8.4. Cache Has No Data Available

8.4 Cache Has No Data Available

Cache                         Router
  ~                             ~
  | <------ Serial Query ------ | R requests data
  | ---- Error Report PDU ----> | C No Data Available
  ~                             ~

Cache                         Router
  ~                             ~
  | <------ Reset Query ------- | R requests data
  | ---- Error Report PDU ----> | C No Data Available
  ~                             ~

The cache may respond to either a Serial Query or a Reset Query informing the router that the cache cannot supply any update at all. The most likely cause is that the cache has lost state, perhaps due to a restart, and has not yet recovered. While it is possible that a cache might go into such a state without dropping any of its active sessions, a router is more likely to see this behavior when it initially connects and issues a Reset Query while the cache is still rebuilding its database.

When a router receives this kind of error, the router SHOULD attempt to connect to any other caches in its cache list, in preference order. If no other caches are available, the router MUST issue periodic Reset Queries until it gets a new usable load from the cache.