DNS Load Balancing: Mapping One Domain to Multiple IPs and Resolution Strategies

DNS load balancing allows a single domain name to resolve to multiple IP addresses, distributing traffic across several servers.

Multiple IPs for a Domain

In theory a domain can map to several IPs; DNS records can be added so that different users receive different IPs when they resolve the domain.

For example, the domain www.itmtx.cn can be pointed to three IPs (1.1.1.1, 2.2.2.2, 3.3.3.3) by creating three A records:

www.itmtx.cn IN A 114.100.20.201;

www.itmtx.cn IN A 114.100.20.202;

www.itmtx.cn IN A 114.100.20.203;

When users in different locations query the domain, DNS returns an IP according to the configured resolution policy, achieving load distribution and higher availability.

DNS Resolution Strategies

Common DNS strategies include:

Round Robin : returns IPs in order to rotate requests.

Weighted : assigns weights to IPs, selecting them proportionally.

Response Time : chooses the IP with the fastest measured response.

For instance, DNSPod uses a combination of weight and random selection.

Advantages of DNS‑Based Load Balancing

Offloads load‑balancing logic to DNS, eliminating the need for dedicated load‑balancer servers.

Simple, low‑cost implementation suitable for most TCP/IP applications.

No code changes required on the application side.

Many DNS services support geographic‑based routing, directing users to the nearest server.

Drawbacks of DNS‑Based Load Balancing

DNS caching at multiple levels can delay propagation of IP changes, causing temporary access failures.

Frequent cache refreshes may increase DNS query traffic.

DNS cannot actively monitor server load or dynamically adjust weights, so it is often combined with higher‑level load balancers for fine‑grained control.