Full form: Domain Name System
Also known as: Domain Name System
Quick Definition
A hierarchical system that translates human-readable hostnames into IP addresses.
DNS resolves domain names (e.g., www.cisco.com) to IP addresses (e.g., 198.133.219.25). When a host needs to resolve a name, it queries its configured DNS server. If that server does not know the answer, it queries upstream DNS servers in the hierarchy (recursive resolution). DNS uses UDP port 53 for most queries and TCP port 53 for large responses or zone transfers.
DNS uses UDP by default (port 53), not TCP. However, TCP is used for DNS responses exceeding 512 bytes and for zone transfers between DNS servers. Both are port 53.
DNS resolves domain names (e.g., www.cisco.com) to IP addresses (e.g., 198.133.219.25). When a host needs to resolve a name, it queries its configured DNS server. If that server does not know the answer, it queries upstream DNS servers in the hierarchy (recursive resolution). DNS uses UDP port 53 for most queries and TCP port 53 for large responses or zone transfers.
DNS uses UDP by default (port 53), not TCP. However, TCP is used for DNS responses exceeding 512 bytes and for zone transfers between DNS servers. Both are port 53.
DNS falls under the IP Services domain of the 200-301 exam. Understanding it in context with related terms like dhcp and udp is essential for answering scenario-based questions correctly.