Re: [lisp] AD Evaluation: draft-ietf-lisp-introduction

Albert Cabellos <> Fri, 16 January 2015 16:14 UTC

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From: Albert Cabellos <>
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Date: Fri, 16 Jan 2015 17:14:07 +0100
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To: Dino Farinacci <>, Brian Haberman <>
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Subject: Re: [lisp] AD Evaluation: draft-ietf-lisp-introduction
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Thank you very much for the review, please see inline my replies:

> On Jan 14, 2015, at 7:10 PM, Dino Farinacci <> wrote:
> Here are some brief responses to your comments Brian. Thanks for doing the throuogh review.
>> On Jan 14, 2015, at 8:26 AM, Brian Haberman <> wrote:
>> All,
>>    I have completed by AD Evaluation of draft-ietf-lisp-introduction
>> as a part of the IETF publication process.  I have some
>> comments/questions that should be resolved prior to starting an IETF
>> Last Call.  Please let me know if you have any questions on these...
>> 1. Section 1
>> * I am going to try and short-circuit the inevitable question that will
>> arise about the reference [Chiappa].  Since it is a web page, the RFC
>> Editor will be concerned by its long-term stability.  Is that the best
>> reference for that text?  Anything similar that has been published in a
>> conference/journal/RFC/etc.?
> I will yield to the authors.

Unfortunately I´ve been unable to find a more “stable” publication. However the exact same document is cited in RFC4423 with the following “disclaimer”:

"(…) the unpublished Internet Draft "Endpoints and Endpoint Names" [10] by Noel Chiappa (…)”

Please let me know if adding a similar sentence is enough.

>> * The text uses the terms underlay and overlay without any context (in
>> the summary bullets).  This is easily fixed by augmenting the text in
>> the 2nd paragraph to identify which networks form the underlay and the
>> overlay.
> Those terms aren't used very much in RFC 6830 because those terms seem to become fashionable with the advent of nv03. If the authors want to continue to use those terms, I have no problem with that, but would suggest that the Definition of Terms section say that the underlay is what is referred to in RFC 6830 as "the underlying core routing system". And that an "overlay" is the encapsulation relationship between ITRs, ETRs, PxTRs, and RTRs.

I think that the second paragraph already introduces many new and important concepts, what about updating the first two bullet points?

   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 unless they are leaked into the underlay network. **The overlay is the encapsulation relationship between LISP-capable routers.**

>> 2. Section 3 (and a few times in 3.5) : s/inetrworking/internetworking/

Thanks for catching this typo.

>> 3. Section 3.2
>> * Is it correct to say that EIDs are only routable at the edge?  This
>> seems to contradict the text in section 3.5 that says EIDs may be
>> injected in the global routing system.
> Well it depends on your reference point. If the overlay is the center of perspective, then the global routing system is a non-LISP site relative to the overlay. The whole point is that EIDs are routable where LISP is not available. And that is true inside of a LISP site where packets are at a point in the data-path pre-encapsulation or post-decapsulation.

What about changing the last sentence to:

Because of this, EIDs are usually routable at the edge (within LISP sites) or in the non-LISP Internet.

>> * I find the PI and PA analogies misleading.  EIDs are global, but they
>> may change their point of attachment.  If that occurs, you are not
>> guaranteed that your EID space does not change.
> It is desirable that your EIDs do not change. But the scope of EID mobility may be limited and if a legacy site wants to continue to use DHCP and address addresses out of, say an enterprise address pool, it should be able to do that while losing session survivability features. That is a decision for the organization that is supporting mobility into its own domain.

I suggest removing both analogies (PI and PA), two sentences overall.

>> * In the example, bullet four mistakenly says that the destination
>> address of the outer header is set to RLOC_B2 (it should be RLOC_b1).


>> 4. Section 3.3.1 introduces the term RTR (Reencapsulating Tunnel
>> Routers) with no real description of how it functions or relates to ITRs
>> and ETRs.
> Well there are references to it in RFC 6830 and there are many use-cases for them which we are not allowed to reference since the drafts are not working group documents.

What about extending the last sentence of the paragraph?

Typically such functions are implemented by Reencapsulating Tunnel Routers (RTRs), **An RTR can be thought as a router that first acts as an ETR by decapsulating packets and then as an ITR by encapsulating them towards another locator.**

>> 5. Section 3.4.3 makes reference to the LISP WG.  Given that this
>> document will probably outlive the WG, I would suggest re-wording to
>> remove a direct reference to the WG.

Updated sentence:

Many of the existing mechanisms to create distributed systems have been explored and considered for the Mapping System architecture:

>> 6. Section 3.4 has no discussion of EIDs and NATs.  Given the global
>> nature of the mapping system, it would seem that NATs don't play well
>> with LISP.  There should be some discussion of that.
> LISP plays very well with NATs and we have many use-cases which are alive and being used. But again the draft on  NAT-traversal is not a working group document so it is hard to reference it. EIDs are translatable by NATs and so are RLOCs. It all depends where the xTR resides (on the public versus private side of the NAT).

I will add a paragraph summarizing section 7 of RFC6832 at the end of section 3.5.

>> 7. Section 4.1
>> * s/requires of a /requires a/


>> * The discussion of SMR should contain a reference to 6830 or a brief
>> discussion of how the SMR is used.

Could you please elaborate further this comment?

      "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."

>> 8. Section 5
>> * I would suggest having a reference to both the MIP and the NEMO specs
>> when discussing mobility.  LISP has the potential to operate in a manner
>> conducive with NEMO if the xTR acts as the NEMO Mobile Router.
> Well if we do that then there are a ton of other cases where a xTR can be co-located with other functions (i.e. a simple reference is say a wifi AP). So singlingly out MIP/NEMO seems to be favoring these technologies versus others. Why would we want to do that?
> Plus, it raises questions more than simplifies the understanding of LISP. This is an intro document.

What about adding the following sentence at the end of section 5?

The decoupled identity and location provided by LISP allows it to operate with other layer 2 and layer 3 mobility solutions.

>> * Should there be some discussion of the mapping system's TTL mechanism
>> impact on mobility support?
> The TTL is not used for mobility to work. It is the SMR and Map-Notify mechanisms between xTRs and the mapping system and xTRs, respectively.

True, but mappings from LISP mobile nodes are expected to have a low TTL (1 min), what about updating the last paragraph to:

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.
>> 9. Section 9 talks about propagating multicast state as (S-EID, G).
>> Does that mean that multicast in LISP is really only allowed to be SSM?
> We are encouraging SSM but an (RP-EID, G) can be used as well. RFC 6831 describes all PIM modes.

What about rephrasing the last sentence of the Multicast section:

LISP [RFC6831] supports all PIM modes, additionally LISP can also support non-PIM mechanisms to maintain multicast state.

>> 10. I am surprised that there are 2 Security Consideration sections (7 &
>> 9).  I am even more surprised that one says "Nothing new here" and the
>> other actually discusses potential issues with the LISP approach.

My fault, Section 7 should be “LISP Security Considerations”

Section 9 describes the security considerations for the document itself.