Technical Tip: Route preference and priority

Description

This article explains how to configure the FortiGate device to select a particular route when two or more Static and/or Dynamic routes to the same destination are present in the FortiGate routing table.

Scope

FortiGate.

Solution

FortiGate maintains its routing information in two tables: RIB and FIB.

RIB: The routing information base, is a routing table containing active, static, connected, and dynamic routes.

FIB: Forwarding information base, is the routing table from the Kernel Point of view.

The commands (and associated outputs) below show the information via the Command Line:

get router info routing-table all  

FGT_3 (root) # get router info routing-table all
Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP
O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
V - BGP VPNv4
* - candidate default

Routing table for VRF=0
S* 0.0.0.0/0 [10/0] via 172.25.183.1, wan1, [1/0]
C 10.80.90.0/24 is directly connected, TestSSID
C 10.253.240.0/20 is directly connected, wqt.root
C 169.254.1.1/32 is directly connected, FGT_Dialup
C 172.25.183.0/24 is directly connected, wan1

get router  info routing-table static  

FGT_3 (root) # get router info routing-table static
Routing table for VRF=0
S* 0.0.0.0/0 [10/0] via 172.25.183.1, wan1, [1/0]

get router info routing-table database  

FGT_3 (root) # get router info routing-table database
Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP
O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
V - BGP VPNv4
> - selected route, * - FIB route, p - stale info

Routing table for VRF=0
S *> 0.0.0.0/0 [10/0] via 172.25.183.1, wan1, [1/0]
C *> 10.80.90.0/24 is directly connected, TestSSID
C *> 10.253.240.0/20 is directly connected, wqt.root
C *> 169.254.1.1/32 is directly connected, FGT_Dialup
C *> 172.25.183.0/24 is directly connected, wan1

get router info routing-table connected

FGT_3 (root) # get router info routing-table connected
Routing table for VRF=0
C 10.80.90.0/24 is directly connected, TestSSID
C 10.253.240.0/20 is directly connected, wqt.root
C 169.254.1.1/32 is directly connected, Z3_Dialup
C 172.25.183.0/24 is directly connected, wan1

get router info kernel

FGT_3 (root) # get router info kernel
tab=255 vf=0 scope=253 type=3 proto=2 prio=0 0.0.0.0/0.0.0.0/0->10.20.30.0/32 pref=10.20.30.5 gwy=0.0.0.0 dev=7(dmz)
tab=255 vf=0 scope=254 type=2 proto=2 prio=0 0.0.0.0/0.0.0.0/0->10.20.30.5/32 pref=10.20.30.5 gwy=0.0.0.0 dev=7(dmz)
tab=255 vf=0 scope=253 type=3 proto=2 prio=0 0.0.0.0/0.0.0.0/0->10.20.30.255/32 pref=10.20.30.5 gwy=0.0.0.0 dev=7(dmz)
tab=255 vf=0 scope=253 type=3 proto=2 prio=0 0.0.0.0/0.0.0.0/0->10.80.90.0/32 pref=10.80.90.1 gwy=0.0.0.0 dev=27(TestSSID)
tab=255 vf=0 scope=254 type=2 proto=2 prio=0 0.0.0.0/0.0.0.0/0->10.80.90.1/32 pref=10.80.90.1 gwy=0.0.0.0 dev=27(TestSSID)
tab=255 vf=0 scope=253 type=3 proto=2 prio=0 0.0.0.0/0.0.0.0/0->10.80.90.255/32 pref=10.80.90.1 gwy=0.0.0.0 dev=27(TestSSID)
tab=255 vf=0 scope=253 type=3 proto=2 prio=0 0.0.0.0/0.0.0.0/0->10.125.124.0/32 pref=10.125.124.3 gwy=0.0.0.0 dev=29(vlantest)
tab=255 vf=0 scope=254 type=2 proto=2 prio=0 0.0.0.0/0.0.0.0/0->10.125.124.3/32 pref=10.125.124.3 gwy=0.0.0.0 dev=29(vlantest)
tab=255 vf=0 scope=253 type=3 proto=2 prio=0 0.0.0.0/0.0.0.0/0->10.125.124.255/32 pref=10.125.124.3 gwy=0.0.0.0 dev=29(vlantest)
tab=255 vf=0 scope=253 type=3 proto=2 prio=0 0.0.0.0/0.0.0.0/0->10.253.240.0/32 pref=10.253.255.254 gwy=0.0.0.0 dev=26(wqt.root)
tab=255 vf=0 scope=254 type=2 proto=2 prio=0 0.0.0.0/0.0.0.0/0->10.253.255.254/32 pref=10.253.255.254 gwy=0.0.0.0 dev=26(wqt.root)
tab=255 vf=0 scope=253 type=3 proto=2 prio=0 0.0.0.0/0.0.0.0/0->10.253.255.255/32 pref=10.253.255.254 gwy=0.0.0.0 dev=26(wqt.root)

A step-by-step guide to achieving this setup is provided in Technical Tip: Routing behavior depending on distance and priority for static routes, and Policy Based Routes.