Subject: [homenet] HNCP and connected interfaces

From: Juliusz Chroboczek <[email-masked]>
Date: Tue, 18 Aug 2015 15:38:40 +0200

Section 6.1 says:

   A node MUST be able to detect whether two of its local internal
   interfaces are connected, e.g., by detecting an identical remote
   interface being part of the Common Links of both local interfaces.

What should the node do if it detects that two interfaces are on the same
link?  (Disable HNCP on one interface?  Speak HNCP on both interfaces but
disable prefix assignment?  Something even more exciting?)

-- Juliusz

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From: james woodyatt <[email-masked]>
Date: Tue, 18 Aug 2015 10:32:45 -0700

> disable prefix assignment?  Something even more exciting?)

Seems like this could be improved by rephrasing it to the effect that a node with multiple interfaces on the same common link MUST NOT advertise inconsistent information among them.

—james

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From: Juliusz Chroboczek <[email-masked]>
Date: Tue, 18 Aug 2015 19:45:27 +0200

> Seems like this could be improved by rephrasing it to the effect that
> a node with multiple interfaces on the same common link MUST NOT
> advertise inconsistent information among them.

That's too weak -- it also needs to take care to perform prefix assignment
only once (although it will probably want to perform address assignment on
both interfaces, especially if they're in ad-hoc mode), to run only one
instance of RA and DHCPv4, etc.

I'd really like to see it spelled out.

-- Juliusz

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From: Steven Barth <[email-masked]>
Date: Tue, 18 Aug 2015 20:08:35 +0200

> I'd really like to see it spelled out.

How about adding "In this case the respective interfaces MUST be treated as
belonging to a single shared Common Link."?

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From: james woodyatt <[email-masked]>
Date: Tue, 18 Aug 2015 11:29:21 -0700

> I'd really like to see it spelled out.

Doesn’t section 6.3.1 already spell that out?

> Set of Shared Links: […] When multiple interfaces are
>       detected as belonging to the same Common Link, prefix assignment
>       is disabled on all of these interfaces except one.

—james

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From: Juliusz Chroboczek <[email-masked]>
Date: Tue, 18 Aug 2015 20:37:04 +0200

> belonging to a single shared Common Link."?

Ah, I missed that.  Steven, yes, this deserves a pointer.

Is that really all there is to it?  I run two instances of PA (but
treating them as a single common link), two instances of RA, two instances
of DHCPv4?

-- Juliusz

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From: Juliusz Chroboczek <[email-masked]>
Date: Fri, 21 Aug 2015 12:55:40 +0200

> link?

Ok, I've looked at the spec, I've looked at my code, and it's still not
entirely clear what needs to be done in that case.  Steven, is the
following correct:

  - the algorithm that causes DNCP to avoid id collisions needs to be
    modified so that a node doesn't attempt to negociate with itself;
  - the definition of precedence in PA needs to be changed so that one of
    the interfaces takes precedence over the other one.

Is that correct, and is that all I need to do?

-- Juliusz