Re: Last Call: <draft-ietf-6man-rfc1981bis-04.txt> (Path MTU Discovery f

Hi,

the last paragraph of the introduction reads:

   An extension to Path MTU Discovery defined in this document can be
   found in [RFC4821].  It defines a method for Packetization Layer Path
   MTU Discovery (PLPMTUD) designed for use over paths where delivery of
   ICMP messages to a host is not assured.

Given that ICMP delivery cannot be assured over the vast majority of paths in 
the current Internet, should this document make a recommendation to implement 
RFC4821?

Also, even if ICMP delivery is assured, there are additional complications for 
UDP, which has been seeing a lot of interest both as a tunneling encapsulation 
and for applications (e.g., QUIC). Many platforms do not provide UDP-sending 
applications any information about arriving ICMP messages that were triggered 
by their transmissions. So even if the path delivers ICMP, the OS makes 
ICMP-based PMTUD for UDP often impossible. Another reason to recommend 4821?

Lars

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