Hi We have Windows 2008 R2 single domain with two sites each site has exchange 2003 single server with local users mailboxes of each site. We are going to upgrade exchange 2003 to exchange 2010 and for that we have installed exchange 2010 single server in each site with mailbox, HUB and CAS roles. Between two sites we have 2MB link and we are planing to create DAG between these two exchange 2010 servers. I want to know it is important or any advantage that we have two NIC interface one for MAPI and one for Replication because first there is only one WAN link and boht traffic will be merge at WAN link and second if we create two VLAN at each site and one for MAPI and one for Replication it has meaning and usefull at local LAN site these VLAN but at WAN link it is no meaning becaue we have one WAN link. So it is not recommended that we use only one interface for both MAPI and Replication if we have DAG and their member are connected with single WAN link. Thanks

You will manage fine with just one NIC if you want/need to. Just look out for performance degradation. If you decide to go with 2 NICs to separate the replication traffic from the MAPI you'll need to remember to collaps the DAG netwoks to get the expected behaviour. DAG Cross Site\Subnet networking – Additional Configuration Jesper Bernle | Blog: http://xchangeserver.wordpress.com

There are some challenges with having two networks with multi-site dags. The main one, is the MAPI network should only be able to communicate with the other MAPI network in the second site, and the Replication Network should only be able to communicate with the other Replication network. So a replication NIC should not be able to communicate with a MAPI NIC, and vice versa. In Cross-site DAGS, without a separate WAN for replication, adding a replication network in my opinion, creates complexity without any added value. The Network requirements section of this article explain it more in depth. http://technet.microsoft.com/en-us/library/dd638104.aspx http://jaworskiblog.com