Airport Extreme 2013 PPPoE Low Performance on Gigabit Connection

Hello,

Configuration 1

I have a MacbookPro Retina 2013 + Thunderbolt <-> Ethernet adapter. I connect directly to my ISP via PPPOE with a normal network cable.

My speed test finished with 930 MBits/second when connecting the laptop directly to my network wall socket.

http://www.speedtest.net/my-result/3102369759

Configuration 2

The same MacbookPro + Ethernet adapter but this time connected to latest generation Airport Extreme (the tall one) to one of the 3 LAN ports on the back.

The Airport Extreme has one gigabit port for WAN + 3 gigabit ports for LAN. It was configured to connect to my ISP with the same account, via PPPOE.

The Airport Extreme is connected to the same network wall socket with same normal network cable linked to the WAN port.

This time the speed results are totally different: 159 Mbits/ second. That's 6 times slower than the direct connection.

http://www.speedtest.net/my-result/3103367833

Looks like the AirPort Extreme is slowing down my connection. Why could this happen? Is there something limiting the bandwidth inside the Airport Extreme?

Or is the hardware inside too slow to handle such speeds? I don't think so, otherwise why 4 gigabit LAN ports?

If you have any idea why is this happening please help me!

Thanks,

Robert