Make local policy behavior explicit
06RFC 1997 allows local modification of communities. Its RFC 8642 update explains why a policy command named set must not be assumed to mean the same thing everywhere.
RFC 8642 requires documented, stable handling when a value becomes well-known. Confirm operational policy; this scene does not recommend deleting propagation safeguards.
Source for this drawing: RFC 1997 · Read RFC source: Operation · p.3 ↗
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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.
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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.
The update documents divergent set behavior and requires vendors to document it and preserve treatment when a community later becomes well-known. It does not standardize one universal set operation.
Read the updated RFC section ↗A speaker may add COMMUNITIES to a route that lacks it, and may modify an existing attribute according to local policy.
- A speaker may add COMMUNITIES to a route that lacks it, and may modify an existing attribute according to local policy.
- RFC 8642 records different set behaviors: replace all, preserve certain well-known values, or add without removing existing values. The drawings compare behavior classes, not current vendor guarantees.
- Under RFC 8642 §6, vendors MUST document set behavior and MUST NOT change treatment of a specific community merely because it later becomes well-known.
- Operators are urged to confirm a neighbor’s handling before announcing NO_EXPORT or another community. Do not infer an export decision from the command spelling or assume a removed tag still provides its restriction.
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 ↗