Ferrite Guidance Hub Interactive Field Runbook #16
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Network & Routing · Dynamic Overlays

BGP Equal-Cost Multi-Path (ECMP) & Asymmetric Route Optimization

Diagnose dual-WAN BGP multipath load balancing, uneven traffic hashing, asymmetric return packet drops, strict Reverse Path Forwarding (RPF) violations and NP7 ASIC ECMP link bonding across 10 consolidated Fortinet TAC knowledge base articles.

RUNBOOK POSITION 16 OF 17 Network & Routing BGP ECMP ⚡ 10 KBs Consolidated
BGP Multipath Limits Verify `ebgp-multipath` and `ibgp-multipath` configuration in `config router bgp`, ensuring the active multipath limit matches available links.
ECMP Algorithm Mode Check `v4-ecmp-mode` in `config system settings` (source-IP-based vs weight-based vs spillover).
Stateful Session Sync Verify whether asymmetric routing is permitted across firewall policies (`set asymroute enable`) if return traffic arrives on alternate interfaces.

Troubleshooting & Optimization Workflow

STEP 01

Verify BGP multipath route installation in FIB

Check if multiple equal-cost next-hop gateways are actively installed into the Forwarding Information Base (FIB).

get router info routing-table bgp
get router info routing-table all
STEP 02

Inspect ECMP hashing distribution across member links

Display real-time traffic counters and session allocation hashes across all ECMP member paths.

diagnose ip router ecmp list
diagnose sys session stat
STEP 03

Detect Reverse Path Forwarding (RPF) packet drops

Verify whether return packets arriving via a secondary ISP link are being discarded by strict RPF kernel checks.

diagnose ip router rpf-check
diagnose debug flow filter dport 443
diagnose debug flow show function-name enable
diagnose debug flow trace start 20
diagnose debug enable
STEP 04

Audit NP7 / NP6 ASIC ECMP hardware offload state

Verify that hardware acceleration (Network Processor) is correctly distributing elephant flows across all physical ports without hash collisions.

diagnose npu np7 ecmp-stats
diagnose npu np7 ipsec-stats
STEP 05

Tune BGP maximum paths & asymmetric route handling

Configure optimal ECMP hashing algorithms and adjust asymmetric routing tolerance for dual-homed internet links.

config router bgp
    set ebgp-multipath enable
    set ibgp-multipath enable
end
config system settings
    set v4-ecmp-mode source-ip-based
    set asymroute enable
end
Operational Caution: Enabling global `set asymroute enable` disables stateful TCP inspection and layer 7 security engines (AV/IPS/WAF) for asymmetric flows. Prefer policy-level loose RPF (`set loose-rpf enable`) whenever full security inspection is required.

Consolidated Fortinet Knowledge Base & Technical References