Question for QUIC Feature with preferred address migration

[YifangZhang]

Dear authors,

I am a relatively new user of both QUIC and aioquic.

Based on RFC 9000 Section 9.6, there is a possible migration on the server side to migrate the whole connection into the server's preferred address.

Is it possible for someone could point out this part of the code in aioquic for me?

I have searched in the aioquic package and can only find keyword "preferred_address" in packet.py (here) and once in connection.py (here).

None of the above seems to be migration with my limited understanding. Please correct me if I am wrong on this.

Thanks a lot!

[rthalley]

As far as I can tell from the source, we currently have support for encoding and decoding, and we check that if it is present in the transport parameters that we are not a server. I don't see any way (if we are a server) to cause it to be transmitted, nor do I see the client preserving the information and delivering it as an event, which I presume would be needed if the client application were going to consider taking the advice. So to summarize: if we see it we can parse it but we ignore it unless we're a server in which case it is an error; we don't send it. I defer to Jeremy if I have missed anything!

[YifangZhang]

Please correct me if I misunderstand the situation @rthalley. So, the package has supported the encoding and decoding for server-side migration but is ignored if we are a server.

I still having trouble understanding the summary part: "if we see it we can parse it but we ignore it unless we're a server in which case it is an error; we don't send it."

On RFC9000 section 9.6 says: "QUIC allows servers to accept connections on one IP address and attempt to transfer these connections to a more preferred address shortly after the handshake. This is particularly useful when clients initially connect to an address shared by multiple servers but would prefer to use a unicast address to ensure connection stability."

In my limited knowledge, I think it means the server can initiate the server-sided migration from the current address to a more preferred address (since I am new to this protocol, maybe my understanding is incorrect). So, I thought if we are a server, we can initiate the server-side migration after handshake to a new preferred address. However, I was not able to find such implementation in the aioquic package.

And apologize ahead if this is just my misunderstanding, and thank you for the deter and answers!

[rthalley]

Your interpretation of the spec is correct, we just don't implement it yet.