recommend registering client-issued CIDs with the proxy first

[marten-seemann]

When the client wishes to issue a new CID for the target, it might be advantageous to register it with the proxy first (and wait for acknowledgement), before actually sending it to the target. That way, if the proxy rejects the CID, there’s no risk that the target already started using that CID, which would lead to the loss of all packets sent using that CID, until that CID is retired (which takes at least 1 RTT).

[marten-seemann]

Looks like I opened this issue too early (reading through the document from top to bottom).

This is already recommended in section 4.2. However, in section 4 it says:

The client sends a REGISTER_CLIENT_CID capsule whenever it advertises a new Client Connection ID to the target

This sentence could probably be reworded by replacing “whenever” with “before”.

[tfpauly]

Yes, it would be useful to clarify the ordering — saying "before" is good there, or at least in the same packet to the proxy so the proxy is able to read the content first before passing along a packet to the next hop.