My company has three Exchange Server 5.5 sites that are connected through permanent 64Kbps WAN links. The Exchange servers use typical messaging connectors to communicate. The central server connects to the Internet to send and retrieve email over an ISDN modem.
This configuration presents a problem, however: When the central server is connected to the Internet, the other two servers are no longer visible. Pinging the other servers produces a timeout. The other servers are visible only when the central server isn't connected to the Internet. Because of my company's high volume of email, the central server is connected to the Internet for most of the day, so users at the other sites receive their mail 2 to 3 hours late—an unacceptable level of service.
To solve this problem, I added static persistent Route commands to the central server's route table. The commands I added use the syntax
route add <destinationIP> mask 255.255.255 <gatewayIP> -p
where destinationIP is the IP address of the server for which I need visibility, and gatewayIP is the IP address of the router that the central server uses. The -p switch makes the Route command persistent, so the command still exists after a reboot.
Now, instead of sending email through the modem in search of a destination Exchange server on the Internet, the central server uses the route table to send the data through the WAN links. The other two servers remain visible, and users receive their mail almost instantly.