Android's DnsResolver is a system service that is responsible for resolving domain names into IP addresses. It provides a set of APIs that allow applications to query DNS servers and receive responses.
The DnsResolver service runs in the background and is responsible for caching DNS responses to improve performance. It also supports DNS over HTTPS (DoH) and DNS over TLS (DoT), which are protocols that encrypt DNS queries and responses for improved security.
Applications can use the DnsResolver APIs to resolve domain names, set DNS server preferences, and control the caching behavior. By default, Android uses the DNS servers provided by the mobile network operator, but users can configure their own DNS servers if they prefer.
The DnsResolver APIs are part of the Android platform and are available to all applications running on Android. They are implemented in the Android system libraries and are documented in the Android SDK documentation.
Overall, the Android DnsResolver service plays a crucial role in the functioning of the Android platform and enables applications to perform DNS lookups efficiently and securely.
Android DnsResolver is a system library in the Android operating system that provides a way for Android apps to perform DNS (Domain Name System) lookups. DNS lookups are used to translate human-readable domain names, such as www.example.com, into IP addresses, which are used by computers to communicate with each other over the Internet.
The DnsResolver library provides a high-level API that allows Android apps to perform DNS lookups without having to deal with the low-level details of the DNS protocol. The library uses a number of DNS servers to perform lookups and can also cache results to improve performance.
The DnsResolver library is used by a wide range of Android apps, including web browsers, email clients, and other networked applications. It is an important part of the Android networking stack and is constantly being improved and updated to provide better performance and security.
The Domain Name System, or DNS, is a crucial part of the infrastructure that enables the Internet to function. DNS is responsible for translating human-readable domain names, like "google.com" or "facebook.com," into IP addresses, which are the unique numerical identifiers that computers use to locate one another on the Internet. Without DNS, users would need to memorize the IP addresses of every website they wanted to visit, which would be impractical and difficult.
The DNS system works as follows: when a user enters a domain name into their web browser or other Internet application, the application first sends a request to the user's local DNS resolver. This resolver is typically provided by the user's Internet service provider (ISP) or other network provider, and is responsible for handling DNS requests on behalf of the user.
The local resolver first checks its cache to see if it has a record of the requested domain name and its corresponding IP address. If the record is found in the cache and is still valid (i.e., not expired), the resolver returns the IP address to the requesting application and the process is complete.
If the record is not found in the cache or is expired, the resolver needs to query one or more authoritative DNS servers to obtain the information it needs. Authoritative DNS servers are responsible for maintaining the "zone files" that contain the DNS records for a particular domain or set of domains. There are typically several authoritative DNS servers for each domain, which are distributed geographically and can be run by different organizations.
To find the authoritative DNS server for a given domain, the resolver first needs to know the IP address of the "root" DNS server. The root DNS servers are a set of 13 servers that are distributed around the world and are responsible for answering queries about the top-level domains (TLDs) like .com, .org, .net, and so on.
Once the resolver has the IP address of a root DNS server, it sends a query asking for the IP address of the authoritative DNS server for the TLD of the requested domain (e.g., .com). The root DNS server responds with the IP address of a "top-level" DNS server for the TLD, which the resolver then queries for the IP address of the authoritative DNS server for the specific domain.
Once the resolver has obtained the IP address of the authoritative DNS server, it sends a query to that server asking for the IP address of the requested domain. The authoritative DNS server looks up the domain's record in its zone file and returns the IP address to the resolver, which in turn returns it to the requesting application.
If there are multiple authoritative DNS servers for a given domain, the resolver may need to query multiple servers to obtain all the necessary information. In addition, if there are any issues with the DNS resolution process (such as a misconfigured DNS server or a network outage), the resolver may need to retry the query with different servers or wait for a timeout before returning an error to the requesting application.
Overall, the DNS system is a complex and distributed network of servers and protocols that enables users to access the vast array of resources available on the Internet. While it can sometimes be prone to issues and vulnerabilities, DNS remains a critical component of the Internet infrastructure and a key focus of ongoing research and development in the field of networking.