[quicwg/base-drafts] Disagreement about Path Liveness (#1495)

Mike Bishop <notifications@github.com> Thu, 28 June 2018 20:53 UTC

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Date: Thu, 28 Jun 2018 20:52:58 +0000
From: Mike Bishop <notifications@github.com>
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Subject: [quicwg/base-drafts] Disagreement about Path Liveness (#1495)
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Follow-on issue from #1465 and #1484. The existing text says that for the first transmission on a new path, you have to use a higher-order CID (greater sequence number) than you've ever used before; once a path exists, you can't use a lower-order CID than you've ever sent or received on the network.

Two scenarios:

> A client has probed an alternate path, but not migrated, and then sends no traffic on that path for a prolonged period of time.  The client considers the path to be idle; the server considers the path to have timed out.  After some time, the client decides to re-probe.  It's permitted to use the same CID that it had previously used.  However, if the server has considered the path closed, it might not remember the old CID that had been bound to a path.
> This will provoke a Stateless Reset from the server in response to the probe, even though the server considers the connection itself to be valid, and would accept the probe if a fresh CID were used.
> An endpoint has advanced to a new CID; the peer, seeing the new CID, now considers older CIDs invalid after a certain period.  A packet with an old CID is severely delayed.  The peer, upon receipt of the delayed packet, considers it to belong to an unknown connection and generates a Stateless Reset.

Possible solution:  We might need to have the side forgetting CIDs explicitly inform the peer that it will no longer use or accept CIDs older than a certain cutoff.  You have to remember old CIDs you've issued until this frame is acknowledged; upon receipt of this frame, you no longer consider the stateless reset tokens valid.

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