Core Network Capacity
Calculate aggregate bandwidth requirements for a network core given distribution layer demand.
About Core Network Capacity
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%)
Worked example
With the default values below, Core Network Capacity returns Usable Capacity (after redundancy) of 200.0. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Number of Uplinksminimum 1
- 4
- Speed per Uplinkminimum 0.1 Gbps
- 100 Gbps
- Redundancy Overheadaccepts 0–90
- 50
Results
- Usable Capacity (after redundancy)
- 200.0 Gbps
- Total Raw Uplink Capacity
- 400.0 Gbps
- Reserved for Failover
- 200.0 Gbps
Step by step
- 1Values used
- 2Usable capacity
- 3Usable Capacity (after redundancy)= 200.0 Gbps
- 4Total Raw Uplink Capacity= 400.0 Gbps
- 5Reserved for Failover= 200.0 Gbps
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
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.