Simulating Network Latency?

ixmo asks: "I've just come around an interesting problem: to simulate low-bandwidth network links without buying expensive WAN simulators, I can connect two old Cisco routers back to back with serial cables, and control the bandwidth via the 'clock rate' IOS command, but how can I simulate network latency? Is there some OS tool or patch (for Linux/OpenBSD) that allows for tuning of network delay? Any hints?"

Comments

Linux QoS

[Phacka]

Network emulator
CONFIG_NET_SCH_NETEM:
Say Y if you want to emulate network delay, loss, and packet re-ordering. This is often useful to simulate networks when testing applications or protocols.

config NET_SCH_DELAY

[Kevin Burtch]

I'm shocked no-one has posted this!

It's been in the kernel for while, though I don't know much about using it. I never bothered even looking at it (had no need) until a coworker wanted to use it (on Thursday) to do some testing and asked me about it.

Here's the chunk of Kconfig:

config NET_SCH_DELAY
tristate "Delay simulator"
depends on NET_SCHED
help
Say Y if you want to delay packets by a fixed amount of
time. This is often useful to simulate network delay when
testing applications or protocols.

To compile this driver as a module, choose M here: the module
will be called sch_delay.

Please reply to this if you have been able to get this working... the tuning parameters to tc we found give errors (and yes, we built installed the latest iproute2 tarball).
Then again, we only spent a few minutes playing with it (he had to leave).