0

If you look at the press releases of various orgs that run the internet, you can see them praise the fact that now they run root server X in city Y, as if that magically makes everyone in city Y get all the relevant resolutions from the local server X, instead of going 200ms across the oceans and lands to other continents for resolutions.

Similarly, the zones of some geographical domain names, like .ru, are being mirrored not just within Europe, but also, for example, in Hong Kong, which is no more, no less, but is about 300ms away from central Europe, since the traffic is often crossing the two oceans on each way.

Doesn't all of this negatively affect DNS performance? Isn't it more of a liability to have a diverse pool of geodispersed authoritative servers, especially if your target audience is quite geographically concentrated?

Perhaps a better question is, are there any DNS resolvers that use something better than the naive round-robin for choosing which authoritative server to contact?

Improve this question
1
  • 1
    All root and 1st sub-level records are being heavily cached. Other takes Anycast if needed. I think you're witch hunting.
    – poige
    Dec 18, 2013 at 18:52

3 Answers 3

Reset to default
2

Anycast is what makes this work well for large DNS servers. The same IP address gets routed to servers all over the world, and the routers closest to you pick the nearest one.

Most geographical diversity for DNS is about making sure it stays up even in the event of large outages.

Improve this answer
2
  • Yes, I forgot to acknowledge anycast in my question, but even with anycast, in case of heterogeneous networks (where the operator doesn't have their own multinational backbone with lots of peering), there's often still a rather noticeable latency present and a non-optimal routing is apparent.
    – cnst
    Oct 29, 2013 at 2:39
  • 1
    I've never seen a press release saying that running DNS servers in a particular city will make them faster without them using Anycast. Generally it doesn't matter - DNS records get cached. What they get by having DNS in cities X, Y and Z is to ensure their DNS stays up even if aliens destroy city X while city Y deals with a massive flood.
    – Grant
    Oct 29, 2013 at 13:03
2

Various caching resolvers will keep track of the response speeds (RTT) of various authoritative servers and prefer them. The behavior of some popular recursors was tested and the results are in this presentation. They tested the most common software: PowerDNS, Unbound, Bind, etc:

https://www.dns-oarc.net/files/workshop-201203/OARC-workshop-London-2012-NS-selection.pdf

In theory, even with a domain whose NS's are anycast'd, the behavior of one of these resolvers that keeps track of RTT and prefers fastest hosts should provide some affinity to the fastest server even if its not the closest in terms of BGP path length.

Improve this answer
1
1

Many of these providers are using Anycast DNS.

http://en.wikipedia.org/wiki/Anycast#Domain_Name_System

Improve this answer

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .