Poor network performance and unable to set MTU above 1500 for RHEL 4 and 5 KVM guests

Solution Verified - Updated -


  • Not able to set network interface MTU above 1500 for KVM guests.
  • Getting following error when setting MTU for KVM guests.

    # ifconfig eth0 mtu 8963 
    SIOCSIFMTU: Invalid argument 
  • The network speed / performance of a RHEL 4 or 5 VM using kvm/libvirt is lower than expected.

  • A  kickstart of a RHEL 4.6 guest on RHEL 6.0 KVM suffers from very very  slow network performance during the Anaconda install.  The same guest  works fine with RHEL 5 and RHEL 6.


  • Red Hat Enterprise Linux (RHEL) 5 or 6 kvm/libvirt host
  • Red Hat Enterprise Linux 4 VM
  • Red Hat Enterprise Linux 5 (prior to update 4) VM

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