A Software Approach to Distributing Requests for DNS Service Using GNU Zebra, ISC BIND 9, and FreeBSD

This paper describes an approach for deploying authoritative name servers using a cluster of hosts, across which the load of client requests is distributed. DNS services deployed in this fashion enjoy high availability and are also able to scale to increasing request loads in a straightforward manner.

The approach described here does not employ any custom load-balancing appliances (e.g. devices commonly marketed as as "layer-four switches", "content switches" or "load-balancers"); instead the individual members of the cluster announce a service address to one or more gateway routers by participating in routing protocols to provide an intra-cluster anycast architecture.

Load-balancing appliances can sometimes present single points of failure to a cluster. This problem is avoided using the technique described in this paper; the only components required to construct the cluster are the hosts that provide the service, and one or more gateway routers which provide access to the rest of the Internet.

The coupling between the DNS software and the routing software needs to be sufficiently robust to ensure that a service address is not advertised while requests cannot be satisfied. This includes a description of a technique for announcing and withdrawing the route for a service address such that availability of the service in the routing system is coupled with the ability to answer requests on individual hosts in the cluster.

The F Root Name Server[9] is deployed using clusters built in this fashion, using FreeBSD[10], GNU Zebra[11] and ISC BIND 9[12].