Hi, On Sep 3, 2014, at 8:42 AM, Guangqing Deng <dengguangq...@cnnic.cn> wrote: > From RFC1034 section 4.1, it seems that the way used for improving the > redundancy and resilience of DNS system is to increase DNS servers. I agree > that for the performance of the DNS system, the redundancy and resilience are > the first goal and low latency is the second goal. Usually, the first goal > mainly depends on the DNS server deployment policy (such as the total number > and geographical distribution of DNS severs) and the second goal relates to > not only the DNS server deployment policy but also the method used for DNS > clients selecting the best DNS server like any cast.
Careful here. Anycast improves redundancy/resiliency for the system as a whole. As typically deployed, it may not improve redundancy/resiliency for a single client. For example, if a DNS server instance in an anycast cloud is no longer responding to DNS queries due to a DoS but the routing announcement of that instance is not pulled down, the clients topologically nearest that instance will not see improved redundancy/resiliency — they’ll not see any responses. Anycast may or may not improve latency — it depends on the routing system. If the “nearest” instance network topologically to a set of clients happens to be on the other planet, latency will not be improved for those clients. Anycast is a very blunt tool. It can help improve redundancy/resiliency and latency if properly deployed, constantly monitored, and maintained, but it is very important to understand its limitations and implications. Regards, -drc
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