You should also take a look at Cisco VIRL (Cisco Virtual Internet Routing Lab Personal Edition). It's $199 for a 1 year license, but provides actual Cisco backed firmware for a ton of Cisco devices. You can create complex networks of up to 20 devices all in a virtual space. Being that it's so powerful it's also somewhat complex. But I've personally found it to be the best for modeling very intricate networks and replicating real life devices in a lab environment. You can even copy and paste actual configurations back and forth between virtual lab and real hardware.
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