Setting Time to Live for your DNS records

Time to Live or TTL refers to when the nameserver checks with the authoritative nameserver to get the latest record. I caches that record for however long the TTL specifies before checking again. The lower the number, the sooner records will be updated.

Many nameservers are set to a default time of 86400 seconds (24 hours). With that setting, it takes 24 hours before all of the DNS servers globally are updated, although some Internet servers will update before others. The lower the number of seconds to live updates, the more often the nameserver will access the authoritative records.

While one’s first inclination might be to lower the TTL number so that nameservers are updated almost immediately, having a setting that is too low can cause too great of a strain on the server. If you change your DNS often, you might want to make the setting lower than one day, but if you only change it once in a while, that default setting might be fine. Some system administrators will lower the setting temporarily if they know they are about to make a big change to critical network services.

Image Source: Wikimedia Commons

Nameserver subnet warnings

Question: What does the following error mean:

WARNING: Not all of your nameservers are in different subnets

Answer: If you are receiving this error, it means that the nameservers for your domain are both originating from the same server (or two servers within the same subnet). Generally speaking, this is actually just a warning and not an error. Your server may still function just fine.

To be in full compliance with networking standards, however, you will need to host one nameserver at a different location, or at least on a different subnet. In other words, your domain registrar will require two IP addresses for your nameservers. You can have one on your actual server and have the other hosted on a separate server.

Some web hosting providers will offer remote nameserver hosting as part of their unmanaged dedicated server offerings. If they do not, there are other DNS hosting services that may offer what you need. As a last resort, you can configure your server to use two distinct IP addresses for each nameserver even if they actually both originate from the same place, although this is not ideal.

Image Source: Wikimedia Commons

DNS Evaluation with intoDNS

Part of managing a server or even a single website is making sure the DNS is sound and in compliance with established networking and Internet standards. While you can evaluate each of your DNS entries manually, there are many services out there that make evaluation very easy.

One such service is called intoDNS, which is currently still listed as beta, but it functions very well. To use it, simply visit intodns.com and type your full domain name (excluding the “www”). Then, click “Report”. It will then scan your domain and report on a number of important issues: Domain Nameserver records, TLD parent check, CNAMEs, etc.

When your domain passes one of the tests, the service will give you a green circle with a check next to it. When there is an area of concern, you will receive a blue circle with an “i” in it. When you have an error, it will give you a red circle with an exclamation mark. All of the information is displayed in basic HTML so that you can easily print or save it.

Using DNS Records: A, CNAME, and MX

Sometimes managing a domain involves more than simply pointing the nameserver entries to your new web host’s servers. You might also need custom DNS records. For example, if you use cloud services, such as Google’s e-mail and applications services, you will need to configure your DNS records. Three common record types you will see are A, CNAME, and MX.

An “A” record, as the name implies, is the primary record. “A” stands for address, and it is used to map hostnames to IP addresses. For example, yourdomain.com would be mapped to 55.555.555.555. That IP address is your site’s IP address, either a unique one or a shared one provided by your web hosting provider.

“CNAME” stands for canonical name. While a domain can only have one “A” record, it can have multiple “CNAME” records. Each one represents an alias. This is the one that is usually used by cloud services to map one or more of your subdomains to their services, while keeping your “A” record pointing to your host’s IP address.

“MX” stands for mail exchange record. Simply put, it identifies your mail server. Usually, you would list the IP addresses provided by your web host here, but if you are using external mail services, just follow the directions that your service gives you.

Free DNS Tools for Web Hosting

Inevitably, there are times when you need to do troubleshooting of your web and email services, or you simply need to make sure all of your network services are operating correctly. For years, I have relied on one free service to handle most of my DNS needs. It is called DNSstuff.com. They offer mail server analysis, DNS reports, SPAM database lookup, traceroute, Whois lookup, reverse DNS lookup, ping, Internet speed test, and much more.

With their full DNS report, you can enter a domain name and find out the name severs and other DNS information. It will also tell you if there are any problems with a particular domain’s DNS setup. Unfortunately, many of their services are no longer free, but there are many other services out there that still offer free advanced DNS tools.

Among the free ones are freednslookup.net, rrlookup.com, and samdns.com. If you need to know the location of an IP address, these tools will help you. If you need to know who owns a domain, you can find that out too. You can even lookup specific DNS records, such as A, MX, CNAME, and NS. Regardless of which tool you choose, it is very important to check these features before you have problems to help prevent them and whenever you have connection issues with your website.

Photo source: SXC