CentOS 6 And Super Jumbo Frames

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CentOS 5 Comments

Hi,

Has anyone using CentOS 6 been able to successfully set an mtu larger than 9710
on an interface.

I am seeing super jumbo frames with length > 10000.
… IP 10.79.4.53.64327 > 10.79.2.53.24294: Flags [.], seq 16060:29200, ack 1, win 32767, length 13140
…

CentOS release 6.7 (Final)

Thanks,

5 thoughts on - CentOS 6 And Super Jumbo Frames

  • Maximum frame size varies from implementation to implementation:
    http://pages.uoregon.edu/joe/jumbo-clean-gear.html

    It’s also worth noting that that due to offloading features in modern NICs, there’s often very little benefit to large frames. Since you
    *really* need all of the devices on any network segment to use the same MTU, the best option might be to eliminate jumbo frames (and test the impact of doing so in terms of throughput and CPU utilization).

  • Hi Gordon,

    Thanks for the response.

    The real issue relates to doing pcap on an interface that is hooked to a span port. The super jumbo frames cause rx_long_length_errors: 2701813
    which show up in our monitoring software and the customer thinks there are error on his network.

    So I wanted to increase the mtu on the interface so these errors would not be reported.

  • Well, ifconfig can be used to set the MTU. The maximum size may depend on the hardware and driver that you’re using.

  • 9K or so is the upper limit for MTU on most NIC cards, and many are less than that. this is a hardware thing, has nothign to do with software.