[DNA] Comments on DNA Solution: Link Identifier based approach

[Syam Madanapalli <syam@samsung.com>]

Hi JinHyeock,

Here few comments and questions on your draft.


1. The draft does not talk about the scenario where there exists a mix of
    modified and unmodified routers.

2. Section 3.1.

        ........
         A router, when it boots or is configured to act as a router (Sec
         6.2.2 in RFC 2461 [1]), first sends an RS and waits for RAs to
         gather prefixes.

       ........

         Once that process is complete, the router will send RAs and
         respond to RSs, but not before that.

   These two statements are conflicting. Is the RS from routers is
   different from Hosts?

   According to one of your statements the routers do not respond to
   RSs unless the process of LinkID establishment is completed. So how
   Does initial RS/RA exchange happen between routers? Or am I missing
   some thing here.

3.  Section 3.2
        ........
         In case the new prefix smaller than the current linkid prefix is
        advertised in LPIO, the router doesn't change the linkid prefix.

   Are you saying if a router receives a new smaller prefix in LPIO, then
   the router will not change the linkid? In other words routers change 
linkid
   if and only of they receive a new smaller prefix in PIO.

   If this is true, then I think there will be some inconsistency in linkids
   being advertised by different routers on the link for some time and slows
   down the linked establishment process.

   Also, is there any reason for not to count LPIOs?


4. What if the life time of all the prefixes that are available falls
   below 3 hours? May be a rare case, but I am wondering if it is worth
   mentioning about this scenario.

5. The host receives RA with different linkid prefix than the host
   is having, the host need to check for the complete prefix list against
   the host linkidprefix list. This is similar to CPL except that the host 
is
   not trying to learn about complete prefix list and now the host does this
   comparison only when it sees a different linkid.

6. I am wondering what could be the disadvantage if we keep the
   Linkid prefix even if we see the new prefix that is smaller.
   I think it is better to keep the same linkid as far as possible.
   If the current Linkid prefix life time does not allow us to keep
   it as linkid prefix, then we can switch to next available smaller
   prefix.
   In this approach the new router that comes up, does not apply the
   algorithm to select a new linked, if it sees a linked (PIO/LPIO with
   'I' flag set). The new router simply takes the received linked as
   the linked for the link.

   I think this way we avoid lot of processing and we will have smaller
   linkidprefix list on the host side.

7. Section 3.4.3

        ........

        For example, assume a router R advertise the linkid prefix P1 and 
the
        second smallest prefix is P2.

       When the valid lifetime of P1 is 7 days, R wants to remove P1 from 
the link.
        If R immediately advertises an RA with 1) P1 with zero lifetime and
       2) P2 with I-bit set, hosts may treat this as a link change, because
        they would discard P1 entirely when seeing it with zero lifetime.

   In this example, is the prefix P2 is also being advertised when P1
   is the linkid prefix? If yes, then a host receives a P1 with zero life 
time,
   it can easily find out that it is still on the same link but the prefix 
P1
   is not valid any more.

   I can see one problem: If Host receives another RA from another router
   with P1 as the linkid, then host think that it has moved, as the host
   discarded the P1 completely because of the earlier RA.

8. And also I am wondering, why we cannot use the longest valid prefix time 
as
   the selector for the linkid prefix. I think this is better because, this 
way
   linkid will be valid for more time.


Thank you,
Syam