Considerations With Dual Provider DNS Redundancy
Using two different DNS companies to achieve redundancy has drawbacks because doing so requires you to reduce capabilities down to a "lowest common denominator," so you are likely to lose valuable traffic routing and security capabilities.
While many DNS service providers support DNSSEC, the security protocol that protects you and your users from DNS hijacking and phishing, there are limitations when you deploy it using two different DNS providers. Some providers cannot support DNSSEC and also function as a secondary DNS to another provider, or be primary in a dual provider set-up. So if security is important to you and / or if you are required to comply with DNSSEC, dual provider configurations aren't for you.
Over the years, DNS has become more sophisticated and many DNS providers offer advanced features that help you route users to the resource that provides the best experience; such as geo-routing, active failover, GSLB and performance-based routing.
These features are implemented using meta data that is associated with the DNS records. This metadata is not part of standard DNS and is different from platform to platform. As a result:
Each DNS provider uses proprietary DNS configuration data used for routing decisions.
This meta data is incompatible across providers, and cannot be transferred by the DNS zone transfer mechanism, AXFR. If for example you want both systems to use geo-routing, you won’t able to synchronize records using a zone transfer.
The options for dealing with this constraint are:
1. Use a Primary/Primary setup and maintain both systems independently.
This entails twice the management overhead.
2. Revert to standard DNS without using the meta data that make traffic routing work.
This results in losing traffic management capabilities.
3. Write scripts or use API's to translate these special DNS records to a format acceptable by the other network.
This essentially automates a primary/primary configuration but can be complex to set up and maintain.