When you first encounter DNS resolution, it may seem like a straightforward pairing of domain names and IP addresses — set it up and you’re done. However, a deeper dive reveals fascinating details within the realm of DNS resolution. What’s more important: wildcard records or explicit entries? Let’s explore the priority issues within DNS resolution.
1. Explicit Records Always Take Precedence
When you set up an explicit DNS record for a domain, such as directing www.example.com to a specific IP address, the DNS query will always prioritize this explicit record. It’s analogous to asking for directions in a village; if someone provides specific guidance, you wouldn’t consult a stray dog for directions.
For instance, consider the following DNS records:
www.example.com→ IP Address: 118.6.150.180panel.example.com→ IP Address: 56.175.162.285*.example.com→ IP Address: 118.6.150.175 (wildcard)
When a user requests www.example.com, DNS will directly refer to the explicit record and return 118.6.150.180. Even with a wildcard record in place, it remains unused. The explicit record stands as the village elder, guiding you without needing other opinions.
2. Wildcard Records: The Backup Friend
Wildcard records serve those domain names that lack explicit entries. They function like a friendly dog in the village; if no one knows the way, it can provide a general direction.
For example, if you request test.example.com, but haven’t set an individual A record for test, DNS will utilize the wildcard record, directing you to 118.6.150.175. Thus, explicit records always hold precedence over wildcards, with the latter only coming into play when explicit records are missing.
TTL: How Often Should Village News Update?
TTL (Time-To-Live) can be understood as the frequency with which local gossip gets refreshed. If updates are regular, everyone can quickly adjust to changes; if updates are infrequent, people may continue sharing old information long after it’s outdated.
1. Explicit Records’ TTL Takes Priority
When you set a TTL of 60 minutes for www.example.com and 5 minutes for the wildcard, DNS queries will adhere to this priority principle. For example:
www.example.com→ TTL: 60 minutes*.example.com→ TTL: 5 minutes
When someone requests www.example.com, the DNS query result will have a TTL of 60 minutes due to the explicit record’s higher priority. Conversely, if a user requests test.example.com, DNS will return the wildcard result with a TTL of 5 minutes. The logic here is straightforward: the village elder’s words stick longer than those of the dog.
2. TTL and Caching: Longevity of Messages
It’s essential to recognize that TTL indicates how long a DNS server can cache a record. For example, a TTL of 1 day means that the DNS server will rely on cached results for 24 hours without querying the parent server for new IP data.
If you set a long TTL (like 1 day) and then decide to change your server’s IP, even adjusting the TTL to 1 minute won’t immediately update the cached information. Until the cache expires, the DNS server will continue utilizing the old IP.
Thus, adjusting the TTL in advance is a useful strategy, provided you allow ample time for the change. Otherwise, if you wait to change the TTL until after moving, you may find many villagers still searching for you at your previous location.
A Reasonable TTL Strategy: When to Use Long vs. Short
Setting an appropriate TTL depends on various scenarios:
Common Hostnames (like
www,@): These are typically stable, so it’s wise to set a longer TTL (like 60 minutes or more) to reduce DNS query frequency and optimize performance.Infrequent or Temporary Subdomains: These might require frequent changes, so a shorter TTL (like 5 minutes) ensures rapid updates take effect.
Wildcard Records: Generally, these should have a relatively short TTL (like 5 minutes) to accommodate potential adjustments promptly.
Importance of DNS Resolution Rules
The rules governing domain resolution are akin to a well-organized village; explicit records are the respected elders, ensuring clear communication and direction, while TTL acts as the frequency indicator for news updates among the villagers. While these may be fundamental concepts, they are often overlooked.
Hopefully, this article will enhance your understanding of DNS resolution priorities and TTL settings, allowing you to navigate changes with confidence. Remember, both the village elder and the stray dog have their roles to play, and it’s up to you to wisely allocate their speaking opportunities.
