Visibility Solutions

Garland Technology is committed to educating the benefits of having a strong foundation of network visibility and access. By providing this insight we protect the security of data across your network and beyond.

Resources

Garland Technology's resource library offers free use of white papers, eBooks, use cases, infographics, data sheets, video demos and more.

Blog

The TAP into Technology blog provides the latest news and insights on network access and visibility, including: network security, network monitoring and appliance connectivity and guest blogs from Industry experts and technology partners

Partners

Our extensive technology partnership ecosystem solves critical problems when it comes to network security, monitoring, application analysis, forensics and packet inspection.

Company

Garland Technology is dedicated to high standards in quality and reliability, while delivering the greatest economical solutions for enterprise, service providers, and government agencies worldwide.

Contact

Whether you are ready to make a network TAP your foundation of visibility or just have questions, please contact us. Ask us about the Garland Difference!

Blogheader image.png

TAP Into Technology

Leading the Way in Network Technology

Network TAP vs SPAN Port: Putting Them to the Test

Posted by Chris Greer | 4/27/17 8:08 AM

For years now we all have read about the difference between data capture off a span/mirror port and an inline network TAP. In fact, many of those comments have come from one of the great moderators of lovemytool.com, Tim O'Neill, the @OldCommGuy who loves the TAP side of the ring.

Packet Pioneer was interested to see the difference between a data stream captured on a network TAP versus a SPAN port. So they set up a test with a few PCs, a TAP, a SPAN port, a couple of hardware network analyzers, and a healthy stream of data.

The results were interesting, to say the least: The study showed that Tim O’Neill is correct!

TAP vs. SPAN Test Setup

Packet Pioneer connected two PCs to a basic Cisco Catalyst Switch at 100Mbps. A throughput test using iPerf was configured and run between the two machines. On one of the PCs, they placed a 100Mbps TAP, and placed a hardware analyzer on it to capture. Lastly, they configured a SPAN on the switch to forward all traffic to and from this port to another hardware analyzer.
Below is a basic drawing of the setup.

TAP-vs-SPAN

 

Download TAP vs SPAN now!

Results

The throughput test finished with a result of 93.1Mbps sustained for 10 seconds between the two PCs.

Tap Capture Results
Packets captured: 133,126
Delta Time at TCP Setup: 243uSec

SPAN Capture Results
Packets captured: 125,221
Delta time of TCP connection setup: 221 uSec

Conclusion

The SPAN data capture showed almost 8,000 packets missing from the trace. This represents almost 8% of the total packets captured by the analyzer on the network TAP. We should also point out that this was on a 100Mbps interface, not a Gigabit interface, and there were no errored frames. The switch bus was not in a near overloaded state.

Also, the difference in the timing between the TCP SYN and SYN ACK in the two traces shows us that the switch is not treating both the SPAN and Destination ports the same. In fact, it was forwarding traffic to the SPAN port faster than the true destination. While the difference is only 21 uSec, it shows that the switch is affected when SPAN is enabled. It is not as seamless as it would appear, and this delay was under no load test. With the switch loaded with traffic, the losses and timing will show greater differential and also dropped packets.

Considering the results of their test, Chris Greer, a network analyst at Packet Pioneer, said, “I am now a full believer in using a real [network] TAP whenever possible, especially when timing and total view of the data is important!”


If you want to learn more about Real Network Visualtion Consideration for Professionals, download our free white paper, TAP vs SPAN.

Topics: Network TAPs, TAPs vs SPAN, Network Security

Written by Chris Greer

Chris focuses on assisting IT professionals in resolving the root cause of network and application performance problems. This is primarily done through use of a protocol analyzer reading and interpreting trace files. Additionally, I teach courses in network analysis and troubleshooting, Wireshark, and several vendor analysis products. Chris supports clients in several regions of the USA, Latin America, and Caribbean.