With this DNAME record in effect, all records and subdomains under r-and-d.example.com are also present under research.example.com. So looking up www.biotech.research.example.com has the same result as looking up www.biotech.r-and-d.example.com. To be backward compatible, the nameserver will “synthesize” a CNAME record for the requested information, along with providing the actual DNAME record. However, apparently some older resolver libraries wouldn’t handle DNAME records properly.

The idea behind bitlabels (also sometimes called “binary labels”) is that the traditional ...4.3.2.1.in-addr.arpa or ...e.f.f.3.ip6.int delegation mechanism is less than perfect because it only allows delegation on 8- or 4-bit boundaries, respectively. So conceptually, a bitlabel is an expression of a very long domain name with individual bits separated by periods. (In the domain name system, the data between two periods is called a “label.”) However, within the DNS protocol, a bitlabel is expressed as a single chunk of binary data, regardless of the number of bits it contains, rather than a long list of individual ASCII labels. In the DNS zone files, bitlabels may be specified in either binary, octal, decimal, or hexadecimal, with an explicit value indicating the length in bits. Listing 5-5 shows several bitlabel representations of the same information.