Port isolation breaks the shared-screen meeting rooms the venue sells — who decides, and what do you write down?

## Why this is an ownership question, not a design question The control works. Isolation removes guest-to-guest reachability, which is exactly what you want on a floor of strangers' devices. It also removes the thing the venue is selling in its meeting rooms: a guest walks in, finds the room's display, and puts a slide deck on it. There is no configuration that gives both. When a control and a revenue line are actually incompatible, the decision belongs to whoever owns the revenue — and the security engineer's contribution is to make sure the choice is informed rather than to make the choice. The common failure is to bring it as a binary: "we need isolation on all guest ports." The events team hears "you want to break the product" and escalates, and the outcome is decided by whoever is more senior in the room rather than by the merits. Bring options with prices instead. ## Three options, honestly priced | Option | What a guest device reaches | What it costs you | |---|---|---| | Isolate every guest port | The gateway only | Shared displays and printing stop working; support calls from paid rooms | | Per-room community, expiring with the booking | Other devices in that room, for that booking | A community and a floor-box mapping per room, plus a reset discipline between events | | One shared-services segment for all displays | Every display site-wide, from any guest port | Cheapest to run; one compromised display is adjacent to a device on every floor | The middle option is usually the right recommendation for a venue, and it is worth saying why in business terms: it keeps the product intact in the rooms that are sold, confines the adjacency to people who are already in the same room together, and it expires by itself. The third option is the one that gets chosen when nobody prices it, because it is the least work. ## What actually goes in writing An exception is a security artefact, not a ticket. It needs: - **Scope in physical terms.** Which floor boxes, in which room — not "the meeting room VLAN", which will quietly grow. - **A named owner** with the authority to accept it, from the business side rather than from IT. If nobody will put their name to it, that is the answer to whether it is needed. - **An expiry** tied to something real: the booking, the contract, the next review. An exception with no end date is a permanent design decision that skipped design review. - **One sentence of consequence, in plain language.** "For the duration of this booking, any device in room 4B can reach any other device in room 4B, including a compromised one." This is what makes the acceptance meaningful; a risk nobody understood was never accepted. - **The reset step**, and who performs it. The control that matters most here is not the isolation, it is the thing that puts the room back afterwards. ## The failure you are really designing against Exceptions do not fail by being wrong when granted. They fail by outliving their reason. The event ends, the community stays, staffing changes, and the room keeps its adjacency for years — which is how an estate ends up with a rule base nobody dares touch. Every exception you grant should be cheaper to remove than it was to add, which in practice means it expires automatically or it is tied to a state the business already changes anyway, such as a booking ending. There is a related trap on the other side: refusing all exceptions produces shadow workarounds. Staff will bring a personal wireless access point into the room so the client can present, and that device is worse than anything you refused — it is unmanaged, it is on your wire, and nobody knows it exists. A recorded exception you dislike beats an unrecorded one you cannot see. ## How to close the answer Say who decides, say what you would recommend and why, say what you would write down, and say how it ends. Interviewers at this level are checking whether you can hold a security position without either surrendering it or forcing it through — and whether you understand that the durable artefact from this argument is the expiry, not the rule.