Balancing FortiGate default routes across multiple ISPs and IPsec tunnels is a common challenge for enterprise network administrators. Misconfigurations can lead to traffic outages, failed VPNs, and asymmetric routing. This guide merges practical troubleshooting tips with advanced BGP and PBR strategies to ensure reliable traffic steering without compromising primary internet paths.
Table of Contents
- Part 1: Understanding Equal-AD Behavior and Route Selection
- Part 2: Policy-Based Routing Best Practices for IPsec
- Part 3: BGP Integration and Failover Strategies
- Part 4: Common Failure Scenarios and Troubleshooting
- Part 5: Validation and Operational Checklist
Part 1: Understanding Equal-AD Behavior and Route Selection
Equal-AD routes do not automatically provide load balancing; FortiGate may prefer routes based on interface index or static route order.
Route selection hierarchy: Prefix length → Administrative Distance → Route Priority → PBR.
Example CLI command to view the routing table:
get router info routing-table allTip: Ensure BGP-learned routes, static defaults, and PBR work together to prevent asymmetric traffic or unintended failovers.
Part 2: Policy-Based Routing Best Practices for IPsec
/32 static routes for VPN endpoints prevent PBR from hijacking primary internet traffic.
Higher AD for secondary default routes ensures that backup paths don’t interfere with main WAN.
PBR rules should be selective: source/destination IP or port-based policies rather than catch-all.
By applying these design patterns, you can steer VPN traffic safely while keeping primary internet paths intact.
Part 3: BGP Integration and Failover Strategies
Dynamic failover: Use BGP weights and route-map policies to prefer primary paths and automatically fail over to backup IPsec tunnels.
Priority management: When advertising default routes, disable recursive-inherit-priority to enforce route-map preferences.
Advanced scenarios: Dual redundant VPN tunnels, branch-to-branch BGP failover, and originating default routes from branches.
Example CLI command to originate default routes via BGP:
set capability-default-originate enablePart 4: Common Failure Scenarios and Troubleshooting
- VPN traffic drops due to missing active routes for PBR
- BGP route-map priority misconfigurations
- Static /32 routes with incorrect interface or AD settings
Troubleshooting tip: Use flow debug and BGP CLI commands to track and resolve routing anomalies.
Part 5: Validation and Operational Checklist
- Verify route table consistency
- Confirm PBR and route priorities
- Test failover paths for dual ISPs or redundant tunnels
- Refresh BGP neighbors after route-map adjustments
- Monitor VPN tunnel stability and logging
Following this checklist minimizes downtime and ensures dual-path routing works as expected.
Conclusion
Effective FortiGate default route design combines practical PBR strategies, advanced BGP management, and careful route validation. Enterprises can prevent routing conflicts, maintain stable internet connectivity, and safely steer VPN traffic.
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FAQ
How can I ensure PBR doesn’t override my primary internet route?
Use /32 static routes for critical destinations and assign higher AD to secondary routes. Apply PBR selectively.
How do I integrate BGP for VPN failover?
Configure route-map priorities and weights for BGP neighbors, disable recursive-inherit-priority, and test failover paths.
What should I verify before applying routing changes in production?
Follow a checklist including route table verification, PBR testing, BGP refresh, tunnel monitoring, and logging.
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