I have a 2008R2 Standard instance (2008R2 SP1 10.50.2500) which has developed strange problems with linked server connections.
All of these linked server connections were working normally at one point, and some of them still are, but others will hang on any direct attempt to use them (using SSMS, openquery, sp_testlinkedserver, etc.) If using code, they run for a 15-30 (or longer) minutes before returning a timeout error. In SSMS, using "test connection" results in the entire SSMS instance locking for the same 15-30 minutes finally resulting in the timeout error.
Other servers in the group with the exact same driver and connection information still connect without issue.
Most of these connections are Oracle, but I have a DB2 connection and an ODBC connection to MySQL that is doing it too. Not all the connections are dead, several of them are working properly.
When the server has been rebooted, the linked server connections function properly, but within 10-30 minutes, they cease to allow any connection.
I've searched everywhere and found no one with these exact problem.