Diverse path functionality is contained within a single cluster; that is, only the clients of a route reflector can be configured to advertise the diverse path. A diverse path is advertised to the clients of a route reflector only if the client is configured to get the additional path.
A shadow route reflector can be added to calculate and advertise the additional path, or an existing route reflector can be configured to calculate and advertise the additional path. In the figure below, instead of adding a shadow route reflector, RR2 (the existing backup RR) is configured to calculate the additional path and advertise it to a particular neighbor.
In the figure below, assume that from the route reflectors, the path to CE1 via PE1 is preferred over the path via PE2. Without the diverse path feature, both route reflectors will advertise to PE3 that the path to CE1 is via PE1. If the connection between RR1 and PE1 fails (or the path between PE1 and CE1 fails), there is no other path.
In the following configuration example based on the figure above, RR2 is configured with an additional path, which is a backup path.
If RR1 and RR2 are not colocated, you must configure the
ignore command before the additional path is calculated. (If RR1 and RR2 are colocated, do not configure that command.)
backup command triggers calculation of the backup path at RR2, which is the path via PE2.
install command installs the backup path if RR2 is in the forwarding plane. (Do not configure this command if RR2 is in the control plane.)
The address of PE3 is 10.1.1.1, and that address is used in the
backup command on RR2. This command triggers advertisement of the backup path to PE3. PE3 will learn the best path, (which is the path via PE1) from RR1, and it will learn the backup path from RR2.