On Apr 20, 2021, at 7:24 PM, Eric Rescorla <[email protected]> wrote:
On Tue, Apr 20, 2021 at 3:42 PM John Scudder
<[email protected]<mailto:[email protected]>> wrote:
On Apr 20, 2021, at 5:32 PM, Eric Rescorla
<[email protected]<mailto:[email protected]>> wrote:
3. Section 6:
* There is a strategy for ensuring that the new peer address is able
to receive and process DTLS records. No such strategy is defined
in this specification.
This is a little mind-boggling to me. I understand this to mean I can’t send
the new address a DTLS record unless I’ve already ensured it can receive and
process that record, right? This seems almost like a classic Catch-22. I feel
like I must be missing something.
This specification *only* allows you to mux, but doesn't allow you to migrate.
We could probably make this point clearer.
Yes, I think so. Various things led me to think this was supposed to be a
feature. For starters, the abstract:
A CID is an identifier carried in the record layer header that gives
the recipient additional information for selecting the appropriate
security association. In "classical" DTLS, selecting a security
association of an incoming DTLS record is accomplished with the help
of the 5-tuple. If the source IP address and/or source port changes
during the lifetime of an ongoing DTLS session then the receiver will
be unable to locate the correct security context.
It’s true the abstract doesn’t promise that I can migrate to the new address,
but I felt led in that direction. But more to the point, §6 itself:
When a record with a CID is received that has a source address
different than the one currently associated with the DTLS connection,
the receiver MUST NOT replace the address it uses for sending records
to its peer with the source address specified in the received
datagram unless the following three conditions are met:
If I understand your reply correctly, the quoted sentence could end “… unless
the following three conditions are met (which will never happen):”. Since that
seems both capricious and pointless, I still think I’m missing something. Is it
that you envision a future specification that does define a strategy that will
fulfill the third condition?
Yes.
Got it, thanks. In that case I think it brings us back to your earlier “we
could probably make this point clearer”.
—John
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