What are the main advantages of paying for DNS hosting like Zerigo or SlickDNS instead of using the one provided for free with web host companies (E.g. Linode's DNS Manager)?
FWIW the SlickDNS name servers are hosted by Linode so I'm a fan of their server hosting. For DNS management, the Linode interface is fine if you have a handful of domains with simple configurations, but beyond that it's unwieldy IMHO.
I'd say the main reason to use a DNS hosting service is to consolidate your DNS management for all of your domains regardless of registrars or server hosting providers. E.g., I personally have domains registered with 5 registrars and use two server providers. And because they specialize in DNS, DNS hosting providers should have superior interfaces, APIs and support for DNS hosting compared to generalist hosting providers.
The SlickDNS interface has two features in particular that I haven't seen in any other DNS hosting service: automatic management of "alias domains" and mapping IP addresses to named servers. See https://www.slickdns.com/features/ for details.
A dedicated DNS provider will often focus on the experience around managing DNS, including APIs and advanced features. Additionally some folks don't like putting all of their eggs in one basket and prefer to have their registrar be one company, their DNS be another and their hosts be another.
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What are the main advantages of paying for DNS hosting like Zerigo or SlickDNS instead of using the one provided for free with web host companies (E.g. Linode's DNS Manager)?
FWIW the SlickDNS name servers are hosted by Linode so I'm a fan of their server hosting. For DNS management, the Linode interface is fine if you have a handful of domains with simple configurations, but beyond that it's unwieldy IMHO.
I'd say the main reason to use a DNS hosting service is to consolidate your DNS management for all of your domains regardless of registrars or server hosting providers. E.g., I personally have domains registered with 5 registrars and use two server providers. And because they specialize in DNS, DNS hosting providers should have superior interfaces, APIs and support for DNS hosting compared to generalist hosting providers.
The SlickDNS interface has two features in particular that I haven't seen in any other DNS hosting service: automatic management of "alias domains" and mapping IP addresses to named servers. See https://www.slickdns.com/features/ for details.
A dedicated DNS provider will often focus on the experience around managing DNS, including APIs and advanced features. Additionally some folks don't like putting all of their eggs in one basket and prefer to have their registrar be one company, their DNS be another and their hosts be another.