Re: [quicwg/base-drafts] Migration with zero-length CID is inadvisable (#3563)

Martin Thomson <> Thu, 30 April 2020 00:57 UTC

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Date: Wed, 29 Apr 2020 17:57:46 -0700
From: Martin Thomson <>
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Subject: Re: [quicwg/base-drafts] Migration with zero-length CID is inadvisable (#3563)
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@martinthomson commented on this pull request.

> @@ -2246,6 +2246,16 @@ that packet numbers cannot be used to correlate activity.  This does not prevent
 other properties of packets, such as timing and size, from being used to
 correlate activity.
+An endpoint SHOULD NOT initiate migration with a peer that uses a zero-length
+connection ID, because traffic over the new path might be trivially linkable to
+traffic over the old one. If the server is able to route packets with a
+zero-length connection ID to the right connection, it means that the server is
+using other information to demultiplex packets. For example, the server can
+assign an address that is unique to the connection using the preferred_address
+transport parameter; see {{preferred-address}}.  Information that might allow

Good catch.  These were done in parallel without thinking much about their interactions.  I've switched to using a different example.

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