A6 - DNS Server
750 points
Last updated
750 points
Last updated
How many web pages do you visit in a day? Would you be able to remember all their IP addresses? Probably not. It turns out that humans are bad at remembering arbitrary sequences of numbers, but reasonably good at remembering names. By assigning names to IP addresses, web browsing becomes doable for humans. Instead of having to remember the sequence 216.58.211.110, you only need to remember www.google.com. Your browser automatically translates this into the correct IP address.
However, this automated translation increases the complexity of the system, which now needs to translate a name into an IP address before it can establish a connection. It would be infeasible for every computer to keep a local, up-to-date copy, of all name-to-address mappings. Instead, computers depend on a globally distributed system called the Domain Name System (DNS) to look up these mappings dynamically.
This system contains a large hierarchy of servers called DNS servers. A DNS server is a computer that keeps track of IP addresses and their associated domain names. DNS servers can ask each other for the IP address matching a certain domain name. It then resolves, or translates, this name into an IP address by looking it up in its local database, or by contacting other DNS servers higher up in the hierarchy.
Your task is to implement your own DNS server that adheres to this protocol and performs recursive queries. Your server should be able to resolve both IPv4 and IPv6 addresses. All the information you need is specified in and .
Start by reading section 2.1 (RFC 1035. Overview). It will give you a high-level operational model of your future DNS server. Then, to get a high-level overview of what DNS responses, requests, and communication between the other DNS servers are see sections 7.1 (RFC 1035. Transforming a user request into a query), 7.2 (RFC 1035. Sending the queries), and 7.3 (RFC 1035. Processing responses).
To construct a DNS request or parse a DNS response, read the structure of a DNS message in section 4 (RFC 1035 message). Every message contains a set of records called RRs. There you will find the most interesting information regarding the requested resource. Read how it is structured in section 3.2 (RR definitions). Each record has its type, and your server should support at least NS, A, CNAME, MX, and AAAA.
Your DNS has to implement mail requests. Check section 8 (Mail Support) and in particular section 8.1 (Mail Exchange Binding). Finally, your server should implement caching as it is prescribed in sections 7.1, 7.2, and 7.3. However, there are exceptions to this rule described in section 7.4 (Use of cache).
Your assignment must present basic DNS server features. In short, your server should implement functionality that enables basic domain name resolving. We define the following requirements as a smaller specification based on the RFC to guide your development process.
Your implementation must resolve requests by communicating with the root server and the servers it lists in its replies. You cannot pass the assignment if you simply forward requests to another DNS server that performs recursive queries.
The server must support both IPv4 and IPv6 requests.
The server must support the following records: NS, A, CNAME, MX, and AAAA.
The server must support mail exchange requests.
Below is a list of free, popular, and public DNS servers. You can analyze their responses to learn more about how to implement your server.
Google (8.8.8.8 and 8.8.4.4)
Quad9 (9.9.9.9 and 149.112.112.112)
OpenDNS (208.67.222.222 and 208.67.220.220)
Your assignment must implement a subset of the features prescribed in and . The following requirements describe the functionality that should be present in your server implementation:
To test your DNS server, you will need to use the (domain information groper) command. Depending on your system, you might have to install dig using your package manager. To run dig with your DNS server and perform a DNS resolve request, execute the following in your terminal:
You can find the addresses of the DNS root servers at .