In the past few years, proposed solutions for the improvement of internet mobility and scalability issues are being studied. One of these proposals introduced is the Locator/ Identifier Separation Protocol (LISP). It is design to overcome this limitation. In this paper, we will briefly introduce, based on theoretical research, the background of this protocol and describe a scenario regarding the mapping system deployed nowadays. This paper specifies the basic elements needed to deploy within this system. Keywords: LISP, Mobility, Routing, Tunneling, Traffic, Internet, Protocol, Mapping

1. LISP: The Novel Approach to the Future of Internet
Architecture
Denis ALBALDEJO, Assia BAKRIM, Nemia BELGA, and Guillaume DANET
UPSSITECH STRI – Université Paul Sabatier TOULOUSE III
Abstract. In the past few years, proposed solutions for the improvement of
internet mobility and scalability issues are being studied. One of these proposals
introduced is the Locator/ Identifier Separation Protocol (LISP). It is design to
overcome this limitation. In this paper, we will briefly introduce, based on
theoretical research, the background of this protocol and describe a scenario
regarding the mapping system deployed nowadays. This paper specifies the
basic elements needed to deploy within this system.
Keywords: LISP, Mobility, Routing, Tunneling, Traffic, Internet, Protocol,
Mapping.
1 Introduction
At present, Internet Service Providers (ISP) continue the traditional way to allocate
official IP addresses to customer networks. [1] These hosts IP addresses both serve as
the devices’ locator and identifier. As a result, these dual categories of each IP
address contribute to the rapid growth of the Internet’s Default Free Zone (DFZ).
Locator/Identifier Separation Protocol (LISP) is one of the most successful
proposals put into practice to cope with this routing scalability problem of existing
Internet. It is one of the ideas discussed by the Internet Research Task with the aim of
designing a new routing architecture for the Internet core routing. [2]
As a result, we have conducted a brief study to depict the general LISP overview
and to illustrate its mapping system that is generally deployed nowadays.
This paper contains concise details, based on theoretical research done by the team.
The first part, Section 2, discusses the problems that LISP can solve. Second, to the
best of our knowledge, the main concept of LISP and basic elements required by the
mapping system are described in Section 3. It then follows the description of several
deployment and implementation done, in Section 4, and enumerates the contribution
of LISP and its drawbacks to the future internet architecture, in Section 5. We
conclude this paper in Section 5 by clarifying the ongoing development and experts’
outlooks for the expansion of this protocol.

2. 2 Problem Statements
Figure 1, extracted from ‘Border Gateway Protocol (BGP) Routing Table analysis’
website, illustrates that the routing tables have expanded aggressively over the years
[3] and will continue to grow in a more complex way when IPv6 is going to be fully
deployed. These are caused by mainly multi-homing, traffic engineering, non
aggregable address allocations and business events such as mergers and acquisitions.
LISP aims to reduce the global routing state through Routing Locator (RLOC, which
is a LISP-enabled router) aggregation.
Fig. 1. Tracking the evolution of BGP routing tables from 1994 till present 1
With the traditional addressing architecture, a network node is represented by an IP
address, this address is used to represent the identity of the device and its location on
the network, and so, it constantly changes as the device switches networks. For
instance, the migration of a virtual machine from a physical server to another, it
requires a new IP address when it changes networks, hence, all the other services
linked to this virtual machine won't be able to detect it until the administrator will
configure a new address to the Virtual Machine.
Another example related to connectivity is when a user of a smart phone changes
from a wireless connectivity to 4G, it needs to change its IP address.
Therefore, at the present time, the study of customer needs in terms of connectivity
and mobility, illustrates that a new addressing architecture is essential to meet with
the customers' expectations.
1
Figure extracted from http://bgp.potaroo.net/, by Geoff Huston, “BGP routing table
analysis reports”, see last visit : February 2015

3. 3 LISP Overview
In this section, we provide the required background in order to elucidate
advantages and the hitch of LISP for the remainder of this paper. We first briefly
outline the concept of LISP protocol (Sec. 3.1) and, next, the mapping system (Sec.
3.2).
3.1 LISP Concept
The main idea of LISP derived from the Separation of Identification and Locator
theory. This approach aims to allocate two addresses to each network node: one for its
location on the Internet's DFZ and another one for its identity. It allows the device to
keep the same IP address since it makes a difference between 'who' and the 'where' in
networking and considers two types of addresses: the Endpoint Identifier (EID) and
the Routing Locator (RLOC). [1, 2]
The difference between EID and RLOC is that: the EID is an IPv4 or IPv6 address
or an arbitrary element, such as, a set of GPS coordinate or a MAC address, which is
given to the node; while, on the other hand, the RLOCs follow the network topology
when EIDs use organization or geographical hierarchy. EID prefixes are generally not
visible in the global routing system which means it is only locally routable. Thus,
RLOCs are assigned to border routers of a subnet while EIDS are assigned to sub-
network systems. [1, 2]
The fundamental idea within IP-Based Architecture of LISP is that EID represents
an end-host IP address, and RLOCs represent the IP addresses’ end host location. The
basic scheme of this architecture is that it follows a map-end-encap scheme where
egress routers EIDs are mapped into RLOCs. The scaling advantages occur when EID
addresses are not routable through the internet as RLOCs are the only addresses that
are globally routable. [3] For example, study has shown that the reduction global
routing table size is possible through roughly two magnitude orders with LISP. [5]
3.2 The Mapping System
The Mapping System is the keystone of LISP. This is where the separation of
location from the identity of an IP device occurs. LISP enabled routers perform
encapsulation and decapsulation of IP traffic travelling across. [1] Thus, LISP
dynamically establishes unidirectional tunnels without any specific configuration of
tunnel endpoints.
Moreover, the Mapping System is queried with the aim to provide the actual
RLOC for any communication need to an EID. It has a very similar function to DNS

4. as it serves as a distributed database that holds billions of identifiers. LISP Basic
elements are depicted in Figure 2.
Fig. 2. LISP Basic Elements
Moreover, in comparison with MPLS, the mapping system is also associated with
tuples. It is linked with an EID prefix to a list of <RLOCs, priority, weight> tuples.
The priority and weight are used to determine the preference of an RLOC to reach a
given EID. RLOCs associated with the highest priority are always in favor. If RLOCs
happen to share the same least priority, then, the weight is then used for load
balancing. [7]
On a LISP domain, as shown in Fig. 2, two types of router functions can be
identified (ITR and ETR) but some LISP routers implement both of these functions
and these routers are called xTR. [4]
 An ITR or Ingress Tunnel Router is a router that simply forwards a packet
to the next hop if it's an IP network, or encapsulates it if the destination is
a LISP network. It also sends map-reply to resolve EID-to-RLOC
mapping.
 An ETR or Egress Tunnel Router is a router that has two functions.
It decapsulate a packet if it has LISP flag on its header, and sends it to the
local EID. It also sends a map-register to the Map Server to save the EID
and RLOC combination.
ITR : Ingress Tunnel Router (LISP Encapsulation)
ETR : Egress Tunnel Router (LISP Decapsulation)
xTR : ITR plus ETR
RLOC : Routing Locator
EID : Endsystem Identifier

5. Having these LISP routers are very essential to the mapping system, as they
perform the encapsulation and decapsulation process of the system.
In addition to these elements, the Mapping System relies on two new entities: the
Map Server (MS) and the Map Resolver (MR). The MS/MRs are a redirection to find
a responsible ETR. The mapping between RLOC and EID is stored in the mapping
database of the ETR.
A control message (request Map-Register) is obtained by the MS containing
mapping information, when a LISP router (xTR) detects a machine in the network and
has access to it. Map Registration messages are transported in UDP and integrity
protected by security credentials that are only known by the LISP routers of a given
site and MS. This information collected is then stored in the MS before sending an
acknowledgment notification (via response Map- Notify). This Map Notify messages
are also used by LISP routers to discover other LISP routers of the same LISP site.
The router xTR identifies the location of a device. MR sends a request (application
Map-Request) to xTR. This request contains an EID of the machine it needs to
identify, corresponding RLOC. MR then sends the request to MS in order to find the
relevant information to send back to xTR (answer Map- Reply). Every Map-Reply has
a TTL for a certain EID. As long as TTL is not equal to zero, the IR will continue to
use the mapping cache entry without re-querying the mapping system for that
corresponding EID. [2,3,4]
Another important principle regarding LISP is to maintain its full connectivity. It is
a protocol that is capable of core network transit and middle box transit. This
exemplifies the reason of LISP traffic requirement to triggers encapsulation of packets
in a tunnel or a traffic that keeps a connection alive. [2, 3]
Tunneling is an important process in LISP. It handles the creation of packets by
xTRs containing outer headers using RLOCs and inner headers using EIDs. In this
manner, the packets are independent from special handling as they are interpreted by
the network equipments without being dropped, since they are following the similar
format of IP packets. [3]
To this point, a number of mapping systems have been suggested for LISP.
Although, there are numerous proposals, only two are currently deployed: LISP
Alternative Topology Device (ALT) and LISP Delegated Database Tree (DDT). ALT
is a mapping model that manages the aggregation of EIDs. It provides EID-to-RLOC
mapping services to the other elements of the network. [2] It is the initial mapping
system for LISP and is dependent on BGP overlay. After a few years of study and
operation, DDT is now designed with manageability and isolation, as ALT was
unwieldy to manage. It functions as DNS-like systems as it contains hierarchy with
LISP DDT servers queried by MS and MP. [2,4]

6. 3.4 Dynamic Management of Mapping Systems
Requirements arising each LISP system require dynamic management to solve
reachability issues. There are several mechanisms for determining RLOC reachability
that are currently defined. [4]
Below are examples of these reachability algorithms used in the LISP system.
RLOC Probing Algorithm
LISP employs the RLOC probing algorithm to determine the reachability status of
locators cached in maps cached. It includes exchange of special MAP-Request and
MAP-Reply messages between the two routers: ITR and ETR in order to confirm
locator reachability. Its asset is its ability to support variety of failure scenarios,
providing the reachable and available path to a specific locator for ITR. Thus, this
brings a robust mechanism for switching to using another locator from the cached
locator. [4]
For specific CISCO version, the locator reachability algorithm is used. LOC-
REACH-ALGORITHM is a command used to enable LISP locator reachability
algorithms. This algorithm is available in CISCO IOS and CISCO IOS XE LISP
versions. This is only used as an option, and can be disabled. [10]
Echo Nonce Algorithm
Nonce echoing is a data-plane mechanism that can be used to determine the
reachability between two LISP capable routers, the ITR and ETR. It is utilised when
data flows in bidirectional way between Locators of different sites. The traffic can be
unidirectional occasionally. Therefore, this mechanism does not guarantee the
complete performance of the solution to forward path reachability problem. [4]
3.5 Scenario
This basic example of scenario in Figure 3 portrays the simple LISP process [4,10].
1. Host B needs to provide its device identification and location (EID and
RLOCs) to the Mapping System. ETR2
registers the information provided by
Host B in the Map Server. This operation is called Map-Registration in
LISP.
2. If the registration takes place successfully, Map-Server replies with a
notification of a proper registration to Host B (Map-Notify)
3. Host A generates Regular IP packet and the source endpoint forwards this
packet to its destination.
2
During operation, an ETR sends periodic Map-Register messages to all its configured map
servers.

7. 4. IP packets are then processed by LISP router (ITR). EID is defined as the
destination hence packets cannot be forwarded to the Internet
5. ITR requests the Mapping System ( global database of the system containing
EIDs and RLOCs)
a. ITR sends a first request “map-request” to the map-resolver in order
to know where (RLOC space) the given EID is.
b. Map-resolver asks the map-server for the location of the given EID.
c. RLOC of the EID is returned if there is at least one RLOC matching
the EID
d. Map-server sends the reply to the ITR : “EID XXXX is in RLOC
YYYY” (Map-reply)
e. ITR receives the mapping system for the EID destination and
selects an RLOC relying on priority field.
Fig. 3: A basic scenario of LISP Mapping System
6. ITR encapsulates LISP Packet original message (source address: ITR
RLOC, destination address: TARGET ETR RLOC) in a basic UDP packet.
Therefore, source address are both RLOCs and can be now forwarded to the
Internet
7. ETR decapsulates the LISP packet
8. After the ITR and ETR havereceived and decapsulated the original packet,
the packets are now ready to be delivered to the final EID of Host B
destination

8. 4 Deployment and Implementation
After exploring the way LISP works, this present section discusses the current
deployment of the LISP protocol.
The conclusion drawn by D. Saucez in 2013[2], shows us that there were 20
official mapping systems recorded in 2010 and only 80 in 2012. This illustrates a
rapid growth with an increasing rate of 100%, demonstrating the dynamism of the
network test.
Moreover, the LISP network is currently deployed by various entities as start-ups,
international companies like Microsoft, Facebook or Verisign, and Operators. We also
have to notice that other smaller companies, universities and research laboratories are
also testing on this protocol. [10]
Additionally, the LISP network was deployed to a large scale since LISP exists in
globally. It exists for the most part in both North America and Europe, but also in
Asia and South America. The map in Figure 3 demonstrates the location of the
different LISP Network nodes in the world from a survey conducted in February
2015.
Fig. 5 The vast deployment of LISP node network worldwide 3
Consequently, there are a range of implementations of LISP protocol showing the
interest of the world community towards it. [11] The best known and most developed
are:
 LISP by Cisco in their Operating Systems: IOS and NX-OS [11]
 OpenLISP, by l’Université Catholique de Louvain for FreeBSD
3
source extracted from www.lispmon.net

9.  LISPmob, open source version for GNU/Linux and Android
The continuous expansion of LISP Test network and diversity in terms of
deployment, demonstrates the interest and curiosity aroused by the new protocol
within the world of computer networks.
5 Advantages and Drawbacks
This present section recapitulates the numerous advantages and major drawbacks
that LISP offers.
5.1 Advantages
There are various underlying principles to deploy LISP that would be very
beneficial for the better architecture of internet. These following advantages are:
 Incremental deployment of LISP
By reusing as much current IP technology as possible and reducing the
impact on the existing infrastructure, LISP offers all the benefits of the
locator/ID split paradigm while being incrementally deployable.
 LISP is IP Friendly
Reusing the IP address space lets LISP fulfill the incremental deployability
and non-disruptive namespace goals. Indeed, it’s just a slight, non disruptive
change in the IP address semantic, and is interoperable with any IP-based
device.
Basically LISP supports any type of combination of EID and RLOC.
Therefore, it is possible to bind IPv6 EIDs addresses with IPv4 RLOCs
addresses or vice versa. Thus, IPv6 islands can be built and connected using
your existing IPv4 Internet connectivity. This is very useful as the transfer of
IPv6 packets on an IPv4 network is achievable. [5]
 Network virtualization with LISP
Network virtualization VPN is normally based on BGP/MPLS protocols and
LISP can replace this with its map-and-encap mechanism. The encapsulation
part will play MPLS role and the mapping part the BGP role.
 LISP supports mobility
In a LISP mobile node, the device itself implements a lightweight version of
LISP. Every mobile node receives an EID address from its home network
and keeps this EID independently of its location. [9]

10. 5.2 Major Drawbacks
Despite the advantages of LISP application described in the section above, there
are some major challenges to improve.
 LISP uses a tunnelling technique to pass from an ITR to an ETR and like all
other tunnelling technique LISP experience potential MTU issues.
 The complexity is also a negative aspect. This paradigm will change the way
we have to see routing. It is a different concept and users will need to adapt
and learn how to use this technology.
 There is delay in the transmission as the first packet in its new destination
can get dropped, the destination lookup takes time. But then, the other next
incoming packets will benefit the destination information cache, so next
incoming packets should flow smoothly without delay. [3]
 Study has shown this can be solved in the next development, as it appears in
theory, according to the Cisco LISP team. [11]
 Some optimizations have been suggested to resolve this delay issue. [2]
Examples of these, are, a list of common known destinations could be pre-
programmed into ITRs; or ITRs could perform DNS reply snooping because
most of the time a DNS lookup will be followed quickly by an initial packet
to that destination. Hence, the work carried out in order to improve
performance of this protocol is to a small step to resolve this delay drawback.
6 Conclusion
The continuous expansion of the Internet presents a number of challenges. Among
the most fundamental of these challenges are scalability and mobility issues. As a
result, LISP has been proposed. It improves the limits encountered as regards to
Internet scalability and mobility. It offers variety of features to enhance the future
Internet architecture.
In this paper, we performed a firsthand investigation regarding LISP overview and
study of pros and cons for LISP implementation. We have drawn to a conclusion that,
as scientific studies and researches are still ongoing, LISP will have great gradual
impact towards the future development regarding the Internet, as LISP
implementation progresses.
Consequently this will allow evaluating the configuration pre-requisite of LISP to
provide flexible guide for future experimentation and analysis. Furthermore, we
expect to study different types, in regards to, configuration, platform, and other
requirements of LISP deployed presently.

11. 7 References
1. W. Kampichler et al., “LISP: A Novel Approach Towards A Future
Communication Infrastructure Multilink Service” Dieter Eier, Frequentis
USA, Inc, Columbia MD, 978-1-4799-1538-5, 2003IEEE
2. D. Saucez, L. Iannone, B. Donnet ,“A First Measurement Look at the
Deployment and Evolution of the Locator/ID Separation Protocol” ACM
SIGCOMM Computer Communication Review (Vol. 43 No. 2), April
2013
3. A. Martinez et al., “An approach to a Fault Tolerance LISP Architecture”,
Neàpolis Building. Rbla. Exposicio, 59-69 0880 Vilanov I la Geltru,
Spain, 2009
4. Farinacci, et al, Experimental, RFC 6830, January 2013
5. Bruno Q et al, “Evaluating the Benefits of the Locator/Identifier
Separation”, MobiArch’07, ACM 978-1-59593-784-8/07/0008, August
27–31, 2007, Kyoto, Japan.
6. D. Saucez et al., “Interdomain Traffic Engineering in a Locator/Identifier
Separation Context,” Proc. Internet Network Management Workshop
(INM 08), IEEE, 2008,pp. 1–6.
7. D. Sauce and B. Donnet, R. Bestak et al. (Eds): NETWORKING 2012,
Part I, LNCS 7289, pp. 385-396, IFIP International Federation for
Information Processing 2012
8. L. Jakab, J. Domingo-Pascual, A. Cabellos Aparicio, F. Coras, A.
Rodriguez-Natal , “LISPmon“ <http://lispmon.net/>, May 2011
9. Luigi Iannone , “OpenLISP” <http://www.openlisp.org>
10. CISCO, “Locator/ Identifier Separation Protocol Q&A”,
http://www.cisco.com, last visit: February 2015
11. Locator/ Identifier Separtation Protocol http://www.lisp4.net/, last visit:
February 2015