Cisco 16-Port 10 Gigabit Ethernet Fiber Module with DFC4XL - Expansion module - 10 GigE - 10GBase-X - 16 ports - for P/N: WS-C6503-E-RF/ WS-C6506-E-RF/ WS-C6509-V-E/ WS-C6509-V-E-RF/ WS-C6513-E