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What is DNS?

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The Domain Name System (DNS) is designed to provide translations, converting hostnames to IP addresses (name resolution) or IP addresses to hostnames (reverse lookup). It also designates the DNS servers (or DNS appliances) which hold the reference DNS information, as well as the DNS protocol used for communication (queries, data transfer…).

DNS brings efficiency to the process of resolving the names of internet sites with their underlying technical addresses, the IP addresses. Hosts across networks are locatable via their IP address. To connect to these hosts, users make use of “friendly names” such as DNS provides a standard naming structure for locating IP-based resources.

Distributed Database

The DNS servers themselves are often referred to as name servers, their main role being to respond to queries from clients or from other name servers. Name servers therefore need to hold the DNS database information for their portion of the namespace, known as a zone. The resolution process executed by a name server can be either recursive or iterative. When processing recursive queries, the name server builds up information about each domain space which can be temporarily stored in the DNS cache. This speeds up processing time for subsequent queries, based on the time-to-live (TTL) specified for cache data.

DNS Server Types

Name servers can be different types: 1) Authoritative  2) Caching-only  3) Forwarder.  Authoritative DNS servers locally store information about a zone and are fully responsible for the first level content of this zone. Caching-only DNS servers obtain information from authoritative servers and store query answers in cache for later use. Forwarders are designated servers to which a particular subset of queries requiring external resolution are sent.

What is DNS-Authoritative-recursive

DNS Master/Slave

When it comes to managing a DNS zone, name servers are defined as either master or slave. The slave’s main role is to ensure redundancy and spread the load from the clients and other DNS servers. The master zone holds the original copy (the master record) of the database, while the slave zone holds a copy of it.  Zones on the master server are provisioned by the network administrator ideally through an IPAM solution, whereas zones on the slave are automatically populated via zone transfer. The three types of zones used are recursive lookup zone, forward lookup zone and conditional forwarder zone. Data stored in the zone files are in the form of Resource Records (RR), with example RR types including A, AAAA, CNAME, MX and SOA.

DNS Security

DNS is “open by design”, created over 30 years ago with limited focus put on DNS security aspects. It is therefore often targeted by hackers, so requires purpose-built security to mitigate DNS attacks such as DDoS, DNS cache poisoning, Phishing, zero-day attacks and data exfiltration. These can affect both public DNS servers and private DNS servers, and can only be effectively thwarted using DNS analytics and threat intelligence based on internal DNS traffic and external data feeds.