TFTP Load Balancing with Citrix NetScaler

To load balance TFTP via NetScaler you first need to create servers, services, monitors and a Load Balanced vServer.

DHCP is configured with options 66/67. Option 66 sends clients to the VIP of the Load Balanced vServer. The Load Balanced vServer contains services for each PVS (Provisioning Services) server in the environment and this way it can load balance boot connections out to each TFTP PVS server.

So within NetScaler we have server objects referencing our PVS servers. TFTP load balanced services with TFTP monitors attached and a load balanced vServer that VMs will contact to retrieve their boot information.

To begin: (I’m using NetScaler VPX 1000 v11 build 64.34)

Make sure you have enabled Load Balancing then navigate to Traffic Management -> Load Balancing -> Servers.

1-min

Click Add.2-min

Enter the name and IP address of your first PVS server and click OK.3-min

Repeat the process for any remaining PVS servers so that you have server objects for each PVS server in your environment.4-min

Navigate to Traffic Management -> Load Balancing -> Add.5-min

Specify a name for your monitor and under Type select USER.6-min

Over on the Special Parameters tab under Script Name select nstftp.pl. Click Create.7-min

Create monitors for your remaining PVS servers.8-min

Once done the monitors you have created will appear in the Monitors view.9-min

Navigate to Traffic Management -> Load Balancing -> Services -> Add.10-min

Give your service a name. Point to an existing PVS server, set the protocol to TFTP, port to 69 and click OK.

11-min

Click 1 Service to Load Balancing Monitor Binding.12-min

Click Add Binding.13-min

Click Click to select.14-min

Attach the relevant monitor. I am creating a service for PVS01 so I will attach the PVS01 monitor I created earlier to this service.15-min

Click Select.16-min

Click Bind.17-min

The TFTP monitor probed PVS01 over UDP port 69 and the probe succeeded as shown below. Click Close.18-min

Click Done.19-min

Repeat the process of creating a service for your remaining PVS servers. Specifying a name, linking to the appropriate PVS server and specifying the protocol and port.20-min

Click 1 Service to Load Balancing Monitor Binding.

21-min

Click Add Binding.22-min

Click Click to select.23-min

Choose the appropriate monitor. This service creation is for PVS02 so the monitor being attached will be for PVS02.24-min

Clic Select.25-min

Click Bind.26-min

The probe also succeeded for PVS02. Click Close.27-min

Click Done.28-min

Both my services now appear in view and are online. 29-min

Navigate to Traffic Management -> Load Balancing -> Virtual Servers -> Add.30-min

Enter a name for your vServer. Select TFTP as the protocol, enter an IP address (VIP) and set the port as 69. Click OK.

31-min

The next step requires us to bind load balanced services to our vServer. Click on No Load Balancing Virtual Server Service Binding.32-min

Click Click to select.33-min

Check boxes beside all the PVS services that we created earlier.34-min

Click Select.35-min

Click Bind.36-min

Click Continue.37-min

Click on the Method box to expand it out to the middle viewing pane.38-min

Under Load Balancing Method I have selected ROUNDROBIN. This is because I want to run a few tests later to prove Load Balancing is working and it is just as easy to use Round Robin for this. By default the persistence method is Least Connection which you in a production environment would use. Click OK.39-min

Click Done.40-min

The vServer appears in the up state.

41-min

Save your running configuration.42-min

Now over on your DHCP server specify the newly created vServer VIP address under DHCP option 66 and ARDBP32.BIN under DHCP option 67.43-min

With both PVS servers online (PVS01 / PVS02) lets boot PVSVM01 (Target Device) and see what happens.44-min

In this first boot instance PVSVM01 boots from PVS01 (192.168.0.170).45-min

The second boot attempt boots from PVS02 (192.168.0.171).46-min

On PVS01 I’ve stopped the Citrix PVS TFTP service.47-min

The PVS TFTP monitor over on NetScaler detects the service is down and marks PVS01 as down. This confirms the monitor is working.48-min

Now PVS01 has been completely shut down.49-min

PVSVM01 has been booted up again, it contacts PVS02.50-min

On the second boot it also contacts PVS02 proving that NetScaler isn’t going to send us to an offline PVS server.51-min


8 Comments

  • Marcel Strohmeyer

    June 13, 2016

    hello nice instruction, but i have to loadbalance the UDP 6910 Port to get this work
    PVS 7.9

    Reply
  • Brian Masias

    August 22, 2016

    At the top of the article can you explain what version you are using of NetScaler
    We have 11515 SDX’s running 11.1.47.14.
    We are using PVS 7.9.

    Thanks,
    B

    Reply
    • George Spiers

      August 22, 2016

      I was using NetScaler VPX 1000 v11 build 64.34. Are you experiencing difficulties?

      Reply
      • Brian

        August 22, 2016

        No not as of yet but I will know soon.
        Thanks,
        B

        Reply
  • Michael Rebmann

    February 8, 2017

    Did you use Source IP in the service group? If no I assume that the streaming traffic would go over the Netscaler.

    If I use Source IP then it cannot download the bootstrap file. If I don’t use it then the server can download the bootstrap, but runs in a “Login request timed out”.

    Any ideas? I just load balance port 69 for tftp, nothing else.

    Reply
    • George Spiers

      February 8, 2017

      Are you referring to a Service Group on NetScaler? The Service Group contains the services for each PVS server. You then attach the Service Group to an LB vServer, and DHCP options 66 points at the LB vServer VIP. The Service Group uses protocol TFTP and the bound services listen on port 69.

      Reply
  • Steven K.

    April 27, 2017

    Netscaler is behind “internal” firewall. Would you know if TFTP communication between “TFTP-LB-PVS-vServer” and endpoints occurs on NSIP or SNIP?

    Reply
    • George Spiers

      April 27, 2017

      It occurs over the SNIP.

      Reply

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