Re: [quicwg/base-drafts] Update draft-ietf-quic-transport.md (#105)

[Martin Thomson <[e-mail]>]

martinthomson commented on this pull request.



> -the maximum packet size appropriately.
+The maximum packet size for QUIC is the maximum size of the entire UDP payload,
+including the public header, encrypted payload, and any authentication fields.
+All QUIC packets SHOULD be sized to fit within the path's MTU to avoid IP
+fragmentation. To optimize bandwidth efficiency, endpoints SHOULD use Path MTU
+Discovery ({{!RFC1191}}, {{!RFC1981}}) for detecting the path's MTU, setting the
+maximum packet size appropriately, and storing the result of previous PMTU
+determinations.
+
+(TODO: Should there be a high minimum MTU for QUIC to avoid ICMP attacks? If so,
+does the endpoint fail over to TCP or simply allow fragmentation?)
+
+QUIC endpoints MUST maintain a separate PMTU estimate for each IP address the
+peer is using in the connection. Endpoints SHOULD maintain an estimate for each
+combination of local and remote IP addresses (as each pairing may have a
+different minimum MTU in the path).

I think that we're going to need a definition for "path", which leads to this being simply: Endpoints MUST maintain a separate PMTU estimate for each path.

The implication of your construction is that different remote IP addresses get a different PMTU estimate, but different local ones might not.  That's probably fine if the endpoint knows that outgoing packets from different local addresses go to the same remote address over the same path, but I'd rather assume nothing in any mandate we make. 

That said, if an endpoint has really good information that paths are the "same", then estimates can be easily copied from one path to another.

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