Re: [quicwg/base-drafts] active_connection_id_limit defaults to 0 (#3197)

Marten Seemann <> Thu, 07 November 2019 02:40 UTC

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Date: Wed, 06 Nov 2019 18:40:41 -0800
From: Marten Seemann <>
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Subject: Re: [quicwg/base-drafts] active_connection_id_limit defaults to 0 (#3197)
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The definition of the transport parameter says:
> The maximum number of connection IDs from the peer that an endpoint is willing to store. This value includes only connection IDs sent in NEW_CONNECTION_ID frames.

So sending a value of 0 (or, as it currently stands, omitting the TP), is a valid thing to do. It's an endpoint declaring that it will never, under no circumstances, change the connection ID, but to keep on using the connection ID provided during the handshake. Of course this also implies that connection migration is effectively disabled.
We might want to decide to make this illegal though. Since the introduction of the Retire Prior To field on the NEW_CONNECTION_ID frame, implementations have the option to retire connection IDs in case their infrastructure requires that. A peer sending a value of 0 would prevent those implementations from rotating their connection ID mapping, which seems like an awkward special case.

As @MikeBishop points out, sending a value of 1 doesn't make any sense, since you can't switch to a new CID without stalling the connection first.

Therefore, I agree with @MikeBishop's suggestion to forbid values below 2. I'm undecided if we should define a default value, and if so, what that value should be.

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