Intel 82599EB Not Working on Linux

I have just received my new X310 + Intel 82599EB. I cannot ping the device.

1. If I connect the X310 to the 1Gb ethernet port of my host then everything works fine;
2. If I connect the X310 to the 10Gb 82599EB with the supplied cable, I cannot ping the device. I have the latest versions of the ixgbe kernel module (4.1.5) and the ethtool utility (4.2).

My kernel version is 3.18.2.

Here is some diagnostic output:

root@blacklist:~# ifconfig eth1
eth1: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        inet 192.168.10.1  netmask 255.255.255.0  broadcast 192.168.10.255
        ether 90:e2:ba:9b:46:ac  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

root@blacklist:~# ethtool eth1
Settings for eth1:
        Supported ports: [ FIBRE ]
        Supported link modes:   10000baseT/Full
        Supported pause frame use: No
        Supports auto-negotiation: No
        Advertised link modes:  10000baseT/Full
        Advertised pause frame use: Symmetric
        Advertised auto-negotiation: No
        Speed: Unknown!
        Duplex: Unknown! (255)
        Port: Direct Attach Copper
        PHYAD: 0
        Transceiver: external
        Auto-negotiation: off
        Supports Wake-on: d
        Wake-on: d
        Current message level: 0x00000007 (7)
                               drv probe link
        Link detected: no

What bothers me is the line "Speed: Unkown!"

If I try to manually set the speed, I get an error:

root@blacklist:~# ethtool -s eth1 speed 1000
Cannot set new settings: Invalid argument
  not setting speed
root@blacklist:~#

Any ideas of what am I doing wrong and what to try?

Figured out the problem. I was trying to connect 10Gb port on the host to a 1Gb port on the device. This doesn't work and I didn't know that that.