8.3. No Incremental Update Available

8.3 No Incremental Update Available

Cache                         Router
  ~                             ~
  | <------ Serial Query ------ | R requests data
  | ------- Cache Reset ------> | C cannot supply update
  |                             |   from specified serial
  | <------ Reset Query ------- | R requests new 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 may respond to a Serial Query with a Cache Reset, informing the router that the cache cannot supply an incremental update from the Serial Number specified by the router. This might be because the cache has lost state, or because the router has waited too long between polls and the cache has cleaned up old data that it no longer believes it needs, or because the cache has run out of storage space and had to expire some old data early. Regardless of how this state arose, the cache replies with a Cache Reset to tell the router that it cannot honor the request. When a router receives this, the router SHOULD attempt to connect to any more-preferred caches in its cache list. If there are no more-preferred caches, it MUST issue a Reset Query and get an entire new load from the cache.