BGP Community Calculator
Convert between AS:value and 32-bit BGP community notation, in hex, and identify well-known community values.
About BGP Community Calculator
RFC 1997 communities are just 32-bit integers, and AS:value is a display convention over them. Because the high half is only 16 bits, a 4-byte ASN cannot own its community space and needs RFC 8092 large communities, which give three 32-bit fields instead. Communities are how transit policy is actually signalled — customer routes, blackhole requests, regional tags — and a mismatch between the notation a peer documents and the notation your platform accepts silently drops the policy.
Formulas
BGP Community
A standard community is a 32-bit value split into a 16-bit AS number and a 16-bit local value, so the decimal form is AS × 65536 + value.
- AS
- High 16 bits — the autonomous system that defines the community's meaning
- value
- Low 16 bits — operator-chosen tag
- well-known
- Reserved values in 0xFFFF0000–0xFFFFFFFF with standardised behaviour
Well-known communities
NO_EXPORT = 0xFFFFFF01, NO_ADVERTISE = 0xFFFFFF02, NO_EXPORT_SUBCONFED = 0xFFFFFF03.
Worked example
With the default values below, BGP Community Calculator returns New Format (AS:value) of 65001:300. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Autonomous system numberaccepts 0–4,294,967,295
- 65,001
- Community valueaccepts 0–65,535
- 300
Results
- New Format (AS:value)
- 65001:300
- 32-bit Decimal
- 4259905836
- Hexadecimal
- 0xfde9012c
- Numeric Value
- 4,259,905,836
- Well-Known Meaning
- Operator-defined community in AS 65001 space
- Needs a Large Community
- No — the ASN fits the 16-bit high half of a standard community
Step by step
- 1Values used
- 2BGP Community
- 3Well-known communities
- 4New Format (AS:value)= 65001:300
- 532-bit Decimal= 4259905836
- 6Hexadecimal= 0xfde9012c
- 7Numeric Value= 4,259,905,836
- 8Well-Known Meaning= Operator-defined community in AS 65001 space
- 9Needs a Large Community= No — the ASN fits the 16-bit high half of a standard community
Assumptions and limits
- The result is derived only from the 2 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 BGP Community calculated?
A standard community is a 32-bit value split into a 16-bit AS number and a 16-bit local value, so the decimal form is AS × 65536 + value. RFC 1997 communities are just 32-bit integers, and AS:value is a display convention over them. Because the high half is only 16 bits, a 4-byte ASN cannot own its community space and needs RFC 8092 large communities, which give three 32-bit fields instead.
Why does BGP Community matter?
Communities are how transit policy is actually signalled — customer routes, blackhole requests, regional tags — and a mismatch between the notation a peer documents and the notation your platform accepts silently drops the policy.
What values do I need to enter?
This calculator takes 2 inputs: Autonomous system number, Community value. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
Why did my community disappear across a peering?
Communities are optional transitive, but many operators strip on ingress by default. Unless the neighbour explicitly documents which communities it honours and preserves, assume yours are removed and confirm with them.