> Thank you for the recent reviews and update of draft-ietf-homenet-dncp.
> Please take the next 3 weeks to make your final reviews.
I strongly support this work. We have recently set up an HNCP experiment
here in Paris (together with Thomas Denecker), and in the superficial
testing we did, it works beautifully.
As I've already mentioned on a number of occasions, however, I think that
in its current state DNCP represents a missed opportunity: it is
impossible to participate in DNCP without contributing a Node-State TLV
and a full set of Neighbor sub-TLVs. This implies that:
(1) it is impossible to reliably snoop the protocol without contributing
a Node-State TLV and a full set of Neighbor sub-TLVs;
(2) it is impossible to publish data within DNCP without contributing
a full set of Neighbor sub-TLVs;
(3) it is impossible to act as a dumb DNCP forwarder without publishing
a Node-State TLV and a full set of Neighbor sub-TLVs.
Point (1) is relevant to network monitors that are not co-located with
a router, or more generally to hosts that wish to learn the network
topology without increasing the amount of replicated state. Point (2) is
relevant to hosts that wish to leverage DNCP in order to publish some data
without increasing the amount of replicated state. Point (3) is important
for routers that don't have any attached hosts, as when connecting two
wired networks over a number of wireless hop-to-hop links.
Fixing this is not complicated -- it just requires making it clear that
publishing Neighbor sub-TLVs is optional, and that, if a node is
publishing no sub-TLVs, then publishing a Node-State TLV is itself
optional. This will require changing the algorithm in Section 5.4 (since
the neighbor graph is no longer necessarily connected). I have no idea
whether it requires changes to the link assignment algorithm.
I think that not lifting the requirement for O(n+e) state in DNCP now
would be a serious missed opportunity, since it seriously reduces the
applicability of the protocol.
-- Juliusz
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