LISP Mapping Request Format

1
LISP Mapping Request Format

• And related topics
• Joel M. Halpern
• joel.halpern_at_ericsson.com

2
What is the mapping system

• Defined by draft-ietf-lisp-ms-04.txt
• Made up conceptually of Map Resolvers, Map
  Servers, and the ALT infrastructure
• ITRs send Map-Request messages
• ITRs receive Map-Reply messages
• Positive reply, with RLOCs to use
• Negative reply, if there is nothing
• Deal with both no such ID, and no available
  RLOCs

3
Two views of the functionality

• How we describe the system shapes how we think it
  should work
• In this case, one can view the system in two
  similar fashions
• I believe the difference between these two views
  is at the center of a debate
• Should Map request messages sent by ITRs have one
  IP header, or two?

4
Mapping System as Relay Agent

• One view of the Mapping system is that its job is
  to deliver a message
• The message is sent by an ITR
• The message is to be delivered to an ETR
  advertising responsibility for a given EID
• The message contains an Map-Request, but the
  mapping system does not care about that

5
Mapping system provides information

• Another view is that the mapping system is
  responsible for providing authoritative RLOCs in
  response to a mapping request
• The system uses expectation of the ETR generating
  the response and sending it directly to an ITR is
  an optimization
• A valid mapping system could keep the mappings
  itself.
• Note that negative responses currently come from
  the system.

6
Result differences as to functionality

• Can there be an encrypted mapping request?
• Does there need to be an IP header with the
  destination EID in the dest IP field?
• Is The ITR responsible for knowing the message
  arrangement for ALT forwarding
• Phrased differently, how much of a change to ALT
  Is transparent to the ITR
• Or, the ALT is routing, why would you change the
  routing header?
• Or, is the Map-Resolver / Map-Serve layer an
  insulation layer, or a convenience for
  connectivity.

7
To recap, the question

• As currently defined,
• an ITR sends a Map-Request by encapsulating an
  Map-Request Message in an IP header, using the
  destination EID as the IP destination.
• This is encapsualted in an additional IP header
  (the outer header) in order to deliver the
  message to the Map responder
• Alternatively, one could encapsulate the
  Map-Request message directly in the outer
  header.

8
Decomposition

• This is personal opinion about how to look at the
  system
• There are times when one wants to shortcut the
  mechanisms
• My take is that the best way to do that is to
  define the components conceptually.
• Then, if you need a different setup, you put
  several logical pieces in the same physical device

9
Combination examples

• An ITR which can send mapping requests directly
  to the ALT
• Is conceptually an ITR plus a Map Responder.
• It is a map responder which does not take
  requests from anyone else, and is not visible in
  any tables of MRs.
• No, there is no need to actually build the
  ITR-gtMR message, and then reprocess it. We are
  discussing architecture, not implementation

10
Why does this matter?

• Allowing conceptual combinations means that the
  needs for special configurations does not
  complicate the definition of the ITR or the ETR.
• Also, the encapsulation between the ITR and the
  MR (or the MS and the ETR) does not need to allow
  for corner cases or unusual deployments.
• It also allows us to use simple concepts,
  assembled simply, to describe what we are
  building.

11
Address Families

• EIDs or RLOCs can be built using IPv4 or IPv6
• Both approaches handle the simple cases well
• EIDs and RLOCs from the same address family
• Or, dual-stack ITR and EIDs from either or both
  address families
• Double Encapsulation does introduce constraints
• The inner header must have an RLOC from the same
  address family as the destination EID

12
Additional issues

• With either path, there are additional questions
  which need to be asked
• What authentication capabilities are needed
  relative to Map-Requests, and what should be
  authenticated?
• Is there value in hiding dimensions of mapping
  from the ALT?
• Is the mapping system part of the data probe
  mechanism, and if so, how?