AS pre-pending is used to influence the returning traffic by a dual homed location or Internet connection. By adding the AS number to the AS Path on the backup link, the returning traffic is forced to the primary connection.
In the following example the AS number 64512 is added two times to the AS Path in the advertisements to neighbor 10.10.0.1.
router bgp 64512
neighbor 10.10.0.1 remote-as 64513
neighbor 10.10.0.1 route-map prepend out
!
route-map prepend permit 10
set as-path prepend 64512 64512
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