Re: [quicwg/base-drafts] Allow ClientHello to span multiple QUIC packets (#3045)

MikkelFJ <> Thu, 19 September 2019 22:15 UTC

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Subject: Re: [quicwg/base-drafts] Allow ClientHello to span multiple QUIC packets (#3045)
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mikkelfj commented on this pull request.

> -cryptographic handshake message, which for TLS is the ClientHello.  Though a
-packet larger than 1200 bytes might be supported by the path, a client improves
-the likelihood that a packet is accepted if it ensures that the first
-ClientHello message is small enough to stay within this limit.
+The first Initial packet from a client starts with its first cryptographic
+handshake message, which for TLS is the ClientHello.  Servers might need to
+parse the entire ClientHello (e.g., to access extensions such as Server Name
+Identification (SNI) or Application Layer Protocol Negotiation (ALPN)) in order
+to decide whether to accept the new incoming QUIC connection.  If the
+ClientHello spans multiple Initial packets, such servers would need to buffer
+the first received fragments, which could consume excessive resources if the
+client's address has not yet been validated.  To avoid this, servers MAY use
+the Retry feature (see Section 8.1 of {{QUIC-TRANSPORT}}) to only buffer
+partial ClientHellos from clients with a validated address.  Though a packet
+larger than 1200 bytes might be supported by the path, a client improves the
+likelihood that a packet is accepted if it ensures that the first ClientHello

If this multiple packet initial thing lands, at least we should limit the packet count / time to arrival or provide guidance. Dribble (slow loris) can happen in fragments or just in many very small complete packets over a very long time.

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