An excavator severs a fibre-optic cable during road works. Within minutes an entire commercial park loses its internet connection. An online retailer based there can no longer process orders, the VoIP phone system falls silent, and access to the cloud-based ERP system is cut off too. Revenue loss per hour: five figures. Repair takes until the next day.
Failure or disruption of communication networks is among the threats with the highest immediate impact on business operations. The BSI lists this threat as G 0.9 — and with 17 mapped ISO controls it is one of the most comprehensively addressed threats in the Grundschutz catalogue.
What’s behind it?
Modern business processes depend in virtually every step on functioning communication networks — whether telephony, email, database access, cloud services or machine control. The more digitalised an organisation is, the harder a communication outage hits.
Causes of failure
- Physical damage — Cable damage during excavation work is the most common cause. A single excavator can paralyse the entire communication infrastructure of a commercial park when all lines run through the same cable duct.
- Equipment failure — Routers, switches, firewalls and other active network components have a limited lifespan. A defective core switch can bring down the entire internal network.
- Configuration errors — Misconfigurations on routers, DNS servers or firewalls can render networks wholly or partly unreachable. Such errors are frequently introduced during maintenance or updates.
- Provider disruptions — Outages at the internet provider or at backbone operators lie outside your own control, but can paralyse operations just as thoroughly as a local defect.
- Overload — DDoS attacks or unexpected load spikes can overload communication networks to the point of unusability.
Impact
Combining voice and data services on the same infrastructure (VoIP, UC) substantially raises the outage risk. If the data network fails, telephony fails at the same time. The organisation loses all communication channels at once — towards customers, partners and internally. In emergency situations this is especially critical.
Practical examples
Fibre-optic cable severed. During excavation work for a new fibre connection in the neighbouring street, the existing fibre cable of the office building is accidentally cut. Internet, VoIP telephony and the VPN connection to headquarters fail simultaneously. The provider dispatches a repair team — but the waiting time is 18 hours. The company has no redundant line.
Misconfiguration after a firewall update. During a routine firmware update of the firewall, a rule is configured incorrectly and blocks outbound DNS traffic. All internal systems can no longer resolve external services — email, cloud services and web access stop working. The cause is found only after three hours, because the connection between the update and the symptoms is not recognised immediately.
VoIP total outage during a power disturbance. An undervoltage in the supply grid (interaction with G 0.8) causes the PoE switches (Power over Ethernet) to restart intermittently. The VoIP phones drop out repeatedly, calls are cut off. Because all telephony runs over VoIP, the company is unreachable to customers for hours.
Relevant controls
The following ISO 27001 controls mitigate this threat. (You’ll find the complete list of 17 mapped controls below in the section ‘ISO 27001 Controls Covering This Threat’.)
Prevention:
- A.8.20 — Networks security: Secure network architecture with redundancy and segmentation.
- A.7.12 — Cabling security: Protection of communication cabling against damage and eavesdropping.
- A.8.21 — Security of network services: SLA agreements with providers that define availability requirements.
- A.7.11 — Supporting utilities: Redundant communication connections as part of the utility infrastructure.
Detection:
- A.8.15 — Logging: Network monitoring detects outages and quality degradation early.
- A.8.6 — Capacity management: Monitoring network utilisation to avoid bottlenecks.
Response:
- A.8.14 — Redundancy of information processing facilities: Failover systems and alternative connections during network outages.
- A.5.23 — Information security for use of cloud services: Securing cloud connectivity and emergency plans for loss of connection.
BSI IT-Grundschutz
G 0.9 is linked in the BSI IT-Grundschutz catalogue to the following modules:
- NET.1.1 (Network architecture and design) — Redundant network architecture, segmentation and resilience.
- NET.3.1 (Routers and switches) — Configuration, hardening and monitoring of active network components.
- NET.3.2 (Firewall) — High availability and change management for firewall systems.
- INF.14 (Building automation) — Network connection and resilience of building automation.
Sources
- BSI: The State of IT Security in Germany — Annual report with current threat statistics
- BSI IT-Grundschutz: Elementary Threats, G 0.9 — Original description of the elementary threat
- ISO/IEC 27002:2022 Section 8.20 — Implementation guidance on networks security