DNS Racing -Multi ISP load balancing with failover using DNS.

Matus UHLAR - fantomas uhlar at fantomas.sk
Mon May 30 09:07:25 UTC 2011

On 30.05.11 05:12, Maren S. Leizaola wrote:
> DNS-Racing is a method of load balancing access to servers which are  
> multi homed and provides lowest latency access to users and network  
> resilience to ISP/routing failure.

like, RRset sorting?

> **What does it do?*
> It permits a server which is connected to two ISPs to use the optimal  
> ISP when transferring data to a user regardless of TCP/UDP protocol.  
> When a user does a DNS look up it will select the IP address of the  
> server to which is closest. If one of the two ISPs is down or there is a  
> routing problem the user will only be offered the IP address of the  
> server it has access to. It also means that traffic will have the lowest  
> latency.

> DNS Racing can be done with 2 or more providers and permits to scale  
> network bandwidth horizontally by adding more providers. In theory up to  
> 14 different ISPs/IPs could be used to do the delivery.
> IT is a poor man’s replacement for BGP multihoming and IP anycast.
> For those that want a full explanation and an implementation guide.
> http://blog.hk.com/index.php?/archives/84-DNS-Racing.-Multi-ISP-load-balancing-with-failover-using-DNS..html
> Hey it is Free and you can implement it using BIND.

So, any server will return the IP that is closer to the _server_, not to the
_client_. It relies on BIND RTT-measring feature that has undergone some
changes in the past and ocasionally tries the far (topologically) server to
see if it's still far, in which case the client will get the worse result...

Matus UHLAR - fantomas, uhlar at fantomas.sk ; http://www.fantomas.sk/
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