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Document why one might want to pad ACKS #4252

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Document why one might want to pad ACKS #4252

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Document why one might want to pad ACKS
ianswett Oct 19, 2020
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ianswett Oct 19, 2020
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17 changes: 10 additions & 7 deletions draft-ietf-quic-transport.md
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Expand Up @@ -4091,13 +4091,16 @@ fragmentation on the path.
A client MUST expand the payload of all UDP datagrams carrying Initial packets
to at least the smallest allowed maximum datagram size of 1200 bytes by adding
PADDING frames to the Initial packet or by coalescing the Initial packet; see
{{packet-coalesce}}. Similarly, a server MUST expand the payload of all UDP
datagrams carrying ack-eliciting Initial packets to at least the smallest
allowed maximum datagram size of 1200 bytes. Sending UDP datagrams of this size
ensures that the network path supports a reasonable Path Maximum Transmission
Unit (PMTU), in both directions. Additionally, a client that expands Initial
packets helps reduce the amplitude of amplification attacks caused by server
responses toward an unverified client address; see {{address-validation}}.
{{packet-coalesce}}. Additionally, a client that expands Initial packets helps
reduce the amplitude of amplification attacks caused by server responses
toward an unverified client address; see {{address-validation}}.

Similarly, a server MUST expand the payload of all UDP datagrams carrying
ack-eliciting Initial packets to at least the smallest allowed maximum datagram
size of 1200 bytes. Note that unexpanded Initial packets extend the peer's
idle timeout, even if the path is not capable of carrying the full MTU.
Sending UDP datagrams of this size ensures that the network path supports a
reasonable Path Maximum Transmission Unit (PMTU), in both directions.

Datagrams containing Initial packets MAY exceed 1200 bytes if the sender
believes that the network path and peer both support the size that it chooses.
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