Simple definition
A route map applies match conditions and actions to route advertisements or selected traffic on supported network platforms.
Purpose and use
A route-map groups ordered conditions and actions to apply policy to routes or, in selected uses, packets.
How does it work?
A sequence can match a prefix-list or community, then modify an attribute or permit processing in its attachment context.
Example and verification
Validate policy by following a representative route and checking the matching sequence and resulting attributes.
Points to watch
The meaning of denial or no match depends on the application point. Do not assume redistribution policy behaves identically to PBR.
In short
A route-map is a policy mechanism whose effect depends on its rules, ordering and attachment point.