8.1. Start or Restart

8.1 Start or Restart

Cache                         Router
  ~                             ~
  | <----- Reset Query -------- | R requests data (or Serial Query)
  |                             |
  | ----- Cache Response -----> | C confirms request
  | ------- Payload PDU ------> | C sends zero or more
  | ------- Payload PDU ------> |   IPv4 Prefix, IPv6 Prefix,
  | ------- Payload PDU ------> |   or Router Key PDUs
  | ------- End of Data ------> | C sends End of Data
  |                             |   and sends new serial
  ~                             ~

When a transport connection is first established, the router MUST send either a Reset Query or a Serial Query. A Serial Query would be appropriate if the router has significant unexpired data from a broken session with the same cache and remembers the Session ID of that session, in which case a Serial Query containing the Session ID from the previous session will allow the router to bring itself up to date while ensuring that the Serial Numbers are commensurate and that the router and cache are speaking compatible versions of the protocol. In all other cases, the router lacks the necessary data for fast resynchronization and therefore MUST fall back to a Reset Query.

The Reset Query sequence is also used when the router receives a Cache Reset, chooses a new cache, or fears that it has otherwise lost its way.

See Section 7 for details on version negotiation.

To limit the length of time a cache must keep the data necessary to generate incremental updates, a router MUST send either a Serial Query or a Reset Query periodically. This also acts as a keep-alive at the application layer. See Section 6 for details on the required polling frequency.