HTTP Sessions handling relies on information found in the TCP session.

In HTTP 1.0 you can only host one website / IP.

The Host Header was introduced in HTTP 1.1 to allow hosting multiple HTTP sites on a single IP address.

HTTP 1.1 uses TCP and UDP for transport (UDP is only used for small entities, e.g icons).

HTTP DIGEST is a secure way to exchange authentication credentials.

Multiple A records can point to a single IP address.

The DS record contains the hash of the parent zone KSK.

A name server will not update cached records if the serial number of the cached entry is still the same.

A server that (authoritatively) hosts a signed zone is directly asked for a record. If the signature of this record is valid, the server will respond with the "authenticated data" (AD) flag set.