How DSR load balancing works - BlueCat DNS Edge

DNS Edge Deployment Guide

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BlueCat DNS Edge

Direct server return (DSR) is a method of load balancing that allows traffic returning from a load-balanced server to be routed asymmetrically, skipping the load balancer and traveling back to clients through the server’s default gateway (or through static routes, if required). This method is common in high-volume sites where offloading the task of routing return traffic back through the load balancers allows the load balancer to be used strictly for load distribution.

  1. The client sends a DNS query to VIP on the public side of the load balancer.
  2. Load balancing by layer 2 address: The load balancer distributes load to service points using MAC addresses.
    Note: The MAC address changes depending on which server is handling a particular request.
  3. Replies from the service points are routed out through the system's default gateway, or by static routes, if necessary.
  4. The client receives the DNS reply, with the source IP and other associated socket parameters of the original query as if the load balancer had replied.