Microsoft Exchange Server'.n DAG (Database Availability Groups) is vital to meet the demands of modern business for uninterrupted and high availability. High data volume finance, healthSuch configurations are quite common in sectors such as e-commerce and government institutions.
However, DAY What is it, how does it work and most importantly, how can you use this structure effectively for your business continuity? In this article, we will answer these questions in detail.
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Exchange Server DAG (Database Availability Groups)
DAG, Database Availability Groupsis the abbreviation of and Exchange ServerIt is a feature designed to provide the highest availability and data durability that a DAYconsists of two or more mailbox servers. These servers store one or more copies of the same mailbox database.
DAG creation is provided by a minimum of 2 and a maximum of 16 Mailbox servers.
Exchange Server DAY, high availability and continuous replication to ensure site resilience and Windows Failover Cluster uses technologies. DAY Each mailbox server in the database monitors each other for errors.(This process is monitored by Active Manager.)
DAG does not complete the task processes alone, it has to obey certain rules. In order to continue the failover processes in case of error and DOWN situations, DAG Active Manager (SAM)(SAM acts as a traffic cop and monitors all Database requests and movements on the servers.) In fact, here, the rules that the DAG must comply with and the Active Manager act as a traffic cop for the DAG.
Exchange Server'in DAY When you perform the creation process, it initially appears empty. DAY After the first servers you add, a failover node is created and with this process, the Network starts an infrastructure that monitors server errors.

Exchange Server DAG Working Logic
Exchange Server DAG provides continuous replication and automatic failover capabilities by combining multiple servers and databases. Here are the key features of DAG:
- A DAG stores copies of an Exchange database simultaneously across multiple servers, so that if one server fails, copies on other servers take over.
- In case of any server failure, the DAG system automatically powers on another copy to provide uninterrupted service. This feature ensures business continuity without the need for human intervention.
- DAG guarantees data security and availability both during planned maintenance work and in unexpected disaster situations.
Exchange Server DAG and Site Resilience Concepts
Exchange Server DAY When we hear the concept, we generally think of 2 or more servers within the same SITE, but the DAG concept is broad and includes the concept of Site Resilience. Since our topic is not about Site Resilince, we will only give a general description.
Database Availability Groups (DAGs) are often the first feature that comes to mind for high availability and data resiliency in Exchange Server solutions. However, DAGs do not only have this function. In fact, DAGs can be one of the cornerstones of a disaster recovery strategy across geographically dispersed data centers. This is at the heart of the concept called “Site Resilience.”
Site Resilience, refers to the ability of an organization to protect its IT infrastructure against various disaster scenarios. This concept aims to ensure business continuity, especially in unexpected situations such as natural disasters, power outages, cyber attacks or hardware failures. In today's digital world, uninterrupted service delivery is vital for customer satisfaction and operational efficiency.
In this context, used for critical systems such as Microsoft Exchange Server Database Availability Group (DAG), is at the core of Site Resilience strategies. DAGs are designed to prevent data loss and keep system downtime to a minimum. This technology ensures uninterrupted operation of email and communication platforms in particular.
Exchange Server Site Resilience Working Logic
An organization's data centers are often located in geographically diverse locations. DAY, supports the survival of the system in the face of natural disasters or regional outages by ensuring data is synchronized between these centers.
- Natural disasters: In cases such as flood, earthquake or hurricane DAY, deploys replicas in an unaffected data center.
- Power Outages: A local power outage DAY is met with automatic failover by.
- Cyber Attacks: DAY, prevents data loss or damage by ensuring the security of backup copies in the system.
Prerequisites for Exchange Server DAG
Exchange Server'in DAY There are some prerequisites for creation;
- At least 2 mailbox servers are required
- Servers Exchange Server versions must be the same
- Servers Windows It is preferable that the versions are the same.
- Servers are the same Domain must be a member. (Exchange Server works dependent on AD.)
- Each server must have sufficient disk space and backup capacity
- DNS settings must be configured correctly.
- There is a Witness Server requirement. This server must be a server other than the Exchange server and DC server.
This article DAY as it mentions the installation instructions Exchange Server and without mentioning their requirements, just Witness server ve DAY we will explain the installation instructions.
Exchange Server Witness Server Configuration Procedures
On Exchange Server DAY to create the structure Witness Server There is a need for this Witness Server The server that will work as Exchange Trusted Subsystem It will be enough to add the group to the Local Admin group. For detailed information;
Exchange Server IPBased and IP-Less DAG Concepts
In Exchange Server infrastructure Database Availability Group (DAG)is at the core of high availability and disaster recovery solutions. DAG offers two different configuration options based on the IP addressing method: IP-Based DAG ve IP-Less DAGIn this article, we will detail the differences between both configurations, usage scenarios, and points to consider.
Features of IP-Less DAG
No CNO Requirement:
- Windows Failover Cluster traditionally works with a CNO (Cluster Name Object), but IP-Less DAG eliminates this requirement entirely.
Exchange Management:
- DAG management is performed via Exchange Server. If necessary, operations can be performed using PowerShell. Management is not performed via Failover Cluster.
IP Address Requirement:
- IP-Less DAG does not require a static IP address on the network. When creating the DAG, the IP address field 255.255.255.255 It is enough to write.
Advantages of IP-Less DAG
- Simplified Configuration:
- No extra IP address or DNS configuration is required.
- Suitable for Dynamic Environments:
- Ideal for environments using dynamic and variable IP addressing systems.
- Easy Maintenance:
- Since Windows Failover Cluster does not require management, the administrative burden is reduced.
Things to Consider When Using IP-Less DAG
- PowerShell Required:
- DAG management is done entirely through PowerShell, so usage habits may vary for administrators who prefer GUI.
- Supported Environments:
- IP-Less DAG is only compatible with Windows Server 2012 R2 or later.
What is IP-Based DAG?
IP-Based DAG, traditional DAY configuration and requires a static IP address and CNO. This configuration allows DAG operations to be managed through Windows Failover Cluster.
Features of IP-Based DAG
- CNO Requirement:
- Cluster Name Object is mandatory for DAG. DAG operations are executed via this object via Windows Failover Cluster.
- Static IP Address:
- When creating a DAG, a static IP address for the MAPI network must be defined.
- Failover Cluster Management:
- DAG management is performed by Windows Failover Cluster and GUI is supported.
Advantages of IP-Based DAG
- Compatibility:
- It is more suitable for traditional configurations and compatible with legacy infrastructures.
- GUI Support:
- Since management can be done via GUI, it provides ease of use for administrators with lower technical knowledge.
Things to Consider When Using IP-Based DAG
- Static IP Address Requirement:
- A free IP address for the MAPI network needs to be configured. This requires additional network management.
- CNO Management:
- Issues with CNO can impact DAG operations. Ensure that CNO is configured correctly in DNS and Active Directory.
Exchange Server IP-Based DAG vs IP-Less DAG
Traits | IP-Based DAG | IP-Less DAG |
---|---|---|
CNO Requirement | Yes | No |
Static IP Requirement | Yes | None (255.255.255.255 is used) |
ACADEMIC AUTHORITIES | Windows Failover Cluster (GUI supported) | Exchange Server (via PowerShell) |
Application Area | Traditional infrastructures and legacy systems | Modern, dynamic network environments |
Installation Complexity | Medium | Low |
Note: If IP-Less DAG is suitable for your environment, you can configure your DAG as IP-Less, which can also reduce the risk of shallow attacks as there will be no need for an existing IP address.
In this article we only IPBased (Cluster Administrative Access Point CAAP) we will perform the installation as I mentioned above. IPLess You need to shape your environment well and decide for the installations.
Exchange Server DAG Network Configuration
In different versions of Microsoft Exchange Server, the use of network adapters (NICs) is important for performance and security. Especially up to Exchange Server 2016, Microsoft's recommendation is, MAPI ve Replication traffic through separate NICs. However, with Exchange Server 2016, this requirement has been made flexible and left to the discretion of system administrators. (Provided it is 10G)
In this article, we will cover modern approaches to using NICs in Exchange Server, their advantages, and considerations.
Exchange Server Replication NIC
In versions prior to Exchange Server 2016, Microsoft recommended a network configuration as follows:
- MAPI Traffic:
- Refers to the basic traffic through which users communicate with Outlook or other clients.
- It was recommended to route through a separate NIC.
- Replication Traffic:
- Traffic used for replication of Exchange Server databases between DAG (Database Availability Group) members.
- It was recommended to configure it on a separate NIC and VLAN.
- The VLAN used for replication only communicates with itself.
What to do for Replication NIC in Exchange Server
1. VLAN and Isolation
- Isolate Traffic:
- Provide isolation by configuring the Replication NIC on a separate VLAN from MAPI or client traffic.
- This prevents network conflicts and ensures that replication traffic continues uninterrupted.
- VLAN Configuration:
- Create a dedicated VLAN for the replication NIC on the switch and assign this VLAN to the port to which the replication NIC is connected.
2. IP Address Identification
- Static IP Usage:
- Use static IP addresses for the Replication NIC. These addresses should be reserved for replication traffic only.
- Subnet:
- To isolate replication traffic, ensure that the replication NICs are on the same subnet.
- Sample:
- Server1 Replication NIC IP: 192.168.10.1
- Server2 Replication NIC IP: 192.168.10.2
3. Disable DNS Records
The Replication NIC should not register with DNS. Otherwise, client connections may be problematic. To do this:

- Disable DNS Records:
- NIC Properties > Internet Protocol Version 4 (TCP/IPV4) > Advanced

Disable the “Register this connection's address in DNS” option.

- Limit DNS Resolution Scope:
- Why Primary DNS SuffixLeave the blank.
- You need to disable the File and Printer Sharing for Microsoft Networks option in the NIC Properties.
- You need to turn off the Client for Microsoft Network option.

- For Replication NIC default gateway Instead, add static routes to enable communication between DAG members only.
Using Single NIC for DAG in Exchange Server
With Exchange Server 2016, Microsoft made it possible to manage MAPI and Replication traffic over a single NIC. This has been a significant enabler for simpler network configurations, especially in small and medium-sized businesses. However, there are some requirements and recommendations:
Using Single NIC in Exchange Server
- Condition:
- Network card for single NIC use 10GbE must be at speed.
- Advantages:
- Provides a simpler configuration.
- Reduces hardware costs.
- It is easy to manage and speeds up the troubleshooting process.
Using Separate NIC and VLAN in Exchange Server
In large and complex architectures, using separate NICs and VLANs for MAPI and Replication traffic is still considered a best practice.
- Replication NIC Features:
- It is used only to communicate between DAG members.
- It is recommended to configure it in a separate VLAN.
- Isolates traffic to improve network performance and prevent conflict with MAPI traffic.
- Configuration Notes:
- The VLAN used for replication must be capable of communicating only within itself.
- NIC settings should be optimized and not used for client traffic.
Configuring Exchange Server DAG
In Microsoft Exchange Server Database Availability Group (DAG)is a structure used to provide high availability and disaster recovery features. DAG allows databases to be copied between different Exchange servers and automatically switch the service to another server in the event of a server outage.
Creating Exchange Server DAG
- Exchange Admin Center (EAC)Open .
- Servers > Database Availability Groups follow your path.
- Create a new DAG by clicking the “+” icon in the top right.

- Database Availability Group Name:
- Specify a group name for the DAG. This name can also be Failover Cluster Name Object (CNO) will be used as.
- Witness Server:
- Enter the fully qualified domain name (FQDN) of a defined Witness Server. This server plays an important role in determining the DAG majority.
- Witness Directory:
- Enter a name for the directory to be created on the Witness Server. For example,
C:DAGWitness
.
- Enter a name for the directory to be created on the Witness Server. For example,
- Database Availability Group IP Addresses:
- Define an IP address for the DAG. If IP-Less DAG If you want to create, click here 255.255.255.255 You just have to write.
- if MAPI ve Replication If you use separate VLANs for , an IP address for the MAPI network must be defined here.
- If it will be provided over a single NIC, an IP address belonging to the MAPI network must be defined.
- After entering the required information Save Press the key to complete the DAG creation process.

After the DAG is created, you will see the relevant DAG on the EAC screen. At the first stage, there is no server in the DAG. Now, we will add our servers to the DAG.

Making Servers Members of DAG in Exchange Server
we created DAY You can follow the steps below to add servers to it.
- On the DAG screen in the EAC, click the “Manage DAG Membership” button.
- In the window that opens “Add or remove servers” Select the servers you want to add to the DAG using the .

- The goal of this process is to test the role and privilege manipulation in order to access the resources of a EX1 ve EX2 If you have two Exchange servers named , select them and add them to the DAG.

- During the process of adding servers to the DAG:
- Active Directory Users and Computers (ADUC) on a Cluster Name Object (CNO) is created.
- A DNS record is assigned for this CNO.
- The IP address you define for the DAG is automatically associated.

- You can view the servers that are JOINed on EAC.

In some cases, you may need to manually create a CNO through ADUC. In this case:
- Create a CNO in ADUC with the name of the DAG you created via EAC.
- CNO Disable set it up.

- To CNO Exchange Trusted Subsystem Add as a member and grant full access.


Including Databases in DAG in Exchange Server
After creating the DAG and making the servers members of the DAG, you need to follow these steps to include your databases in replication within the DAG.
- EAC > Servers > Databases follow your path.
- Here you can view your existing databases.

- Add Database Copy Copy an existing database to other servers in the DAG using the .
For example:- Attach a database located on server EX2 to server EX1 as a passive copy.

While including Database in DAG in Exchange Server, Circular Logging feature must be disabled.
Mailbox Database Name:
- Select the name of the database to be replicated.
- Specify Mailbox Server:
- Select the target server to which the database will be copied.
- For example, you can passively copy the active database in EX2 to EX1.
- Activation Preference Number: The Activation Preference Number is a number used to determine the failover order of databases within a Database Availability Group (DAG) configuration in Exchange Server. Each database copy is assigned an Activation Preference Number. This number indicates which server you would ideally prefer to have the database active on. The number 1 is typically used for the server on which you want a database to be kept active. That is, the lowest number (1) indicates the highest preference.
- Assign a preference number to determine the failover order.
- 1: The primary server where you want the database to run actively.
- 2 and above: Passive servers.
- Assign a preference number to determine the failover order.
- Save Press the button to start the copying process.
- Once the copy is complete, you can view the copied databases and their status via EAC.

These operations must be repeated for all your databases on the Exchange Server to become DAG members.

The active database is on EX1 and the passive database is on EX2, and the Resynchorizing process is ongoing on the Passive server. Once this is completed, both servers will continue to operate in Healthy mode.

Our databases work with a DAG configuration and will continue to work on the passive database in case of any outage on one of the active servers.

Conclusion
In Exchange Server, DAG plays a critical role to ensure high availability and data security. With the right configuration steps, DAG improves system performance and minimizes downtime. By following the steps outlined in this article, you can successfully complete your DAG configuration and create a robust disaster recovery solution in your Exchange Server environment.
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