Subject: Re: I-D ACTION:draft-ietf-manet-lanmar-00.txt

From: Richard <[email-masked]>
Date: Sun, 03 Dec 2000 13:40:26 -0800

I have a question about the new draft on Landmark Routing (LANMAR).
Regarding the computation of a shortest path between a landmark and
a drifter, Section 5.4.2 states:

  "If an entry of incoming DFDV indicates that the current
  node is its next hop to the landmark, i.e., the current node is on 
  the drifter's shortest path to the landmark, the current node will 
  insert or update its drifter list."

Section 4.3 explains this further, where l is the drifter and L
is the landmark:

  "When i transmits its distance vector to neighbor, say j, 
  then j will retain the entry to member l only if d(j,l) 
  is smaller than the scope or d(j,L) is smaller than d(i,L). 
  The latter condition occurs if j is on the shortest path from i 
  (and therefore from l) to L."

Actually, the latter condition occurs if j is on *any* shortest
path from i to L, and there could be several such shortest paths.

Does LANMAR somehow ensure that only nodes along a *single*
shortest path between the landmark and drifter need to 
maintain the distance information to the drifter?

If not, then the overhead analysis for drifters in 
Section 7 would be affected significantly.

An alternative way to treat drifters (which was probably already
considered) that avoids this problem is for the drifter
to inform its "home" landmark of its new "foreign" landmark,
as in mobile IP.  Triangle routing can then be avoided
(as in mobile IPv6) by informing any correspondent node
of this binding.

Richard

-----------------------
Richard Ogier
Sr. Research Engineer
SRI International
333 Ravenswood Ave.
Menlo Park, CA 94025
Tel: 650-859-4216
Fax: 650-859-4812
Email: [email-masked]
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