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From Dag Sonstebo <>
Subject Re: VMs Connection break under two isolate network
Date Fri, 22 Feb 2019 09:26:25 GMT
Hi Haijiao,

We've come across similar things in the past. In short - what is your XenServer bond mode?
Is it active-active (mode 7) or LACP (mode 4)? (see

In short if your switches don't keep up with MAC address changes on the XS hosts then you
will get traffic flapping with intermittent loss of connectivity (root cause is a MAC address
moves to another uplink, but the switch only checks for changes every X seconds so it takes
a while for it to catch up). LACP mode 4 has a much more robust mechanism for this but obviously
needs configured both XS and switch end. Normal active-active (mode 7) seems to always cause

My general advise would be to simplify and just go active-passive (mode 1) - unless you really
need the bandwidth this gives you a much more stable network backend.

Dag Sonstebo
Cloud Architect

On 22/02/2019, 07:14, "Haijiao" <> wrote:

    Hi, Devs and Community Users
    To be more specific,  our environment is built with 
    * 2 Dell R740XD Servers + Dell Compellent Storage w/ iSCSI
    * Each server equiped with two Mellanox Connect-4 LX 25GbE network adapters, and configured
with bond mode(active+active) in XenServer
    * CloudStack 4.11.2 LTS + XenServer 7.1CU2(LTS) Enterprise
    Everything goes fine with shared network, but the weird thing is if we setup 2 isolated
networks,  try to use 'iperf',  'wget' or 'SCP' to test the network performance betwen two
VMs located in these 2 isolated networks,  the traffic will drop to zero in about 200-300
seconds,  even though we were still able to ping or SSH VM B1 from A1 or verse. 
    VM A1 ---> VR A(Isloated Network A) ----> VR B(Isolated Network B)  ----> VM
    We have checked the configuration on switches, upgraded Mellanox driver for XenServer,
 but no luck. 
    Meanwhile, we can not re-produce this issue in another environment (XenServer 7.1CU2+ACS
4.11.2+ Intel Gb network). 
     It seems it might be related to Mellanox adapter, but we have no idea what part we could
possibly miss in this case. 
    Any advice would be highly appreciated !   Thank you !
    在2019年02月22 13时09分, "gu haven"<>写道:
    hi ,all 
          I try iperf wget scp connection will break after 200 seconds ,Do  need any optimization
in vr ?
    environment infomation below:        
    cloudstack 4.11.2
    xenserver 7.1 CU2 Enterprise
    NIC :MLNX 25GbE 2P ConnectX4LX 
    bond mode in xenserver : acitce-active
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