Network topologies
Read physical and logical network diagrams together, including redundant paths, security enforcement, and shared failure dependencies.
The idea
A topology describes network relationships. Physical topology concerns actual links; logical topology concerns how traffic behaves through addressing, switching, routing, and overlays. Common teaching shapes include star, mesh, bus, and ring. Modern environments may combine several. A security diagram should show redundancy, critical dependencies, management paths, and enforcement boundaries, not only a pleasing arrangement of icons.
In practice
Two switches have redundant physical links, but their logical configuration controls which paths are active and which VLANs traverse them.
A common misunderstanding
A mesh diagram does not automatically prove resilience or isolation. Configuration and failure behavior matter.
Check your understanding
What should a useful topology review test?
Think it through: Normal paths, failure paths, expected restrictions, and management reachability.
Compare the cable picture with the traffic picture
Imagine a fictional lab has two switches connected by two cables. The physical drawing shows redundancy, but the logical configuration determines which paths carry traffic and how loops are handled. Two lines on a slide do not prove that every service survives a failure.
An overlay or tunnel can also create a logical path that is not obvious from the physical layout. The useful question is how a specific communication moves through the configured system, including any encapsulation or enforcement boundaries.
Redundancy can share a failure
Suppose both switches use one power source or both external links depend on the same upstream provider. The design may survive one cable failure while remaining vulnerable to a different shared dependency. Resilience should be described against explicit failure cases.
For the lab, distinguish a failed client port, a failed switch, a lost power circuit, and a lost inter-site path. Each case can affect different users and services. Avoid using “redundant” as an unrestricted guarantee.
Failover may change visibility
A backup path can bypass a monitoring location or a traffic restriction if the design does not account for it. Reviewing the normal path alone can therefore miss changes in security behavior during a failure.
Document where traffic should be observed and controlled in both normal and degraded conditions. If a backup path intentionally changes the level of protection, that tradeoff needs an owner and a clear operational decision rather than an accidental configuration.
For a paper exercise, draw a small star-shaped access network with a redundant upstream path. Mark a service, its security boundary, and its monitoring point. Remove one link and trace the new path. State which requirements still hold and which require verification in an authorized test. A topology becomes useful when it explains behavior under specific conditions, not merely when it resembles a familiar teaching shape.
Keep exploring
References & further reading
Original explanations, with primary references for deeper study.
Cisco: Networking basics