DSR — The pros and cons of using Direct Server Return for application delivery

A customer was having challenges deploying load balancers in their Cisco ACI environment. So we set to work finding a solution.

For the uninitiated, layer 4 DR mode is a high performance load balancing method available on our appliances. It works by having all response traffic flow from the servers straight back to the clients.

Direct server return, direct routing - no matter what you call it, using DSR maximises the throughput of return traffic and allows for near endless scalability. Here's why we still love it.

For the uninitiated, Direct Server Return is a clever trick which entails directly routing packets to the chosen real server.

Direct Server Return (DSR) is my favorite way to load balance application servers because it’s simple, transparent, and super fast.

L3 DSR is an alternative technique to achieve direct server return at Layer 3. Instead of using an IPIP tunnel like LVS-TUN it changes the destination IP address like LVS-NAT when sending the traffic to the real server.

LVS-DR and LVS-TUN are both forms of Direct Server Return where the load balancer only has to deal with one half of the connection.

Microsoft Print Server provides a great way to share printers throughout your organisation, but when the print server falls over, the phone quickly starts to ring.

One of the (many) traditional problems with load balancing is the requirement to change your infrastructure in order to implement a hardware load balancer.

Direct Routing aka. Direct Server Return (DSR) aka. N-Path is a great load balancing method. And it is, without doubt, the fastest method possible.