Replace xxxx with your as-number. The only part of this that is beyond your control is if you ISP or another upstream provider is aggregating the address space. You should first check a bgp looking glass to see if your specific /24 route is in the internet routing table or not. If it is, you should be good to go with this setup. If not, then you need to contact your ISP and ask them to allow your specific /24 out to the internet. Failing to do this step will result in your secondary connection being the preferred path because it will be more specific then your primary connections route, basically you will have the exact opposite result as you intended to have, with Location B being the primary for Location A's subnet and vice versa.

GL

locationa:

ip prefix-list locationA permit 192.168.2.0/24

ip prefix-list locationB permit 192.168.3.0/24

route-map bgp-out permit 10

match ip add prefix locationA

!

route-map bgp-out permit 10

match ip add prefix locationB

set as-path prepend xxxx xxxx xxxx

!

router bgp xxxx

neighbor y.y.y.y route-map bgp-out out

locationb:

ip prefix-list locationA permit 192.168.2.0/24

ip prefix-list locationB permit 192.168.3.0/24

route-map bgp-out permit 10

match ip add prefix locationB

!

route-map bgp-out permit 10

match ip add prefix locationA

set as-path prepend xxxx xxxx xxxx

!

router bgp xxxx

neighbor w.w.w.w route-map bgp-out out