Network Deployment and Connection:
 
Here the FortiGate (192.168.200.2) has gateways on a different device but within the same subnet - GW_1 (192.168.200.1) and GW_2 (192.168.200.254). The gateways are reachable from the same outgoing interface (Port1).
config router static
edit 1
set gateway 192.168.200.1
set device "port1"
next
edit 2
set gateway 192.168.200.254
set distance 100
set device "port1"
next
end
Link-monitor is configured for IP connection passing through GW_1. It is necessary to set the gateway to specifically monitor the connection on GW_1 gateway 192.168.200.1.
config system link-monitor
edit "GW_1"
set addr-mode ipv4
set srcintf "port1"
set server-config default
set server "8.8.8.8"
set protocol ping
set gateway-ip 192.168.200.1
set source-ip 0.0.0.0
set interval 500
set probe-timeout 500
set failtime 5
set recoverytime 5
set probe-count 30
set ha-priority 1
set update-cascade-interface enable
set update-static-route enable
set update-policy-route enable
set status enable
set diffservcode 000000
unset class-id
set service-detection disable
next
end
When Link-Monitor is up/alive, the routing table shows that the default route is going to 192.168.200.1.
diag sys link-monitor status
Link Monitor: GW_1, Status: alive, Server num(1), HA state: local(alive), shared(alive)
Flags=0x1 init, Create time: Sun Dec 3 03:47:13 2023
Source interface: port1 (3)
Gateway: 192.168.200.1
Interval: 500 ms
Service-detect: disable
Diffservcode: 000000
Class-ID: 0
Peer: 8.8.8.8(8.8.8.8)
Source IP(192.168.200.2)
Route: 192.168.200.2->8.8.8.8/32, gwy(192.168.200.1)
protocol: ping, state: alive
Latency(Min/Max/Avg): 6.145/10.428/7.010 ms
Jitter(Min/Max/Avg): 0.023/3.889/0.601
Packet lost: 0.000%
Number of out-of-sequence packets: 0
Fail Times(0/5)
Packet sent: 1008, received: 1008, Sequence(sent/rcvd/exp): 1009/1009/1010
get router info routing-table database
<>
S 0.0.0.0/0 [100/0] via 192.168.200.254, port1
S *> 0.0.0.0/0 [10/0] via 192.168.200.1, port1
C *> 192.168.200.0/24 is directly connected, port1
When Link-Monitor goes down/dead, only the static route with the gateway is affected and removed from the routing table.
Route going to 192.168.200.1 is tagged as Inactive, while static route going to 192.168.200.254 is still active.
The default route failed over to 192.168.200.254.
diag sys link-monitor status
Link Monitor: GW_1, Status: dead, Server num(1), HA state: local(dead), shared(dead)
Flags=0x9 init log_downgateway, Create time: Sun Dec 3 03:47:13 2023
Source interface: port1 (3)
Gateway: 192.168.200.1
Interval: 500 ms
Service-detect: disable
Diffservcode: 000000
Class-ID: 0
Peer: 8.8.8.8(8.8.8.8)
Source IP(192.168.200.2)
Route: 192.168.200.2->8.8.8.8/32, gwy(192.168.200.1)
protocol: ping, state: dead
Packet lost: 11.000%
Number of out-of-sequence packets: 0
Recovery times(0/5) Fail Times(2/5)
Packet sent: 1246, received: 1232, Sequence(sent/rcvd/exp): 1247/1234/1235
get router info routing-table database
<>
Routing table for VRF=0
S *> 0.0.0.0/0 [100/0] via 192.168.200.254, port1
S 0.0.0.0/0 [10/0] via 192.168.200.1, port1 inactive
C *> 192.168.200.0/24 is directly connected, port1
When the IP connection (link-monitor) recovers, the static routes will automatically recover as well.
Also, the active gateway will fail over to GW_1 - 192.168.200.1.
diag sys link-monitor status
Link Monitor: GW_1, Status: alive, Server num(1), HA state: local(alive), shared(alive)
Flags=0x1 init, Create time: Sun Dec 3 03:47:13 2023
Source interface: port1 (3)
Gateway: 192.168.200.1
Interval: 500 ms
Service-detect: disable
Diffservcode: 000000
Class-ID: 0
Peer: 8.8.8.8(8.8.8.8)
Source IP(192.168.200.2)
Route: 192.168.200.2->8.8.8.8/32, gwy(192.168.200.1)
protocol: ping, state: alive
Latency(Min/Max/Avg): 6.831/10.159/8.740 ms
Jitter(Min/Max/Avg): 0.000/3.154/1.197
Packet lost: 85.000%
Number of out-of-sequence packets: 0
Fail Times(0/5)
Packet sent: 1555, received: 1247, Sequence(sent/rcvd/exp): 1556/1556/1557
get router info routing-table database
<>
Routing table for VRF=0
S 0.0.0.0/0 [100/0] via 192.168.200.254, port1
S *> 0.0.0.0/0 [10/0] via 192.168.200.1, port1
C *> 192.168.200.0/24 is directly connected, port1
Related article:
Technical Tip: Link monitor.
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