LEARN. PRACTICE. GROW.Concept and mechanism
A port number is useful when connected to a protocol and service configuration. SFTP over SSH is not FTPS, even though both support protected transfer. Confirm endpoint, agreed port, authentication, and server-identity validation. NAT changes addresses and NAPT/PAT also uses ports to distinguish flows; it does not automatically encrypt content. An HTTP flow does not become confidential merely because it leaves through NAT. Draw where encryption starts and ends. If TLS terminates at a load balancer, the next segment needs its own analysis; the client padlock does not document that backend.
Guided application
In IPv6, a link-local address belongs to one link scope. With two interfaces, fe80::1 may identify neighbors on distinct links, so tools need the appropriate zone or interface. Public DNS or NAT does not solve that problem. For availability, count dependencies and failure modes as well as devices. Two routers and two carriers may still connect to one PDU. The project team should bring physical, logical, and operational designs together: power, paths, DNS, management, credentials, and responsibilities. Define the event the test must withstand. Disabling an interface demonstrates something different from losing rack power or an entire site.
An SFTP transfer fails before authentication: first confirm the agreed service and endpoint, including the expected host key.
Common pitfalls
Treating encrypted protocols as interchangeable; NAT as encryption; link-local IP without an interface; two devices as complete independence.
Related topics: Routing, switching, and physical installation · Operations, services, and recovery
Document each connection’s concrete properties and the dependency each redundancy is meant to remove.
Reference: Traditional NAT · N10-009 V9