DNS

Recursive query

A query sent from a client to the designated DNS server which manages and continues the lookup process until the DNS record is found.

Iterative query

A query sent from one DNS server to another DNS server for DNS information - server responds with the best information it has but does not continue to query

Zones

A zone is a discrete portion of the DNS namespace. Zones consist of entire domains or subdomains. Zones can contain multiple domains but they must be contiguous in the namespace. i.e. 2 child zones must have the parent zone included as well

Stub Zone

Configured with the IP address of the server that hosts the zone, stub zone forwards requests or replies to a request with a referral.

Reverse name resolution

Converts an IP address into a DNS name Uses the in-addr.arpa domain which is designed for reverse name resolution

Secondary zone

Creates a duplicate of primary on another server (text file on local drive). Can only update resource records in a secondary zone by replicating the primary master zone file - zone transfer. If primary zone stored in ADS, a secondary zone or zone transfers are not required as ADS replicates the data.

Cname Canonical Name

Creates an alias that points to the real name of a host as identified by it's a record. An alternative name for a host.

Resolvers

DNS client service the generates DNS queries that are sent to DNS servers. Client should have at least 1 DNS server configuration

SOA Start of Authority

Indicates that the server is the authoritative source for the zone. Each zone must have a SOA record and only one record.

Caching

Caching increases the speed that information is returned. If a resource record or an authoritative server is changed it may take time for cached records to be timed out (TTL value expires) and for records to be rerequested.

Client Resolver task

Client Resolver first checks client cache and then sends a name resolution request to its DNS Server

DNS Server task

DNS server first checks cache then checks its resource records to see if it is authoritative - if it has a resource record for the URL requested. If not DNS server generates an iterative query and submits it to a root name server.

Name Servers

DNS server service that maintains DNS information. Responds to queries for information that it hosts (is authoritative for) or forwards queries to other name servers in other domains.

MX Mail Exchanger

Directs email traffic to an address in the domain

DNS namespace

Domain FQDN fully qualified domain name Each domain contains resource records that contain host names, IP addresses and other information. DNS queries retrieve information from a domain.

Root Hints

Every DNS server must be able to contact root name servers for name resolution. DNS servers are preconfigured with names and addresses of multiple root name servers - root hints. 13 root name servers names using the letters of the alphabet are located in root-servers.net Can modify root hints via DNS server property sheet

PTR Pointer

IP to name mapping for reverse lookup

NS Name Server

Identifies a DNS server that is an authority for a zone Each DNS server in a zone must have a NS record

DNS zone types

Primary zone Secondary zone Stub zone Active Directory integrated zones

TTL configuration

Lower TTL means more current information in cache as cached content times out sooner Higher TTL means better performance as less iterative queries are made. To modify TTL Properties of DNS server, SOA tab and TTL value.

Primary Zone

Master copy of the zone database - stored in ADS if option selected or stored as text file on local drive

A record

Name to IP address mapping for a IPv4 host

AAAA quadA record

Name to IP address mapping for a IPv6 host

Referral

Process of sending a name resolution request from one DNS server to another

Forwarder

Special recursive query sent from one DNS server to another that hands over DNS query role to another DNS server. Forwarder is often an ISP DNS server DNS, Properties, Forwarders, add IP of DNS forwarder server

Installing DNS role

Use Add roles and features wizard. This installs caching only services for clients making requests to it and the DNS Manager Console

Active Directory integrated zones

Stores the zone in Active Directory Only available if the DNS server is a domain controller DNS resource records stored in AD DS database DNS data is automatically replicated to other DCs in the domain, can be configured to replicate to all DCs in enterprise, or any DC (including those not hosting DNS) DNS records can be modified on any DC hosting DNS and be auto updated to other DCs

DNS Server iterative query

The DNS Server receives information from root server and sends a new iterative query to top level domain server.

DNS Server final iterative query

The DNS Server sends a new iterative query to second level domain name server. If it is authoritative, it checks records and replies with requested record to DNS server. DNS server caches the record and transmits IP address to resolver on client system. Web page is delivered

DNS Process

User makes request for URL Client Resolver --> DNS server --> Root Server --> DNS server iterative query --> top level DNS server --> DNS server iterative query to 2nd level DNS server --> cache record --> send IP to client

Root Server task

The root name server checks it records to find the authoritative server for the URL's top-level domain. The root server sends a referral for the IP of the top level domain back to the DNS server

Top level domain server task

The top level server checks the 2nd level domain in the URL and transmits a referral for the IP of authoritative server for the 2nd level domain back to the client DNS server. Note: Often the root and top level records are hosted on the same server so it becomes a single step.

Zone Delegation

Zones can be stored on different DNS servers and management of zone can be delegated to different administrators. In most cases, create multiple zones on a server and delegate most to other servers for hosting.