BGP communities are labels attached to route announcements. They let a network signal preferences to its peers and customers without rewriting the entire policy language every time. For someone leasing IPs or running a small ASN, a few communities can control how traffic enters and leaves.
What they are used for
- Asking a provider to prepend the AS path (make the route less preferred).
- Setting local preference so inbound traffic prefers one upstream over another.
- Marking routes for blackhole or selective advertisement.
- Geographic or peer-group signaling in larger networks.
Exact community values are provider-specific. Documentation from the upstream is required; guessing is a good way to create an outage.
Why a hosting customer might care
If you announce your own space or care which path return traffic takes, communities are one of the levers. If you only use provider-assigned addresses and default routing, you can ignore them until a specific traffic-engineering need appears.
When you do need them, the ticket usually goes better if you already know which community you want and why. The looking glass and the provider’s community list are the two references that matter most.
Written at the desk
ChadBe the first to weigh in.