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Establishing a connection across a NAT or firewall

If your source and target are on opposite sides of a NAT or firewall, you will need special configurations to accommodate the complex network environment. Additionally, you must have the hardware already in place and know how to configure the hardware ports. If you do not, see the reference manual for your hardware.

In this environment, you must have static mapping where a single, internal IP address is always mapped in a one-to-one correlation to a single, external IP address. Double-Take Availability cannot handle dynamic mappings where a single, internal IP address can be mapped to any one of a group of external IP addresses managed by the router.

1. Double-Take Availability uses specific ports for communication between the Double-Take Availability servers and Double-Take Availability clients. In order to use Double-Take Availability through a NAT or firewall, you must first verify the current Double-Take Availability port settings so that you can open the correct ports on your hardware to allow Double-Take Availability machines to communicate with each other. Using the following table, locate and record your port settings for each of the Double-Take Availability ports. The port setting can be found in the following locations.
• Replication Console—From the Replication Console, select File, Options, and the Configuration tab.
• Failover Control Center—From the Failover Control Center, select Settings, Communications.

• Double-Take Availability server—From the Replication Console, right-click on a server in the tree in the left pane of the Replication Console, select Properties, and the Network tab.

   

  Replication Console Status Transmit Port

  The Status Transmit Port sends and receives directed UDP communications to display status and statistics in the Replication Console. The default setting is 1505.

  Replication Console Heartbeat Advertisement

  The Heartbeat Advertisement port sends and receives broadcast UDP communications to populate the Replication Console tree with Double-Take Availability servers. The default setting is 1500.

  Failover Control Center Service Transmit Port

  The Service Transmit Port sends and receives TCP communication between Double-Take Availability servers and between Double-Take Availability servers and Double-Take Availability clients. The default setting is 1500.

  Failover Control Center Heartbeat Listen Port

  The Heartbeat Listen Port send and receives broadcast UDP communications to populate the Failover Control Center with Double-Take Availability servers. The default setting is 1500.

  Double-Take Availability Server Service Listen Port

  The Service Listen Port sends and receives TCP communication between Double-Take Availability servers and between Double-Take Availability servers and Double-Take Availability clients. The default setting is 1500.

  Double-Take Availability Server Heartbeat Transmit Port

  The Heartbeat Advertisement port sends and receives broadcast UDP communications to populate the Replication Console tree with Double-Take Availability servers. The default setting is 1500.

  Double-Take Availability Server Status Listen Port

  The Status Listen Port sends directed UDP communications to display status and statistics in the Replication Console. The default setting is 1505.

  Double-Take Availability Server Statistics Logging Port

  The port used for statistics logging is not available through a client. You must use the get and set DTCL commands to modify that port. See the Scripting Guide for details on the commands and the StatsPort option. The default setting is 1506.

   

2. You need to configure your hardware so that Double-Take Availability traffic is permitted access through the router and directed appropriately. Using the port information from the previous section, configure your router identifying each Double-Take Availability server, its IP address, and the Double-Take Availability and router ports. Also, note the following caveats.

   • Since Double-Take Availability communication occurs bidirectionally, make sure you configure your router for both incoming and outgoing traffic for all of your Double-Take Availability servers and Double-Take Availability clients.
   • In addition to UDP heartbeats, Double-Take Availability failover can use ICMP pings to determine if the source server is online. If you are going to use ICMP pings and a router between the source and target is blocking ICMP traffic, failover monitors cannot be created or used. In this situation, you must configure your router to allow ICMP pings between the source and target.

   Since there are many types of hardware on the market, each can be configured differently. See your hardware reference manual for instructions on setting up your particular router.

3. If your network is configured to propagate UDP broadcasts, your servers will be populated in the Replication Console from across the router. If not, you have to manually insert the servers, by selecting Insert, Server. Type the IP address of the router the server is connected to and the port number the server is using for heartbeats.

4. Once your server is inserted in the Replication Console, you can use the Connection Wizard or the Connection Manager to establish your connection.

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