BGP Community Calculator
Convert between AS:value and 32-bit BGP community notation, in hex, and identify well-known community values.
Inputs
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
Values used
Autonomous system number = 65,001; Community value = 300
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.
Well-known communities
NO_EXPORT = 0xFFFFFF01, NO_ADVERTISE = 0xFFFFFF02, NO_EXPORT_SUBCONFED = 0xFFFFFF03.
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
How it works
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.
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.