Configuration
R1 - NSM
1. Enable multipath support and set the maximum number of paths to be installed in the Forwarding Information Base (FIB):
#configure terminal | Enter configure mode |
(config)#maximum-paths 2 | Create maximum paths 2 |
(config)#commit | Commit the candidate configuration to the running configuration |
(config)#exit | Exit interface mode |
Note: User can save and reboot to bring changes into effect.
R1 - OSPF
1. Configure OSPF on all interfaces on R1, R2, and R3.
R1 learns about R3 through 2 nexthops (both networks N1 and N2).
#configure terminal | Enter configure mode |
(config)#router ospf 1 | Enter ospf router mode |
(config-router)#router 1.1.1.1 | Specify router id |
(config-router)#net 10.11.1.1/30 a 0 | Configure ospf network in area 0 |
(config)#commit | Commit the candidate configuration to the running configuration |
(config)#end | Exit interface mode |
R2 - OSPF
#configure terminal | Enter configure mode |
(config)#router ospf 1 | Enter ospf router mode |
(config-router)#router 2.2.2.2 | Specify router id |
(config-router)#net 10.11.1.2/30 a 0 | Configure ospf network in area 0 |
(config)#commit | Commit the candidate configuration to the running configuration |
(config)#end | Exit interface mode |
R3 - OSPF
#configure terminal | Enter configure mode |
(config)#router ospf 1 | Enter ospf router mode |
(config-router)#router 3.3.3.3 | Specify router id |
(config-router)#net 10.1.1.2/30 a 0 | Configure ospf network in area 0 |
(config)#commit | Commit the candidate configuration to the running configuration |
(config)#end | Exit interface mode |
Validation
R1 - OSPF
Run the show ip ospf route command on R1. The OSPF routing table displays that it can reach R3 through both of the nexthops:
R1#show ip ospf route
OSPF process 100:
Codes: C - connected, D - Discard, 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
C 10.10.10.0/24 [10] is directly connected, eth1, Area 0.0.0.0
C 10.10.11.0/24 [10] is directly connected, eth2, Area 0.0.0.0
O 20.10.10.0/24 [11] via 10.10.10.3, eth1, Area 0.0.0.0
via 10.10.11.3, eth2, Area 0.0.0.0
Run the show ip route command on R1. It displays that R1 has installed both nexthops to reach R3 in the NSM routing table:
R1#show ip route
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, E - EVPN,
v - vrf leaked
* - candidate default
IP Route Table for VRF "default"
C 10.10.10.0/24 is directly connected, eth1, 00:17:08
C 10.10.11.0/24 is directly connected, eth2, 00:16:49
O 20.10.10.0/24 [110/11] via 10.10.11.3, eth2, 00:08:52
[110/11] via 10.10.10.3, eth1
C 127.0.0.0/8 is directly connected, lo, 00:25:21
C 192.168.52.0/24 is directly connected, eth0, 00:25:16
Gateway of last resort is not set
Last modified date: 08/28/2023