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 is 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.

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

  • Virtual Service on eth0: 192.168.10.10/24
  • Virtual Server: 192.168.10.12
  • Real Server on eth1: 10.10.10.10/24

With Subnet Originating Requests enabled, the Real Server sees traffic originating from 10.10.10.10 (LoadMaster eth1 address) and responds directly.

If Subnet Originating Requests is disabled, the Real Server sees traffic originating from 192.168.10.10 (the Virtual Service address) and responds directly. In some environments this can lead to asymmetric routing which is why we recommend enabling Subnet Originating Requests unless specified otherwise

When Subnet Originating Requests is enabled globally, it is automatically enabled on all Virtual Services.

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.