Simulating network latency

[Mike Jeays]

We have a proprietary application which will not work properly over our
WAN, even though there is more than enough bandwidth. It works fine on a
LAN.   We suspect a latency problem, mainly because we can't think of
anything else it might be. We are not getting any help from the vendor.

Is there a way to set up a machine with two network cards, which will
simply forward every packet from one card to the other, but will
introduce an arbitrary delay period?  Ideally, the delay period should
be adjustable, and optionally different in the two directions.

Or is there some other way to do the same thing?