this may be something stupid but I am new to Exchange so here is my issue.

 we have 2 exchange servers and I have them set up in a DAG with a witness server, the dag works great but my issue we had today is that one server went offline and we lost all connection to the exchange environment, no clients could reconnect to exchange or to the OWA. there is no load balancing as all traffic first this exchange server1 and  exchange server 2 runs in the background for the DAG, I have all mail flow set up to be sent from Exchange 1 but can be received by both, the server that went down today is Exchange 2, both servers have the mailbox role and the transport role.

 any thoughts?

You need to have 2 servers holding CAS role (can be colocated with mailbox role). CAS is the point where client is connected to. The 2 CAS must be load balanced so that if CAS1 is down, client can connect failover to CAS2.

yes the both have the CAS role, sorry this is also in Exchange 2013.  How do I configured or what is required to load balance?

You need,

• Hardware load balancer (1 unit, or a pair preferably)
• A hostname and an IP assigned to the load balancer
• An SSL certificate contains the hostname

https://technet.microsoft.com/en-us/library/jj898588%28v=exchg.150%29.aspx?f=255&MSPPError=-2147217396

You need,

• Hardware load balancer (1 unit, or a pair preferably)
• A hostname and an IP assigned to the load balancer
• An SSL certificate contains the hostname

https://technet.microsoft.com/en-us/library/jj898588%28v=exchg.150%29.aspx?f=255&MSPPError=-2147217396

• Proposed as answer by Winnie LiangMicrosoft contingent staff, Moderator 23 hours 9 minutes ago

Hi,

Please configure Load Balance for Client Access Server in Exchange 2013. For your reference:

http://blogs.technet.com/b/exchange/archive/2014/03/05/load-balancing-in-exchange-2013.aspx

http://www.msexchange.org/articles-tutorials/exchange-server-2013/high-availability-recovery/introducing-load-balancing-exchange-server-2013-part2.html

Regards,