In short: Configure only the IP addresses, prefix lengths and gateways assigned to the service. Keep console access open while changing networking, and apply equivalent firewall policy to IPv4 and IPv6.
Collect the handover details
- Assigned IPv4 address and prefix or netmask.
- IPv4 gateway.
- Assigned IPv6 address or subnet and prefix length.
- IPv6 gateway or routing method.
- Resolver addresses where provided.
Make the configuration persistent
Use the network-management method supported by the installed operating system. Temporary command-line changes may disappear at reboot. Record existing configuration and keep the out-of-band console available.
Test in stages
- Confirm the interface is up and has the intended addresses.
- Reach the local gateway.
- Test an external address over IPv4 and IPv6 separately.
- Test DNS resolution.
- Test the actual service listener and firewall from an external network.
- Reboot during the maintenance window and retest persistence.
Avoid remote lockout: A wrong prefix, gateway or interface name can end the SSH session immediately. Never make an untested network replacement without console or rollback access.
Firewalls and listeners
An application may listen on IPv4 but not IPv6, or a firewall may protect only one protocol. Check both. Do not publish an AAAA record until the service is reachable and secured over IPv6.
When contacting support
Provide the service identifier, configured addresses and routes, operating system, exact failing test and time. Redact passwords and private keys.
