them.
Finally, the LISP architecture emphasizes incremental deployment.
Given that LISP represents an overlay to the current Internet
architecture, endhosts as well as intra and inter-domain routers
remain unchanged, and the only required changes to the existing
infrastructure are to routers connecting the EID with the RLOC space.
Additionally, LISP requires the deployment of an independent Mapping
System, such distributed database is a new network entity.
The following describes a simplified packet flow sequence between two
nodes that are attached to LISP sites. Please note that typical
LISP-capable routers are xTRs (both ITR and ETR). Client HostA wants
to send a packet to server HostB.
/----------------\
| Mapping |
| System |
.| |-
` \----------------/ `.
,` \
/ `.
,' _,..-..,, ',
/ -` `-, \
.' ,' \ `,
` ' \ '
+-----+ | | RLOC_B1+-----+
HostA | | | RLOC |-------| | HostB
EID_A--|ITR_A|----| Space | |ETR_B|--EID_B
| | RLOC_A1 |-------| |
+-----+ | | RLOC_B2+-----+
, /
\ /
`', ,-`
``''-''``
Figure 2.- Packet flow sequence in LISP
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1. HostA retrieves the EID_B of HostB, typically querying the DNS
and obtaining an A or AAAA record. Then it generates an IP
packet as in the Internet, the packet has source address EID_A
and destination address EID_B.
2. The packet is routed towards ITR_A in the LISP site using
standard intra-domain mechanisms.
3. ITR_A upon receiving the packet queries the Mapping System to
retrieve the locator of ETR_B that is servicing HostB's EID_B.
In order to do so it uses a LISP control message called Map-
Request, the message contains EID_B as the lookup key. In turn
it receives another LISP control message called Map-Reply, the
message contains two locators: RLOC_B1 and RLOC_B2 along with
traffic engineering policies: priority and weight per locator.
Note that a Map-Reply can contain more locators if needed. ITR_A
also stores the mapping in a local cache to speed-up forwarding
of subsequent packets.
4. ITR_A encapsulates the packet towards RLOC_B1 (chosen according
to the priorities/weights specified in the mapping). The packet
contains two IP headers, the outer header has RLOC_A1 as source
and RLOC_B1 as destination, the inner original header has EID_A
as source and EID_B as destination. Furthermore ITR_A adds a
LISP header, more details about LISP encapsulation can be found
in Section 3.3.1.
5. The encapsulated packet is forwarded by the Internet core as a
normal IP packet, making the EID invisible from the Internet
core.
6. Upon reception of the encapsulated packet by ETR_B, it
decapsulates the packet and forwards it to HostB.
3.3. Data-Plane
This section provides a high-level description of the LISP data-
plane, which is specified in detail in [RFC6830]. The LISP data-
plane is responsible for encapsulating and decapsulating data packets
and caching the appropriate forwarding state. It includes two main
entities, the ITR and the ETR, both are LISP capable routers that
connect the EID with the RLOC space (ITR) and vice versa (ETR).
3.3.1. LISP Encapsulation
ITRs encapsulate data packets towards ETRs. LISP data packets are
encapsulated using UDP (port 4341), the source port is usually
selected by the ITR using a 5-tuple hash of the inner header (so to
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be consistent in case of multi-path solutions such as ECMP [RFC2992])
and ignored on reception. LISP data packets are often encapsulated
in UDP packets that include a zero checksum [RFC6935] [RFC6936] that
is not verified when it is received, because LISP data packets
typically include an inner transport protocol header with a non-zero
checksum. By omitting the additional outer UDP encapsulation
checksum, xTRs can forward packets more efficiently. If LISP data
packets are encapsulated in UDP packets with non-zero checksums, the
outer UDP checksums are verified when the UDP packets are received,
as part of normal UDP processing.
LISP-encapsulated packets also include a LISP header (after the UDP
header and before the original IP header). The LISP header is
prepended by ITRs and striped by ETRs. It carries reachability
information (see more details in Section 4.2) and the Instance ID
field. The Instance ID field is used to distinguish traffic to/from
different tenant address spaces at the LISP site and that may use
overlapped but logically separated EID addressing.
Overall, LISP works on 4 headers, the inner header the source
constructed, and the 3 headers a LISP encapsulator prepends ("outer"
to "inner"):
1. Outer IP header containing RLOCs as source and destination
addresses. This header is originated by ITRs and stripped by
ETRs.
2. UDP header (port 4341) with zero checksum. This header is
originated by ITRs and stripped by ETRs.
3. LISP header that contains various forwarding-plane features (such
as reachability) and an Instance ID field. This header is
originated by ITRs and stripped by ETRs.
4. Inner IP header containing EIDs as source and destination
addresses. This header is created by the source end-host and is
left unchanged by LISP data plane processing on the ITR and ETR.
Finally, in some scenarios Re-encapsulating and/or Recursive tunnels
are useful to choose a specified path in the underlay network, for
instance to avoid congestion or failure. Re-encapsulating tunnels
are consecutive LISP tunnels and occur when a decapsulator (an ETR
action) removes a LISP header and then acts as an encapsultor (an ITR
action) to prepend another one. On the other hand, Recursive tunnels
are nested tunnels and are implemented by using multiple LISP
encapsulations on a packet. Such functions are implemented by
Reencapsulating Tunnel Routers (RTRs). An RTR can be thought of as a
router that first acts as an ETR by decapsulating packets and then as
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an ITR by encapsulating them towards another locator, more
information can be found at [RFC6830].
3.3.2. LISP Forwarding State
In the LISP architecture, ITRs keep just enough information to route
traffic flowing through them. Meaning that, ITRs retrieve from the
LISP Mapping System mappings between EID-prefixes (blocks of EIDs)
and RLOCs that are used to encapsulate packets. Such mappings are
stored in a local cache called the Map-Cache for subsequent packets
addressed to the same EID prefix. Note that, in case of overlapping
EID-prefixes, following a single request, the ITR may receive a set
of mappings, covering the requested EID-prefix and all more-specifics
(cf., Section 6.1.5 [RFC6830]). Mappings include a (Time-to-Live)
TTL (set by the ETR). More details about the Map-Cache management
can be found in Section 4.1.
3.4. Control-Plane
The LISP control-plane, specified in [RFC6833], provides a standard
interface to register and request mappings. The LISP Mapping System
is a database that stores such mappings. The following first
describes the mappings, then the standard interface to the Mapping
System, and finally its architecture.
3.4.1. LISP Mappings
Each mapping includes the bindings between EID prefix(es) and set of
RLOCs as well as traffic engineering policies, in the form of
priorities and weights for the RLOCs. Priorities allow the ETR to
configure active/backup policies while weights are used to load-
balance traffic among the RLOCs (on a per-flow basis).
Typical mappings in LISP bind EIDs in the form of IP prefixes with a
set of RLOCs, also in the form of IPs. IPv4 and IPv6 addresses are
encoded using the appropriate Address Family Identifier (AFI)
[RFC3232]. However LISP can also support more general address
encoding by means of the ongoing effort around the LISP Canonical
Address Format (LCAF) [I-D.ietf-lisp-lcaf].
With such a general syntax for address encoding in place, LISP aims
to provide flexibility to current and future applications. For
instance LCAFs could support MAC addresses, geo-coordinates, ASCII
names and application specific data.
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3.4.2. Mapping System Interface
LISP defines a standard interface between data and control planes.
The interface is specified in [RFC6833] and defines two entities:
Map-Server: A network infrastructure component that learns mappings
from ETRs and publishes them into the LISP Mapping System.
Typically Map-Servers are not authoritative to reply to queries
and hence, they forward them to the ETR. However they can also
operate in proxy-mode, where the ETRs delegate replying to queries
to Map-Servers. This setup is useful when the ETR has limited
resources (i.e., CPU or power).
Map-Resolver: A network infrastructure component that interfaces
ITRs with the Mapping System by proxying queries and in some cases
responses.
The interface defines four LISP control messages which are sent as
UDP datagrams (port 4342):
Map-Register: This message is used by ETRs to register mappings in
the Mapping System and it is authenticated using a shared key
between the ETR and the Map-Server.
Map-Notify: When requested by the ETR, this message is sent by the
Map-Server in response to a Map-Register to acknowledge the
correct reception of the mapping and convey the latest Map-Server
state on the EID to RLOC mapping. In some cases a Map-Notify can
be sent to the previous RLOCs when an EID is registered by a new
set of RLOCs.
Map-Request: This message is used by ITRs or Map-Resolvers to
resolve the mapping of a given EID.
Map-Reply: This message is sent by Map-Servers or ETRs in response
to a Map-Request and contains the resolved mapping. Please note
that a Map-Reply may contain a negative reply if, for example, the
queried EID is not part of the LISP EID space. In such cases the
ITR typically forwards the traffic natively (non encapsulated) to
the public Internet, this behavior is defined to support
incremental deployment of LISP.
3.4.3. Mapping System
LISP architecturally decouples control and data-plane by means of a
standard interface. This interface glues the data-plane, routers
responsible for forwarding data-packets, with the LISP Mapping
System, a database responsible for storing mappings.
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With this separation in place the data and control-plane can use
different architectures if needed and scale independently. Typically
the data-plane is optimized to route packets according to
hierarchical IP addresses. However the control-plane may have
different requirements, for instance and by taking advantage of the
LCAFs, the Mapping System may be used to store non-hierarchical keys
(such as MAC addresses), requiring different architectural approaches
for scalability. Another important difference between the LISP
control and data-planes is that, and as a result of the local mapping
cache available at ITR, the Mapping System does not need to operate
at line-rate.
Many of the existing mechanisms to create distributed systems have
been explored and considered for the Mapping System architecture:
graph-based databases in the form of LISP+ALT [RFC6836], hierarchical
databases in the form of LISP-DDT [I-D.ietf-lisp-ddt], monolithic
databases in the form of LISP-NERD [RFC6837], flat databases in the
form of LISP-DHT [I-D.cheng-lisp-shdht],[Mathy] and, a multicast-
based database [I-D.curran-lisp-emacs]. Furthermore it is worth
noting that, in some scenarios such as private deployments, the
Mapping System can operate as logically centralized. In such cases
it is typically composed of a single Map-Server/Map-Resolver.
The following focuses on the two mapping systems that have been
implemented and deployed (LISP-ALT and LISP+DDT).
3.4.3.1. LISP+ALT
The LISP Alternative Topology (LISP+ALT) [RFC6836] was the first
Mapping System proposed, developed and deployed on the LISP pilot
network. It is based on a distributed BGP overlay participated by
Map-Servers and Map-Resolvers. The nodes connect to their peers
through static tunnels. Each Map-Server involved in the ALT topology
advertises the EID-prefixes registered by the serviced ETRs, making
the EID routable on the ALT topology.
When an ITR needs a mapping it sends a Map-Request to a Map-Resolver
that, using the ALT topology, forwards the Map-Request towards the
Map-Server responsible for the mapping. Upon reception the Map-
Server forwards the request to the ETR that in turn, replies directly
to the ITR using the native Internet core.
3.4.3.2. LISP-DDT
LISP-DDT [I-D.ietf-lisp-ddt] is conceptually similar to the DNS, a
hierarchical directory whose internal structure mirrors the
hierarchical nature of the EID address space. The DDT hierarchy is
composed of DDT nodes forming a tree structure, the leafs of the tree
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are Map-Servers. On top of the structure there is the DDT root node
[DDT-ROOT], which is a particular instance of a DDT node and that
matches the entire address space. As in the case of DNS, DDT
supports multiple redundant DDT nodes and/or DDT roots. Finally,
Map-Resolvers are the clients of the DDT hierarchy and can query
either the DDT root and/or other DDT nodes.
/---------\
| |
| DDT Root|
| /0 |
,.\---------/-,
,-'` | `'.,
-'` | `-
/-------\ /-------\ /-------\
| DDT | | DDT | | DDT |
| Node | | Node | | Note | ...
| 0/8 | | 1/8 | | 2/8 |
\-------/ \-------/ \-------/
_. _. . -..,,,_
-` -` \ ````''--
+------------+ +------------+ +------------+ +------------+
| Map-Server | | Map-Server | | Map-Server | | Map-Server |
| EID-prefix1| | EID-prefix2| | EID-prefix3| | EID-prefix4|
+------------+ +------------+ +------------+ +------------+
Figure 3.- A schematic representation of the DDT tree structure,
please note that the prefixes and the structure depicted
should be only considered as an example.
The DDT structure does not actually index EID-prefixes but eXtended
EID-prefixes (XEID). An XEID-prefix is just the concatenation of the
following fields (from most significant bit to less significant bit):
Database-ID, Instance ID, Address Family Identifier and the actual
EID-prefix. The Database-ID is provided for possible future
requirements of higher levels in the hierarchy and to enable the
creation of multiple and separate database trees.
In order to resolve a query LISP-DDT operates in a similar way to the
DNS but only supports iterative lookups. DDT clients (usually Map-
Resolvers) generate Map-Requests to the DDT root node. In response
they receive a newly introduced LISP-control message: a Map-Referral.
A Map-Referral provides the list of RLOCs of the set of DDT nodes
matching a configured XEID delegation. That is, the information
contained in the Map-Referral points to the child of the queried DDT
node that has more specific information about the queried XEID-
prefix. This process is repeated until the DDT client walks the tree
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structure (downwards) and discovers the Map-Server servicing the
queried XEID. At this point the client sends a Map-Request and
receives a Map-Reply containing the mappings. It is important to
note that DDT clients can also cache the information contained in
Map-Referrals, that is, they cache the DDT structure. This is used
to reduce the mapping retrieving latency[Jakab].
The DDT Mapping System relies on manual configuration. That is Map-
Resolvers are manually configured with the set of available DDT root
nodes while DDT nodes are manually configured with the appropriate
XEID delegations. Configuration changes in the DDT nodes are only
required when the tree structure changes itself, but it doesn't
depend on EID dynamics (RLOC allocation or traffic engineering policy
changes).
3.5. Internetworking Mechanisms
EIDs are typically identical to either IPv4 or IPv6 addresses and
they are stored in the LISP Mapping System, however they are usually
not announced in the Internet global routing system. As a result
LISP requires an internetworking mechanism to allow LISP sites to
speak with non-LISP sites and vice versa. LISP internetworking
mechanisms are specified in [RFC6832].
LISP defines two entities to provide internetworking:
Proxy Ingress Tunnel Router (PITR): PITRs provide connectivity from
the legacy Internet to LISP sites. PITRs announce in the global
routing system blocks of EID prefixes (aggregating when possible)
to attract traffic. For each incoming packet from a source not in
a LISP site (a non-EID), the PITR LISP-encapsulates it towards the
RLOC(s) of the appropriate LISP site. The impact of PITRs in the
routing table size of the Default-Free Zone (DFZ) is, in the
worst-case, similar to the case in which LISP is not deployed.
EID-prefixes will be aggregated as much as possible both by the
PITR and by the global routing system.
Proxy Egress Tunnel Router (PETR): PETRs provide connectivity from
LISP sites to the legacy Internet. In some scenarios, LISP sites
may be unable to send encapsulated packets with a local EID
address as a source to the legacy Internet. For instance when
Unicast Reverse Path Forwarding (uRPF) is used by Provider Edge
routers, or when an intermediate network between a LISP site and a
non-LISP site does not support the desired version of IP (IPv4 or
IPv6). In both cases the PETR overcomes such limitations by
encapsulating packets over the network. There is no specified
provision for the distribution of PETR RLOC addresses to the ITRs.
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Additionally, LISP also defines mechanisms to operate with private
EIDs [RFC1918] by means of LISP-NAT [RFC6832]. In this case the xTR
replaces a private EID source address with a routable one. At the
time of this writing, work is ongoing to define NAT-traversal
capabilities, that is xTRs behind a NAT using non-routable RLOCs.
PITRs, PETRs and, LISP-NAT enable incremental deployment of LISP, by
providing significant flexibility in the placement of the boundaries
between the LISP and non-LISP portions of the network, and making it
easy to change those boundaries over time.
4. LISP Operational Mechanisms
This section details the main operational mechanisms defined in LISP.
4.1. Cache Management
LISP's decoupled control and data-plane, where mappings are stored in
the control-plane and used for forwarding in the data plane, requires
a local cache in ITRs to reduce signaling overhead (Map-Request/Map-
Reply) and increase forwarding speed. The local cache available at
the ITRs, called Map-Cache, is used by the router to LISP-encapsulate
packets. The Map-Cache is indexed by (Instance ID, EID-prefix) and
contains basically the set of RLOCs with the associated traffic
engineering policies (priorities and weights).
The Map-Cache, as any other cache, requires cache coherence
mechanisms to maintain up-to-date information. LISP defines three
main mechanisms for cache coherence:
Time-To-Live (TTL): Each mapping contains a TTL set by the ETR, upon
expiration of the TTL the ITR can't use the mapping until it is
refreshed by sending a new Map-Request. Typical values for TTL
defined by LISP are 24 hours.
Solicit-Map-Request (SMR): SMR is an explicit mechanism to update
mapping information. In particular a special type of Map-Request
can be sent on demand by ETRs to request refreshing a mapping.
Upon reception of a SMR message, the ITR must refresh the bindings
by sending a Map-Request to the Mapping System. Further uses of
SMRs are documented in [RFC6830].
Map-Versioning: This optional mechanism piggybacks in the LISP
header of data-packets the version number of the mappings used by
an xTR. This way, when an xTR receives a LISP-encapsulated packet
from a remote xTR, it can check whether its own Map-Cache or the
one of the remote xTR is outdated. If its Map-Cache is outdated,
it sends a Map-Request for the remote EID so to obtain the newest
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mappings. On the contrary, if it detects that the remote xTR Map-
Cache is outdated, it sends a SMR to notify it that a new mapping
is available.
Finally it is worth noting that in some cases an entry in the map-
cache can be proactively refreshed using the mechanisms described in
the section below.
4.2. RLOC Reachability
In most cases LISP operates with a pull-based Mapping System (e.g.,
DDT), this results in an edge to edge pull architecture. In such
scenario the network state is stored in the control-plane while the
data-plane pulls it on demand. This has consequences concerning the
propagation of xTRs reachability/liveness information since pull
architectures require explicit mechanisms to propagate this
information. As a result LISP defines a set of mechanisms to inform
ITRs and PITRS about the reachability of the cached RLOCs:
Locator Status Bits (LSB): LSB is a passive technique, the LSB field
is carried by data-packets in the LISP header and can be set by a
ETRs to specify which RLOCs of the ETR site are up/down. This
information can be used by the ITRs as a hint about the reachability
to perform additional checks. Also note that LSB does not provide
path reachability status, only hints on the status of RLOCs.
Echo-nonce: This is also a passive technique, that can only operate
effectively when data flows bi-directionally between two
communicating xTRs. Basically, an ITR piggybacks a random number
(called nonce) in LISP data packets, if the path and the probed
locator are up, the ETR will piggyback the same random number on the
next data-packet, if this is not the case the ITR can set the locator
as unreachable. When traffic flow is unidirectional or when the ETR
receiving the traffic is not the same as the ITR that transmits it
back, additional mechanisms are required.
RLOC-probing: This is an active probing algorithm where ITRs send
probes to specific locators, this effectively probes both the locator
and the path. In particular this is done by sending a Map-Request
(with certain flags activated) on the data-plane (RLOC space) and
waiting in return a Map-Reply, also sent on the data-plane. The
active nature of RLOC-probing provides an effective mechanism to
determine reachability and, in case of failure, switching to a
different locator. Furthermore the mechanism also provides useful
RTT estimates of the delay of the path that can be used by other
network algorithms.
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It is worth noting that RLOC probing and Echo-nonce can work
together. Specifically if a nonce is not echoed, an ITR could RLOC-
probe to determine if the path is up when it cannot tell the
difference between a failed bidirectional path or the return path is
not used (a unidirectional path).
Additionally, LISP also recommends inferring reachability of locators
by using information provided by the underlay, in particular:
ICMP signaling: The LISP underlay -the current Internet- uses the
ICMP protocol to signal unreachability (among other things). LISP
can take advantage of this and the reception of a ICMP Network
Unreachable or ICMP Host Unreachable message can be seen as a hint
that a locator might be unreachable, this should lead to perform
additional checks.
Underlay routing: Both BGP and IBGP carry reachability information,
LISP-capable routers that have access to underlay routing information
can use it to determine if a given locator or path are reachable.
4.3. ETR Synchronization
All the ETRs that are authoritative to a particular EID-prefix must
announce the same mapping to the requesters, this means that ETRs
must be aware of the status of the RLOCs of the remaining ETRs. This
is known as ETR synchronization.
At the time of this writing LISP does not specify a mechanism to
achieve ETR synchronization. Although many well-known techniques
could be applied to solve this issue it is still under research, as a
result operators must rely on coherent manual configuration
4.4. MTU Handling
Since LISP encapsulates packets it requires dealing with packets that
exceed the MTU of the path between the ITR and the ETR. Specifically
LISP defines two mechanisms:
Stateless: With this mechanism the effective MTU is assumed from the
ITR's perspective. If a payload packet is too big for the
effective MTU, and can be fragmented, the payload packet is
fragmented on the ITR, such that reassembly is performed at the
destination host.
Stateful: With this mechanism ITRs keep track of the MTU of the
paths towards the destination locators by parsing the ICMP Too Big
packets sent by intermediate routers. ITRs will send ICMP Too Big
messages to inform the sources about the effective MTU.
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Additionally ITRs can use mechanisms such as PMTUD [RFC1191] or
PLPMTUD [RFC4821] to keep track of the MTU towards the locators.
In both cases if the packet cannot be fragmented (IPv4 with DF=1 or
IPv6) then the ITR drops it and replies with a ICMP Too Big message
to the source.
5. Mobility
The separation between locators and identifiers in LISP is suitable
for traffic engineering purpose where LISP sites can change their
attachment points to the Internet (i.e., RLOCs) without impacting
endpoints or the Internet core. In this context, the border routers
operate the xTR functionality and endpoints are not aware of the
existence of LISP. This functionality is similar to Network Mobility
[RFC3963]. However, this mode of operation does not allow seamless
mobility of endpoints between different LISP sites as the EID address
might not be routable in a visited site. Nevertheless, LISP can be
used to enable seamless IP mobility when LISP is directly implemented
in the endpoint or when the endpoint roams to an attached xTR. Each
endpoint is then an xTR and the EID address is the one presented to
the network stack used by applications while the RLOC is the address
gathered from the network when it is visited. This functionality is
similar to Mobile IP ([RFC5944] and [RFC6275]).
Whenever the device changes of RLOC, the xTR updates the RLOC of its
local mapping and registers it to its Map-Server, typically with a
low TTL value (1min). To avoid the need of a home gateway, the ITR
also indicates the RLOC change to all remote devices that have
ongoing communications with the device that moved. The combination
of both methods ensures the scalability of the system as signaling is
strictly limited the Map-Server and to hosts with which
communications are ongoing. In the mobility case the EID-prefix can
be as small as a full /32 or /128 (IPv4 or IPv6 respectively)
depending on the specific use-case (e.g., subnet mobility vs single
VM/Mobile node mobility).
The decoupled identity and location provided by LISP allows it to
operate with other layer 2 and layer 3 mobility solutions.
6. Multicast
LISP also supports transporting IP multicast packets sent from the
EID space, the operational changes required to the multicast
protocols are documented in [RFC6831].
In such scenarios, LISP may create multicast state both at the core
and at the sites (both source and receiver). When signaling is used
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to create multicast state at the sites, LISP routers unicast
encapsulate PIM Join/Prune messages from receiver to source sites.
At the core, ETRs build a new PIM Join/Prune message addressed to the
RLOC of the ITR servicing the source. An simplified sequence is
shown below
1. An end-host willing to join a multicast channel sends an IGMP
report. Multicast PIM routers at the LISP site propagate PIM
Join/Prune messages (S-EID, G) towards the ETR.
2. The join message flows to the ETR, upon reception the ETR builds
two join messages, the first one unicast LISP-encapsulates the
original join message towards the RLOC of the ITR servicing the
source. This message creates (S-EID, G) multicast state at the
source site. The second join message contains as destination
address the RLOC of the ITR servicing the source (S-RLOC, G) and
creates multicast state at the core.
3. Multicast data packets originated by the source (S-EID, G) flow
from the source to the ITR. The ITR LISP-encapsulates the
multicast packets, the outter header includes its own RLOC as the
source (S-RLOC) and the original multicast group address (G) as
the destination. Please note that multicast group address are
logical and are not resolved by the mapping system. Then the
multicast packet is transmitted through the core towards the
receiving ETRs that decapsulates the packets and sends them using
the receiver's site multicast state.
Please note that the inner and outer multicast addresses are in
general different, unless in specific cases where the underlay
provider implements a tight control on the overlay. LISP
specifications already support all PIM modes [RFC6831].
Additionally, LISP can support as well non-PIM mechanisms in order to
maintain multicast state.
7. Use Cases
7.1. Traffic Engineering
A LISP site can strictly impose via which ETRs the traffic must enter
the the LISP site network even though the path followed to reach the
ETR is not under the control of the LISP site. This fine control is
implemented with the mappings. When a remote site is willing to send
traffic to a LISP site, it retrieves the mapping associated to the
destination EID via the mapping system. The mapping is sent directly
by an authoritative ETR of the EID and is not altered by any
intermediate network.
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A mapping associates a list of RLOCs to an EID prefix. Each RLOC
corresponds to an interface of an ETR (or set of ETRs) that is able
to correctly forward packets to EIDs in the prefix. Each RLOC is
tagged with a priority and a weight in the mapping. The priority is
used to indicates which RLOCs should be preferred to send packets
(the least preferred ones being provided for backup purpose). The
weight permits to balance the load between the RLOCs with the same
priority, proportionally to the weight value.
As mappings are directly issued by the authoritative ETR of the EID
and are not altered while transmitted to the remote site, it offers
highly flexible incoming inter-domain traffic engineering with even
the possibility for a site to support a different mapping policy for
each remote site. routing policies.
7.2. LISP for IPv6 Co-existence
LISP encapsulations allows to transport packets using EIDs from a
given address family (e.g., IPv6) with packets from other address
families (e.g., IPv4). The absence of correlation between the
address family of RLOCs and EIDs makes LISP a candidate to allow,
e.g., IPv6 to be deployed when all of the core network may not have
IPv6 enabled.
For example, two IPv6-only data centers could be interconnected via
the legacy IPv4 Internet. If their border routers are LISP capable,
sending packets between the data center is done without any form of
translation as the native IPv6 packets (in the EID space) will be
LISP encapsulated and transmitted over the IPv4 legacy Internet by
the mean of IPv4 RLOCs.
7.3. LISP for Virtual Private Networks
It is common to operate several virtual networks over the same
physical infrastructure. In such virtual private networks, it is
essential to distinguish which virtual network a packet belongs and
tags or labels are used for that purpose. When using LISP, the
distinction can be made with the Instance ID field. When an ITR
encapsulates a packet from a particular virtual network (e.g., known
via the VRF or VLAN), it tags the encapsulated packet with the
Instance ID corresponding to the virtual network of the packet. When
an ETR receives a packet tagged with an Instance ID it uses the
Instance ID to determine how to treat the packet.
The main usage of LISP for virtual private networks does not
introduce additional requirements on the underlying network, as long
as it is running IP.
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7.4. LISP for Virtual Machine Mobility in Data Centers
A way to enable seamless virtual machine mobility in data center is
to conceive the datacenter backbone as the RLOC space and the subnet
where servers are hosted as forming the EID space. A LISP router is
placed at the border between the backbone and each subnet. When a
virtual machine is moved to another subnet, it can keep (temporarily)
the address it had before the move so to continue without a transport
layer connection reset. When an xTR detects a source address
received on a subnet to be an address not assigned to the subnet, it
registers the address to the Mapping System.
To inform the other LISP routers that the machine moved and where,
and then to avoid detours via the initial subnetwork, mechanisms such
as the Solicit-Map-Request messages are used.
8. Security Considerations
This section describes the security considerations associated to the
LISP protocol.
While in a push mapping system, the state necessary to forward
packets is learned independently of the traffic itself, with a pull
architecture, the system becomes reactive and data-plane events
(e.g., the arrival of a packet for an unknown destination) may
trigger control-plane events. This on-demand learning of mappings
provides many advantages as discussed above but may also affect the
way security is enforced.
Usually, the data-plane is implemented in the fast path of routers to
provide high performance forwarding capabilities while the control-
plane features are implemented in the slow path to offer high
flexibility and a performance gap of several order of magnitude can
be observed between the slow and the fast paths. As a consequence,
the way data-plane events are notified to the control-plane must be
thought carefully so to not overload the slow path and rate limiting
should be used as specified in [RFC6830].
Care must also be taken so to not overload the mapping system (i.e.,
the control plane infrastructure) as the operations to be performed
by the mapping system may be more complex than those on the data-
plane, for that reason [RFC6830] recommends to rate limit the sending
of messages to the mapping system.
To improve resiliency and reduce the overall number of messages
exchanged, LISP offers the possibility to leak information, such as
reachabilty of locators, directly into data plane packets. In
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environments that are not fully trusted, control information gleaned
from data-plane packets should be verified before using them.
Mappings are the centrepiece of LISP and all precautions must be
taken to avoid them to be manipulated or misused by malicious
entities. Using trustable Map-Servers that strictly respect
[RFC6833] and the lightweight authentication mechanism proposed by
LISP-Sec [I-D.ietf-lisp-sec] reduces the risk of attacks to the
mapping integrity. In more critical environments, secure measures
may be needed. The way security is implemented for a given mapping
system strongly depends on the architecture of the mapping system
itself and the threat model assumed for the deployment. Thus, the
mapping system security has to be discussed in the relevant documents
proposing the mapping system architecture.
As with any other tunneling mechanism, middleboxes on the path
between an ITR (or PITR) and an ETR (or PETR) must implement
mechanisms to strip the LISP encapsulation to correctly inspect the
content of LISP encapsulated packets.
Like other map-and-encap mechanisms, LISP enables triangular routing
(i.e., packets of a flow cross different border routers depending on
their direction). This means that intermediate boxes may have
incomplete view on the traffic they inspect or manipulate. Moreover,
LISP-encapsulated packets are routed based on the outer IP address
(i.e., the RLOC), and can be delivered to an ETR that is not
responsible of the destination EID of the packet or even to a network
element that is not an ETR. The mitigation consists in applying
appropriate filtering techniques on the network elements that can
potentially receive un-expected LISP-encapsulated packets
More details about security implications of LISP are discussed in
[I-D.ietf-lisp-threats].
9. IANA Considerations
This memo includes no request to IANA.
10. Acknowledgements
This document was initiated by Noel Chiappa and much of the core
philosophy came from him. The authors acknowledge the important
contributions he has made to this work and thank him for his past
efforts.
The authors would also like to thank Dino Farinacci, Fabio Maino,
Luigi Iannone, Sharon Barkai, Isidoros Kouvelas, Christian Cassar,
Florin Coras, Marc Binderberger, Alberto Rodriguez-Natal, Ronald
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Bonica, Chad Hintz, Robert Raszuk, Joel M. Halpern, Darrel Lewis,
David Black as well as every people acknowledged in [RFC6830].
11. References
11.1. Normative References
[I-D.ietf-lisp-ddt]
Fuller, V., Lewis, D., Ermagan, V., and A. Jain, "LISP
Delegated Database Tree", draft-ietf-lisp-ddt-02 (work in
progress), October 2014.
[I-D.ietf-lisp-lcaf]
Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical
Address Format (LCAF)", draft-ietf-lisp-lcaf-07 (work in
progress), December 2014.
[I-D.ietf-lisp-sec]
Maino, F., Ermagan, V., Cabellos-Aparicio, A., and D.
Saucez, "LISP-Security (LISP-SEC)", draft-ietf-lisp-sec-07
(work in progress), October 2014.
[I-D.ietf-lisp-threats]
Saucez, D., Iannone, L., and O. Bonaventure, "LISP Threats
Analysis", draft-ietf-lisp-threats-12 (work in progress),
March 2015.
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
November 1990.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets", BCP
5, RFC 1918, February 1996.
[RFC2992] Hopps, C., "Analysis of an Equal-Cost Multi-Path
Algorithm", RFC 2992, November 2000.
[RFC3232] Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by
an On-line Database", RFC 3232, January 2002.
[RFC3963] Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
Thubert, "Network Mobility (NEMO) Basic Support Protocol",
RFC 3963, January 2005.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821, March 2007.
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[RFC4984] Meyer, D., Zhang, L., and K. Fall, "Report from the IAB
Workshop on Routing and Addressing", RFC 4984, September
2007.
[RFC5944] Perkins, C., "IP Mobility Support for IPv4, Revised", RFC
5944, November 2010.
[RFC6275] Perkins, C., Johnson, D., and J. Arkko, "Mobility Support
in IPv6", RFC 6275, July 2011.
[RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
Locator/ID Separation Protocol (LISP)", RFC 6830, January
2013.
[RFC6831] Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, "The
Locator/ID Separation Protocol (LISP) for Multicast
Environments", RFC 6831, January 2013.
[RFC6832] Lewis, D., Meyer, D., Farinacci, D., and V. Fuller,
"Interworking between Locator/ID Separation Protocol
(LISP) and Non-LISP Sites", RFC 6832, January 2013.
[RFC6833] Fuller, V. and D. Farinacci, "Locator/ID Separation
Protocol (LISP) Map-Server Interface", RFC 6833, January
2013.
[RFC6834] Iannone, L., Saucez, D., and O. Bonaventure, "Locator/ID
Separation Protocol (LISP) Map-Versioning", RFC 6834,
January 2013.
[RFC6835] Farinacci, D. and D. Meyer, "The Locator/ID Separation
Protocol Internet Groper (LIG)", RFC 6835, January 2013.
[RFC6836] Fuller, V., Farinacci, D., Meyer, D., and D. Lewis,
"Locator/ID Separation Protocol Alternative Logical
Topology (LISP+ALT)", RFC 6836, January 2013.
[RFC6837] Lear, E., "NERD: A Not-so-novel Endpoint ID (EID) to
Routing Locator (RLOC) Database", RFC 6837, January 2013.
[RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and
UDP Checksums for Tunneled Packets", RFC 6935, April 2013.
[RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement
for the Use of IPv6 UDP Datagrams with Zero Checksums",
RFC 6936, April 2013.
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[RFC7052] Schudel, G., Jain, A., and V. Moreno, "Locator/ID
Separation Protocol (LISP) MIB", RFC 7052, October 2013.
[RFC7215] Jakab, L., Cabellos-Aparicio, A., Coras, F., Domingo-
Pascual, J., and D. Lewis, "Locator/Identifier Separation
Protocol (LISP) Network Element Deployment
Considerations", RFC 7215, April 2014.
11.2. Informative References
[DDT-ROOT]
LISP DDT ROOT, , "http://ddt-root.org/", August 2013.
[I-D.cheng-lisp-shdht]
Cheng, L. and J. Wang, "LISP Single-Hop DHT Mapping
Overlay", draft-cheng-lisp-shdht-04 (work in progress),
July 2013.
[I-D.curran-lisp-emacs]
Brim, S., Farinacci, D., Meyer, D., and J. Curran, "EID
Mappings Multicast Across Cooperating Systems for LISP",
draft-curran-lisp-emacs-00 (work in progress), November
2007.
[Jakab] Jakab, L., Cabellos, A., Saucez, D., and O. Bonaventure,
"LISP-TREE: A DNS Hierarchy to Support the LISP Mapping
System, IEEE Journal on Selected Areas in Communications,
vol. 28, no. 8, pp. 1332-1343", October 2010.
[Mathy] Mathy, L., Iannone, L., and O. Bonaventure, "LISP-DHT:
Towards a DHT to map identifiers onto locators. The ACM
ReArch, Re-Architecting the Internet. Madrid (Spain)",
December 2008.
[Quoitin] Quoitin, B., Iannone, L., Launois, C., and O. Bonaventure,
""Evaluating the Benefits of the Locator/Identifier
Separation" in Proceedings of 2Nd ACM/IEEE International
Workshop on Mobility in the Evolving Internet
Architecture", 2007.
Appendix A. A Brief History of Location/Identity Separation
The LISP architecture for separation of location and identity
resulted from the discussions of this topic at the Amsterdam IAB
Routing and Addressing Workshop, which took place in October 2006
[RFC4984].
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A small group of like-minded personnel spontaneously formed
immediately after that workshop, to work on an idea that came out of
informal discussions at the workshop and on various mailing lists.
The first Internet-Draft on LISP appeared in January, 2007.
Trial implementations started at that time, with initial trial
deployments underway since June 2007; the results of early experience
have been fed back into the design in a continuous, ongoing process
over several years. LISP at this point represents a moderately
mature system, having undergone a long organic series of changes and
updates.
LISP transitioned from an IRTF activity to an IETF WG in March 2009,
and after numerous revisions, the basic specifications moved to
becoming RFCs at the start of 2013 (although work to expand and
improve it, and find new uses for it, continues, and undoubtly will
for a long time to come).
A.1. Old LISP Models
LISP, as initially conceived, had a number of potential operating
modes, named 'models'. Although they are no used anymore, one
occasionally sees mention of them, so they are briefly described
here.
LISP 1: EIDs all appear in the normal routing and forwarding tables
of the network (i.e. they are 'routable');this property is used to
'bootstrap' operation, by using this to load EID->RLOC mappings.
Packets were sent with the EID as the destination in the outer
wrapper; when an ETR saw such a packet, it would send a Map-Reply
to the source ITR, giving the full mapping.
LISP 1.5: Similar to LISP 1, but the routability of EIDs happens on
a separate network.
LISP 2: EIDs are not routable; EID->RLOC mappings are available from
the DNS.
LISP 3: EIDs are not routable; and have to be looked up in in a new
EID->RLOC mapping database (in the initial concept, a system using
Distributed Hash Tables). Two variants were possible: a 'push'
system, in which all mappings were distributed to all ITRs, and a
'pull' system in which ITRs load the mappings they need, as
needed.
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Authors' Addresses
Albert Cabellos
UPC-BarcelonaTech
c/ Jordi Girona 1-3
Barcelona, Catalonia 08034
Spain
Email: acabello@ac.upc.edu
Damien Saucez (Ed.)
INRIA
2004 route des Lucioles BP 93
Sophia Antipolis Cedex 06902
France
Email: damien.saucez@inria.fr
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