6. Protocol Timing Parameters

Since the data the cache distributes via the RPKI-Router protocol are retrieved from the Global RPKI system at intervals which are only known to the cache, only the cache can really know how frequently it makes sense for the router to poll the cache, or how long the data are likely to remain valid (or, at least, unchanged). For this reason, as well as to allow the cache some control over the load placed on it by its client routers, the End Of Data PDU includes three values that allow the cache to communicate timing parameters to the router:

Refresh Interval: This parameter tells the router how long to wait before next attempting to poll the cache and between subsequent attempts, using a Serial Query or Reset Query PDU. The router SHOULD NOT poll the cache sooner than indicated by this parameter. Note that receipt of a Serial Notify PDU overrides this interval and suggests that the router issue an immediate query without waiting for the Refresh Interval to expire. Countdown for this timer starts upon receipt of the containing End Of Data PDU.

• Minimum allowed value: 1 second
• Maximum allowed value: 86400 seconds (1 day)
• Recommended default: 3600 seconds (1 hour)

Retry Interval: This parameter tells the router how long to wait before retrying a failed Serial Query or Reset Query. The router SHOULD NOT retry sooner than indicated by this parameter. Note that a protocol version mismatch overrides this interval: if the router needs to downgrade to a lower protocol version number, it MAY send the first Serial Query or Reset Query immediately. Countdown for this timer starts upon failure of the query and restarts after each subsequent failure until a query succeeds.

• Minimum allowed value: 1 second
• Maximum allowed value: 7200 seconds (2 hours)
• Recommended default: 600 seconds (10 minutes)

Expire Interval: This parameter tells the router how long it can continue to use the current version of the data while unable to perform a successful subsequent query. The router MUST NOT retain the data past the time indicated by this parameter. Countdown for this timer starts upon receipt of the containing End Of Data PDU.

• Minimum allowed value: 600 seconds (10 minutes)
• Maximum allowed value: 172800 seconds (2 days)
• Recommended default: 7200 seconds (2 hours)

If the router has never issued a successful query against a particular cache, it SHOULD retry periodically using the default Retry Interval, above.

Caches MUST set Expire Interval to a value larger than either Refresh Interval or Retry Interval.