Date: Tue, 1 Sep 2015 21:50:29 -0700 (PDT) From: Don Lewis <truckman@FreeBSD.org> To: freebsd-net@FreeBSD.org Subject: CoDel and ECN questions Message-ID: <201509020450.t824oTKP057556@gw.catspoiler.org>
next in thread | raw e-mail | index | archive | help
Bufferbloat on my DSL link to the outside world has been bugging me lately. I was considering adding an OpenWrt box between my DSL modem and my FreeBSD firewall in order to get CoDel, when I discovered that CoDel had been quietly added to FreeBSD 11. Unfortunately the documentation is severely lacking. The ALTQ(4) man page mentions CoDel and points to pfctl(8) and pf.conf(5) for details, but pf.conf(5) discusses cbq, priq, hfsc, and red, but not codel. I'm currently using ipfw and not pf, but it looks like ipfw can connect to altq, so I'm good there. I need to limit bandwidth in both directions, but altq only controls outbound traffic on an interface, which makes sense. If this box was just forwarding packets between two interfaces, I could also use altq on the inward-facing interface to limit download bandwidth to control the queue depth on the ISP side of my DSL link. The problem is that some of the inbound traffic terminates on the firewall box itself, and in the future I may have more than one inside interface. Dummynet is able to control bandwidth in both directions, but it only implements RED and gRED but not CoDel (or at least it's not documented). The OpenWrt implementation can account for extra per-packet overhead in its bandwidth calculations. That could be significant for me because of the additional PPPoE and ATM overhead, which is pretty large for small packets. Do we have anything similar? Can we combine ECN with CoDel? Pf.conf(5) says that ECN implies RED. I'm using 6rd and gif(4) for IPv6 connectivity. Does gif copy the ECN bits when encapsulating and decapsulating packets? According to <https://en.wikipedia.org/wiki/Explicit_Congestion_Notification>, Apple has announced that OS X 10.11 and iOS 9 will enable ECN by default. Have we given any thought to changing our default? Linux can control ECN separately for incoming and outgoing connections. It sounds like the default is now to accepting ECN for incoming connections, but not request it for outgoing connections.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201509020450.t824oTKP057556>