Hop Count-Based Path Selection
Learn how Branch Gateways use hop count as a routing metric to optimize path
selection across multi-site SD-WAN deployments.
| Where Can I Use This? | What Do I Need? |
|---|
- Prisma SD-WAN (Managed by Strata Cloud Manager)
|
- Prisma SD-WAN
- Physical and virtual ION devices running software version 6.8.1
and higher for Branch Gateway hop count support
|
Prisma SD-WAN Branch Gateways use hop count as a primary routing metric to select the
most direct available path to each destination. This path selection criteria applies
equally to locally originated traffic (LAN-to-WAN) and transit traffic (WAN-to-WAN).
A path that reaches the destination through fewer intermediate sites (a lower hop count)
is always preferred over longer paths, even when path policies would otherwise favor the
longer path. This ensures that traffic follows the shortest physical route across the
SD-WAN fabric, optimizing latency and reducing load on transit sites.
Initial Path Selection
When multiple paths to the same destination are available, the system filters
candidate paths to include only those with the lowest hop count, then applies
standard path selection criteria to choose among that optimal subset.
| Path Scenario | Path A State | Path B State | Path A Hop Count | Path B Hop Count | Path A Type | Path B Type | Selected Path |
|---|
| Single Path (HC1) | Available | - | 1 | - | Active | - | Path A |
| Single Path (HC2) | Available | - | 2 | - | Active | - | Path A |
| Optimal Active Wins | Available | Available | 1 | 2 | Active | Active | Path A (lower hop count) |
| Alternate Active Wins | Available | Available | 2 | 1 | Active | Active | Path B (lower hop count) |
| Hop Count Override | Available | Available | 2 | 1 | Active | Backup | Path B (Hop Count overrides Active/Backup) |
| Standard Active Wins (HC1) | Available | Available | 1 | 1 | Active | Backup | Path A (same hop count, Active wins) |
| Standard Active Wins (HC2) | Available | Available | 2 | 2 | Active | Backup | Path A (same hop count, Active wins) |
Path Re-evaluation
To maintain session stability, the system does not automatically migrate active
sessions to a newly available shorter path if the current path remains functional.
Path re-evaluation occurs only when the current path fails or when transitioning
back from a degraded state.
For example, if a session is using a 2-hop Active path and a 1-hop path becomes
available, the session continues on the current path to avoid disruption. However,
if the current path used is a Backup / L3 failure path and an Active path comes up,
the system re-evaluates all available paths and migrates to the optimal path with
the lowest hop count.
Asymmetry Handling
When routing asymmetry is detected—where forward and return traffic for the same
session follow different paths—the system automatically attempts to restore
symmetric routing by adjusting the return path. For WAN-to-WAN flows, the Branch
Gateway evaluates whether a path with a lower hop count is available and, if so,
switches the return traffic to that path. This encourages the downstream branch to
also migrate to the optimal path when it receives the return traffic. If the hop
count is identical on both paths, the system maintains the current routing to avoid
unnecessary path changes. This asymmetry correction applies to both ingress and
egress flow directions, with the system checking routing tables for ingress flows
and path policies for egress flows to ensure the selected path is valid and
optimal.
