Enable Subnet Originating Requests Globally

It is best practice to enable the Subnet Originating Requests option globally.

In a one-armed setup (where the Virtual Service and Real Servers are on the same network/subnet), Subnet Originating Requests are usually not needed. However, enabling Subnet Originating Requests should not affect the routing in a one-armed setup.

In a two-armed setup where the Virtual Service is on network/subnet A, for example, and the Real Servers are on network B, Subnet Originating Requests should be enabled on LoadMasters with firmware version 7.1-16 and above.

Because this application can run at Layer 4, transparency is enforced. Transparency takes a higher priority than Subnet Originating Requests. Therefore, if transparency is enabled on the Virtual Service and Subnet Originating Requests is enabled globally, the Virtual Service still uses transparency. The Real Server sees traffic from this virtual service originating with the client’s source IP address (transparency). See the Transparency Feature Description on the documentation page for more details.

In the diagram above, you can see the following details:

  • Client: 10.0.0.100/24
  • Virtual Service on eth0: 10.0.0.15/24
  • Real Server on eth1: 10.20.20.25/24

With Subnet Originating Requests enabled, the Real Server sees traffic originating from 10.20.20.21 (LoadMaster eth1 address) and responds correctly.

With Subnet Originating Requests disabled, the Real Server sees traffic originating from 10.0.0.15 (LoadMaster Virtual Service address on eth0) and responds to eth0 causing asymmetric routing.

When Subnet Originating Requests is enabled globally, it is automatically enabled on all Virtual Services. If the Subnet Originating Requests option is disabled globally, you can choose whether or not to enable Subnet Originating Requests on a per-Virtual Service basis.

To enable Subnet Originating Requests globally, follow the steps below:

  1. In the main menu of the LoadMaster Web User Interface (WUI), go to System Configuration > Miscellaneous Options > Network Options.
  2. Select the Subnet Originating Requests check box.