Measuring Forwarding Performance

Following the discussion about the various aspects of router performance, it is important to understand how to measure and test it. This is a significant part of evaluating a platform for a particular role within a deployed network. Consistent and universally accepted test methodologies should be observed for objective evaluations.

Most often, router performance is associated with its forwarding capabilities. Resource requirements can typically be addressed by increasing the router memory or selecting more powerful processors; however, the forwarding performance is generally limited by the platform design. For this reason, the focus of this section is on the best practices for measuring the IPv6 throughput of a router.

Regardless of the IP protocol type, forwarding performance testing is best performed in a black-box environment. The stimulus and the measurements are independent of the device tested and its architecture. RFC 2544 provides general guidelines and requirements for throughput testing:

• Throughput, as defined in RFC 1242, is measured as nondrop rate (NDR), the maximum traffic rate with no packet drop.

• The NDR should be determined in steps of 60 or fewer seconds and then verified by forwarding traffic for a minimum of a 60-second time interval at the determined NDR.

• Frame sizes tested should cover the set recommended for the various media types. In the case of Ethernet, for example, 64, 128, 256, 512, 1024, 1280, and 1518 bytes.

• Traffic should be bidirectional, unless otherwise specified.

Note

These recommendations are made to evaluate the performance of forwarding unicast traffic. However, it is also important to evaluate the forwarding performance of multicast traffic, too. This type of traffic will most likely be present in the IPv6 deployments. With multicast, the test options are multiple because there are various ways in which the router can replicate traffic. For this reason, it is best for the evaluation to be performed based on traffic patterns and requirements specific to the network role for which the router is evaluated.

Note

The larger IPv6 addresses require more intense lookups, and that can impact the router performance, as mentioned in the previous section. For this reason, it is more important to evaluate a router's forwarding performance for prefixes of various lengths in the /16 and /64 range in IPv6 than in IPv4.

All major test tool vendors provide RFC 2544based test suites that can be used to measure the NDR of devices under test (DUT). These suites can be executed with both IPv4 and IPv6 traffic. They are well suited to black-box testing, and they offer a certain level of consistency for this type of measurement.

Note

The test tool suites offer multiple tuning parameters, so it is important to be aware of their settings and ensure they meet the requirements of RFC 2544.

The test tools that form the shell around the DUT should be complemented with a few probes that acquire data from the DUT itself. Relevant data that should be collected during test includes memory utilization and integrity, CPU values at box or linecard level, and general system messages. Although throughput data in itself is important as far as a standalone router is concerned, sometimes NDR is obtained at 100 percent use of the CPU. From a network operation perspective, this is unacceptable because the router might have to totally neglect its control-plane to meet the measured NDR.

Note

Considering all the parameters that are being measured during the evaluation, it is always a good practice to define a baseline for the test environment that is being used.

The advantage of the black-box testing approach is that it allows for a consistent evaluation of forwarding performance of raw traffic as well as complex traffic that includes higher-layer content or extension headers. It also provides a good way to evaluate the impact on performance of advanced features (access lists, for example) enabled on the DUT. A black-box approach to testing allows for a clear one-to-one comparison of the results obtained in each of these cases. It also allows for meaningful comparisons between IPv4 and IPv6 throughput performance data.

Note

Note that the minimum packet size for IPv6 is larger than IPv4 (IPv6 header: 40 bytes; IPv4 header: 20 bytes). This is important when considering the low-packet-size performance data.

It is important to mention that there are also two different ways to look at the throughput performance of a router:

• Interface-to-interface throughput refers to measuring the NDR by sending bidirectional traffic through two same-type interfaces of the DUT.

• System throughput refers to measuring the NDR by sending bidirectional traffic through all interfaces of a router that is fully populated in terms of linecards and interfaces.

Both tests are conceptually similar, and they should observe the RFC 2544 recommendations.

It is generally expected that a router's IPv6 forwarding performance is similar to its IPv4 forwarding performance and as close as possible to the line rate of the tested interface.