Attach policy tags to routes
01BGP means Border Gateway Protocol. Its peers exchange routes to destinations. A community groups destinations with a shared property; a route can carry several community values.
R2 receives the tagged route. An illustrative local policy matches 64512:80; that match is not a universal BGP preference or proof of ownership.
Source for this drawing: RFC 1997 · Read RFC source: COMMUNITIES attribute · p.2 ↗
New to this? Start hereA quick picture + helpful background
A message needs an address.
Think of a packet as a small addressed envelope. Devices pass it onward; transport protocols decide what delivery promises an application gets.
Helpful first, if these ideas are unfamiliar
These pictures are analogies to help you learn. The linked RFC explains the actual rules.
Terms in this drawing
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
COMMUNITIES is an optional transitive path attribute, Type Code 8, containing a set of four-octet community values.
- COMMUNITIES is an optional transitive path attribute, Type Code 8, containing a set of four-octet community values.
- The attribute travels with route information, not inside every user data packet. An ordinary tag has the meaning assigned by its AS administrator.
- An autonomous system (AS) is a routing administration. The shown accept/prefer/export policy is an example; a tag alone does not install a route or authenticate its owner.
Fictional routes and private AS numbers. These are bounded teaching examples, not a complete BGP implementation. Display a tag as AS:local only to help read its two 16-bit parts; the wire contains four octets.
Read the RFC section ↗