A DNS name is a sequence of labels. In the presentation form
www.example.com., the dots separate the labels
www, example, and com. The final
dot represents the root’s empty label. Reading from right to left walks
from general to specific:
. root
└── com. top-level domain
└── example.com. delegated domain
└── www.example.com.The absolute name has a wire limit of 255 octets, including length bytes and the terminating root label. Each ordinary label is at most 63 octets. DNS names are not inherently UTF-8 strings. Internationalized names are normally converted by applications into ASCII-compatible labels before DNS sees them.
DNS comparison is case-insensitive for ordinary ASCII letters, although the original spelling can be preserved. A robust implementation therefore needs a canonical comparison rule without losing the bytes required for encoding.
In rgbdns, src/name.rs represents a name as a vector of
byte-vector labels. Construction validates label and total lengths.
Parsing accepts the familiar dotted form and backslash escapes. The type
provides parent and subdomain operations, case-insensitive ordering,
display formatting, and wire encoding. Making invalid names difficult to
construct removes repeated checks from the rest of the system.
The namespace is one tree; a zone is an administratively served portion of that tree. The two are not identical.
The zone example.com. might contain records for
www.example.com. and mail.example.com., then
delegate research.example.com. to other servers. The child
remains below example.com. in the namespace but is outside
the parent zone’s authoritative contents.
A delegation is expressed by NS records at the cut. If a named server lies inside the delegated child, a resolver cannot first resolve that server’s name through the child—it needs its address in order to reach the child. The parent therefore supplies an address record called glue. Glue is navigation data, not an assertion that the parent is authoritative for every fact about the host.
The root zone delegates top-level domains. A cold recursive resolver starts with a small configured set of root server addresses, asks the root where to find a top-level domain, asks that domain where to find the next child, and continues.
A wildcard such as *.example.com. does not mean “return
this record for every name ending in example.com.” It participates only
when the queried name does not exist, and the closest-encloser rules
determine which wildcard, if any, can synthesize an answer. Existing
intermediate names can block a wildcard.
rgbdns stores wildcard records under their literal wildcard owner and
its zone lookup searches from the queried name toward the closest
existing ancestor. It synthesizes the queried owner in returned records.
This is more precise than a string suffix match and is one reason the
Zone abstraction tracks known nodes in addition to
records.