Comparing ALIAS and CNAME Records

There are 4 types of DNS records, namely: A, CNAME, ALIAS, and URL.

The A record, maps a name to one or more IP addresses.

The URL record, redirects to the target link using http 301.

So far so good.

The CNAME record, maps a name to another name.

The ALIAS record, maps a name to another name.

Um… what??? ALIAS and CNAME look quite the same, don’t they? So when to use what?

It turns out for ALIAS, the recursive lookup will happen at the server side, so that will speed things up a lot. Also the final output is an IP, so that acts the same as an A record. Whereas for CNAME, you need to do recursive client calls to resolve all the way to the A record, then one more lookup to get the IP. That could take longer.

But the disadvantage of using ALIAS is that, the routers don’t have your geographical info, so may end up giving you sub-optimal results, i.e. An IP that’s far away from your location, but closest to your authoritative DNS server.


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