Cisco Packet Tracer is a powerful network simulator that can be utilized in training for CCNA TM and CCNP TM certification exam by allowing students to create networks with an almost unlimited number of devices and to experience troubleshooting without having to buy real CiscoTM routers or switches.
Cisco Packet Tracer features an array of simulated Application layer protocols (HTTP, DNS, …), as well as basic routing with RIP, OSPF, and EIGRP, to the extent required by the current CCNA TM curriculum. It also includes Cisco IOS 15 with licence features which was introduced in the CCNA exam in 2013.
Cisco Packet Tracer 6.3 has been released on 22th december 2015 by Cisco. This is a maintenance version with netacad login enabled at application startup. It replaces Cisco Packet Tracer 6.2 Student and Cisco Packet Tracer 6.2 Instructor. Cisco Packet Tracer 6.2 includes an ASA 5505 firewall with command line configuration (but no Adaptive Security Device Manageror CCP tools). It also includes a netflow collector as a Desktop application in the server device, routing protocols for IPv6 (OSPFv3, EIGRPv6 , RIPNg), DHCP snooping commands, IPv6 CEF, IPSEC ...
Packet Tracer 6.2 introduced 3G/4G telephony support as well as a new Cisco 819 ISR router with a embedded wireless Access Point. OSPF and EIGRP enhancements were also added in this new version.
Update 06/02/2017 :Try Cisco DevNET sandbox labs offering dedicated Cisco hardware for integration testing. The labs are available for free 24x7 and can be booked dynamically with a DevNet account. Enjoy the networking, datacenter, collaboration and IoT labs !!
Update 22/03/2017 :Cisco announced NX-OSv Nexus 7000 image (Titanium) end of development. Development efforts in the NXOS operating system, are now strongly focused on moving to the next generation NXOS as implemented today on the NEXUS 9000-series platform. The first virtual machine platform using the next generation NXOS operating system is NXOSv9000 which has been released late 2016 on CiscoVIRL 1.2.83.