Configuring Downstream Servers

As dnsdist is a loadbalancer and does not do any DNS resolving or serving by itself, it needs downstream servers. To add downstream servers, either include them on the command line:

dnsdist -l -a 2620:0:ccc::2 2620:0:ccd::2

Or add them to the configuration file:


These two equivalent configurations give you sane load balancing using a very sensible distribution policy. Many users will simply be done with this configuration. It works as well for authoritative as for recursive servers.


dnsdist uses a health check, sent once every second, to determine the availability of a backend server.

By default, an A query for “” is sent. A different query type and target can be specified by passing, respectively, the checkType and checkName parameters to newServer().

The default behavior is to consider any valid response with an RCODE different from ServFail as valid. If the mustResolve parameter of newServer() is set to true, a response will only be considered valid if its RCODE differs from NXDomain, ServFail and Refused.

The number of health check failures before a server is considered down is configurable via the maxCheckFailures parameter, defaulting to 1. The CD flag can be set on the query by setting setCD to true. e.g.:

newServer({address="", checkType="AAAA", checkName="", mustResolve=true})

Source address selection

In multi-homed setups, it can be useful to be able to select the source address or the outgoing interface used by dnsdist to contact a downstream server. This can be done by using the source parameter:

newServer({address="", source=""})
newServer({address="", source="eth1"})
newServer({address="", source=""})

The supported values for source are: - an IPv4 or IPv6 address, which must exist on the system - an interface name - an IPv4 or IPv6 address followed by ‘@’ then an interface name

Please note that specifying the interface name is only supported on system having IP_PKTINFO.