IPv6 Anycast Calculator
Plan IPv6 anycast service addresses across sites and estimate the routing spread each instance serves.
Inputs
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
Values used
Service prefix = 2001:db8:acad:1::; Anycast instances advertising it = 6 nodes; Total requests per second = 90,000 req/s
IPv6 Anycast
Every instance advertises the same address, so load per instance = total requests ÷ instances, and after one failure = total ÷ (instances − 1).
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
How it works
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
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.