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Edge Devices Perform More Tasks Than Any Other Layer

October 29, 2014

Your edge devices play a critical role in your network management. While the muscle (or core) of your network does the heavy lifting – forwarding packets of data to other network layers – the edge houses crucial functions such as network security and content filtering. Whether in the LAN, WAN or data center, devices on the network edge require much greater performance capabilities.


The edge of your network simply requires more protocols and features, which means greater configuration. But configuring the right set of appliances and devices is a complex ordeal. Joel Snyder of BizTech recommends that you “switch where you can, [and] route where you must.”

The IT consultant with over 30 years’ experience believes that a good start to better network management is separating the user access component of your network from data center elements. These “zones,” as he calls them, have very different performance and reliability requirements. This clear separation gives you the ability to emphasize the purpose of a network when you are designing it. Using an edge device for each layer protects those different zones.

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Solving Problems With Edge Devices

An article on Network Computing details the many high-performance functions carried out by edge connectors and other devices. In the LAN edge, for example, implementing QoS policy here is critical. It’s implemented closest to the source. For instance, you should be protecting the network traffic at the edge, so implementing a QoS policy here is a recommended best practice.

On the other side of the equation is the edge of data center networks, where virtualization has made defining the edge here a little less black and white. But it is essentially a virtual access switch.

Orhan Ergun of Network Computing provides the following example, discussing Cisco’s FabricPath:

“While the FabricPath leaf layer is implemented at the aggregation layer, the spine might be at the core. While the spine only knows how to route at Layer 2 to the leaf switches, the leaf nodes can learn the addresses from both the classical Ethernet side and from the FabricPath core.”

Edge devices simply help you maintain the sanctity of a network by safeguarding against oversubscription and maintaining network fluidity and performance, whether in the LAN, WAN or data center.

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Heartbeats Packets Inside the Bypass TAP

If the inline security tool goes off-line, the TAP will bypass the tool and automatically keep the link flowing. The Bypass TAP does this by sending heartbeat packets to the inline security tool. As long as the inline security tool is on-line, the heartbeat packets will be returned to the TAP, and the link traffic will continue to flow through the inline security tool.

If the heartbeat packets are not returned to the TAP (indicating that the inline security tool has gone off-line), the TAP will automatically 'bypass' the inline security tool and keep the link traffic flowing. The TAP also removes the heartbeat packets before sending the network traffic back onto the critical link.

While the TAP is in bypass mode, it continues to send heartbeat packets out to the inline security tool so that once the tool is back on-line, it will begin returning the heartbeat packets back to the TAP indicating that the tool is ready to go back to work. The TAP will then direct the network traffic back through the inline security tool along with the heartbeat packets placing the tool back inline.

Some of you may have noticed a flaw in the logic behind this solution!  You say, “What if the TAP should fail because it is also in-line? Then the link will also fail!” The TAP would now be considered a point of failure. That is a good catch – but in our blog on Bypass vs. Failsafe, I explained that if a TAP were to fail or lose power, it must provide failsafe protection to the link it is attached to. So our network TAP will go into Failsafe mode keeping the link flowing.

Glossary

  1. Single point of failure: a risk to an IT network if one part of the system brings down a larger part of the entire system.

  2. Heartbeat packet: a soft detection technology that monitors the health of inline appliances. Read the heartbeat packet blog here.

  3. Critical link: the connection between two or more network devices or appliances that if the connection fails then the network is disrupted.

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