Understanding DNS and IP Addressing: How a Single Domain Can Have Multiple IP Addresses

Many website owners and developers are often curious about the intricacies of DNS and IP addressing. One such complexity is how a single domain name can map to multiple IP addresses. This phenomenon is not only possible but also highly useful for providing redundancy and improving website reliability.

What Does It Mean for a Single DNS Name to Have Multiple IP Addresses?

Yes, it is absolutely possible for a single DNS name to have multiple IP addresses. This technique is often employed to ensure that if one of the IP addresses becomes unavailable, traffic can seamlessly be routed to another IP address. This provides a level of redundancy and resilience to the service.

Real-World Demonstration

To illustrate this concept, let's explore a practical example using the dig command:

Request 1: From Singapore

digDiG 9.16.1-Ubuntuglobal options: cmdGot answer:-HEADER- opcode: QUERY status: NOERROR id: 34793flags: qr rd raQUERY: 1 ANSWER: 6 AUTHORITY: 0 ADDITIONAL: 1OPT PSEUDOSECTION:EDNS: version: 0 flags: udp: 65494QUESTION SECTION:ttt IN AANSWER SECTION:tt 248 IN A 74.125.68.101tt 248 IN A 74.125.68.138tt 248 IN A 74.125.68.100tt 248 IN A 74.125.68.102tt 248 IN A 74.125.68.113tt 248 IN A 74.125.68.139

This example shows the DNS query results from a user's home in Singapore, indicating that the domain name 'tt' has six different IP addresses.

Request 2: Just 5 Minutes Later, Same Home in Singapore

digDiG 9.16.1-Ubuntuglobal options: cmdGot answer:-HEADER- opcode: QUERY status: NOERROR id: 22005flags: qr rd raQUERY: 1 ANSWER: 6 AUTHORITY: 0 ADDITIONAL: 1OPT PSEUDOSECTION:EDNS: version: 0 flags: udp: 65494QUESTION SECTION:ttt IN AANSWER SECTION:tt 110 IN A 142.251.10.102tt 110 IN A 142.251.10.100tt 110 IN A 142.251.10.101tt 110 IN A 142.251.10.113tt 110 IN A 142.251.10.139tt 110 IN A 142.251.10.138

Note how the IP addresses have completely changed, demonstrating the dynamic nature of DNS resolution.

Request 3: From a Virtual Private Server in San Francisco

digDiG 9.11.3-1ubuntu1.17-Ubuntuglobal options: cmdGot answer:-HEADER- opcode: QUERY status: NOERROR id: 56797flags: qr rd raQUERY: 1 ANSWER: 1 AUTHORITY: 0 ADDITIONAL: 1OPT PSEUDOSECTION:EDNS: version: 0 flags: udp: 512QUESTION SECTION:ttt IN AANSWER SECTION:tt 84 IN A 142.250.188.14

Request 4: Just Two Minutes Later from the Same VPS in San Francisco

digDiG 9.11.3-1ubuntu1.17-Ubuntuglobal options: cmdGot answer:-HEADER- opcode: QUERY status: NOERROR id: 55538flags: qr rd raQUERY: 1 ANSWER: 1 AUTHORITY: 0 ADDITIONAL: 1OPT PSEUDOSECTION:EDNS: version: 0 flags: udp: 512QUESTION SECTION:ttt IN AANSWER SECTION:tt 238 IN A 172.217.164.110

The IP address has further changed, showcasing how DNS queries can resolve to different IP addresses over time.

How Does It Work?

This behavior is achieved by deploying multiple IP addresses for a single domain through various DNS settings. This can be done when a website is hosted on multiple servers, with load balancers ensuring that traffic is distributed evenly across these servers. The DNS system can then return different IP addresses to different clients at different times or from different locations, further enhancing the redundancy and reliability of the service.

Use Cases

One of the primary use cases for this technique is load balancing. By distributing traffic among multiple servers, website owners can avoid overloading any single server and ensure better performance and reliability. Additionally, it helps in failover scenarios, where if one server goes down, another can take over seamlessly.

Conclusion

The ability of a single domain to map to multiple IP addresses is a powerful tool in modern Web development. It is not just a technicality but a practical solution that enhances the resilience and performance of websites. The technique used by domain name systems to achieve this—be it over time (round-robin) or based on the source IP of the DNS query (space)—is fascinating and essential for understanding the complexities of the internet infrastructure.

It is the same technique that hides literally thousands of root DNS servers behind just 13 public IP addresses (26 if you count IPv6). This further underlines the efficiency and scalability of the IP addressing system we use today.