ORs SHOULD generate a new server descriptor and a new extra-info document whenever any of the following events have occurred:
- A period of time (18 hrs by default) has passed since the last time a descriptor was generated. - A descriptor field other than bandwidth or uptime has changed. - Its uptime is less than 24h and bandwidth has changed by a factor of 2 from the last time a descriptor was generated, and at least a given interval of time (3 hours by default) has passed since then. - Its uptime has been reset (by restarting). - It receives a networkstatus consensus in which it is not listed. - It receives a networkstatus consensus in which it is listed with the StaleDesc flag. [XXX this list is incomplete; see router_differences_are_cosmetic() in routerlist.c for others]
ORs SHOULD NOT publish a new server descriptor or extra-info document if none of the above events have occurred and not much time has passed (12 hours by default).
Tor versions older than 0.3.5.1-alpha ignore uptime when checking for bandwidth changes.
After generating a descriptor, ORs upload them to every directory authority they know, by posting them (in order) to the URL
Server descriptors may not exceed 20,000 bytes in length; extra-info documents may not exceed 50,000 bytes in length. If they do, the authorities SHOULD reject them.