Date: Tue, 18 Sep 2012 17:28:21 -0400 From: Matt Van Mater <matt.vanmater@gmail.com> To: freebsd-ipfw@freebsd.org Subject: Problems with dummynet delay in VMWare guest Message-ID: <CACeGjstNDF_8PNFJFi1wCTm9vsd8NDNqnN9X=s%2B67x4HK8x47A@mail.gmail.com>
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The subject says it all... I have built several freebsd9.0-release (+updates) virtual machines with open-vm-tools installed. Each VM has 2 vNICs (on separate vswitches) and has static IPs on those vNICs and static routes forming a virtual hub and spoke topology, with the edge node NATing using natd (to allow for internet access, testing, etc). The intent is to use dummynet to emulate a production network that has multi-hop terrestrial and satellite links with distinct bandwidth, delay and loss. However during testing I have noticed the delay is significantly off from what I have configured in ipfw. Has anyone else encountered this problem running dummynet inside a VMWare ESXi 4.1.0 (build260247) hypervisor? I have a hunch is is due to bad timing due to the use of VMware and I have tried changing the /boot/loader.conf kern.hz setting to 1000, and 100 but it seems to have no effect. For example: If I do not have any dummnet configuration, a ping from my edge vm to my external gateway is about .8 ms (perfectly acceptable) If I have a dummynet config with 7ms delay, the same ping shows a latency of .8ms (seemingly ignoring the dummynet config, not good) If I have a dummynet config with 10ms delay, i will sometimes get ~11ms latency (good, expected) and if i re-apply the config i get about 21ms latency (about twice what i expect) if i have a dummynet config with 30 ms delay, i consistently get 55ms latency. etc.. Simply put, I am seeing more latency than i expect. It is often twice what i configured, but not always in a nice predictable way. I could live with a very predictable offset (i.e.a 2x increase over my dummynet delay configuration) but it doesn't seem predictable. Any words of wisdom to help troubleshoot this? Thanks, Matt
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