The DNS Virtual Server

The dns virtual server is an example of using dns style functionality in FreeRADIUS.

The Virtual Server

This is the dns virtual server.

It’s not meant to be fast. Don’t use it as a root server, or as a server for an ISP with millions of users. But it should be able to do thousands to tens of thousands of queries per second, without really trying hard.

It’s meant to be a flexible DNS server. Want to give different answers to VoIP phones and desktops, or other types of split horizon? It can do that.

Because DNS uses the Header.Rcode to communicate the result of a query (instead of opcode) the DNS state machine works differently to other protocols.

Requests will pass through the following processing sections: - A recv { … } section matching the opcode. e.g. recv Query { … }. Query processing and response formulation should be done here. If this section returns anything other than ok or updated, a reply.Header.Rcode value is set. - An error { … } section matching reply.Header.Rcode. e.g. error Server-Fail { … }. If the recv { … } section produced a reply.Header.Rcode value other than No-Error and a error { … } section matching the reply.Header.Rcode is provided, it is executed. Error sections are intended only for simplifying logging, and as such, the rcode of the section is ignored. Error sections can manipulate the reply, e.g. setting a new value for reply.Header.Rcode, but this will not cause additional `error { … } section to be executed. - A send { … } section matching the opcode. e.g. send Query-Response { … }. This can be used for general massaging of the reply. Return codes are ignored.

server dns {

namespace: The protocol / dictionary to use.

	namespace = dns

	listen {
		type = Query

		transport = udp

Dont use "port = 53" unless you want to break things

		udp {
			ipaddr = *
			port = 53
		}
	}

recv Query {
	if (Question[0].Name == 'foo.example.com') {
		reply.Resource-Record := {
			Name = 'foo.example.com'
			Type = ::A
			Class = ::Internet
			TTL = 0
			Type.A.IP = 127.0.0.1
		}
	}

	ok
}

send Query-Response {
	ok
}
}