Re: [quicwg/base-drafts] Clarify client anti-amplification response (#3445)

Christian Huitema <> Wed, 19 February 2020 02:48 UTC

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From: Christian Huitema <>
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Subject: Re: [quicwg/base-drafts] Clarify client anti-amplification response (#3445)
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huitema commented on this pull request.

> -handshake deadlock, clients MUST send a packet upon a probe timeout, as
-described in {{QUIC-RECOVERY}}. If the client has no data to retransmit and does
-not have Handshake keys, it MUST send an Initial packet in a UDP datagram of
-at least 1200 bytes.  If the client has Handshake keys, it SHOULD send a
-Handshake packet.
+Loss of an Initial or Handshake packet from the server can cause a deadlock if
+the client does not send additional Initial or Handshake packets.  The server
+can reach its anti-amplification limit, but if the client has received
+acknowledgements for all the data is has sent, it has no reason to send more
+packets. In this case, where the client would otherwise not send any
+additional packets, the server will be unable to send because it has not
+received enough from the client or validated the clients address. To prevent
+this deadlock, clients MUST send a packet on a probe timeout, or PTO;
+see Section 5.3 of {{QUIC-RECOVERY}}. In this case, the client MUST send an
+Initial packet in a UDP datagram of at least 1200 bytes if it does not have
+Handshake keys, and otherwise send a Handshake packet.

I would favor pure pad, personally, so as to not require its own ack, retransmit, etc. Also, sending it with the proper DCID will get the server out of the DOD amplification control mode.

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