Description
In a previous article, Tony Reix have explained how to setup the netem tool to emulate various network behaviours.
In this test, we have setup a configuration of netem to emulate the internet behaviour on a Gigabit local aera network. To validate this configuration we have tried to reproduce a known NFSv4 WAN bug on a local network. This bug is WAN-specific and is not reproductible on a fast local network, such as our gigabit ethernet network.
Test
A netem environement, is created with this parameters:
- 300ms rtt
- 3.0ms rtt variation using a normal distribution
- 1.5% packet loss
- 0.1% duplicate packets
- 20% packet reordered each 5 packets.
Most of this parameters have been measured in previous experiences.
A NFSv4 share is done between two ia32 machines, crossing the netem environement. Next, fsx-linux have been run. As expected, the NFS server have been blocked after a while : the internet behaviour have been successfully reproducted on a local network.
Conclusion
Netem have permited to reproduce on a LAN a WAN-only bug..
Netem and the proposed paramters should be use to debug NFSv4 on WAN.
