Details on DFS failover fixes included in KB933860 and Vista SP1.

Hello All,

Vista SP1 is here and if you are wondering how Vista SP1 can resolve potential issue on Vista clients connecting to a Distributed File System (DFS) root then allow me to enlighten you by providing the following information.

In a nutshell, when one DFS root server is offline, the Vista client cannot fail over to another DFS root server. The Vista client still tries to contact the offline DFS server and then encounter the problem.

If a domain's DFS root server is unavailable, a client computer that is running Windows Vista cannot connect to another DFS server that is listed in the referral when the client computer tries to connect to the DFS root server. DFS failover does not occur. When the client computer tries to connect to the offline DFS server, you receive an error message that resembles the following:

System error 1214 has occurred. The format of the specified network name is invalid.

If you wonder why this is happening in your environment and would like to understand better, then suppose the DFS root has two replicas. One DFS root server is offline. When the Vista client gets the DFS referral list, it contacts the first DC which is already offline. It tries to setup the TCP session on either 445 or 139 but cannot receive the response. Then the transport layer returns an error. Since the error cannot trigger the Vista client to failover to the next DFS root server in the referral list, the client receives the previously mentioned error.

What is the resolution? Apply the required hotfix as stated in KB933860, or know that this hotfix is included in Vista SP1.

Thanks,
Jasmin