MsExchange Blog Spot Telnet25

April 20, 2010

Understanding DAG & Automatic Failover On Complete Server shutdown PART#1

Filed under: General — telnet25 @ 12:44 pm

Now you decided to give less impact to MAPI clients when One of the Exchange Server goes down in DAG group. Remember MAPI clients are still able to connect if both servers are up and running.

Things to remember

  • Each MailboxDatabase has attribute called RpcClientAccessServer
  • This is the end point that MAPI clients ( outlook users ) mailboxes  use to connect to the  their corresponding database.
  • MAPI Clients connecting trough this EndPoint

MAPI Clients ———->Looks for mail database to connect too——–> They read the attribute ( RpcClientAccessServer ) this Attribute tells the MAPI client & clients which DB to connect too.

  • My user name is Dedealoc My mailbox is located on server called mail1.smtp25.local , my mailbox resides on database called DB1



  • Now we want to control this by creating CAS array here is the link
  • We want MAPI ( outlook Clients to connect to) look for to connect DNS entry we will create

**** Remember if DAG member wont shut down ( Exchange server) you are safe no need to update DNS at all, if Server shuts down you will have to update below record to make the client successfully connect to remaining server & DAG member*****



  • After creating this A record for your CAS configuration fallow the steps to change the TTL
  • Connect to your AD/DNS click View and chose “advance”


  • Find the A record you have created for the


  • Now we will modify the TTL to 3 minutes



  • In in a two server Multi-role environment (MB,CAS,HTS) for automatic failover, if one of the DAG members shuts down you will need to have a load balancer.
  • You need to purchase to load balance the load balancer if you wish not to operate on one leg, so double the $$$$$
  • You can make manual DNS updates , IF DAG member shuts down, it takes seconds ( with lowering TTL on DNS) you will save $$$ and achieve same results. 

I have been keep taking about same things over and over again last couple articles as many similar questions I was asked in this subject. If you get your hands on settings up DAG and see how outlook clients freaks out when Server has the active database shuts down, I am sure you will understand more and start seeing the process very simple.

Best regards,
Oz Casey , Dedeal
MCSE 2003, M+, S+, MCDST
Security+, Project +, Server +
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