Unofficial guide to the LISP
map-encap solution for the routing scalability problemTo the main
Robin Whittle firstname.lastname@example.org 2009-07-31
and link to the official LISP site
This page is my attempt at maintaining an
up-to-date list of LISP
Internet drafts (IDs) and other documents, created when the LISP
people did not yet
have such a page.
From late July 2008, they have a page:
www.lisp4.net <<<< Please refer to this page
for authoritative info from the LISP team.
site has tutorials, articles, presentations, diagrams, links to
Internet Drafts etc.
See also the LISP mailing list: http://www.ietf.org/mail-archive/web/lisp/current/maillist.html
In March 2009, there are plans for an IETF Experimental Working
Group for LISP.
My page still contains a bunch of hopefully
useful things about LISP, so I will keep it going - not least the
section on some of the critiques of LISP.
Please let me know of
any errors or
suggestions for improvements, and don't confuse what you read below
with what the LISP developers themselves write or how they depict their
I need to update this page!
>>> Introduction>>> Main LISP web pages and documents>>> Internet Drafts>>> Significant RRG messages>>>
A diagram from Dino
Farinacci. Please see related explanation in the RRG list
LISP (Locator Identity Separation Protocol)
is the most prominent of
the "map-encap" schemes being considered by the IRTF Routing
"Map-encap" or means "map and encapsulate".
The ITR (Ingress
Tunnel Router) receives a traffic packet to a "mapped address" and
looks up some mapping information for that destination address.
then encapsulates the packet in an outer header and so tunnels the
packet to an ETR (Egress Tunnel Router) specified in that mapping
information, where it is decapsulated and sent to the proper
destination. See my introduction to this field for Newbies: psg.com/lists/rrg/2008/msg00623.html
.I am critical of LISP and
believe that my own proposal, Ivip, or APT would be better than
Despite all this activity, including major
contributions from engineers at Cisco
- who build most of the Internet's routers and have a reputation for
extraordinarily reliable equipment and great support - I find LISP a
generally unadventurous and technically problematic set of proposals.
are various LISP Internet Drafts (IDs), by various authors and some of
them are different
solutions to a single problem. For instance, one would not
implement more than one of the mapping distribution solutions: CONS,
ALT, NERD or Modified Distributed Hash Tables. So it can be
reading these documents trying to imagine a complete system. Be
to check the RRG list psg.com/lists/rrg/
and before 2007-09-12 the RAM list www.ietf.org/mail-archive/web/ram/
for discussions on these proposals.
If you find LISP IDs hard to
understand, you are not alone, as one RRG member wrote on
. Internet Drafts are technically dense, and my original
monolithic Ivip ID has been too much for some folks.
The RRG home page www.irtf.org/charter?gtype=rg&group=rrg
lists the charter of the group. The charter and a December 2007
announcement by the co-chairs: psg.com/lists/rrg/2007/msg00686.html
is the best information I know of regarding the RRG process. My
summary of this is that the RRG is developing various proposals to deal
with the routing scalability problem, with a view to achieving rough
consensus in March 2009 on what to recommend to the IESG for
development in one or perhaps more IETF WGs.
All the proposals
are listed at the RRG wiki page: www3.tools.ietf.org/group/irtf/trac/wiki/RoutingResearchGroup
. You may well find more up-to-date LISP information there than what I
have below. In the event that a central, comprehensive, LISP
appears, I will point to it from here and delete most of the links, but
will probably retain links to major critiques of LISP.
Main LISP web pages
LISP Internet Drafts
have not been able to keep this up to date . . .
is a list of LISP IDs, in approximate date order of first publication
with my quick notes. I link to the generic name, not the latest
* Those with an asterisk were not
mentioned in the list of IDs in the above-mentioned BOF proposal of
2009-03-14, and so should probably not be considered as part of the
overall LISP project from that date.
See also the link above to
draft-brim-lisp-analysis, which evaluates LISP with respect to the RRG
To find the LISP IDs in the IETF system (some
mentioned below were not in the system yet): https://datatracker.ietf.org/idtracker/?search_filename=lisp
Basic architectural ID. Be
sure to read this before any of the others. Assumed reading for
anyone who is involved in the RRG.draft-lear-lisp-nerd
Eliot Lear's proposal for a full-push mapping system distribution for
All ITRs get (or rather retrieve for themselves) the full mapping
database. This is likely to be pretty slow (my guess is latencies
such as 30 minutes or more). Please see my analysis of mapping
approaches for a quick summary and list of benefits and critiques of
NERD, and of other approaches: psg.com/lists/rrg/2008/msg00707.html
The good thing is all ITRs can forward packets without delay. The
bad news is that it is probably overkill and prohibitively expensive to
push the full mapping database to every ITR on the planet.
While this ID is not in the list of other LISP IDs in the
above-mentioned BOF proposal, it remains an important ID, since it is
the only one of the map-encap proposals which involves "full push" of
the whole mapping database to every ITR.
A fancy full-pull mapping distribution
system involving a novel global query server system. Superseded by ALT around late
approach to dealing with the problem of the delay of initial packet(s)
in a new communication session while the ITR waits for its mapping
request to be replied to. This is a problem with LISP-CONS,
LISP-ALT and any other pure pull system, such as TRRP - but TRRP has
"Waypoint Routers" as a potential solution. There is a multicast arrangement over the ALT network
for sending the traffic packets out from the ITR, so they arrive by
some means at the correct ETR. I critiqued this (to do: link to
the RRG message) and the proposal hasn't been mentioned much since.draft-fuller-lisp-alt
alternative network is created both for sending mapping queries from
ITRs to the authoritative query servers (typically ETRs) and for
transporting packets from the ITRs to those ETRs before the ITR has the
mapping information. In practice, the two tasks are achieved at
once - the traffic packet is the request. The mapping reply could
come back via the ALT network, but it is faster to send it back via the
ordinary Internet. The IPv4 ALT network is comprised of router
functions (typically implemented in actual routers) operating with the
IPv4 address space, but completely separately from the IPv4 Internet.
The ALT routers are linked by tunnels, forming a global virtual
network, whose structure is determined by strong address aggregation,
rather than geographic proximity.
ALT is a pure pull system - a global query server system, which
also delivers packets to ETRs before the ITR has the mapping
information for that packet's EID prefix.
Please see the diagram
above regarding LISP+ALT and the explanation of it at: psg.com/lists/rrg/2008/msg01667.html
How to make LISP incrementally deployable
supporting packets sent from hosts in networks which do not have
ITRs. There are two approaches - LISP-NAT and Proxy Tunnel Routers (PTRs)
PTRs are the same mechanism, purpose and results as Ivip's
OITRDs (Open ITRs in the DFZ, previously known as "anycast ITRs in the
For comparison, see the Ivip material in the parent directory,
based on the idea first publicly documented in the RAM list on
and APT's approach to the same problem: www.ops.ietf.org/lists/rrg/2008/msg00468.html
(2008-02-21) and more fully: www.cs.ucla.edu/~meisel/draft-apt-incremental-00.txt
I think PTRs are essential to LISP's ability to be incrementally
deployed, and that LISP-NAT has to many problems and limitations to be
used. See my critique below.
Description of an
implementation of LISP on FreeBSD,
separate from the one being developed by Dino and the other LISP people
at Cisco Systems.draft-mathy-lisp-dht
(2008-02-25, but not yet in the IETF system - still not there in July
This can be found at: inl.info.ucl.ac.be/publications/lisp-dht-towards-dht-map-identifiers-locators
which points to: inl.info.ucl.ac.be/system/files/draft-mathy-lisp-dht-00.txt
. I wrote to the RRG list requesting further information,
including examples, exactly how a mapping request and response would be
handled etc. In an off-list reply, I was told the authors were
working on an updated version which would answer these questions.
Hash Tables are a way of building a distributed system of servers to
store information and to respond to queries about this information.
This proposal is an alternative to NERD and ALT (and before that
to CONS) - a full pull
distribution system for LISP (global query server system), based on
some modifications of the traditional DHT.
Proposal for a /16 of IPv6
space to be reserved for LISP-ALT.
Abstract: "This draft describes how
inter-domain multicast routing will function in an environment where
Locator/ID Separation is deployed using the LISP architecture."
Some critiques of LISP
are many critiques of LISP, by me and other folks. Here is list
of my main critiques since November 2007 - and one from Christian
Vogt. These URLs are for the RRG list. They do not list all
the discussions, but some of them are for responses from the LISP team.
Please read the full discussion to get a better picture of the
debate than you will get just from these linked-to messages.
are far more critiques of LISP than of other proposals (APT, Ivip and
TRRP). This is probably largely attributable to LISP being the
first such map-encap proposal, to so many people writing IDs for it and
to the fact that LISP's major developers work for the world's biggest
The fact that there has been essentially no
detailed critique of Ivip does not necessarily mean that Ivip has less
weaknesses (though I think it has far fewer problems than LISP).
I think that the absence of such critical attention for APT, Ivip
and TRRP is largely to do with people not reading up on these proposals
as much as they have the LISP IDs. Mailing list discussions tend
to thrive on negative sentiment, so if you have something positive to
say about any of these proposals, it would be good to write to the list
about it. The absence of such messages could give the developers
the impression that no-one is reading their proposals.LISP-ALT & NERD inefficient - and some
sprawling discussion starting on 2008-01-22: 2008/msg00176.html
I write that ALT and NERD wouldn't be deployed together, prompted
by Dino Farinacci's suggestion that two approaches could be
. I then take a stock standard NERD deployment and soup it up
with query servers, caching ITRs etc. The result starts to
delaying initial packets matters
structure of the ALT network is highly aggregated, which precludes the
structure of linkages and of which router aggregates which prefix being
optimized according to geography. Consequently, as a packet
ascends the hierarchy of routers, until it gets to a level which covers
its destination and then starts its descent towards that destination,
it will be traveling over many links between these routers. Since
each router could be almost anywhere, it is reasonable to expect that
the paths will tend to be very long.
Consequently, in many
cases, packets traversing the ALT
network will tend to take circuitous paths
These are initial traffic packets which function as a map request
and are sent
by the ITR on the ALT network to get them to the right ETR ASAP, while
the ITR awaits mapping information. The response is best sent
back directly over the Net from the authoritative ETR to the ITR.
initial critique ALT's strong
aggregation often leads to *very* long paths 2008/msg00229.html
(2008-01-29). There were dozens of responses, generally not from the
LISP team, many of whom were busy with a new product release at the
time. K. Sriram illustrated the problem with a diagram: www.antd.nist.gov/~ksriram/strong_aggregation.png
and discussed it in messages including: 2008/msg00235.html
A defense of this critique from Scott Brim appeared in the
thread "Why delaying initial packets matters" (2008-03-04) 2008/msg00584.html
. (To do: response to this.)
if ALT was in some way optimised, with more meshiness to generally give
shorter paths, I still think it is a bad idea. I think any global
query server system for mapping is a bad idea, due to inherent delays
and chances of query and response packets being lost.
earlier critique of ALT and EMACS (multicasting initial traffic packets
so they get to the ETR before the ITR has mapping) is this message 2007/msg00540.html
(2007-11-16), which Scott Brim responded to in separate threads on
and EMACS 2007/msg00546.html
long path debate continued in June 2008:
LISP-ALT's Aggregation implies provider
dependence LISP gleaning looks insecure and therefore
A long discussion ensued from this
. (To do: add links to some defenses.)
fragmentation problemsdraft-lewis-lisp-interworkingDebate about whether
LISP's RLOC and EID roles for addresses involve separate namespacesCritique of Mobile
LISP draft-meyer-lisp-mn-00 and a suggestion to use the TTR approach