Controlling redundant links by cost
In this scenario, two FortiGate units have redundant links: one link between their WAN1 interfaces and another between their WAN2 interfaces.
FortiGate 1 should learn the route to network 192.168.182.0 and FortiGate 2 should learn the route to network 10.160.0.0. Under normal conditions, they should learn these routes through the WAN1 link. The WAN2 link should be used only as a backup.
With the default settings, each FortiGate unit learns these routes from both WAN1 and WAN2.
FortiGate 1:
FGT1 # get router info ospf neighbor
OSPF process 0:
Neighbor ID Pri State Dead Time Address Interface
10.2.2.2 1 Full/Backup 00:00:33 10.182.0.187 wan1
10.2.2.2 1 Full/Backup 00:00:31 10.183.0.187 wan2
FGT1 # get router info routing-table ospf
O*E2 0.0.0.0/0 [110/10] via 10.183.0.187, wan2, 00:00:01
[110/10] via 10.182.0.187, wan1, 00:00:01
O 192.168.182.0/23 [110/20] via 10.183.0.187, wan2, 00:02:04
[110/20] via 10.182.0.187, wan1, 00:02:04
FortiGate 2:
FGT2 # get router info ospf neighbor
OSPF process 0:
Neighbor ID Pri State Dead Time Address Interface
10.1.1.1 1 Full/DR 00:00:38 10.182.0.57 wan1
10.1.1.1 1 Full/DR 00:00:38 10.183.0.57 wan2
FGT2 # get router info routing-table ospf
O 10.160.0.0/23 [110/20] via 10.183.0.57, wan2, 00:00:39
[110/20] via 10.182.0.57, wan1, 00:00:39
Adjusting the route costs
On both FortiGate units, the cost of the route through WAN2 is adjusted higher so that this route will only be used if the route through WAN1 is unavailable. The default cost is 10. The WAN2 route will be changed to a cost of 200.
On both FortiGate units:
config router ospf
config ospf-interface
edit "WAN2_higher_cost"
set cost 200
set interface "wan2"
end
Now both FortiGate units use only the WAN1 route:
FortiGate 1:
FGT1 # get router info routing-table ospf
O*E2 0.0.0.0/0 [110/10] via 10.182.0.187, wan1, 00:00:40
O 192.168.182.0/23 [110/20] via 10.182.0.187, wan1, 00:00:40
FortiGate 2:
FGT2 # get router info routing-table ospf
O 10.160.0.0/23 [110/20] via 10.182.0.57, wan1, 00:09:37
LSDB check on FortiGate 1:
FGT1 # get router info ospf database router lsa
Router Link States (Area 0.0.0.0)
LS age: 81
Options: 0x2 (*|-|-|-|-|-|E|-)
Flags: 0x0
LS Type: router-LSA
Link State ID: 10.1.1.1
Advertising Router: 10.1.1.1
LS Seq Number: 8000000b
Checksum: 0xe637
Length: 60
Number of Links: 3
Link connected to: Stub Network
(Link ID) Network/subnet number: 10.160.0.0
(Link Data) Network Mask: 255.255.254.0
Number of TOS metrics: 0
TOS 0 Metric: 10
Link connected to: a Transit Network
(Link ID) Designated Router address: 10.183.0.187
(Link Data) Router Interface address: 10.183.0.57
Number of TOS metrics: 0
TOS 0 Metric: 200
Link connected to: a Transit Network
(Link ID) Designated Router address: 10.182.0.57
(Link Data) Router Interface address: 10.182.0.57
Number of TOS metrics: 0
TOS 0 Metric: 10
LS age: 83
Options: 0x2 (*|-|-|-|-|-|E|-)
Flags: 0x2 : ASBR
LS Type: router-LSA
Link State ID: 10.2.2.2
Advertising Router: 10.2.2.2
LS Seq Number: 8000000e
Checksum: 0xfc9b
Length: 60
Number of Links: 3
Link connected to: Stub Network
(Link ID) Network/subnet number: 192.168.182.0
(Link Data) Network Mask: 255.255.254.0
Number of TOS metrics: 0
TOS 0 Metric: 10
Link connected to: a Transit Network
(Link ID) Designated Router address: 10.183.0.187
(Link Data) Router Interface address: 10.183.0.187
Number of TOS metrics: 0
TOS 0 Metric: 200
Link connected to: a Transit Network
(Link ID) Designated Router address: 10.182.0.57
(Link Data) Router Interface address: 10.182.0.187
Number of TOS metrics: 0
TOS 0 Metric: 10
Verifying route redundancy
Bring down WAN1 and then check the routes on the two FortiGate units.
FortiGate 1:
FGT1 # get router info routing-table ospf
FGT1 # get router info routing-table ospf
O*E2 0.0.0.0/0 [110/10] via 10.183.0.187, wan2, 00:00:06
O 192.168.182.0/23 [110/210] via 10.183.0.187, wan2, 00:00:06
FortiGate 2:
FGT2 # get router info routing-table ospf
O 10.160.0.0/23 [110/210] via 10.183.0.57, wan2, 00:00:14
The WAN2 interface is now in use on both units.
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