IPv6 Anycast Calculator
Plan IPv6 anycast service addresses across sites and estimate the routing spread each instance serves.
About IPv6 Anycast Calculator
Anycast reuses one address at many locations and lets routing pick the nearest. The subnet-router anycast address is the all-zeros interface identifier inside a prefix, which every router on the link must answer. Sizing each instance for the post-failure load, not the average, is the difference between anycast absorbing a site outage and cascading into a full outage.
Formula
IPv6 Anycast
Every instance advertises the same address, so load per instance = total requests ÷ instances, and after one failure = total ÷ (instances − 1).
- nodes
- Number of sites advertising the anycast prefix
Worked example
With the default values below, IPv6 Anycast Calculator returns Subnet-Router Anycast Address of 2001:db8:acad:1::. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Service prefix
- 2001:db8:acad:1::
- Anycast instances advertising itaccepts 1–500 nodes
- 6 nodes
- Total requests per secondaccepts 1–100,000,000 req/s
- 90,000 req/s
Results
- Subnet-Router Anycast Address
- 2001:db8:acad:1::
- Requests per Instance
- 15,000
- Load per Instance After One Failure
- 18,000
- Distinct Addresses Needed
- 1
Step by step
- 1Values used
- 2IPv6 Anycast
- 3Subnet-Router Anycast Address= 2001:db8:acad:1::
- 4Requests per Instance= 15,000
- 5Load per Instance After One Failure= 18,000
- 6Distinct Addresses Needed= 1
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 whole numbers, 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
How is IPv6 Anycast calculated?
Every instance advertises the same address, so load per instance = total requests ÷ instances, and after one failure = total ÷ (instances − 1). Anycast reuses one address at many locations and lets routing pick the nearest. The subnet-router anycast address is the all-zeros interface identifier inside a prefix, which every router on the link must answer.
Why does IPv6 Anycast matter?
Sizing each instance for the post-failure load, not the average, is the difference between anycast absorbing a site outage and cascading into a full outage.
What values do I need to enter?
This calculator takes 3 inputs: Service prefix, Anycast instances advertising it, Total requests per second. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.