dns id in requests

RD> I have noticed that the corporate dns server is
RD> sending out dns requests with same id but different
RD> udp src port for consecutive requests. I was under the
RD> impression that the "dns_id must be different for
RD> requests from hostA to serverB as they are used to
RD> match requests with responses. The udp src port can be
RD> same for consecutive requests(this from earlier
RD> discussions on bind in this forum)".

<URL:http://cr.yp.to/djbdns/forgery.html>

RD> I searched dns rfcs back to 1034/1035 but [...]

.... not forward to RFC 2181.