[krbdev.mit.edu #3334] libkrb5 treats all KDC errors as terminal

[Ken Raeburn via RT]

On Jan 10, 2006, at 16:06, lukeh at padl.com via RT wrote:
> If a KDC returns KDC_ERR_SVC_UNAVAILABLE, it appears that that the
> client library will not failover to the next KDC. All error codes,
> except for KDC_ERR_RESPONSE_TOO_BIG, are treated as terminal.


Looks like this error code was quietly added from RFC 1510 -> RFC  
4120 (somewhere between draft 03, 11/98, and draft 04, 6/99), without  
any definition besides the not-very-helpful text "A service is not  
available."  There is no indication in the main text when this error  
code might be returned.  If it said "the KDC service is not  
available", that might've been clearer, but "*a* service"??  What,  
should we return this error if the local SMTP handler has been shut  
down?

Also, the MIT code has no concept of "failing over to the next KDC".   
If it gets a response back from any KDC, the loop querying the KDCs  
terminates.  RESPONSE_TOO_BIG is handled by starting the whole  
process up again but looking only for TCP servers.

Handling this properly -- assuming failing over to the next KDC is in  
fact the right response to this error code -- will probably involve  
rewriting the query loop to add a callback to examine the returned  
data and decide whether or how to continue the current query loop,  
which servers to drop, etc.  This would also be a better way of  
handling RESPONSE_TOO_BIG, as well.

Ken