I have 4-ports Intel 82571EB Gigabit adapter. It uses e1000e driver. The test machine is running Ubuntu 9.10, clients 9.10/10.04. I tried link aggregation (mode 4) and adaptive load balancing (mode 6). The setup is as follows:

server == 4-port NIC == 4 cat6 cables == Linksys SRW2024 switch == 4 or more clients.

I am testing with iperf and TCP. For mode 4 I setup a LAG in the switch. For mode 6 - no. My tests are:

4 or more clients, all of which have 1 Gbps connections are iperf clients. They run simultaneously. The server already listens for these connections (I had iperf -s running there). The results are the same as the server is running 1 Gbps only and not 4 Gbps combined. If I use one client I get 1 Gbps. If I have 4 or 8 clients the bandwidth per client goes down to 250 or 125 Mbps (these numbers are for illustration purposes only).

Why I can't get 4 Gbps to and out of the server? How I can fix it?

  • 1
    Look at the arp tables in all of the devices.
    – dbasnett
    Jul 11, 2011 at 14:22
  • Seems to work at geekomatic.ch/2010/08/09/1281357060000.html
    – Paul
    Jul 11, 2011 at 14:35
  • In the link the server and the switch were both running LACP. Not clear if that is what the OP is doing.
    – dbasnett
    Jul 11, 2011 at 14:59
  • @dbasnett - your first comment was the key. I needed to do ifdown on the respective interfaces to clean it up for sure. It took a bit of playing on the server side. Please add it as an answer so I could mark it as correct one. Thanks!
    – grs
    Jul 12, 2011 at 20:31

2 Answers 2


Load balancing across links in a port aggregation group is not done strictly per frame. The switch and the server both use a methodology taking some combination of source mac address, destination mac address, source and/or destination tcp or udp port, etc. into account to prevent out of order packet delivery for a single session.

You might find you'll see the performance you expect if your run multiple iperf sessions on different listening ports with each client connection to a different session...depending on the load balancing methods being employed.


I remember reading somewhere about bonding that it does not scales linearly, so with 4x 1Gbps NICs you should see something around 2.5-2.8 Gbps. If i find the source I'll update my answer.

  • Not usually. I've got systems with 4x NICs that can push 3.2Gbps+ throughput (which is the expected throughput with ~20% overhead).
    – Chris S
    Jul 28, 2011 at 2:53

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