Two network connections are not necessarily two independent paths. Real diversity depends on the physical route, carrier infrastructure, upstream networks, equipment, power and building entry.
1) Logical redundancy versus physical diversity
Logical redundancy means there are multiple configured links or routes. Physical diversity means those links avoid the same cables, conduits, poles, rooms, equipment and failure events.
A design can have two provider names and still share a local fibre, street duct or upstream facility.
2) Building entry and internal pathways
Diverse services should enter through separate building points and follow separate internal routes where practical. If both circuits cross the same construction area or terminate in the same room, one incident may affect both.
Power and cooling for network equipment should also be reviewed.
3) Carrier and upstream diversity
Resellers may use the same underlying carrier. Separate carriers may peer or buy transit from the same upstream network. Diversity claims should therefore be traced beyond the sales contract.
Ask for route diagrams, demarcation details and the limits of any diversity commitment.
4) Routing behavior
Physical diversity does not guarantee that traffic will use the intended path. Routing policy, failover timers, DNS and firewall state can determine whether the alternate link is actually usable.
Testing should include inbound and outbound traffic, not only whether the circuit reports as up.
5) Failure-state capacity
The surviving link must carry the required load. If two links normally share traffic, each may need enough spare capacity to support priority services when the other fails.
Traffic shaping and service priorities can help maintain essential functions during degraded operation.
6) Evidence to retain
- Carrier and circuit identifiers
- Physical entry and route information
- Demarcation and equipment locations
- Upstream and resale relationships
- Failover test results
- Capacity under single-link operation
Operational review questions
Use these questions to connect the concept to a real service or environment:
- Which services depend on this network function?
- What physical and upstream paths are shared?
- How would traffic behave during partial failure?
- What monitoring evidence would reveal degradation?
- Is failure-state capacity sufficient for priority traffic?
Related guides
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