Layer 4 switching: The magic combination

Network managers are turning more and more to Layer 4 switching to alleviate overloaded servers. What makes Layer 4 switching so special? It combines two proven technologies in a clever way.

In a traditional network configuration, each server has a unique IP address. In this situation, one server may be fully loaded while another server sits idly by simply because all of the users have targeted their server requests at the first available IP address. In this case, Layer 4 switching can help.

Layer 4 switches offer a powerful combination of Network Address Translation (NAT) with higher-layer address screening. In fact, the term "Layer 4 Switch" is really a misnomer: These products may make forwarding decisions based upon information at any OSI layer from 4 through 7, depending upon the particular product. In fact, some of the so-called "Layer 4 Switches" even monitor the state of individual sessions from beginning to end, just as firewalls do, in which case they're referred to as "session switches".

With so much functionality, Layer 4 switches can alleviate server load by balancing traffic across a cluster of servers based upon individual session information and status. Essentially, a Layer 4 switch is placed in front of cluster of servers running a particular application. When a client makes a request for that application, the switch determines which server should handle the request, often based upon current server loads. Once the forwarding decision is made, the switch binds that session to a particular server.

Of course, thanks to NAT running in the switch, the server cluster appears as a single server with a single IP address.

If you're trying to off-load processing from an overloaded server, consider Layer 4 switching as one possible approach. It's a technology that's proven itself over the past few years as a successful technique for balancing traffic among several servers. It's proven particularly valuable in high-volume network environments such as those commonly found in large corporate data centers or Internet Service Providers. The combination of NAT and higher-layer screening has turned Layer 4 switching into a formidable technology.

[What do you think of Layer 4 switching? Voice your opinion at www.nwfusion.com/forum/0208face.html]

Next week, we'll look at some different ways to balance traffic among servers in the cluster.

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