Date: Tue, 21 Apr 2015 12:47:45 -0700 From: Scott Larson <stl@wiredrive.com> To: freebsd-net@freebsd.org Subject: net.inet.ip.forwarding impact on throughput Message-ID: <CAFt8naGoDDN%2B64snnCtwWfRMN5BkFJ0tc%2BBytifk-7u5_FgCsQ@mail.gmail.com>
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We're in the process of migrating our network into the future with 40G
at the core, including our firewall/traffic routers with 40G interfaces. An
issue which this exposed and threw me for a week turns out to be directly
related to net.inet.ip.forwarding and I'm looking to just get some insight
on what exactly is occurring as a result of using it.
What I am seeing is when that knob is set to 0, an identical pair of
what will be PF/relayd servers with direct DAC links between each other
using Chelsio T580s can sustain around 38Gb/s on iperf runs. However the
moment I set that knob to 1, that throughput collapses down into the 3 to
5Gb/s range. As the old gear this is replacing is all GigE I'd never
witnessed this. Twiddling net.inet.ip.fastforwarding has no apparent effect.
I've not found any docs going in depth on what deeper changes enabling
forwarding does to the network stack. Does it ultimately put a lower
priority on traffic where the server functioning as the packet router is
the final endpoint in exchange for having more resources available to route
traffic across interfaces as would generally be the case?
*[image: userimage]Scott Larson[image: los angeles]
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