2. Glossary

The following terms are used with special meaning.

Global RPKI: The authoritative data of the RPKI are published in a distributed set of servers at the IANA, Regional Internet Registries (RIRs), National Internet Registries (NIRs), and ISPs; see [RFC6481].

Cache: A cache is a coalesced copy of the published Global RPKI data, periodically fetched or refreshed, directly or indirectly, using the rsync protocol [RFC5781] or some successor. Relying Party software is used to gather and validate the distributed data of the RPKI into a cache. Trusting this cache further is a matter between the provider of the cache and a Relying Party.

Serial Number: "Serial Number" is a 32-bit strictly increasing unsigned integer which wraps from 2^32-1 to 0. It denotes the logical version of a cache. A cache increments the value when it successfully updates its data from a parent cache or from primary RPKI data. While a cache is receiving updates, new incoming data and implicit deletes are associated with the new serial but MUST NOT be sent until the fetch is complete. A Serial Number is not commensurate between different caches or different protocol versions, nor need it be maintained across resets of the cache server. See [RFC1982] on DNS Serial Number Arithmetic for too much detail on the topic.

Session ID: When a cache server is started, it generates a Session ID to uniquely identify the instance of the cache and to bind it to the sequence of Serial Numbers that cache instance will generate. This allows the router to restart a failed session knowing that the Serial Number it is using is commensurate with that of the cache.

Payload PDU: A payload PDU is a protocol message which contains data for use by the router, as opposed to a PDU which conveys the control mechanisms of this protocol. Prefixes and Router Keys are examples of payload PDUs.