1. Should a word about the forwarding servers be included in Introduction?
  2. Is telnet(1) really needed in this section? --CezaryMorga

I don't see why telnet is there either. --ceri

I had proposed this privately before the Document was published in 2005: "note that ping or telnet can be used to show hostname lookups as the systems sees." So no need to telnet to domain port, just a quick way to do a gethostname(3) lookup.

On at least NetBSD, telnet uses getaddrinfo(3) and ping uses gethostbyname(3) which both basically use the name-service switch dispatcher (nsswitch). The book probably doesn't need details like this, but knowing that other tools are available is good. --reed

Nevertheless I'd suggest removing ping(1) and telnet(1) from this section: it's getting quite big without two additional commands that are not meant to query for domain name IP address translation. --CezaryMorga

We have a few DNS sections, so we need to make sure they don't duplicate topics but point to section as applicable. Such as Determine who is responsible for a DNS zone and Understand various "domain" contexts. Also we may also move these topics next to each other in the book. --reed