[lisp] Roman Danyliw's Discuss on draft-ietf-lisp-6834bis-12: (with DISCUSS and COMMENT)

[Roman Danyliw via Datatracker <[e-mail]>]

Roman Danyliw has entered the following ballot position for
draft-ietf-lisp-6834bis-12: Discuss

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DISCUSS:
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On the -11 document, I initial wrote the following: The SECDIR review by Donald
Eastlake asked about handling roll-over/wrap-around of the Map Version Number. 
Specifically, can a “Map Version Number advance[e] … so quickly that an old
version number is encountered that appears to be newer than or equal to the
current version number. Why can't this happen? Or if it can, why doesn't that
hurt?”  It would appear that a number of the conclusions of the ITR or ETR on
arriving packets in Section 7.1 and 7.2 wouldn’t be correct.

I then saw the -12 document published on June 1 which added the following text
to Section 7:
   Map Version Number incrementing
   and mappings' TTL MUST be managed so that an old version number will
   not be confused as a new version number.

Thank you for adding this text.  Practically, this identifies the desired
intent, but doesn’t seem describe the mechanics.  Can more be said about how
this confusion will be mitigated at the ITR/ETRs?  I also don't follow how to
use the TTLs here.

Consider the situation that Donald noted where the Map Version advanced so
quickly that it wraps around so that:

(a) the new Map Version Number value equals the old Map Version Number.  If one
followed the guidance in Section 7.1 of:
   1.  The packet arrives with the same Dest Map-Version number stored
       in the EID-to-RLOC Database.  This is the regular case.  The ITR
       sending the packet has in its EID-to-RLOC Map-Cache an up-to-date
       mapping.  No further actions are needed.

It would seem that the ITR wouldn’t do a Map-Request and would misroute the
packet based on the old mapping.

(b) the new Map Version Number is now smaller (but in fact fresher/newer)  If
one followed the guidance of Section 7.1. of:

3.  The packets arrive with a Dest Map-Version number smaller (i.e.,
       older) than the one stored in the EID-to-RLOC Database.  This
       means that the ITR sending the packet has an old mapping in its
       EID-to-RLOC Map-Cache containing stale information.

Per bullet #3, if there was wrap-around would the ITR in fact be sending stale
mapping information?


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COMMENT:
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Thank you to Donald Eastlake for the SECDIR review.

I support Paul Wouter’s DISCUSS position.