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When you need to distribute website traffic across multiple servers without investing in a hardware or cloud load balancer, Round Robin DNS offers a simple and cost-effective solution.

It is one of the oldest and most commonly used DNS load balancing techniques, especially for websites hosted on multiple servers with identical configurations.

In this guide, we’ll explain how Round Robin DNS works, how to configure it in BIND, and the impact of TTL and DNS caching on load balancing performance.

What Is Round Robin DNS?

Round Robin DNS is a load balancing mechanism in which a DNS server rotates multiple IP addresses for a single domain name. Instead of returning the same IP address every time, the DNS server cycles through a list of IPs.

This helps distribute traffic across multiple servers and improves availability.

For example:

If a domain has three A records:

example.com. 1301 IN A 192.168.1.10
example.com. 1301 IN A 192.168.1.11
example.com. 1301 IN A 192.168.1.12

The DNS server returns the IPs in cyclic order:

• First request → 192.168.1.10
• Second request → 192.168.1.11
• Third request → 192.168.1.12
• Fourth request → 192.168.1.10 (rotation continues)

This rotation is controlled by the RR-set order in DNS.

How Round Robin DNS Works

1. A client requests a domain name.
2. The DNS server checks for multiple A records.
3. It returns the IP addresses in cyclic (round-robin) order.
4. The selected IP is used for that session.

Important:
Round Robin DNS distributes traffic per session, not per HTTP request. Once a client connects to an IP, it continues using that server until the session ends.

How to Configure Round Robin DNS in BIND

To enable cyclic ordering in BIND, edit the configuration file:

/etc/named.conf

Add:

options {
    rrset-order {
        order cyclic;
    };
};

Available RR-set Orders

Order Type	Description
fixed	Returns records in the same order
random	Returns records randomly
cyclic	Returns records in round-robin order

You can also configure it more specifically:

options {
    rrset-order {
        class IN type ANY name "*" order cyclic;
    };
};

By default, many DNS servers already rotate Resource Records when multiple entries exist for the same domain.

The Role of TTL in Round Robin DNS

DNS caching significantly affects the effectiveness of Round Robin DNS.

• If TTL is too high → Clients reuse cached IPs → Less load distribution
• If TTL is set to 0 → Every request hits the DNS server → Higher DNS load

Recommended TTL

For balanced performance:

Set TTL between 10–15 minutes

This allows:

• Effective caching
• Better traffic distribution
• Reduced DNS server load

Advantages of Round Robin DNS

• Simple to configure
• No additional hardware required
• Cost-effective
• Improves traffic distribution
• Supports multiple A and MX records

Limitations of Round Robin DNS

• No health checks (unlike advanced load balancers)
• Does not detect server failure
• Affected by DNS caching
• Not true real-time load balancing

If one server goes down, DNS may still send traffic to it unless manually removed from the zone file.

Round Robin DNS vs Traditional Load Balancers

Feature	Round Robin DNS	Hardware/Cloud Load Balancer
Cost	Low	Medium to High
Health Checks	No	Yes
Real-time Failover	No	Yes
Session Awareness	Limited	Advanced
Setup Complexity	Simple	Moderate

Round Robin DNS is ideal for basic traffic distribution but not for high-availability enterprise setups.

When Should You Use Round Robin DNS?

• Multiple web servers with identical content
• Geographically distributed servers
• Basic redundancy needs
• Budget-conscious hosting environments

It works best when combined with proper monitoring and failover strategies.

Conclusion

Round Robin DNS is a lightweight and effective method for distributing traffic across multiple servers. While it lacks advanced health checks and real-time failover capabilities, it remains a practical solution for small to medium-sized deployments.

By properly configuring RR-set order in BIND and optimizing TTL values, you can significantly improve traffic distribution without investing in expensive load balancing solutions.

If you require assistance configuring Round Robin DNS or optimizing your server environment, professional server administration support can help ensure optimal performance and reliability.