Size standby bandwidth for a network failover design. Starting with primary peak traffic, this calculator applies the share that must survive an outage, expected growth, and failover overhead. It then divides the requirement across active standby links and shows total installed capacity. Use it to compare N+1-style options without assuming every backup must mirror the entire primary link.
The main result is the aggregate backup bandwidth needed to carry the protected traffic after all allowances. Per-link capacity assumes even load distribution across the entered standby links.
This model assumes the standby links are simultaneously usable and independent of the failed path. Shared conduits, providers, power, or routing control planes can invalidate apparent redundancy.
For 800 Mbps peak traffic, 100% failover coverage, 20% growth, 10% overhead, and two standby links, aggregate backup requirement is 1,056 Mbps, or 528 Mbps per link.
It protects 100% of entered peak traffic after allowances, which may be lower or higher than the nominal primary port speed.
Yes, if routing can distribute traffic across all entered links during the modeled failure.
This calculator compounds both percentages. The order does not change the result because both are multiplicative factors.
No. Enter only the links expected to remain available in the failure scenario you want to test.
Growth and failover overhead can push the protected requirement above today’s measured peak.
| Variable | Meaning | Unit |
|---|---|---|
| P | Primary carried peak | Mbps |
| c | Protected traffic share | % |
| g | Growth allowance | % |
| o | Failover overhead | % |