Advanced Network Configuration
Networks rely on specialized servers to translate IP addresses into URLs, and vice versa, and to assign IP addresses on networks. Networks also use specialized virtual methods to improve security.
DNS
A DNS server performs a variety of functions on a network, including translating friendly URLs like www.google.com into IP addresses, providing the URLs of the mail servers that receive email addresses for a particular domain name, and storing text and machine-readable data, including spam management, for a particular domain name.
Address
The most recognized feature of a DNS server is its function of translating URLs into IP addresses. It can perform this function because it stores information about domains and their IP addresses. These are stored in two types of records: A and AAAA.
A
An A record points a friendly URL to the IPv4 address used by the URL’s domain. For example, an A record would be used to point google.com to Google’s host IP address 74.125.224.147. Some websites have more than one A record to allow load balancing.
AAAA
An AAAA record performs the same function as an A record, but for the IPv6 address of a particular domain. Mail Exchange A mail exchange (MX) record stores the mail exchange information, including the SMTP mail server and its priority, for a particular domain.
Text
A text (TXT) record is used for a variety of purposes, the most common of which are spam management (following section) and identification of the owner of the domain.
Spam Management
TXT records typically include a number of records designed to help block spam. These include DKIM, SPF, and DMARK. DomainKeys Identified Mail DomainKeys Identified Mail (DKIM) has two components: a DKIM record stored in the TXT portion of the domain’s DNS record and a DKIM header attached to all email coming from that specific domain. Email lacking matching DKIM information is rejected as spam. To see examples of DKIM and the servers that use this type of record, see www.cloudflare.com/learning/dns/dns-records/dns-dkim-record.
Sender Policy Framework
Sender Policy Framework (SPF) records the authorized email-sending servers in a particular domain. It can also identify email spoofers.
The SPF line in the microsoft.com DNS TXT record looks like the following as this book went to press:
