Re: [quicwg/base-drafts] Request to Retire Locally Issued CIDs (#2769)

[Mike Bishop <[e-mail]>]

MikeBishop commented on this pull request.

This is straddling the line between "request" (5037) and "require" (998).  Pick one.  Given that you're going to kill the connection if they don't comply, "request" doesn't seem like a strong enough statement here.  But the issuer only MAY kill the connection if the peer doesn't comply, so....  🤷‍♀️

If connection destruction is the intended result, go stronger.  You SHOULD set the timer and blow up the connection if it expires; you MUST retire the CIDs upon receipt of an increased RPT field.

> @@ -994,6 +994,14 @@ packets sent from only one local address.  An endpoint that migrates away from a
 local address SHOULD retire all connection IDs used on that address once it no
 longer plans to use that address.
 
+The endpoint can explicitly request its peer to retire connection IDs by sending
+a NEW_CONNECTION_ID frame that contains a Retire Prior To field.  The peer is
+required to retire these connection IDs in a timely manner.  On receipt of the
+acknowledgement for the packet that contained the NEW_CONNECTION_ID frame, the
+endpoint may start a 3 PTO timer, which on expiring may close the connection
+with a PROTOCOL_VIOLATION error if all the connection IDs were not retired as
+requested.
+

Mostly because "change immediately" is a difficult requirement to police.  Couching it in more concrete terms -- error on use of this CID in a packet with a higher packet number than the one which carried the ACK -- makes it easier to police in theory, but highlights what different parts of the system have to be coordinated to do it in practice.

Frankly, I'd even be okay with no longer recognizing those CIDs 3xPTO after sending the frame.  Fewer moving parts, easy to understand, but a small risk of stateless reset if the packet is severely delayed.

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