I'm looking to use auto-negotiation and send Ethernet pause frames across a connection between an Intel X520 NIC and a Stratix IV FPGA using a 10G direct attach copper SFP. Ethtool is telling me that these functions are not supported, and when I try to set them with 'ethtool -A eth2 autoneg on rx on tx on', nothing changes. Intel's webpage says that these functions should be supported for the X520 family. The network driver is ixgbe 3.9.15-k, which supports auto-negotiation and flow control by default. Also, I thought auto-negotiation had to be supported for any 1G/10G connections, as an IEEE standard. Is the problem a compatibility issue, or is there a configuration I'm missing?

Output from ethtool eth2:

Settings for eth2:
        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: No
        Advertised auto-negotiation: No
        Speed: 10000Mb/s
        Duplex: Full
        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: yes

Output from end of dmesg:

ixgbe 0000:04:00.0: eth2: detected SFP+: 3
ixgbe 0000:04:00.0: eth2: NIC Link is Up 10 Gbps, Flow Control: RX/TX
ADDRCONF(NETDEV_CHANGE): eth2: link becomes ready
eth2: no IPv6 routers present
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1 Answer 1


I'm not sure about the IEEE standard, but Avaya switches only support autonegotiation for 10/100/1000 Mpbs. Autonegotiation isn't supported for 10 Gig connections.

This guy breaks it down a little bit. http://networkn3rd.wordpress.com/2013/04/15/10g-auto-negotiation/

  • Thanks, it looks like I misunderstood how the auto-negotiation is used. The problem remains with the flow control, though. I definitely need the device to support receiving ethernet pause frames, and I think that can happen without auto-negotiation for this connection.
    – James
    Jun 19, 2014 at 17:57
  • I'm not sure why ethtool says pause frames are unsupported when your link says flow control is enabled. What does your switch say when the link is up? Have you done a packet capture to see if you're sending or receiving pause frames? Jun 22, 2014 at 15:06

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