N600 LAN ports not giving Gigabit speeds

I have a N600 dual band wireless router and am unable to see 1000Mbs when connected to any of the four ports. If I plug my Imac directly into my able modem I can connect at 1000mbs. I have swapped cables and changed the network settings on the Imac to 1000Baset Full Duplex to no avail. This unit is sold as Gigabit Lan ports but I am unable to get this connection. 

Any ideas for me to try?