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[public-dns-discuss] Re: Google DNS on 8.8.8.8 not showing selected domains



There are several possible reasons that Google Public DNS resolvers might not get any response from the single name server while other services would.

One would be a routing problem between our network and yours. This problem can occur with any DNS client, and is one of the main reasons that Internet RFCs recommend (and many testing tools warn) that you should not have a single DNS server, and that your DNS servers should be on independent networks.

The other might be that your single DNS server was getting too many (duplicate?) requests from our name servers, which can happen if it is slow to respond and clients send multiple requests on 8.8.8.8 and 8.8.4.4 and queries are load balanced on multiple resolvers that end up appearing to be from the same IP address. This can cause firewalls to block traffic and DNS name servers that implement response rate limiting (RRL) to drop replies. Explicitly allowing all IP address ranges (https://developers.google.com/speed/public-dns/faq#locations) used by Google Public DNS and exempting them from RRL and firewall blocking can help prevent these problems.



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