Maintain Effective Functional Separation Between Servers
Each server should perform its own distinct function and not share a machine or operating environment with unrelated server roles. Keeping server functions separate means that if one server is compromised, overloaded or fails, the problem stays contained and does not automatically spread to other services. This control is about the design choice to host different roles (for example a web server, a database server and an email server) on separate servers rather than bundling them together.
Plain language
Think of each server as a separate room with its own locked door, rather than running everything in one big open space. When the email service, the website and the customer database each live on their own server, a break-in or breakdown in one is much less likely to knock over the others. If everything runs together on a single server, one weakness gives an attacker access to all of it at once, and one crash can take down everything. "Functional separation" simply means giving each major job its own server, so an issue in one place does not become an issue everywhere.
Framework
ASD Information Security Manual (ISM)
Control effect
Preventative
Classifications
NC, OS, P, S, TS
ISM last updated
June 2026
Control Stack last updated
18 June 2026
E8 maturity levels
N/A
Guideline
Guidelines for networkingOfficial control statement
Servers maintain effective functional separation from each other.
Why it matters
Without functional separation, compromising or crashing one server can spread to every service it shares with, turning a single fault into a widespread outage or breach.
Operational notes
Review server roles whenever services are added or systems are consolidated, so unrelated functions do not gradually end up sharing one server.
Implementation tips
- The IT or infrastructure team should list every server and the exact role it performs, then identify any server that is hosting more than one unrelated function so those roles can be split onto separate servers.
- System architects should design new systems so that high-risk, internet-facing roles (such as web servers) never share a server with sensitive internal roles (such as databases or authentication services).
- System administrators should disable or remove any service or software on a server that is not needed for that server's intended function, so each server does only its one job.
- The team should use separate virtual machines or containers for each function when running on shared hardware, rather than installing multiple roles into the same operating system instance.
- Whoever manages change control should require that any request to add a new service to an existing server is reviewed, so unrelated functions are not quietly combined onto one server over time.
Audit / evidence tips
- Askthe IT team to walk through which function each server performs and whether any single server hosts multiple unrelated rolesLook ata current server inventory or role-assignment documentGoodshows each major function running on its own dedicated server or isolated instance
- Askhow internet-facing servers are kept apart from internal and sensitive serversLook atnetwork and hosting diagrams showing where each role sitsGoodshows web-facing roles are not on the same server as databases or authentication services
- Askhow the team prevents extra, unrelated services being added to a serverLook atchange-control records for server buildsGoodshows new services are reviewed before being placed on an existing server
- Askhow unnecessary services are removed from each serverLook ata sample server's installed services or build standardGoodshows only the services needed for that server's one function are running
- Askwhether shared hardware uses separate virtual machines or containers per functionLook atthe virtualisation or container configurationGoodshows each role is isolated rather than several roles sharing one operating system instance
Cross-framework mappings
How ISM-0385 relates to controls across ISO/IEC 27001, ISO/IEC 42001, Essential Eight, and ASD ISM.
ISO 27001
| Control | Notes | Details |
|---|---|---|
sync_altPartially overlaps(1)expand_less | ||
| Annex A 8.31 | ISM-0385 requires servers to maintain effective functional separation from other servers so they can operate independently | |
handshakeSupports(1)expand_less | ||
| Annex A 8.22 | ISM-0385 requires servers to be functionally separated so each server can operate independently without interference from others | |
These mappings show relationships between controls across frameworks. They do not imply full equivalence or certification.
Related ASD ISM controls in Networking
See all Guidelines for networking controls, or browse the full ASD ISM library.