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

[Igor Lubashev <[e-mail]>]

igorlord commented on this pull request.



>  
-Traditional ICMP-based path MTU discovery in IPv4 {{!PMTUDv4}} is potentially
-vulnerable to off-path attacks that successfully guess the IP/port 4-tuple and
-reduce the MTU to a bandwidth-inefficient value. TCP connections mitigate this
-risk by using the (at minimum) 8 bytes of transport header echoed in the ICMP
-message to validate the TCP sequence number as valid for the current
-connection. However, as QUIC operates over UDP, in IPv4 the echoed information
-could consist only of the IP and UDP headers, which usually has insufficient
-entropy to mitigate off-path attacks.
+ICMP error messages used in classical Path MTU discovery may be classified into
+messages with an on-path proof and without an on-path proof.  ICMP messages with

(As for an 8-byte proof, it is sufficient for TCP but not QUIC.  Hence this entire discussion.)

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