A company has a Prisma Access deployment for mobile users in North America and Europe.

Because the two data centers are joined by a private link, without any additional filtering each service connection can learn the mobile user IP pool routes for both regions and re-advertise them across that private inter-data-center link, creating a path for return traffic destined to European mobile users to be pulled toward the North American service connection (and vice versa) rather than staying within its own region. In default Prisma Access routing mode, the cleanest and most deterministic fix is applied at the source of the advertisement: configuring each service connection ' s outbound route filtering to exclude the mobile user pool prefixes belonging to the other region. This ensures the data center only ever learns the " local " region ' s mobile user routes from its adjacent service connection, so return traffic naturally stays on the correct, geographically appropriate path without depending on BGP path-selection tie-breaking. Options A and C attempt to solve the problem through CPE-side BGP attribute manipulation (community string preference or MED preference); while conceptually plausible in isolation, this places the burden of correct routing on customer-managed equipment reacting to attributes rather than eliminating the unwanted route at the source, and is not the documented approach for default routing mode. AS-path prepending (option D) only influences path preference when multiple paths exist for the same prefix — it does not prevent an undesired prefix from being learned or selected at all, making it an unreliable mechanism for this scenario.