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

From: Martin Thomson <[email-masked]>
Date: Tue, 31 Mar 2020 16:24:26 -0700

Not making a design/editorial call here.  There is new normative language, so maybe it is design.  But this is really just documenting an emergent property of the existing system.  There are no concrete changes other than a stronger recommendation against migration in cases where it either doesn&#39;t work or would not provide the privacy properties we have attempted to guarantee.

Closes #3559.
You can view, comment on, or merge this pull request online at:

  https://github.com/quicwg/base-drafts/pull/3563

-- Commit Summary --

  * Migration with zero-length CID is inadvisable

-- File Changes --

    M draft-ietf-quic-transport.md (7)

-- Patch Links --

https://github.com/quicwg/base-drafts/pull/3563.patch
https://github.com/quicwg/base-drafts/pull/3563.diff

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From: ianswett <[email-masked]>
Date: Tue, 31 Mar 2020 16:47:28 -0700

I think we already knew this, but it's also not that relevant to most migration scenarios when the client is migrating and has a 0-len CID, so I think it's fine.

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From: ianswett <[email-masked]>
Date: Tue, 31 Mar 2020 16:48:57 -0700

@ianswett commented on this pull request.

> @@ -2246,6 +2246,13 @@ 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 when a peer that requests the use of
+a zero-length connection ID. If the peer routes incoming packets using the
+source address, migration might not be successful. If the peer routes incoming
+packets by assigning a unique destination address to the connection, which
+might be achieved using using the preferred_address transport parameter (see
+{{preferred-address}}), packets sent on different paths will be linkable.

```suggestion
{{preferred-address}}), packets sent on different paths are likely to be linkable.
```

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From: ianswett <[email-masked]>
Date: Tue, 31 Mar 2020 16:49:00 -0700

@ianswett approved this pull request.

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From: David Schinazi <[email-masked]>
Date: Tue, 31 Mar 2020 16:52:53 -0700

@DavidSchinazi commented on this pull request.

I'm not sure this guidance is correct. If the server has reason to believe migration won't work (due to source-IP routing or otherwise) it should send the disable_migration TP. It's perfectly reasonable to migrate when zero-length CIDs are in use if the server only has one connection on this port. Therefore I think we should stay away from the implicit signal "CID is zero-length" and instead use the explicit signal disable_migration.

I'm failing to parse this first sentence.

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From: Martin Thomson <[email-masked]>
Date: Tue, 31 Mar 2020 17:26:20 -0700

@martinthomson pushed 1 commit.

caf949d0d2c0f00f614205644b9895d2a63011cd  Wordz is harrd

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