How to Choose IP Addresses for Your IxLoad Test

December 29, 2014 by Ixia Blog Team

IP addresses are the basic building block for any network test. You will need to configure some sort of IP address (static IP, DHCP, SLAAC etc.) before you run any test in IxLoad. All the examples given below assume you configure static IPs using the IP plug-in. However, the same applies to any other method of obtaining IP addresses.

Choosing IP addresses for an IxLoad test seems trivial: just pick any subnets that are appropriate for the network topology you want to test and hit the Run button. However, in order to obtain the best possible results from your devices and avoid certain validations that the product might throw, it is preferable that you keep certain rules of thumb in mind, which will be presented below.

Make sure the test IP addresses do not overlap with the control network

Each Ixia port has a network interface dedicated to the communication between the port and the control modules (the IxServer and/or IxLoad client). If you configure your test to use the same IP address as the administrative interface, some of the test traffic might end up on the interface between the port and the IxServer machine. This can cause the port to appear unresponsive and, depending your control network configuration, flood your control network.

For the Ixia hardware ports, the IP subnet used by the control interface is well known: Each port has the address 10.0.card.port (e.g., for the 3rd port of the card in slot 2). IxLoad will check the IP addresses used in your test, and will throw an error if it detects any IP overlapping with the control network.

For Ixia Virtual Ports, the IP address of the control network is obtained through DHCP and can have any value from the IPv4 space. IxLoad is not aware of this address and therefore cannot validate any duplication errors. In this case, the responsibility of checking the test IPs against the control network belongs to the user. The addresses assigned to the ports can be checked and/or customized through the Ixia Deployment Wizard.

Make sure you have unique MACs for all tests using the same switch

When configuring an IxLoad test running over Ethernet, you will have a MAC plug-in in the Network Settings. By default, the MAC addresses used for the test interfaces are automatically generated from the IP addresses by using a simple algorithm. So you only need to configure the IP addresses and you will have the MAC addresses as well.

Of course, this means that using duplicate IP addresses will lead to duplicate MACs. IxLoad will check for such situations and will not let the test run if it detects duplicate IPs.

However, such validations cannot be enforced when running multiple tests from different IxLoad clients. This means that if you run two IxLoad tests with the same MAC addresses and all the ports from those two tests are connected in the same switch, the switch might get confused and either flood the packets on all interfaces, or send packets from test A to the ports from test B. In IxLoad this translates to lost, out-of-order, or duplicate packets. This can happen either during session establishment, leading to failed sessions, or during the running of the test— in which case you will see the packets in the statistics.

There are several things you can do in order to avoid this behavior:

  1. Make sure you are the only one using the switch. This is the easiest solution, but it's not really feasible if the switch is the device under test.
  2. Use VLANs. This is a solution that requires additional configuration on the DUT, making it less attractive if you are at the beginning of the testing cycle.
  3. Use different IP addresses for each test. This will ensure that the MAC addresses will also be unique. However, this is not always possible, especially if you need to use a specific address.
  4. Configure your own MAC addresses. Go to the network configuration, on the MAC plug-in and uncheck the “Auto-generate MAC” option from all the ranges from your test. You will now be able to modify the MAC address and increment. Don't forget to do this for all Network Traffics.

As you can see, it is not always trivial to choose the IP addresses for your IxLoad test. We hope this blogpost has helped you understand the existing limitations. If you need more information, you can find technical details and step-by-step instructions for implementing these rules in your test by consulting the IxLoad User Guide.

Additional Resources


IxLoad User Guide