Given that WANem is Linux-based, it really acts as a (relatively) pretty front end for Linux's native Netem and TC functionalities. However, with WANem, setup is quite a lot faster than the manual approach. WANem exposes almost all of the functionality of Netem, so unlike some other Linux-based Netem/TC wrappers, it's capable of fully emulating jitter and reordering, as well as asymmetrical bandwidth limits -- helpful when emulating a DSL or cable connection. But because of its extra bells and whistles, it's more complicated to learn if you're new to WAN emulation or network engineering in general.
WAN-Bridge is another free Linux-based WAN emulation distribution. If your goal is to set up a bridge-based WAN emulator and you don't care about emulating jitter, reordering, or asymmetrical bandwidth, this may be the simplest and easiest tool you'll find. As with WANem, WAN-Bridge is a Knoppix-based Live CD that uses Netem and TC. Unlike WANem, it's not graphical in any way, but the textual interface is simple enough that very few will have a problem using it.
The downside to WAN-Bridge is that it doesn't expose the full feature set of Netem or TC. The distribution includes the extremely helpful Ntop tool, which gives you an idea of what kind of traffic is flowing across the WAN emulator.
Vyatta is a Linux-based software router owned by Brocade; it's a commercial product, but free versions are available. If your needs are a bit more complicated and you require the full feature set of a real hardware router but don't want to buy one, Vyatta can be pressed into service as both a router and a WAN emulator. Its network emulation feature set doesn't have the same depth of latency controls as a manual Netem (or WANem) implementation would, but Vyatta lets you easily implement fairly complicated configurations that involve more than a pair of interfaces or dynamic routing protocols.
Vyatta can also serve as a good DIY home firewall. That means you could also use its network emulation features to mess with your significant other while he or she tries to watch Netflix (it's hilarious, trust me).
Deciding how to test
After you've decided on a tool that fits your needs, the next thing to do is figure out where and how to insert it on your network. The answer to that question will depend on what you're trying to accomplish and how many changes you're comfortable making to your production network.
The biggest decision is whether to use a WAN emulator in a routed or bridged configuration. If you're OK with implementing a new subnet on your network for your testing machines, then using a routed configuration will probably be best. Having separate subnets on both sides of the emulator removes some of the odd behaviors that can result from implementing traffic shaping and delay introduction in a bridge. However, if you'd like to make your testing as simple and transparent as possible, using a bridged configuration means not having to make any addressing changes on your network.
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