I have a few questions and comments about DNCP. (I haven't finished
grokking HNCP yet, so that will have to wait.)
1. Fragmentation
The minimum MTU in IPv6 is 1280 bytes, and the minimum maximum packet size
(before fragmentation) is 1500 bytes. This means that a Short Network
Status can carry information about 160 nodes or so, which is a little
tight for comfort. Is there a fragmentation mechanism I've missed
somewhere?
Related to that -- what happens if you receive a Node Data Request, and
the reply doesn't fit in the MTU? Are you allowed to split it into
multiple Node Data Replies? If so, how do you know if you've received the
whole set?
2. Packet loss
What happens on packet loss?
* what happens when the reply to a Node Data Request doesn't arrive?
Are you supposed to resend the request? With exponential or linear
backoff, and with what constants?
* is there a way to detect that a link exhibits packet loss? There are
no sequence numbers in state updates (there's the state seqno, but
that's not incremented with each message), so you cannot easily find
how many you've missed.
* Are you allowed to do something special when you have new data to
publish over a connection that exhibits packet loss? For example
keeping I at Imin for two or three updates?
3. Extensibility
What should I do if I receive an unknown TLV? I assume I should silently
ignore it if it's inside a Data TLV, and include it in my database and
flood it if it's within a Data TLV, right?
Which messages are allowed to contain extra TLVs? For example, what
should I do if I receive a Long Network State Update with a bunch of
unknown TLVs interleaved with the Node State TLVs?
4. Jitter
Am I missing something or you're not applying jitter to keepalives?
5. Connections
There's a single connection for all neighbours on a given interface,
right? Why not call that an Interface, then?
6. Link-local addresses
You're assuming a link-local multicast group, right? What about the
sender address and unicast packets? What should I do if I receive a DHCP
message from a global address? Discard it, right?
7. Neighbor graph
The notion of "neighbor graph" suddenly appears in Section 5.4. It's
pretty obvious what you mean, but this should be precisely defined
somewhere.
-- Juliusz
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