Vocabulary And Concepts
Common DNS Records
Infoblox makes use of the most common DNS record types that are familiar to individuals responsible for requesting DNS changes at UT Austin. A brief description of the most common DNS records supported by the Infoblox GUI are provided below.
|Forward DNS (A)||The Address (A) record associates a host name with an IP address.|
|Reverse DNS (PTR)||The Pointer (PTR) record maps IP addresses to host names.|
|Forward DNS - IPv6 (AAAA)||The IPV6 address (AAAA) record maps a host name to a 128-bit Ipv6 address. Regular DNS addresses are mapped for 32-bit IPv4 addresses. As of November 2015, UT Austin is not yet using IPv6.|
|Aliasing Names (CNAME)||The Canonical Name (CNAME) record is used to create aliases that point to other names. It is commonly used to map WWW, FTP and MAIL to a domain name.|
|DNS Name Servers (NS)||The Name Server (NS) record identifies the authoritative DNS servers for a domain. A second name server is required for redundancy, and two NS records must be in each zone file (one for the primary; one for the secondary).|
|Location of Service (SRV)||Service Records (SRV) are used to specify the location of a service. They are most commonly used with directory servers such as LDAP (Lightweight Directory Access Protocol), and Windows directory services.|
|Descriptive Text (TXT)||The TXT record is used to hold general information about a domain name but often used for Sender Policy Framework (SPF) records.|
DNS add/change/remove requests most often involve A records and PTR (reverse) records. There are a number of items that should be noted regarding A and PTR records.
A records are created and maintained separately from their associated PTR records. UTNIC has automated the process of creating PTR records when A records are requested.
UTNIC has automated the process of removing PTR records when their associated A records are deleted. Because there is no governing application linking A records and PTR records - A records can be deleted while leaving stale PTR records behind.
Infoblox has provided a record type called a "Host" record, that binds an A record and PTR record together. This prevents stale PTR records from building up unintentionally.
The Infoblox "Host" Record
The Infoblox Host record provides a convenient method for creating the forward record and having the corresponding reverse (PTR) generated and associated with the host name. As noted, this prevents the buildup of stale PTR records which can occur when A records are deleted but their associated PTR records are forgotten. DNS administrators should create Host records and avoid A records. In most instances, an A record should only be used if the record cannot have an associated PTR record. An example of this would be when using a host on the UT Web system where the PTR record for the target address should only resolve to utweb-prod.its.utexas.edu. Another example involves the use of the whitelisting system for scan-to-email where the whitelist system can generate an error if more than one response is returned for a PTR lookup.
When To Use Host Records vs A/PTR Records:
DNS administrators should use Host record to ensure that forward and reverse records are linked together.
DNS administrators should use an A record when they wish to suppress associated PTR records. Under some circumstances, an A record without an associated PTR record is required. An example would be multiple host names are bound to single IP address that only requires one PTR record for reverse lookups. In this example, DNS administrators would create multiple A records (rather than Host records) and then independently configure a single associated PTR record.