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Benchmarking at Ultra-Low Latency

Since we started shipping the Nexus 3548 with AlgoBoost to our customers in the beginning of November, there has been more and more interest in testing and verifying the switch’s latency in different traffic scenarios. What we have found so far is while network engineers might be well experienced in testing the throughput capabilities of a switch, verifying the latency can be challenging, especially when latency is measured in the tens and low hundreds of nanoseconds!
I discussed this topic briefly when doing a hands-on demo for TechWise TV a short time ago.

The goal of this post is to give an overview of the most common latency tests, how the Nexus 3548 performs in those tests, and to detail some subtleties of low latency testing for multicast traffic. This post will also address some confusion we’ve heard some vendors try to emphasize with the two source multicast tests.

Unicast Traffic

The most common test case is to verify throughput and latency when sending unicast traffic. RFC 2544 provides a standard for this test case. The most stressful version of the RFC 2544 test uses 64-byte packets in a full mesh, at 100 percent line rate. Full mesh means that all ports send traffic at the configured rate to all other ports in a full mesh pattern.

Figure 1 – Full Mesh traffic pattern

The following graph shows the Nexus 3548 latency results for Layer 3 RFC 2544 full mesh unicast test, with the Nexus 3548 operating in warp mode.

Figure 2 -- Layer 3 RFC 2544 full mesh unicast test

We can see that the Nexus 3548 consistently forwards packets of all sizes under 200 nanoseconds at 50% load, and less than 240 nanoseconds at 100% load.

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