Showing results for 
Search instead for 
Did you mean: 

Disable LRO on UCS / UC Application deployments






    Large Receive Offload (LRO) is a technique for increasing inbound throughput of high-bandwidth network connections by reducing CPU overhead. It works by aggregating multiple incoming packets from a single stream into a larger buffer before they are passed higher up the networking stack, thus reducing the number of packets that have to be processed. This however has a negative impact on Realtime applications like the Unified Communications suite.

    It's therefore considered a requirement to disable LRO setting for UCS deployments running virtualized UC applications.

    LRO Settings enabled usually lead to TCP perfomance problems and odd behaviours. A few example the common problems identified by CISCO TAC include:

    • SDL Links Out of Service.
    • Phones unregistering due to Keepalive timeout and network connectivity problems.
    • DRF Backup failing due to TCP packets out of order, and slow transfer rate to the SFTP server.
    • CTI Manager problems due to messages out of sequence impacting UCCX, Attendant Console and 3rd party applications.

    Recommended Procedure ESXi 4.1 ESXi 5.0

    Follow below mentioned steps to make the changes pertaining to LRO settings on ESXi 4.1 or ESXi 5.0

    Login directly to ESXi Host or vCenter server in case ESXi host is being managed by a vCenter





    Click on the Configuration tab and then Click on Advanced Settings. Advanced Settings dialog will popup.



    In the Advanced Settings dialog, choose the 'Net' Settings and scroll down until LRO related options are reached.

    Change the following 5 parameters from 1 to 0

    • Net.VmxnetSwLROSL
    • Net.Vmxnet3SwLRO
    • Net.Vmxnet3HwLRO
    • Net.Vmxnet2SwLRO
    • Net.Vmxnet2HwLRO


    Recommended Procedure ESXi 4.0

    In ESXi 4.0 there's no support for SSH access to the ESXi Server. Commands needs to be run from the Console of the server via Physical Access, IP KVM or CIMC KVM.
    esxcfg-nics -l
    Then disable LRO for each NIC:
    ethtool -K <ethx> lro off
    Please note this change is not persistent upon reboot. For it to persist you will need to add the ethtool command to a startup script.


    Additional References


    This issue is documented under This Knowledge Base Articule . Currently the UC REL is not able to change the LRO setting through the vmnet drivers therefore the changed need to be performed on the host itself.

    Not applicable

    Just want to clarify that when having ESXi 4.0, this procedure needs to be done via CLI-SSH.

    In when you have to Disable LRO and when you don't

    Cisco Employee

    Actually, for ESX 4.0, LRO need to be disabled on Guest VMs, not on ESX itself.


    Test: Adding comment regarding document....testing

    Depending on the version of your UC application, disabling of LRO may not be required. Please see this DocWiki for reference:


    Would I need to apply these settings within VMware 6.0?

    Clifford Aldan
    Cisco Employee

    According to the document,

    "Disable LRO if on ESX 4.1 and app version < 8.6.

    Otherwise disable LRO is optional. If you experience FTP/TCP latency, then disable LRO."

    Clifford Aldan
    Cisco Employee

    Disabling LRO only applies if you have voice apps running on ESX/ESXi 4.1 

    "VMware vSphere ESXi 4.1 introduced a new setting called "Large Receive Offload (LRO)". When enabled on VMs running ESXi 4.1 or later, you may experience slow TCP performance on certain operating systems (depending on which Collaboration application and version). This setting usually needs to be disabled on an ESXi host running Collaboration app VMs (either new install of ESXi 4.1+, or upgrade from ESXi 4.0 to 4.1+ followed by upgrading VMwareTools in app VMs to 4.1+)."