Hi Pascal
See my comment below.
On 10/5/21 12:40 PM, Pascal Thubert (pthubert) wrote:
Hello Dario
Please see below;
Le 5 oct. 2021 à 20:15, Dario Tedeschi <[email protected]> a écrit :
Hi Pascal,
Thank you for new draft. However I do have some comments/questions.
What benefit does the ‘M’ bit provide over simply detecting a
multicast address in the Target Address field?
The IPv6 multicast address type is clearly defined in RFC 4291
(section 2.4)
<https://datatracker.ietf.org/doc/html/rfc4291#section-2.4>, and the
detection of such an address is trivial. Most (if not all) Stacks
have a simple function/macro to do that job and many existing
protocols already use this mechanism to distinguish between unicast
and multicast addresses. It seems to me that a special bit to
indicate multicast registration would be redundant and require
handling for 4 different cases, 2 of which would be errors:
* M = 1, Target = multicast addr
* M = 1, Target= unicast addr — ERROR
* M = 0, Target = multicast addr — ERROR
* M = 0, Target= unicast addr
True enough. Dario.
I’ve been pondering that too. On the one hand it seems cleaner to
announce the service that the 6LN expects. Otoh as you point out it
can be inferred from the address.
Another way of seeing this is that the error cases that you indicate
can be detected if we have the bit otherwise they can’t.
[DT] I take your point about detecting the errors, assuming an
implementation could do something useful with that knowledge, other than
just discarding the message.
Then there’s anycast which is missing from both RPL and ND , which
cannot be distinguished by the look of the address and thus requires a
bit.
[DT] As for the anycast address, I suppose the question to ask is what
would a router do differently knowing such information? I suspect we
would have to define some new behavior along with the new bit.
Then there’s possibly the need of an IPv4 AF. All in all I tended to
favor having the bit but that’s really not a strong position, happy to
be convinced otherwise.
[DT] I presume you are talking of "IPv4-Compatible" and "IPv4-Mapped"
IPv6 addresses. If my presumption is correct, aren't these still easily
identifiable through their unique prefixes (::/96 and ::ffff/96,
respectively)?
What do others think?
[DT] I have no strong opinion. The M bit just seemed redundant.
I also wonder about the requirement for non-storing RPL networks to
propagate multicast membership up the DODAG. My understanding is that
non-storing networks typically use MPL (RFC 7731)
<https://www.rfc-editor.org/rfc/rfc7731.html> which does not need
multicast memberships to be propagated throughout the DODAG. It uses
a flooding mechanism to forward multicast datagrams, and does not
unicast at L2. Could the new document accommodate non-storing
networks using MPL?
Sure;
Bottom line here is that for MPL all the multicast packets of interest
for the LLN are flooded throughout so I suspect that there is no need
for the 6LR to signal to the root.
[DT] Yes, that's my understanding as well.
If that’s the case then there’s nothing to standardize. All I need to
clarify is that the RPL behavior in the spec is the one expected in a
RPL domain that supports mop 3 otherwise what is done is out of scope
for this doc.
Do you see it otherwise?
[DT] I agree that only RPL mode 3 needs to be defined and other modes
are left out of scope.
I mean should the 6LR signal unicast to the root like for unicast
traffic when serving a RPL unaware leaf?
[DT] That certainly could be an optimization for non-storing mode so
that a border-router might know what multicast groups to forward from
outside the network. Unfortunately though there is no MOP that is
"Non-storing with multicast", although one could argue semantics and
simply use MOP 1.
[DT] If we were to opt for such behavior, 6LR nodes could simply add RPL
Target options to their DAO's, for the multicast groups they were
interested in (including those requested by leaf nodes).
If so wouldn’t it be expected that the Root makes n unicast to all
6LRs that have listeners?
[DT] I'm not sure that would make sense when MPL is being used, but it
makes for an interesting alternative to MPL.
Should we describe that mode as well?
[DT] As an alternative to MPL? Sure.
Pascal
Regards
Dario
On Sep 27, 2021, at 6:32 AM, Pascal Thubert (pthubert)
<[email protected]
<mailto:[email protected]>> wrote:
Dear all:
This draft is a continuation of our work on RFC 8505, 8928, and 8929.
Comments welcome!
Pascal
-----Original Message-----
From: [email protected] <mailto:[email protected]>
<[email protected] <mailto:[email protected]>>
Sent: lundi 27 septembre 2021 15:29
To: Eric Levy- Abegnoli (elevyabe) <[email protected]
<mailto:[email protected]>>; Pascal Thubert (pthubert)
<[email protected] <mailto:[email protected]>>
Subject: New Version Notification for
draft-thubert-6lo-unicast-lookup-01.txt
A new version of I-D, draft-thubert-6lo-unicast-lookup-01.txt
has been successfully submitted by Pascal Thubert and posted to the
IETF repository.
Name:draft-thubert-6lo-unicast-lookup
Revision:01
Title:IPv6 Neighbor Discovery Unicast Lookup
Document date:2021-09-27
Group:Individual Submission
Pages:15
URL:
https://www.ietf.org/archive/id/draft-thubert-6lo-unicast-lookup-01.txt
Status:
https://datatracker.ietf.org/doc/draft-thubert-6lo-unicast-lookup/
Html:
https://www.ietf.org/archive/id/draft-thubert-6lo-unicast-lookup-01.html
Htmlized:
https://datatracker.ietf.org/doc/html/draft-thubert-6lo-unicast-lookup
Diff:
https://www.ietf.org/rfcdiff?url2=draft-thubert-6lo-unicast-lookup-01
Abstract:
This document updates RFC 8505 in order to enable unicast address
lookup from a 6LoWPAN Border Router acting as an Address Registrar.
The IETF Secretariat
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