Re: [quicwg/base-drafts] Required state for retaining unacked RETIRE_CONNECTION_ID frames is unbound (#3509)

Kazuho Oku <notifications@github.com> Fri, 27 March 2020 02:36 UTC

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Date: Thu, 26 Mar 2020 19:35:58 -0700
From: Kazuho Oku <notifications@github.com>
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Subject: Re: [quicwg/base-drafts] Required state for retaining unacked RETIRE_CONNECTION_ID frames is unbound (#3509)
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@ianswett 
> If the peer doesn't acknowledge your retirement, then you shouldn't be issuing more CIDs, because you might exceed their limit.

I think the framing is incorrect. The peer can enforce an endpoint to retire a CID (e.g., by changing RPT or discarding a path). As @martinduke points out, an endpoint is encouraged issue a new CID at this point, rather than withholding than until the ACK of RCID is received.

Note also that RCID carries the CID that *the endpoint sends* carries the CID that the peer has issued, while NCID that the endpoint carries the CID that that endpoint issues. Therefore, I am not sure what the rationale for withholding the emission of NCID until receiving an ACK for RCID would be.

> In my opinion, running out of CIDs is not a big crisis. You can always create a new connection with 0-RTT with a relatively small overhead. We should be biased towards simplicity rather than never running out of CIDs.

I agree. An endpoint is not expected to consume CID at high rate. We already discourage such behavior; see https://quicwg.org/base-drafts/draft-ietf-quic-transport.html#section-5.1.1-5.

That's why I'm fine with the leaky behavior that @martinthomson has suggested.

@martinduke 
> I'm really coming around to your cumulative retire idea, but will have another go at this tomorrow.

As previously stated, I am hesitant to have a new machinery that is unique to this purpose. There is a risk of creating something buggy, both in terms of specification and implementation. My preference goes to accepting the risk (and recommending mitigations, such as the leaky behavior), or reusing a design pattern that we already have (i.e. introduce MAX_CONNECTION_IDS frame).

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