Re: [quicwg/base-drafts] Allow connections to share a port by adding restrictions on zero-length connection IDs (#2851)

[Kazuho Oku <[e-mail]>]

kazuho commented on this pull request.

:+1: The requirements look good to me. I only have one editorial suggestion.

> -connection. An endpoint whose peer has selected a zero-length connection ID MUST
-continue to use a zero-length connection ID for the lifetime of the connection
-and MUST NOT send packets from any other local address.
+A zero-length connection ID can be used when a connection ID is not needed
+to route to the correct endpoint. An endpoint SHOULD NOT use a zero-length
+connection ID unless it can use only its IP address and port to identify a
+connection. The IP address and port used by a peer cannot be used for routing
+or connection identification as these values can change during a connection's
+lifetime, and the peer can reuse a given address and port for additional
+connections. Similarly, the peer's connection IDs cannot be used for routing
+or identification, as they are not transmitted in the short header packets
+they send. Note that multiplexing while using zero-length connection IDs and
+relying on the four-tuple of IP addresses and ports for routing will cause
+failures in the presence of connection migration, NAT rebinding, and client
+port reuse; and therefore MUST NOT be done unless an endpoint is certain that
+those protocol features are not in use.

I think it might be a good idea to move the "MUST NOT unless" up front, then explain the cases where a zero-length connection ID can be used. E.g.,

"Multiplexing while using zero-length connection IDs and relying on the four-tuple of IP addresses and ports for routing will cause failures in the presence of connection migration, NAT rebinding, and client port reuse; and therefore MUST NOT be done unless an endpoint is certain that those protocol features are not in use. A zero-length connection ID can be used when a connection ID is not needed to route to the correct endpoint. An endpoint SHOULD NOT use a zero-length connection ID unless it can use only its IP address and port to identify a connection. ..."

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