Application Delivery Controllers the Swiss Army Knife

The Application Delivery Controller continues to increase market share in the enterprise networking space, but I’m not sure everyone understands the value of this device, and why this network component has become an important part of the enterprise.


The most common task of an ADC is load balancing, and not that long ago most of these devices were called load balancers, but these devices evolved into ADC’s.  I’ve always tried to correct people when they call the Netscaler a Load Balancer, because this doesn’t do it justice, the Netscaler is like my swiss army knife, where it has many functions and I can solve many architecture challenges.

The fundamental different between ADC’s and other network devices like firewalls/routers and switches is the ADC is a proxy, and therefore terminates TCP and UDP connections, and creates new connections between the proxy and resource.  It is this fundamental difference that gives the device so much power

and flexibility over other network devices that are generally just routing or switching packets.

Here is a list of feature that most ADC’s will have

  • Load Balancing
  • SSL Offloading
  • Caching/Compression
  • TCP Multiplexing
  • Authentication
  • Authorization
  • Auditing
  • Routing
  • Switching
  • Content Switching
  • Application Firewall
  • DNS
  • Global Server Load Balancing
  • Many HTTP features

As HTTP has become the protocol of choice for some many applications today, the ADC’s has become the master of controlling, manipulating and transforming the HTTP protocol.

The placement of the ADC is commonly placed between the user’s and the server’s, so it is common to have this device in the data center network to control application delivery.  It is also common to have this device in the DMZ to be used as a reverse proxy between the internet and data center network.  It is also becoming popular to use the ADC in the data center network between internally data center services, for example front end web server’s and the database.

I believe the ADC will become an essential component in the enterprise.  Software Defined Network (SDN) will enable these devices to be easily architectured into the network, especially with the emerging technologies like Network Services Header (NSH) that will enable service chaining.


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