我们有个客户的域名，使用了好几家的DNS服务，考虑的真周全。DNS服务器如下：
NS1.CLOUDWEBDNS.COM
NS2.CLOUDWEBDNS.COM
F1G1NS1.DNSPOD.NET
F1G1NS2.DNSPOD.NET
ELLE.NS.CLOUDFLARE.COM
NORM.NS.CLOUDFLARE.COM
NS3.CLOUDWEBDNS.COM
NS4.CLOUDWEBDNS.COM
NS43.DOMAINCONTROL.COM
NS44.DOMAINCONTROL.COM
包括了godddy、cloudflare、dnsbed、dnspod四家。这样会不会有问题呢？我个人认为问题不大。一个专业搞DNS的兄弟如下答复：
The main “gotcha” to watch out for is if the response size with that many nameservers is over 512 bytes then you will set the truncate bit and the resolver would (should?) retry over tcp.
That can slow things down, and I’ve seen some mobile clients not handle it well.
Also, the initial lookups, they have to check the RTT to all the servers, again, possibly slowing things down.
But other than that it should work fine as long as the data is consistent across all of them.
YOu might want to drop the number of servers but keep spread out across the multiple providers if you want to avoid the 512 byte issue but keep multi-provider redundancy.
简言之就是DNS服务器太多，可能导致响应包超过512字节，从而要求客户端TCP重传，影响效率。而且太多的名字服务器，对于Cache服务器，在首次查询时，会对各个名字服务器进行一次RTT计算，这同样导致响应变慢。除此外，只要DNS记录在各个名字服务器保持一致，就应该问题不大。