Re: [quicwg/base-drafts] Updated ICMP PMTU section (#1412)

[Igor Lubashev <[e-mail]>]

igorlord commented on this pull request.



> +  and can therefore be identified as spurious.
+
+* Store IP ID field of the sent datagrams to validate that ICMP message is
+  refering to an outstanding packet.
+
+Any ICMP messages that fail validation MUST be discarded.
+
+It is important that any problems are detected quickly during the connection
+handshake, because the client may be able to mitigate them by switching to
+alternative IP addresses or protocols.  Hence, an endpoint SHOULD reduce Path
+MTU in response to an ICMP Packet Too Big (PTB) message during a handshake,
+unless then would cause a reduction to a Path MTU value smaller than 1280
+octets.
+
+If during a handshake a client receives an ICMP TPB message that requests it to
+reduce Path MTU to a value smaller than 1280 octets, then:

This is specifically done during the handshake.  The language here is trying to stay in agreement with the decision that PMTU < 1280 does not support QUIC.  Which ones of the statements is the concern:
1. to switch IPs (but stick w/ QUIC), if multiple IPs are available for the server?
2. to switch protocols, if we have an on-path validation of the signal?

Would you rather see all PMTU<1280 signals ignored (and not switch to TCP, if available, for example)?

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