SD-WAN Routing and Policy
Domain 2: SD-WAN Routing and Policy
This domain examines how Prisma SD-WAN learns routes, builds the overlay, and chooses a path per application. Expect questions on static versus dynamic routing, BGP/OSPF peering, network policy topology, application policy match order, path-quality profiles, business priority, QoS, and local internet breakout.
Core rules
- Underlay routing connects the ION to LAN/core devices; the overlay carries traffic between IONs over IPsec fabric tunnels. Route exchange can use static routes, BGP, or OSPF, with BGP commonly peering to a data-center router and advertising branch LAN prefixes.
- Network policy defines site topology, allowed paths, and QoS; application policy matches traffic and decides path, fallback, and business priority.
- Application policy is first-match. The default rule catches unmatched traffic, so place specific SaaS or voice rules above broad rules.
- Path quality profiles measure latency, jitter, and loss; when a threshold is exceeded, the policy can fail over to another eligible circuit or use FEC/packet duplication.
- Business priority (real-time, interactive, bulk) maps to queue treatment; it is not the same as path selection.
Worked example
A branch has MPLS and broadband. Voice must use MPLS while Office 365 should break out locally. Create an application policy for voice with path MPLS, fallback broadband, real-time priority, and a strict loss/latency profile. Create a second rule for Office 365 with direct internet breakout and fallback to MPLS if the broadband SLA fails. Put both above the default rule. The network policy must allow the broadband path and the MPLS path; otherwise the application rule has no eligible path. Verify BGP advertises the branch LAN so return traffic reaches the site.
Traps
Reversing rule order sends SaaS traffic to the default path. Forgetting the return route causes one-way flows. Using an aggressive SLA threshold causes path flapping. Treating business priority as a routing decision rather than QoS is a common error.