bufferbloat in the fediverse

bufferbloat in the fediverse

The BBR folk at google use ECN differently than RFC3168 and disable negotation of it entirely... while apple clients tend to request it, and it's enabled by default across the rest of the internet. There was a patch rejected long ago that did the right thing here, and other patches to just make BBR obey RFC3168, also rejected... I am seeing a lot of BBR uptake (say, 11% of websites), without also disabling ECN negotiation, which means that fq_codel, cake, etc go around marking packets madly instead of dropping them, to no observable effect when BBR is in play.

Mess. My rightest answer would be to make BBRv1 do RFC3168-style ecn, perhaps not dropping the rate by half as per that spec, but by initiating a probe phase. Others differ.

As for recommendations as to good defaults, a lot of the non-controversial fixes have landed in the kernel and become defaults, tsq, bql, pacing, fq_codel, etc.

and, BBR has been shown to be a good step forward for many applications, and I do think it's probably a better transport than cubic for the kinds of long running, periodically bursty, autonomous applications like those in the fediverse, and especially over lte. It's also been shown to be problematic in multiple respects, but BBRv2 is hung up in testing, partially hinged on the non-backward compatible treatment of ECN in it.

It would be nice if more people were aware of these issues, taking packet captures, and worrying about the impacts on the network.

I'm sorry that the amount of "publicity" and discussions these problems have got is not easily visible on today's internet. Perhaps talking about it here will help, and a few more beleaguered sysadmins and users lean in. Google does not index mailing lists like ietf's tsvwg or bufferbloat.net's bloat list all that well, anymore, with over a decades worth of discussion on each.