Hello,

I hope this is a good list to post this on, I have a feeling the solution is 
somewhere obscure in the networking layer.

I've set up an IPS system, using:

* FreeBSD 10.1 (guest OS, plenty of RAM/CPU)
* ESXi 5.5 (host OS, using Intel X520 10Gb cards. Not overloaded, all graphs 
show it's got plenty of RAM/CPU spare at all times)
* vmxnet3 drivers
* ipfw (very small ruleset, basically just a divert rule)
* suricata, in ipfw divert mode

I'm having a couple of major issues. 

The first is that every so often, even with relatively little traffic, the load 
on the box suddenly spikes and pings to a neighbouring router (via the divert 
rule) go from <1ms to >300ms. Generally this resolves itself after a few 
minutes, although last night it went on for an hour until I restarted ipfw and 
suricata.

The second is that if I do a large download, eg a FreeBSD ISO, the download 
usually hangs somewhere between 5MB and 100MB through. I can see traffic trying 
to get through on neighbouring routers, it's just the interface with the divert 
to suricata where they disappear into a black hole. The connection speed is 
around 50Mb, btw.

Now it's possible it's suricata being weird, but there's nothing untoward in 
its events and stats logs, and if I replay the traffic from a pcap file then 
suricata processes everything fine (a pcap taken over a 90s period during a 
slowdown is processed in under a second). So my guess is that if suricata takes 
slightly longer than normal to process a packet, something in the networking or 
ipfw divert system is tripping itself up. Maybe a queue is filling up?

I've set net.inet.ip.fw.dyn_buckets=16384, and done an ipfw flush, but 
net.inet.ip.fw.curr_dyn_buckets is stubbornly sticking at 256: have I done 
something wrong? Other tunables I've set are:

kern.random.sys.harvest.ethernet=0
kern.random.sys.harvest.point_to_point=0
kern.random.sys.harvest.interrupt=0 
kern.ipc.soacceptqueue=1024 

Can anyone suggest either tests to see what might be going wrong, or tunables 
to help things run smoother? Both myself and a colleague have used FreeBSD for 
over 15 years, and never quite seen anything like it.

Many thanks,

Oliver.

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