Core Network Capacity Calculator
Calculate usable core network capacity from uplink count, speed, and redundancy overhead.
Inputs
Capacity reserved for failover (e.g. 50% if uplinks are deployed in active/active N+1 pairs)
Usable Capacity (after redundancy)
200.0Gbps
Total Raw Uplink Capacity
400.0Gbps
Reserved for Failover
200.0Gbps
Step by step
Values used
Number of Uplinks = 4; Speed per Uplink = 100 Gbps; Redundancy Overhead = 50
Usable capacity
capacity = uplinks × speed × (1 − redundancy_overhead%)
Usable Capacity (after redundancy)
= 200.0 Gbps
Total Raw Uplink Capacity
= 400.0 Gbps
Reserved for Failover
= 200.0 Gbps
How it works
Core network capacity planning must account for redundancy, since uplinks are typically deployed in redundant pairs or groups so the network survives a link or device failure — but that means some of the raw aggregate capacity can never be used for production traffic under normal conditions, because it must remain available to absorb the load if a sibling link fails. A 50% redundancy overhead models an N+1 or active/active design sized so that losing half the links still carries full traffic; lower percentages model designs with more links than the minimum needed for failover.
Formula
Usable capacity
capacity = uplinks × speed × (1 − redundancy_overhead%)
Frequently Asked Questions
Why reserve 50% for redundancy instead of just adding one spare link?
In an active/active design sized for N+1 resilience, every link carries live production traffic, so if any one fails its traffic must shift onto the survivors — sizing usable capacity at half of a two-link pool guarantees the remaining link can absorb 100% of the load without oversubscription during a failure.
How does redundancy overhead differ between active/active and active/passive designs?
Active/passive (one link idle as a hot standby) effectively has ~50% overhead built into the architecture regardless of link count, while active/active designs spread load across all links but must reserve capacity proportional to how many links can fail simultaneously and still meet demand — more links in the group generally lowers the required overhead percentage for the same failure tolerance.
Should I plan capacity for a single link failure or multiple simultaneous failures?
Most enterprise core designs plan for a single link or device failure (N+1) as the baseline, reserving capacity accordingly — planning for simultaneous multi-link failure (N+2 or better) is typically reserved for mission-critical facilities where the cost of extra bandwidth headroom is justified by the availability requirement.