A highly redundant Application Delivery Controller Setup with KempTechnologies


The goal was to make sure the KempTechnologies LoadMaster Application Delivery Controller was capable to handle the traffic to all load balanced virtual machines in a high volume data and compute environment. Needless to say the solution had to be highly available.

A highly redundant Application Delivery Controller Setup with KempTechnologies

The environment offers rack and row as failure units in power, networking and compute. Hyper-V clusters nodes are spread across racks in different rows. Networking is high to continuously available allowing for planned and unplanned maintenance as well as failure of switches. All racks have redundant PDUs that are remotely managed over Ethernet. There is a separate out of band network with remote access.

The 2 Kemp LoadMasters are mounted a different row and different rack to spread the risk and maintain high availability. Eth0 & Eth2 are in active passive bond for a redundant management interface, eth1 is used to provide a secondary backup link for HA. These use the switch independent redundant switches of the rack that also uplink (VLT) to the Force10 switches (spread across racks and rows themselves). The two 10GBps ports are in an active-passive bond to trunked ports of the two redundant switch independent 10 Gbps switches in the rack. So we also have protection against port or cable failures.


Some tips: Use TRUNK for the port mode, not general with DELL switches.

This design allows gives us a lot of capabilities.We have redundant networking for all networks. We have an active-passive LoadMasters which means:

  • Failover when the active on fails
  • Non service interrupting firmware upgrades
  • The rack is the failure domain. As each rack is in a different row we also mitigate “localized” issues (power, maintenance affecting the rack, …)

Combine this with the fact that these are bare metal LoadMasters (DELL R320 with iDRAC –  see Remote Access to the KEMP R320 LoadMaster (DELL) via DRAC Adds Value) we have out of band management even when we have network issues. The racks are provisioned with PDU that are managed over Ethernet so we can even cut the power remotely if needed to resolve issues.


The results are very good and we get “zero ping loss” failover between the LoadMaster Nodes during testing.

We have a solid, redundant Application Deliver Controller deployment that does not break the switch independent TOR setup that exists in all racks/rows. It’s active passive on the controller level and active-passive at the network (bonding) level. If that is an issue the TOR switches should be configured as MLAGs. That would enable LACP for the bonded interfaces. At the LoadMaster level these could be configured as a cluster to get an active-active setup, if some of the restrictions this imposes are not a concern to your environment.

Important Note:

Some high end switches such as the Force10 Series with VLT support attaching single homes devices (devices not attached to both members on an VLT). While VLT and MLAG are very similar MLAGs come with their own needs & restrictions. Not all switches that support MLAG can handle single homed devices. The obvious solution is no to attach single homed devices but that is not always a possibility with certain devices. That means other solutions are need which could lead to a significant rise in needed switches defeating the economics of affordable redundant TOR networking (cost of switches, power, rack space, operations, …) or by leveraging MSTP and configuring a dedicates MSTP network for a VLAN which also might not always be possible / feasible so solve the issue. Those single homed devices might very well need to be the same VLANs as the dual homed ones. Stacking would also solve the above issue as the MLAG restrictions do not apply. I do not like stacking however as it breaks the switch independent redundant network design; even during planned maintenance as a firmware upgrade brings down the entire stack.

One thing that is missing is the ability to fail over when the network fails. There is no concept of a “protected” network. This could help try mitigate issues where when a virtual service is down due to network issues the LoadMaster could try and fail over to see if we have more success on the other node. For certain scenarios this could prevent long periods of down time.

Windows Server 2012 NIC Teaming Mode “Independent” Offers Great Value

There, I said it. In switching, just like in real life, being independent often beats the alternatives. In switching that would mean stacking. Windows Server 2012 NIC teaming in Independent mode, active-active mode makes this possible. And if you do want or need stacking for link aggregation (i.e. more bandwidth) you might go the extra mile and opt for  vPC (Virtual Port Channel a la CISCO) or VTL (Virtual Link Trunking a la Force10 – DELL).

What, have you gone nuts? Nope. Windows Server 2012 NIC teaming gives us great redundancy with even cheaper 10Gbps switches.

What I hate about stacking is that during a firmware upgrade they go down, no redundancy there. Also on the cheaper switches it often costs a lot of 10Gbps ports (no dedicated stacking ports). The only way to work around this is by designing your infrastructure so you can evacuate the nodes in that rack so when the stack is upgraded it doesn’t affect the services. That’s nice if you can do this but also rather labor intensive. If you can’t evacuate a rack (which has effectively become your “unit of upgrade”) and you can’t afford the vPort of VTL kind of redundant switch configuration you might be better of running your 10Gbps switches independently and leverage Windows Server 2012 NIC teaming in a switch independent mode in active active. The only reason no to so would be the need for bandwidth aggregation in all possible scenarios that only LACP/Static Teaming can provide but in that case I really prefer vPC or VLT.

Independent 10Gbps Switches


  • Cheaper 10Gbps switches
  • No potential loss of 10Gbps ports for stacking
  • Switch redundancy in all scenarios if clusters networking set up correctly
  • Switch configuration is very simple


  • You won’t get > 10 Gbps aggregated bandwidth in any possible NIC teaming scenario

Stacked 10Gbps Switches


  • Stacking is available with cheaper 10Gbps switches (often a an 10Gbps port cost)
  • Switch redundancy (but not during firmware upgrades)
  • Get 20Gbps aggregated bandwidth in any scenario


  • Potential loss of 10Gbps ports
  • Firmware upgrades bring down the stack
  • Potentially more ‘”complex” switch configuration

vPC or VLT 10Gbps Switches


  • 100% Switch redundancy
  • Get > 10Gbps aggregated bandwidth in any possible NIC team scenario


  • More expensive switches
  • More ‘”complex” switch configuration

So all in all, if you come to the conclusion that 10Gbps is a big pipe that will serve your needs and aggregation of those via teaming is not needed you might be better off with cheaper 10Gbps leverage Windows Server 2012 NIC teaming in a switch independent mode in active active configuration. You optimize 10Gbps port count as well. It’s cheap, it reduces complexity and it doesn’t stop you from leveraging Multichannel/RDMA.

So right now I’m either in favor of switch independent 10Gbps networking or I go full out for a vPC (Virtual Port Channel a la CISCO) or VTL (Virtual Link Trunking a la Force10 – DELL) like setup and forgo stacking all together. As said if you’re willing/capable of evacuating all the nodes on a stack/rack you can work around the drawback. The colors in the racks indicate the same clusters. That’s not always possible and while it sounds like a great idea, I’m not convinced.


When the shit hits the fan … you need as little to worry about as possible. And yes I know firmware upgrades are supposed to be easy and planned events. But then there is reality and sometimes it bites, especially when you cannot evacuate the workload until you’re resolved a networking issue with a firmware upgrade Confused smile Choose your poison wisely.