All cluster nodes should have a dedicated connection to all other nodes in the cluster. However the cluster can propagate the data as long as all nodes are connected to at leastone other node.
The network connection is done via the GRE protocol (IP protocol number 47. For more information, refer toWikipedia: List of IP protocol numbers. Since GRE is anIP protocol, it is not based on either TCP or UDP and has no concept of ports. It is anIP protocol by itself. That means that it can not simply be made available with a portforwarding behind a NAT (Network Address Translation). A fully transparent VPN solutionwill be required if the cluster is supposed to be installed over different locations.
If you do have network equipment that is able to encapsulate the protocol, you mightstill run into the issue of network address complications. This is easiest worked aroundby setting up the systems in a simpler network configuration (e.g. same site) and latershipment/reconfiguration.
A cluster node will never forward traffic between two other nodes to avoid networkingloops. Compared to using the spanning tree protocol (STP), this means that a brokennetwork connection between two nodes will not trigger any downtime of other connections.
If you prefer the dynamic loop prevention behavior, you could add managed switches infront of the Application Interfaces of the Hardware Appliances. Please note that if the networktopology change prevents network traffic between the nodes for too long, your cluster nodesmight stop operation and require manual interaction. Rapid Spanning Tree Protocol (RSTP)might be an interesting alternative to STP in this case.
