Re: [quicwg/base-drafts] Compatible version upgrade (#1901)

[MikkelFJ <[e-mail]>]

mikkelfj commented on this pull request.



>  
 The client MUST use the long header format and include its selected version on
 all packets until it has 1-RTT keys and it has received a packet from the server
 which is not a Version Negotiation packet.
 
 A client MUST NOT change the version it uses unless it is in response to a
-Version Negotiation packet from the server.  Once a client receives a packet
-from the server which is not a Version Negotiation packet, it MUST discard other
-Version Negotiation packets on the same connection.  Similarly, a client MUST
-ignore a Version Negotiation packet if it has already received and acted on a
-Version Negotiation packet.
+Version Negotiation packet from the server, or if the server picks a different,
+but compatible version (see {{version-upgrade}}).  Once a client receives a
+packet from the server which is not a Version Negotiation packet, it MUST
+discard other Version Negotiation packets on the same connection.  Similarly, a
+client MUST ignore a Version Negotiation packet if it has already received and
+acted on a Version Negotiation packet.

The client is not allowed to respond to version {C} because it is only allow to handle one VN packet (which is important to avoid loops). But as I wrote, a client could make a new connection attempt which amounts to the same thing, so stricly speaking the connection would fail on timeout as the second VN packet is ignored.

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