LISP Working Group                                            N. Chiappa
Internet-Draft                              Yorktown Museum of Asian Art
Intended status: Informational                              July 9, 2012
Expires: January 10, 2013

                 An Architectural Analysis of the LISP
                  Location-Identity Separation System


   LISP upgrades the architecture of the IPvN internetworking system by
   separating location and identity, current intermingled in IPvN
   addresses.  This is a change which has been identified by the IRTF as
   a critically necessary evolutionary architectural step for the
   Internet.  In LISP, nodes have both a 'locator' (a name which says
   _where_ in the network's connectivity structure the node is) and an
   'identifier' (a name which serves only to provide a persistent handle
   for the node).  A node may have more than one locator, or its locator
   may change over time (e.g. if the node is mobile), but it keeps the
   same identifier.

   One of the chief novelties of LISP, compared to other proposals for
   the separation of location and identity, is its approach to deploying
   this upgrade.  In general, it is comparatively easy to conceive of
   new network designs, but much harder to devise approaches which will
   actually get deployed throughout the global network.  LISP aims to
   achieve the near-ubiquitous deployment necessary for maximum
   exploitation of an architectural upgrade by i) minimizing the amount
   of change needed (existing hosts and routers can operate unmodified);
   and ii) by providing significant benefits to early adopters.

   This document gives additional architectural insight into LISP, and
   analyzes a number of aspects of LISP from a long-term perspective.

   NOTE: This is an initial rough draft, a much better version will be
   out shortly.

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Table of Contents

   1.  Introduction
   2.  Architectual Frameworks
     2.1.  'Double-Ended' Approach
     2.2.  Critical State
     2.3.  Need for a Mapping System
     2.4.  Piggybacking of Control on User Data
   3.  Namespaces
     3.1.  LISP EIDs
       3.1.1.  Residual Location Functionality in EIDs
     3.2.  RLOCs
     3.3.  Overlapping Uses of Existing Namespaces
     3.4.  LCAFs
   4.  Fault Discovery/Handling
   5.  Scalability
     5.1.  Demand Loading of Mappings
     5.2.  Caching of Mappings
     5.3.  Amount of State
     5.4.  Scalability of The Indexing Subsystem
   6.  Security
     6.1.  Basic Philosophy
     6.2.  Design Guidance
       6.2.1.  Security Mechanism Complexity
     6.3.  Security Overview
     6.4.  Securing Mappings
     6.5.  Securing the xTRs
   7.  Robustness
   8.  Optimization
   9.  Open Issues
   10. Additional Material
   11. Acknowledgments
   12. IANA Considerations
   13. Security Considerations
   14. References
     14.1. Normative References
     14.2. Informative References
   Appendix A.  RefComment
   Appendix B.  Glossary/Definition of Terms
   Appendix C.  Other Appendices

1.  Introduction

   This document begins by introducing some high-level architectural
   frameworks which have proven useful for thinking about the LISP
   location-identity separation system.  It then discusses some
   architectural aspects of LISP (e.g. its namespaces).  The balance
   (and bulk) of the document contains architectural analysis of the
   LISP system; that is, it reviews from a long-term perspective various
   aspects of that system; e.g. its scalability, security, robustness,

   NOTE: This document assumes a fair degree of familiarity with LISP;
   in particular, the reader should have a good 'high-level'
   understanding of the overall LISP system architecture, such as is
   provided by [Introduction], "An Introduction to the LISP System".

   By "architecture" above, the restricted meaning used there is: 'How
   the system is broken up into subsystems, and how those subsystems
   interact; when does information flows from one to another, and what
   that information is.'  There is obviously somewhat more to
   architecture (e.g. the namespaces of a system, their syntax and
   semantics), and that remaining architectural content is covered here.

2.  Architectual Frameworks

   When considering the overall structure of the LISP system at a high
   level, it has proven most useful to think of it as another packet-
   switching layer, run on top of the original internet layer - much as
   the Internet first ran on top of the ARPANET.

   All the functions that a normal packet switch has to undertake - such
   as ensuring that it can reach its neighbours, and they they are still
   up - the devices that make up the LISP overlay also have to do, along
   the 'tunnels' which connect them to other LISP devices.

   There is, however, one big difference: the fanout of a typical LISP
   ITR will be much larger than most classic physical packet switches.
   (ITRs only need to be considered, as the LISP tunnels are all
   effectively unidirectional, from ITR to ETR - the ETR needs to keep
   no per-tunnel state, etc.)

   LISP is, fundamentally, a 'tunnel' based system.  Tunnel system
   designs do have their issues (e.g. the high inter-'switch' fan-out),
   but it's important to realize that they also can have advantages,
   some of which are listed below.

2.1.  'Double-Ended' Approach

   LISP may be thought of as a 'double-ended' approach to enhancing the
   architecture, in that it uses pairs of devices, one at each end of a
   communication stream.  In particular, to interact with the population
   of 'legacy' hosts (which will be, inevitably, the vast majority, in
   the early stages of deployment) it requires a LISP device at both
   ends of the 'tunnel'.

   This is in distinction to, say, NAT systems, which only need a device
   deployed at one end: the host at the 'other end' doesn't need a
   matching device at its end to massage the packets, but can simply
   consume them on its own, as they are fully normal packets.  This
   allows any site which deploys such a device to get the full benefit
   whilst acting entirely on its own.  [Wasserman]

   The issue is not that LISP uses tunnels.  Designs like HIP
   ([RFC4423]) and ILNP ([ILNP]), which do not involve tunnels, inhabit
   a similar space to tunnel-based designs like LISP, in that unless
   both ends are upgraded - or there is a proxy at the un-upgraded end -
   one doen't get any benefits.  So it's really not the tunnel which is
   the key aspect, it's the 'all at one end' part which is key.  Whether
   the system is tunnel, versus non-tunnel, is not that important.

   However, the double-ended approach of LISP does have advantages, as
   well as costs.  To put it simply, the 'feature' of the alternative
   approach, that there's only a box at one end, has a 'bug': there's
   only a box at one end.  There are things which such a design cannot
   accomplish, because of that.  To put it another way, does the fact
   that the packet has only a single name in it, because it is a
   'normal' packet, present a limitation?  Put that way, it would seem
   natural that it should.

   To compile as complete list of such situations is beyond the scope of
   this document, but one example is mobility with open connections.

   It is also possible to use LISP to tunnel IPv6 traffic over IPv4
   infrastructure, or vice versa, invisibly to the hosts on both ends.

   In the longer term, having having tunnel boxes would allow us to wrap
   packets in non-IP formats: perhaps to take direct advantage of the
   capabilities of underlying switching fabrics (e.g.  MPLS); perhaps to
   deploy new carriage protocols, etc, where non-standard packet formats
   will allow extended semantics.

2.2.  Critical State

   LISP does have 'critical state' in the network (i.e. state which, if
   if lost, causes the communication to fail).  However, because LISP is
   designed as an overall system, 'designing it in' allows for a
   'systems' approach to its state issues.  In LISP, this state has been
   designed to be maintained in an 'architected' way, so it does not
   produce systemic brittleness in the way that the state in NATs does.

   For instance, throughout the system, provisions have been made to
   have redundant copies of state, in multiple devices, so that the loss
   of any one device does not necessarily cause a failure of an ongoing

2.3.  Need for a Mapping System

   LISP does need to have a mapping system, which brings design,
   implementation, configuration and operational costs.  Surely all
   these costs are a bad thing?  However, having a mapping system have
   advantages, especially when there is a mapping layer which has global
   visibility (i.e. other entities know that it is there, and have an
   interface designed to be able to interact with it).  This is unlike,
   say, the mappings in NAT, which are 'invisible' to the rest of the

   In fact, one could argue that the mapping layer is LISP's greatest
   strength.  Wheeler's Axiom* ('Any problem in computer science can be
   solved with another level of indirection') indicates that the binding
   layer available with the LISP mapping system will be of great value.
   Again, it is not the job of this document to list them all - and in
   any event, there is no way to forsee them all.

   The author of this document has often opined that the hallmark of
   great architecture is not how well it does the things it was designed
   to do, but how well it does things it was never expected to have to
   handle.  Providing such a powerful and generic binding layer is one
   sure way to achieve the sort of lasting flexibility and power that
   leads to that outcome.

   [Footnote *: This Axiom is often mis-attributed to Butler Lampson,
   but Lampson himself indicated that it came from David Wheeler.]

2.4.  Piggybacking of Control on User Data

   LISP piggybacks control transactions on top of user data packets.
   This is a technique that has a long history in data networking, going
   back to the early ARPANET.  [McQuillan] It is now apparently regarded
   as a somewhat dubious technique, the feeling seemingly being that
   control and user data should be strictly segregated.

   It should be noted that _none_ of the piggybacking of control
   functionality in LISP is _architecturally fundamental_ to LISP.  All
   of the functions in LISP which are performed with piggybacking could
   be performed almost equally well with separate control packets.

   The "almost" is solely because it would cause more overhead (i.e.
   control packets); neither the response time, robustness, etc would
   necessarily be affected - although for some functions, to match the
   response time observed using piggybacking on user data would need as
   much control traffic as user data traffic.

   This technique is particularly important, however, because of the
   issue identified at the start of this section - the very large fanout
   of the typical LISP switch.  Unlike a typical router, which will have
   control interactions with only a few neighbours, a LISP switch could
   eventually have control interactions with hundreds, or perhaps even
   thousands (for a large site) of neighbours.

   Explicit control traffic, especially if good response times are
   desired, could amount to a great deal of overhead in such a case.

3.  Namespaces

   One of the key elements in any architecture, or architectural
   analysis, are the namespaces involved: what are their semantics and
   syntax, what are the kinds of things they name, etc.

   LISP has two key namespace, EIDs and RLOCs, but it must be emphasized
   that on an architectural level, neither the syntax, or, to a lesser
   degree, the semantics, of either are absolutely fixed.  There are
   certain core semantics which are unchanging (such as the notion that
   EIDs provide only identity, whereas RLOCs provide location), but as
   we will see, there is a certain amount of flexibility available for
   the long-term.

   In particular, all of LISP's key interfaces always include an Address
   Family Identifier (AFI) [AFI], so that new forms can be introduced at
   any time the need is felt.  Of course, in practise such an
   introduction would not be a trivial exercise - but neither is is
   impossibly painful, as is the case with IPv4's 32-bit addresses,
   which are effectively impossible to upgrade.

3.1.  LISP EIDs

   A 'classic' EID is defined as a subset of the possible namespaces for
   endpoints.  [Chiappa] Like most 'proper' endpoint names, as proposed
   there, they contain contain no information about the location of the
   endpoint.  EIDs are the subset of possible endpoint names which are:
   fixed length, 'reasonably' short', binary (i.e. not intended for
   direct human use), globally unique (in theory), and allocated in a
   top-down fashion (to achieve the former) .

   LISP EIDs are, in line with the general LISP deployment philosophy, a
   reuse of something already existing - i.e.  IPvN addresses.  For
   those used as in LISP as EIDs, LISP removes much (or, in some cases,
   all) of the location-naming function of IPvN addresses.

   In addition, the goal is to have EIDs name hosts (or, more properly,
   their end-end communication stacks), whereas the other LISP namespace
   group (RLOCs) names interfaces.  The idea is not just to have two
   namespaces (with different semantics), but also to use them to name
   _different classes of things_ - classes which currently do not have
   clearly differentiated names.  This should produce even more

3.1.1.  Residual Location Functionality in EIDs

   LISP retains, especially in the early stages of the deployment, in
   many cases some residual location-naming functionality in EIDs, This
   is to allow the packet to be correctly routed/forwarded to the
   destination node, once it has been unwrapped by the ETR - and this is
   a direct result of LISP's deployment philosophy (see [Introduction],
   Section "Deployment").

   Clearly, if there are one or more unmodified routers between the ETR
   and the desination node, those routers will have to perform a routing
   step on the packet, for which it will need _some_ information as to
   the location of the destination.

   One can thus view such LISP EIDs, which retain 'stub' location
   information, as 'addresses' (in the definition of the generic sense
   of this term, as used here), but with the location information
   restricted to a limited, local scope.

   This retention of some location functionality in LISP EIDs, in some
   cases, has led some people to argue that use of the name 'EID' is
   improper.  In response, it was suggested that LISP use the term
   'LEID', to distinguish LISP's 'bastardized' EIDs from 'true' EIDs,
   but this usage has never caught on.

   It has also been suggested that one usage mode for LISP EIDs, in
   existing software loads, is to assign them as the address on an
   internal virtual interface; all the real interfaces would have RLOCs
   only.  [Templin] This would make such LISP EIDs functionally
   equivalent to 'real' EIDs - they are names which are purely identity,
   have no location information of any kind in them, and cannot be used
   to make any routing decisions anywhere outside the host.

   It is true that even in such cases, the EID is still not a 'pure'
   EID, as it names an interface, not the end-end stack directly.
   However, to do a perfect job here (or on separation of location and
   identity) is impossible without modifying existing hosts (which are,
   inevitably, almost always one end of an end-end communication) - and
   that has been ruled out, for reasons of viable deployment.

   The need for interoperation with existing unmodified hosts limits the
   semantic changes one can impose, much as one might like to provide a
   cleaner separation.  (Future evolution can bring us toward that
   state, however: see Section XXX.)

3.2.  RLOCs

   RLOCs are basically pure 'locators' [RFC1992], although their syntax
   and semantics is restricted at the moment, because in practise the
   only forms of RLOCs supported are IPv4 and IPv6.

3.3.  Overlapping Uses of Existing Namespaces

3.4.  LCAFs

   --- Key-ID
   --- Instance-IDs

4.  Fault Discovery/Handling

   Any global communication system must be robust, and to be robust, it
   must be able to discover and handle problems.  LISP's general
   philosophy of robustness is usually to have overlapping, simple
   mechanisms to discover and repair problems.

5.  Scalability

   As with robustness, any global communication system must be scalable,
   and scalable up to almost any size.  As previously mentioned, the
   large fanouts to be seen with LISP, due to its 'overlay' nature,
   present a special challenge.

   One likely saving grace is that as the Internet grows, most sites
   will likely only interact with a limited subset of the Internet; if
   nothing else, the separation of the world into language blocks means
   that content in, e.g.  Chinese, will not be of interest to most of
   the rest of the world.  This tendency will help with a lot of things
   which could be problematic if constant, full, N^2 connectivity were
   likely on all nodes, for example the caching of mappings.

5.1.  Demand Loading of Mappings

   One question that many will have about LISP's design is 'why demand-
   load mappings - why not just load them all'?  It is certainly true
   that with the growth of memory sizes, the size of the complete
   database is such that one could reasonably propose keeping the entire
   thing in each LISP device.  (In fact, one proposed mapping system for
   LISP, named NERD, did just that.  [NERD])

   A 'pull'-based system was chosen over 'push' for several reasons; the
   main one being that the issue is not just the pure _size_ of the
   mapping database, but its _dynamicity_.  Depending on how often
   mappings change, the update rate of a complete database could be
   relatively large.

   It is especially important to realize that, depending on what
   (probably unforseeable) uses eventually evolve for the
   identity->location mapping capability, the update rate could be very
   high indeed.  E.g. if LISP is used for mobility, that will greatly
   increase the update rate.  Such a powerful and flexible tool is
   likely be used in unforseen ways (Section 2.3), so it's unwise to
   make a choice that would preclude any which raise the update rate

   Push as a mechanism is also fundamentally less desirable than pull,
   since the control plane overhead consumed to load and maintain
   information about unused destinations is entirely wasted.  The only
   potential downside is the delay required for the demand-loading of

   (It's also probably worth noting that many issues that some people
   have with the mapping approach of LISP, such as the mapping database
   size, etc are the same - if not worse - for push as they are for

   Also, for IPv4, as the address space becomes more highly used, it
   will become more fragmented - i.e. there will tend to be more,
   smaller, entries.  For a routing table, which every router has to
   hold, this is problematic.  For a demand-loaded mapping table, it is
   not bad.  Indeed, this was the original motivation for LISP -
   although many other useful and desirable uses for it have since been
   enumerated (see [Introduction], Section "Applications").

   For all of these reasons, as long as there is locality of reference
   (i.e. most ITRs will use only a subset of the entire set), it makes
   much more sense to use the a pull model, than the classic push one
   heretofore seen widely at the internetwork layer (and thus somewhat
   novel to people who work at that layer).

   It may well be that some sites (e.g. large content providers) may
   need non-standard mechanisms - perhaps something more of a 'push'
   model.  This remains to be determined, but it is certainly feasible.

5.2.  Caching of Mappings

   It should be noted that the caching spoken of here is likely not
   classic caching, where there is a fixed/limited size cache, and
   entries have to be discarded to make room for newly needed entries.
   The economics of memory being what they are, there is no reason to
   discard mappings once they have been loaded (although of course
   implementations are free to chose to do so, if they wish to).

   This leads to another point about the caching of mappings: the
   algorithms for management of the cache are purely a local issue.  The
   algorithm in any particular ITR can be changed at will, with no need
   for any coordination.  A change might be for purposes of
   experimentation, or for upgrade, or even because of environmental
   variations - different environments might call for different cache
   management strategies.

   The replacability of the cache management is the architectural aspect
   of the design; the exact algorithm, which is engineering, is not.

5.3.  Amount of State

   -- Mapping cache size
   --- Mention studies
   -- Delegation cache size (in MRs)
   --- Mention studies
   -- Any others?

5.4.  Scalability of The Indexing Subsystem

   LISP initially used an indexing subsystem called ALT.  [ALT] ALT was
   relatively easy to construct from existing tools (GRE, BGP, etc), but
   it had a number of issues that made it unsuitable for large-scale
   use.  ALT is now being superseded by DDT.  [DDT]

   The basic structure and operation of DDT is identical to that of
   TREE, so the extensive simulation work done for TREE applies equally
   to DDT, as do the conclusions drawn about TREE's superiority to ALT.

   From an architectural point of view, the main advantage of DDT is
   that it enables client side caching of information about intermediate
   nodes in the resolution hierarchy, and also enables direct
   communication with them.  As a result, DDT has much better scaling
   properties than ALT.

   The most important result of this change is that it avoids a
   concentration of resolution request traffic at the root of the
   indexing tree, a problem which by itself made ALT unsuitable for a
   global-scale system.  The problem of root concentration (and thus
   overload) is almost unavoidable in ALT (even if masses of 'bypass'
   links are created).

   ALT's scalability also depends on enforcing an intelligent
   organization that aincreases aggregation.  Unfortunately, the current
   backbone routing BGP system shows that there is a risk of an organic
   growth of ALT, one which does not achieve aggregation.  DDT does not
   display this weakness, since its organization is inherently
   hierarchical (and thus inherently aggregable).

   The hierarchical organization of DDT also reduces the possibility for
   a configuration error which interferes with the operation of the
   network (unlike the situation with the current BGP DFZ).  DDT
   security mechanisms can also help produce a high degree of
   robustness, both against misconfiguration, and deliberate attack.
   The direct communication with intermediate nodes in DDT also helps to
   quickly locate problems when they occur, resulting in better
   operational characteristics.

   Next, since in ALT mapping requests must be transmitted through an
   overlay network, a significant share of requests can see
   substantially increased latencies.  Simulation results in the TREE
   work clearly showed, and quantified, this effect.

   The simulations also showed that the nodes composing the ALT and DDT
   networks for a mapping database of full Internet size could have
   thousands of neighbours.  This is not an issue for DDT, but would
   almost certainly have been problematic for ALT nodes, since handling
   that number of simultaneous BGP sessions would likely to be

6.  Security

   Security in LISP faces many of the same challenges as security for
   other parts of the Internet: good security usually means work for the
   users, but without good security, things are vulnerable.

   The Internet has seen many very secure systems devised, only to see
   them fail to reach wide adoption; the reasons for that are complex,
   and vary, but being too much work to use is a common thread.  It is
   for this reason that LISP attempts to provide 'just enough' security
   (see [Introduction], Section "Design-Security").

   The _good_ thing about the Internet is that it brings the world to
   your doorstep - masses of information from all around the world are
   instantly available on your computing device.  The _bad_ thing about
   the Internet is that it brings the world to your doorstep - including
   legions of crackers, thieves, and general scum and villainy.  Thus,
   any node may be the target of fairly sophisticated attack - often
   automated (thereby reducing the effort required of the attacker to
   spread their attack as broadly as possible).

6.1.  Basic Philosophy

   To square this circle, of needing to have very good security, but of
   it being to difficult to use very good security, the general concept
   is for LISP to have a series of 'graded' security measures available,
   with the 'ultimate' security mechanisms being very high-grade indeed.

   The concept is to devise a plan in which LISP can simultaneously
   attempt to have not just 'ultimate' security, but also one or more
   'easier' modes, ones which will be easier to configure and use.  This
   'easier' mode can be both an interim system (with the full powered
   system available for when it it needed), as well as the system used
   in sections where security is less critical (following the general
   rule that the level of any security should generally be matched to
   what is being protected).

   The challenge is to do this in a way that does not make the design
   more complex, since it has to include both the 'full strength'
   mechanism(s), and the 'easier to configure' mechanism(s).  This is
   one of the fundamental tradeoffs to struggle with: it is easy to
   provide 'easier to configure' options, but that may make the overall
   design more complex.

   As far as making it hard to implement to begin with (also something
   of a concern initially, although obviously not for the long term): we
   can make it 'easy' to deploy initially by simply not implementing/
   configuring the heavy-duty security early on.  (Provided, of course,
   that the packet formats, etc, are all included in the design to begin

6.2.  Design Guidance

   In designed the security, there are a small number of key points that
   will guide the design:

   - Design lifetime
   - Threat level

   How long is the design intended to last?  If LISP is successful, a
   minimum of a 50-year lifetime is quite possible.  (For comparison,
   IPv4 is now 34 at the time of writing this, and will be around for at
   least several decades yet, if not longer; DNS is 28, and will
   probably last indefinitely.)

   How serious are the threats it needs to meet?  As mentioned above,
   the Internet can bring the baddest actors anywhere to any location,
   in a flash.  Their sophistication level is rising all the time: as
   the easier holes are plugged, they go after others.  This will
   inevitably eventually require the most powerful security mechanisms
   available to counteract their attacks.

   Which is not to say that LISP needs to be that secure _right away_.
   The threat will develop and grow over a long time period.  However,
   the basic design has to be capable of being _securable_ to the
   expanded degree that will eventually be necessary.  However,
   _eventually_ it will need to be as securable as, say, DNS - i.e. it
   _can_ be secured to the same level, although people may chose not to
   secure their LISP infrastructure as well as DNSSEC does.

   In particular, it should be noted that historically many systems have
   been broken into, not through a weakness in the algorithms, etc, but
   because of poor operational mechanics.  (The well-known 'Ultra'
   breakins of the Allies were mostly due to failures in operational
   procedure.)  So operational capabilities intended to reduce the
   chance of human operational failure are just as important as strong
   algorithms; making things operationally robust is a key part of
   'real' security.

6.2.1.  Security Mechanism Complexity

   Complexity is bad for several reasons, and should always be reduced
   to a minimum.  There are three kinds of complexity cost: protocol
   complexity, implementation complexity, and configuration complexity.
   We can further subdivide protocol complexity into packet format
   complexity, and algorithm complexity.  (There is some overlap of
   algorithm complexity, and implementation complexity.)

   We can, within some limits, trade off one kind of complexity for
   others: e.g. we can provide configuration _options_ which are simpler
   for the users to operate, at the cost of making the protocol and
   implementation complexity greater.  And we can make initial (less
   capable) implementations simpler if we make the protocols slightly
   more complex (so that early implementations don't have to implement
   all the features of the full-blown protocol).

   It's more of a question of some operational convenience/etc issues -
   e.g.  'How easy will it be to recover from a cryptosystem
   compromise'.  If we have two ways to recover from a security
   compromise, one which is mostly manual and a lot of work, and another
   which is more automated but makes the protocol more complicated, if
   compromises really are very rare, maybe the smart call _is_ to go
   with the manual thing - as long as we have looked carefully at both
   options, and understood in some detail the costs and benefits of

6.3.  Security Overview

   First, there are two different classes of attack to be considered:
   denial of service (DoS, i.e. the ability of an intruder to simply
   cause traffic not to successfully flow) versus exploitation (i.e. the
   ability to cause traffic to be 'highjacked', i.e. traffic to be sent
   to the wrong location).

   Second, one needs to look at all the places that may be attacked.
   Again, LISP is a relatively simple system, so there are not that many
   subsystems to examine.

   -- Lookups
   --- Nonces
   -- Indexing
   -- Mappings

6.4.  Securing Mappings

   Two approaches have been taking to securing the provision of
   mappings.  The first, which is of course not completely satisfactory,
   is to secure the channel between the ITR and the entities involved in
   providing mappings for it.  The second is to secure the mappings
   themselves, by signing them 'at birth' (much the same way in which
   DNS Security operates).  [RFC4033].

   Tie-in to space allocation security?

6.5.  Securing the xTRs

   --- Cache management
   --- Unsoliticed Map-Replies are _very bad_ - must go through
       mapping system to verify that the sender is authoritative for
       that range of EIDs

7.  Robustness

   -- Depends on deployment as well as design
   -- Replication
   -- Overlapping mechanisms (ref redundancy as key for robustness)

8.  Optimization

   -- Philosophy
   -- Piggybacking
   -- 'Wiretapping' return mappings
   --- Security is an issue on that

9.  Open Issues

   -- Provider lock-in for mapping database
   -- Automated ETR synch
   --- Liveness can be gathered now from some IGPs
   -- EID reachability within a LISP Site
   --- Existing problem with any border router

10.  Additional Material

   - An architectural document on LISP, starting with
       a brief motivation and problem definition, then
       a protocol overview, then more detailed discussion
       of funtional elements, tradeoffs, etc.

    - A more high level document covering what Loc/ID
      separation is, why it's important, its history,
      and then why LISP is a good solution.

    - A 'potential future evolution' document, covering
      what the impacts of LISP could/would be, and how it
      might evolve in the future.

   - Future work
   -- Better ETR sync for mappings
   -- Detect and deal with gonzo ETRs

   - Long-term Advantages
   -- Impossible to list all the long-term uses
   --- Lampson's (sic - actually Wheeler's) Law
   -- EID Address space utilization
   -- Allows use of class E space (240/4) for RLOCs
   -- Core routing overhead reduction
   --- PI space
   -- Easier introduction of new names-spaces

   - Routing Evolution {not sure we want this? - JNC}
   -- Some short term (TE, etc)
   -- Biggest long-term improvement comes inside LISP core,
       if we can get the network to that point
   --- Withdrawal of EID routes in the LISP core
   -- Support of non-LISP core is tricky (requires
       route reconstitution)

   - Long-term Evolution {Not sure we want this? Maybe it
       should be a whole  separate document. - JNC}
   -- Evolution
   --- Have a long term plan, but keep what's actually
       done simple to begin with
   --- Leave 'hooks' for long-term evolution
   --- The Internet painted itself into a corner,
       evolution-wise - LISP has opened a mouse-hole, but
       we need to make sure it doesn't just lead to another
       painted-in corner
   -- Better indexing system (may be obsolete, now that
       we have DDT?)
   -- 'Ringfence' of xTRs provides natural boundary between
       change domains
   -- New namespaces (the semantic issues involved with
       introducing new namespaces - initially RLOCs, but
       potentially EIDs as well - the latter are
       much harder as it changes host-host semantics)
   -- Separation of host/host and router/router
       interfaces / packet formats
   -- More?

11.  Acknowledgments

   The author would like thank the core LISP group for their willingness
   to allow him to add himself to their effort, and for their enthusiasm
   for whatever assistance he has been able to provide.  He would also
   like to thank (in alphabetical order) Vina Ermagan, Vince Fuller, and
   Joel Halpern for their careful review of, and helpful suggestions
   for, this document.  Grateful thanks also to Darrel Lewis for his
   help with material on non-Internet uses of LISP, and to Vince Fuller
   for help with XML.  A final thanks is due to John Wrocklawski for the
   author's organizational affiliation.

12.  IANA Considerations

   This document makes no request of the IANA.

13.  Security Considerations

14.  References

14.1.  Normative References

   [DDT]           V. Fuller, D. Lewis, and D. Farinacci, "LISP
                   Delegated Database Tree",
                   draft-fuller-lisp-ddt-01.txt (work in progress),
                   March 2012.

   [Introduction]  J.N. Chiappa, "An Introduction to the LISP Location-
                   Identity Separation System",
                   draft-chiappa-lisp-introduction-00.txt (work in
                   progress), July 2012.

   [AFI]           IANA, "Address Family Indicators (AFIs)", Address
                   Family Numbers, January 2011, <

14.2.  Informative References

   [RFC1992]       I. Castineyra, J. N. Chiappa, and M. Steenstrup, "The
                   Nimrod Routing Architecture", RFC 1992, August  1996.

   [RFC4033]       R. Arends, R. Austein, M. Larson, D. Massey, and
                   S. Rose, "DNS Security: Introduction and
                   Requirements", RFC 4033, March 2005.

   [RFC4423]       R. Moskowitz and P. Nikander, "Host Identity Protocol
                   (HIP) Architecture", RFC 4423, May 2006.

   [ALT]           D. Farinacci, V. Fuller, D. Meyer, and D. Lewis,
                   "LISP Alternative Topology (LISP-ALT)",
                   draft-ietf-lisp-alt-10.txt (work in progress),
                   December 2011.

   [NERD]          E. Lear, "NERD: A Not-so-novel EID to RLOC Database",
                   draft-lear-lisp-nerd-09.txt (work in progress),
                   April 2012.

   [ILNP]          R.J. Atkinson and S.N. Bhatti, "ILNP Architectural
                   Description", draft-irtf-rrg-ilnp-arch-05.txt (work
                   in progress), May 2012.

   [Chiappa]       J. N. Chiappa, "Endpoints and Endpoint Names: A
                   Proposed Enhancement to the Internet Architecture",
                   Personal draft (work in progress), 1999,

   [Jakab]         L. Jakab, A. Cabellos-Aparicio, F. Coras, D. Saucez,
                   and O. Bonaventure, "LISP-TREE: A DNS Hierarchy to
                   Support the LISP Mapping System", in 'IEEE Journal on
                   Selected Areas in Communications', Vol. 28, No. 8,
                   pp. 1332-1343, October 2010.

   [McQuillan]     J. M. McQuillan, W. R. Crowther, B. P. Cosell,
                   D. C. Walden, and F. E. Heart, "Improvements in the
                   Design and Performance of the ARPA Network",
                   Proceedings AFIPS 1972 FJCC, Vol. 40, pp. 741-754.

   [Templin]       F. Templin, "LISP WG", LISP WG list
                   message, Message-ID: 39C363776A4E8C4A94691D2BD9D1C9A1
         , 13
                   March 2009,, <

   [Wasserman]     M. Wasserman, "IPv6 networking: Bad news for small
                   biz", IETF list message, Message-Id:
                   5 April 2012, <

Appendix A.  RefComment

Appendix B.  Glossary/Definition of Terms

   -  Address
   -  Locator
   -  EID
   -  RLOC
   -  ITR
   -  ETR
   -  xTR
   -  PITR
   -  PETR
   -  MR
   -  MS
   -  DFZ

Appendix C.  Other Appendices

   -- Location/Identity Separation Brief History
   -- LISP History
   -- Old models (LISP 1, LISP 1.5, etc)
   -- Different mapping distribution models (e.g. LISP-NERD)
   -- Different mapping indexing models (LISP-ALT
       forwarding/overlay model),
       LISP-TREE DNS-based, LISP-CONS)

Author's Address

   J. Noel Chiappa
   Yorktown Museum of Asian Art
   Yorktown, Virginia