It is recommended, though not strictly required, that you run your DRBD replication over a dedicated connection. At the time of this writing, the most reasonable choice for this is a direct, back-to-back, Gigabit Ethernet connection. If and when you run DRBD over switches, use of redundant components and the Linux bonding driver (in active-backup mode) is recommended.

It is generally not recommended to run DRBD replication via routers, for reasons of fairly obvious performance drawbacks (adversely affecting both throughput and latency).

In terms of local firewall considerations, it is important to understand that DRBD (by convention) uses TCP ports from 7788 upwards, with every TCP resource listening on a separate, configurable, but unchanging TCP port. DRBD uses two separate TCP connections (one in either direction) for every resource configured. For proper DRBD functionality, it is required that these connections are allowed by your firewall configuration.

Security considerations other than firewalling may also apply if a Mandatory Access Control (MAC) scheme such as SELinux or AppArmor is enabled. You may have to adjust your local security policy so it does not keep DRBD from functioning properly.

You must, of course, also ensure that the TCP ports you will be using for DRBD are not already being used by another application.

	Note
	It is not possible to configure a DRBD resource to support more than one TCP connection. If you want to provide for DRBD connection load-balancing or redundancy, you can easily do so at the Ethernet level (again, using the bonding driver).

For the purposes of this guide, we assume a very simple setup: