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8.2. Typical Exchange

8.2 Typical Exchange​

Cache                         Router
  ~                             ~
  | -------- Notify ----------> |  (optional)
  |                             |
  | <----- Serial Query ------- | R requests data
  |                             |
  | ----- 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
  ~                             ~

The cache server SHOULD send a Notify PDU with its current Serial Number when the cache's serial changes, with the expectation that the router MAY then issue a Serial Query earlier than it otherwise might. This is analogous to DNS NOTIFY in [RFC1996]. The cache MUST rate-limit Serial Notifies to no more frequently than one per minute.

When the transport layer is up and either a timer has gone off in the router or the cache has sent a Notify PDU, the router queries for new data by sending a Serial Query, and the cache sends all data newer than the serial in the Serial Query.

To limit the length of time a cache must keep old withdraws, a router MUST send either a Serial Query or a Reset Query periodically. See Section 6 for details on the required polling frequency.

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