A Guide To DNS
For clients new to hosting a website, the concepts of DNS (Doman Name System) can be a bit difficult to understand. These terms and concepts will help you to better understand how the system works and how changes to your DNS zone can impact your site.
Root Nameservers
A root nameserver is the highest level nameserver that contains information that makes up the root zone, which is the global list of top-level domains. This root zone contains:
- Certain Top-level Domains like .com, .net, .org
- Country code TLDs
- Internationalized TLDs - generally equivalents of country code top-level domain names written in the countries’ local character sets.
Nameservers
Also referred to as a DNS server, nameservers are servers that contain the DNS zone files for routing traffic to associated domains. As an example, your domain has been pointed to a nameserver through the NS records. When visitors navigate to the site the lookup request will route to the nameserver and then be directed to a hosting server location.
TLD (Top-Level Domain)
A TLD (Top-Level Domain) is a level of the hierarchical DNS system that is management by the root zone. This correlates to the root nameserver where the root zone is managed. The most common TLDs are .com, .net, and .org.
Resolver
A DNS resolver is a server that is contacted during the routing phase. This server is responsible for then reaching out to multiple authoritative nameservers, which contain the DNS zone files, to be routed to the host servers.
Propagation
Propagation is a term used to express the concept of the DNS (nameservers) synchronizing to present the same data values for DNS records across the internet’s resolvers. This process can take up to 48 hours to complete in some cases. You can generally expect 4-8 hours for local propagation and 24-48 hours for global propagation to fully complete.
TTL
TTL (Time To Live) is a data value in a DNS record that instructs the DNS server a time frame to discard that record and retrieve a new instance of the data set for that record. This value is expressed in seconds with the standard values of 14400 (4hours) and 86400 (24hours). Adjusting the TTL values of the data set can help influence the amount of time for DNS propagation.
Uncommon Records
MX Records
MX (mail exchange) records are used to instruct email traffic where to go for resolution. These records are only utilized from the perspective of incoming traffic. When you send an email message to a user, the mail server is then responsible for performing a lookup of the recipient domain to determine how to route your message to that incoming mail server. It is the MX record that provides that route location.
Example:
| Domain | Type | Value | Priority | TTL |
|---|---|---|---|---|
domain.com |
MX | mail.servermail.com |
10 | 86400 |
Note: While not necessarily uncommon, MX records are generally configured on the assumption that you will be using the host’s mail services.
PTR Records
PTR (pointer) records are used for reverse DNS lookups. When your hosting server attempts to establish a connection to another system it will send its name and IP address. A common method to determine the legitimacy of the source host server is to reverse lookup the IP address of the system. The PTR record is then used to identify the IP lookup and correlate it to the name of the system. If there is a match, then the system can be more certain that the connecting server is who it says it is. This process helps to cut down on malicious traffic.
SRV Records
SRV (service) records are used to provide rudimentary information regarding available services. A common use case for this record is the autodiscover functionality provided by many mail systems. In that particular use case, the SRV record can be invoked by local email clients to pull configuration information for connecting to a mail system (ports, server names, and protocols.)
Example:
| Domain | Type | Value | pritority | weight | port | TTL |
|---|---|---|---|---|---|---|
_autodiscover._tcp.domain.com |
SRV | mail.servermail.com |
0 | 0 | 443 | 86400 |
HTTP Redirection Records
HTTP Redirection records are used to redirect requests from site visitors to the content of another domain. This is implemented by taking a domain name and then redirecting the traffic to a domain value. This process can also include redirection type called masking which allows for the content of the domain value to be presented under the URL of the domain name and not the domain name of the data value.
Example:
| Domain | Type | Value | Redirected Type | TTL |
|---|---|---|---|---|
domain.com |
HTTPRED | example.com |
Masked | 86400 |
When masking is included as a part of the record, the content of example.com will be presented under the URL of domain.com. This allows the webmaster to alias content without really needing to involve configuration of the example.com environment.
CNAME
A CNAME record is a resource record used to specify a domain as an alias for another domain name record within the DNS zone file. This kind of DNS record will allow for the domain name to mirror the source IP address of another domain without needing to make changes to both records. Instead of making the change to the source domain name, the change will reflect for the domain name that is aliasing the other.
Note: This is not to be confused with ‘Domain Aliasing’ as this is just aliasing the record of a domain name in the DNS zone file not the content of that domain.
Example:
| Domain | Type | Value | TTL |
|---|---|---|---|
domain.com |
CNAME | example.com |
86400 |