Maintain an IP inventory
Record each address or block, its owning server, routed interface, purpose, reverse DNS name and firewall policy. Confirm the owning hostname before changing a resource. Treat a block as a routed resource rather than assuming every address is configured identically on the operating system.
Configure reverse DNS
Create reverse DNS only after the forward A or AAAA record already points to the same address. Use a fully qualified hostname and verify the forward and reverse results from an external resolver. Mail servers often require this alignment, but reverse DNS alone does not authorise a sender.
Build firewall and routing rules
Start with explicit required services and administrator source networks, order rules from specific to general and keep an out-of-band recovery path. Apply routing only to resources assigned to the server and verify return traffic before removing the previous path.
Interpret traffic
Compare inbound and outbound traffic with application requests, monitoring and known deployments over the same time range. A bandwidth spike can be legitimate traffic, a backup or abuse; a sudden drop can be application failure, routing or simply lower demand. Network graphs alone do not establish the cause.
Connect servers privately
Order an eligible private network, attach the intended servers and assign a private addressing plan that does not overlap existing networks. Test reachability and maximum transmission unit before moving database or replication traffic. Detach routes only after confirming no workload still depends on them.
Prepare for a network change
Record the current reverse DNS, firewall and routes, maintain an unaffected access method and define a rollback. Use a maintenance window when there is no redundant path, and verify both inbound service access and outbound return traffic before closing the change.
