Using No-Export Community to Filter Transit Routes
RFC 1997 defined several well-known BGP communities recognized by almost all BGP implementations. One of them is the NO_EXPORT community, defined as:
All routes received carrying a communities attribute containing this value MUST NOT be advertised outside a BGP confederation boundary (a stand-alone autonomous system that is not part of a confederation should be considered a confederation itself).
Forgetting the weird wording, the NO_EXPORT community attached to a BGP prefix means “do not advertise this one over EBGP sessions” – seemingly an ideal solution to our do not leak transit routes challenge. You’ll practice that scenario in this lab exercise.
This is a challenging lab. We expect you have completed most of the foundational labs and know what you’re doing. All you’ll get from us are a few basic guidelines.