purging old router information, revocation

James Muir jamuir at scs.carleton.ca
Wed Feb 21 19:09:31 UTC 2007

I'd like to know how directories are cleaned up after a router leaves 
the Tor network.  I've read through the specs distributed with but I haven't been able to find a discussion on this. 
Maybe some readers who run onion routers have had some practical 
experience on this that they can share.

If an OR leaves the network and no longer accepts incoming connections, 
then I understand that the directory authorities will no longer list it 
as "Running" in their network-status documents ("Running" means the DA 
was able to connect to it sometime in the last 30mins).  How long will 
the DAs keep trying to connect to an OR that doesn't respond?  At what 
point do the DAs purge their stored descriptors for that router and no 
longer list it in their network-status document (assuming that they do, 
in fact, purge information)?

Eventually, the onion key for a router that has left the network will 
expire (the default lifetime is 1 week).  If a descriptor contains an 
expired onion key, do the DAs detect this, or is it up to the Tor 
clients do to this?

I just noticed that src/or/or.h seems to give some clues to these questions:

/** How old do we allow a router to get before removing it
  * from the router list? In seconds. */
#define ROUTER_MAX_AGE (60*60*48)
/** How old can a router get before we (as a server) will no longer
  * consider it live? In seconds. */
#define ROUTER_MAX_AGE_TO_PUBLISH (60*60*20)
/** How old do we let a saved descriptor get before force-removing it? */
#define OLD_ROUTER_DESC_MAX_AGE (60*60*24*5)
/** How old do we let a networkstatus get before ignoring it? */
#define NETWORKSTATUS_MAX_AGE (60*60*24)


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