LogID 0100041984: Kernel IPsec Tunnel Interface Status Changed to DOWN
Linux kernel netlink driver abruptly unplumbs route-based virtual IPsec tunnel interfaces upon transient Dead Peer Detection (DPD) keepalive timeouts, purging dynamic BGP routes from the FIB and blackholing site-to-site enterprise network traffic.
Technical Root Cause Analysis
In route-based IPsec deployments, FortiOS binds Phase 1 / Phase 2 Security Associations to a virtual kernel interface. The user-space IKE daemon (/bin/iked) coordinates with the Linux kernel network stack via an asynchronous Netlink socket channel.
When underlay internet links experience momentary jitter or packet loss bursts, Dead Peer Detection (DPD) retry probes fail to receive acknowledgments before the timeout threshold expires. iked notifies the kernel via Netlink, which immediately executes netlink_tunnel_down and removes the virtual interface carrier state.
The interface drop causes dynamic routing daemons (BGP and OSPF) to immediately tear down neighbor adjacencies and withdraw all prefix advertisements. If Phase 2 lacks set auto-negotiate enable, the tunnel remains stalled even after underlay internet connectivity stabilizes, because no user traffic can route to the downed interface to trigger an on-demand renegotiation.
Affected Firmware & Blast Radius Matrix
| FortiOS Branch | Vulnerable Builds | Confirmed Clean Build | Status & Workaround |
|---|---|---|---|
| FortiOS 7.2 | 7.2.0 – 7.2.9 | Tune DPD & Auto-Negotiate | Set DPD on-idle and auto-negotiate enable |
| FortiOS 7.4 | 7.4.0 – 7.4.4 | 7.4.3+ (Dampened) | Apply interface link-down-failover dampening |
| FortiOS 7.0 | 7.0.0 – 7.0.16 | Tune DPD on-idle | Enable keepalive on Phase 2 selectors |
Platform Impact: Universal vulnerability affecting all FortiGate appliances running route-based IPsec VPN tunnels with dynamic routing protocols (BGP/OSPF/SD-WAN) across variable internet underlays.
Step 01: Free Verification CLI (Safe Read-Only)
Execute these diagnostic commands to confirm whether LogID 0100041984 events have triggered and verify the current kernel netlink interface state:
Diagnostic Commands
# 1. Search event logs for tunnel interface down events
execute log filter category 1
execute log filter field logid 0100041984
execute log display
# 2. Query active IKE Phase 1 gateway state and DPD counters
diagnose vpn ike gateway list | grep -E "name|state|dpd"
# 3. Check virtual tunnel netlink carrier flags in the kernel
diagnose netlink interface list <tunnel_interface_name>
# 4. Check active IPsec Phase 2 SA status
diagnose vpn tunnel listRemediation & Workaround Steps (Teaser Preview)
Follow the complete step-by-step remediation guide in the Ferrite interactive platform:
Frequently Asked Questions
If DPD mode is set to 'on-demand', DPD probes are only sent when egress data is actively queued. If upstream packet loss delays probe replies beyond the retry count, the FortiGate declares the peer dead and shuts down the virtual interface.
Without auto-negotiate, Phase 2 relies on traffic hitting the interface to trigger IKE negotiation. Since the interface is DOWN, no routing table entry points to it, causing a permanent chicken-and-egg lock. Auto-negotiate ensures the FortiGate actively brings up Phase 2 proactively.
Yes. Executing diagnose vpn ike gateway clear name <gateway> resets Phase 1/2 SAs cleanly and commands netlink to re-initialize the virtual carrier.