Proposal: Increase QUIC Amplification Limit to 5x

[Nick Banks <[e-mail]>]

Hello Folks,

We've had this discussion on Slack in the past, and I wanted to bring it here to get some additional feedback. As some of you know, I have a project on GitHub (microsoft/quicreach<https://github.com/microsoft/quicreach>) that is a simple ping-like reachability tool for QUIC, and I run a periodic action to test the top 5000 hostnames for QUIC-reachability and then breaks the handshake down by whether it (a) requires multiple round trips, (b) exceeds the specified amplification limit or (c) connects in 1-RTT under the limit. It produces this dashboard<https://microsoft.github.io/quicreach/>:

[cid:image001.png@01DAE268.3B37CDC0]

The main point in sending this email is to focus on the large percentage of servers that are ignoring the 3x amplification limit today, and what we should do (if anything) about that. I ran a quick experiment (PR<https://github.com/microsoft/quicreach/pull/243>) this morning to test how the breakdown would look if we had different amplification limits (3x<https://github.com/microsoft/quicreach/actions/runs/10161649574/job/28100572606#step:6:1>, 4x<https://github.com/microsoft/quicreach/actions/runs/10162466467/job/28103201648#step:6:1>, 5x<https://github.com/microsoft/quicreach/actions/runs/10162939158/job/28104656720#step:6:1>) and found that if we used a 5x limit we would find ourselves in a place where most servers are now under the limit.

[cid:image002.png@01DAE268.3B37CDC0]

So, my ask to the group is if we should more officially bless a 5x limit as 'Ok' for servers to use. This would more impact those servers that currently take multiple round trips because they are correctly enforcing the 3x limit on themselves, resulting in longer handshake times. If we say they can/should change their logic from 3x to 5x, then their handshake times will improve, and largely things will speed up for clients when using QUIC. Personally, I'd like to update MsQuic to use this new limit based on this data, but I wanted to get a feel from the group first.

Thanks,
- Nick

Sent from Outlook<http://aka.ms/weboutlook>