Re: [quicwg/base-drafts] Describe PMTU probing that includes source connection ID for routing … (#2402)

Kazuho Oku <> Mon, 04 February 2019 02:39 UTC

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From: Kazuho Oku <>
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Subject: Re: [quicwg/base-drafts] Describe PMTU probing that includes source connection ID for routing … (#2402)
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kazuho commented on this pull request.

Looks mostly fine to me.

Besides some minor comments (see below), I think it might be a good idea to add a reference to this section from "12.2. Coalescing Packets".

> @@ -3274,6 +3274,22 @@ The considerations for processing ICMP messages in the previous section also
 apply if these messages are used by DPLPMTUD.
+### PMTU Probes Containing Source Connection ID
+Endpoints that rely on the destination connection ID for routing QUIC packets
+are likely to require that connection ID included in PMTU probe packets in order
+to route resulting ICMP messages ({{icmp-pmtud}}) back to the correct endpoints.
+Only long header packets ({{long-header}}) contain source connection IDs, but
+long header packets will not be acknowledged once the connection has been
+established.  One way to construct a PMTU probe is to coalesce (see
+{{packet-coalesce}}) a Handshake packet ({{packet-handshake}}) with a short

It might make sense to:
* Call the datagram "a probe", rather than referring to the short header packet as "a probe".
* it might be better to suggest use of _any_ coalescible long header packet rather than specifically suggesting the use of a Handshake packet.

Therefore something like: _One way to construct a PMTU probe is to coalesce a Long header packet with a Length field and a short header packet into a single UDP datagram, If the datagram reaches the endpoint, the short header packet will be acknowledged. If the datagram elicits an ICMP message, that message will likely contain the source connection ID within the quoted portion of the datagram._

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