Basic Configuration
Topology
Figure 13-112 shows the configuration to enable the basic ISIS LFA feature.
Figure 13-112: ISIS LFA-FRR
R1
#configure terminal | Enter configure mode. |
(config)#int eth1 | Enter interface mode. |
(config-if)#ip address 10.10.10.142/24 | Configure the IP address of the interface. |
(config-if)#ip router isis 1 | Enable ISIS routing on interface for area 49 with instance 1 |
(config-if)#isis circuit-type level-1 | Enable circuit type on interface |
(config-if)#isis metric 5 | Configure isis metric value for interface |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode. |
(config)#int eth2 | Enter interface mode. |
(config-if)#ip address 20.20.20.142/24 | Configure the IP address of the interface. |
(config-if)#ip router isis 1 | Enable ISIS routing on interface for area 49 with instance 1 |
(config-if)#isis circuit-type level-1 | Enable circuit type on interface |
(config-if)#isis metric 5 | Configure isis metric value for interface |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode. |
(config)#int eth3 | Enter interface mode. |
(config-if)#ip address 30.30.30.142/24 | Configure the IP address of the interface. |
(config-if)#ip router isis 1 | Enable ISIS routing on interface for area 49 with instance 1 |
(config-if)#isis circuit-type level-1 | Enable circuit type on interface |
(config-if)#isis metric 15 | Configure isis metric value for interface |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode. |
(config)#router isis 1 | Create an IS-IS routing instance for area 49 with instance 1 |
(config-router)#net 49.0000.0000.0001.00 | Establish a Network Entity Title for this instance, specifying the area address and the system ID. |
(config-router)#bfd all-interfaces | Enable BFD for ISIS on all interfaces |
(config-router)#fast-reroute per-prefix level-1 proto ipv4 all | Configure LFA-FRR to calculate the available backup path for all L1 ipv4 prefixes learnt |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-router)#exit | Exit router mode. |
(config)#exit | Exit config mode. |
R2
#configure terminal | Enter configure mode. |
(config)#int eth1 | Enter interface mode. |
(config-if)#ip address 10.10.10.141/24 | Configure the IP address of the interface. |
(config-if)#ip router isis 1 | Enable ISIS routing on interface for area 49 with instance 1 |
(config-if)#isis circuit-type level-1 | Enable circuit type on interface |
(config-if)#isis metric 5 | Configure isis metric value for interface |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode. |
(config)#int eth2 | Enter interface mode. |
(config-if)#ip address 40.40.40.141/24 | Configure the IP address of the interface. |
(config-if)#ip router isis 1 | Enable ISIS routing on interface for area 49 with instance 1 |
(config-if)#isis circuit-type level-1 | Enable circuit type on interface |
(config-if)#isis metric 5 | Configure isis metric value for interface |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode. |
(config)#router isis 1 | Create an IS-IS routing instance for area 49 with instance 1 |
(config-router)#net 49.0000.0000.0002.00 | Establish a Network Entity Title for this instance, specifying the area address and the system ID. |
(config-router)#bfd all-interfaces | Enable BFD for ISIS on all interfaces |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-router)#exit | Exit router mode. |
(config)#exit | Exit config mode. |
R3
#configure terminal | Enter configure mode. |
(config)#int eth1 | Enter interface mode. |
(config-if)#ip address 20.20.20.143/24 | Configure the IP address of the interface. |
(config-if)#ip router isis 1 | Enable ISIS routing on interface for area 49 with instance 1 |
(config-if)#isis metric 5 | Configure isis metric value for interface |
(config-if)#isis circuit-type level-1 | Enable circuit type on interface |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode. |
(config)#int eth2 | Enter interface mode. |
(config-if)#ip address 50.50.50.143/24 | Configure the IP address of the interface. |
(config-if)#ip router isis 1 | Enable ISIS routing on interface for area 49 with instance 1 |
(config-if)#isis metric 10 | Configure isis metric value for interface |
(config-if)#isis circuit-type level-1 | Enable circuit type on interface |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode. |
(config)#router isis 1 | Create an IS-IS routing instance for area 49 with instance 1 |
(config-router)#net 49.0000.0000.0003.00 | Establish a Network Entity Title for this instance, specifying the area address and the system ID. |
(config-router)#bfd all-interfaces | Enable BFD for ISIS on all interfaces |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-router)#exit | Exit router mode. |
(config)#exit | Exit config mode. |
R4
#configure terminal | Enter configure mode. |
(config)#int eth1 | Enter interface mode. |
(config-if)#ip address 30.30.30.144/24 | Configure the IP address of the interface. |
(config-if)#ip router isis 1 | Enable ISIS routing on interface for area 49 with instance 1 |
(config-if)#isis metric 15 | Configure isis metric value for interface |
(config-if)#isis circuit-type level-1 | Enable circuit type on interface |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode. |
(config)#int eth2 | Enter interface mode. |
(config-if)#ip address 60.60.60.144/24 | Configure the IP address of the interface. |
(config-if)#ip router isis 1 | Enable ISIS routing on interface for area 49 with instance 1 |
(config-if)#isis metric 5 | Configure isis metric value for interface |
(config-if)#isis circuit-type level-1 | Enable circuit type on interface |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode. |
(config)#router isis 1 | Create an IS-IS routing instance for area 49 with instance 1 |
(config-router)#net 49.0000.0000.0004.00 | Establish a Network Entity Title for this instance, specifying the area address and the system ID. |
(config-router)#bfd all-interfaces | Enable BFD for ISIS on all interfaces |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-router)#exit | Exit router mode. |
(config)#exit | Exit config mode. |
R5
#configure terminal | Enter configure mode. |
(config)#int eth1 | Enter interface mode. |
(config-if)#ip address 40.40.40.145/24 | Configure the IP address of the interface. |
(config-if)#ip router isis 1 | Enable ISIS routing on interface for area 49 with instance 1 |
(config-if)#isis metric 5 | Configure isis metric value for interface |
(config-if)#isis circuit-type level-1 | Enable circuit type on interface |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode. |
(config)#int eth2 | Enter interface mode. |
(config-if)#ip address 50.50.50.145/24 | Configure the IP address of the interface. |
(config-if)#ip router isis 1 | Enable ISIS routing on interface for area 49 with instance 1 |
(config-if)#isis metric 10 | Configure isis metric value for interface |
(config-if)#isis circuit-type level-1 | Enable circuit type on interface |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode. |
(config)#int eth3 | Enter interface mode. |
(config-if)#ip address 60.60.60.145/24 | Configure the IP address of the interface. |
(config-if)#ip router isis 1 | Enable ISIS routing on interface for area 49 with instance 1 |
(config-if)#isis metric 5 | Configure isis metric value for interface |
(config-if)#isis circuit-type level-1 | Enable circuit type on interface |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode. |
(config)#router isis 1 | Create an IS-IS routing instance for area 49 with instance 1 |
(config-router)#net 49.0000.0000.0005.00 | Establish a Network Entity Title for this instance, specifying the area address and the system ID. |
(config-router)#bfd all-interfaces | Enable BFD for ISIS on all interfaces |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-router)#exit | Exit router mode. |
(config)#exit | Exit config mode. |
Validation
R1
ISIS neighborship:
R1#show clns neighbors
Total number of L1 adjacencies: 3
Total number of L2 adjacencies: 0
Total number of adjacencies: 3
Tag 1: VRF : default
System Id Interface SNPA State Holdtime Type Protocol
0000.0000.0002 eth1 5254.002a.230a Up 27 L1 IS-IS
0000.0000.0003 eth2 5254.00dc.2f11 Up 7 L1 IS-IS
0000.0000.0004 eth3 5254.00f5.35a4 Up 7 L1 IS-IS
R2#show clns neighbors
Total number of L1 adjacencies: 2
Total number of L2 adjacencies: 0
Total number of adjacencies: 2
Tag 1: VRF : default
System Id Interface SNPA State Holdtime Type Protocol
0000.0000.0001 eth1 5254.00dc.0b76 Up 6 L1 IS-IS
0000.0000.0005 eth2 5254.00b3.110c Up 7 L1 IS-IS
R3#show clns neighbors
Total number of L1 adjacencies: 2
Total number of L2 adjacencies: 0
Total number of adjacencies: 2
Tag 1: VRF : default
System Id Interface SNPA State Holdtime Type Protocol
0000.0000.0001 eth1 5254.00a1.6afe Up 22 L1 IS-IS
0000.0000.0005 eth2 5254.0056.7a3d Up 27 L1 IS-IS
R4#show clns neighbors
Total number of L1 adjacencies: 2
Total number of L2 adjacencies: 0
Total number of adjacencies: 2
Tag 1: VRF : default
System Id Interface SNPA State Holdtime Type Protocol
0000.0000.0001 eth1 5254.0011.a028 Up 21 L1 IS-IS
0000.0000.0005 eth2 5254.00d3.fb41 Up 21 L1 IS-IS
R5#show clns neighbors
Total number of L1 adjacencies: 3
Total number of L2 adjacencies: 0
Total number of adjacencies: 3
Tag 1: VRF : default
System Id Interface SNPA State Holdtime Type Protocol
0000.0000.0002 eth1 5254.007e.5ade Up 27 L1 IS-IS
0000.0000.0003 eth2 5254.00a8.940d Up 6 L1 IS-IS
0000.0000.0004 eth3 5254.00e2.aece Up 7 L1 IS-IS
Check the ISIS route installation with primary and backup paths in the ISIS table and RIB table.
Primary paths:
R1#show ip isis route
Codes: C - connected, E - external, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, D - discard, e - external metric
** - invalid
Tag 1: VRF : default
Destination Metric Next-Hop Interface Tag
C 10.10.10.0/24 5 -- eth1 0
C 20.20.20.0/24 5 -- eth2 0
C 30.30.30.0/24 15 -- eth3 0
L1 40.40.40.0/24 10 10.10.10.141 eth1 0
L1 50.50.50.0/24 15 20.20.20.143 eth2 0
L1 60.60.60.0/24 15 10.10.10.141 eth1 0
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, 00:43:14
C 10.12.30.0/24 is directly connected, eth0, 01:42:55
C 20.20.20.0/24 is directly connected, eth2, 00:43:14
C 30.30.30.0/24 is directly connected, eth3, 00:43:14
i L1 40.40.40.0/24 [115/10] via 10.10.10.141, eth1, 00:16:42
i L1 50.50.50.0/24 [115/15] via 20.20.20.143, eth2, 00:16:55
i L1 60.60.60.0/24 [115/15] via 10.10.10.141, eth1, 00:16:42
C 127.0.0.0/8 is directly connected, lo, 01:42:55
Gateway of last resort is not set
R1#FRR backup paths:
R1#show ip isis route fast-reroute
Tag : 1 VRF : default
Codes : L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area,
D - discard, LP - Link Protecting, NP - Node Protecting,
BP - Broadcast Interface Disjoint, Pri - Primary Path,
Sec - Secondary Path, DP - Downstream Path
L1 40.40.40.0/24
Primary Path via : 10.10.10.141, eth1
FRR Backup Path via : 30.30.30.144, eth3
FRR Metric : 25
Protection Provided : LP NP BP
L1 50.50.50.0/24
Primary Path via : 20.20.20.143, eth2
FRR Backup Path via : 10.10.10.141, eth1
FRR Metric : 20
Protection Provided : LP NP BP
L1 60.60.60.0/24
Primary Path via : 10.10.10.141, eth1
FRR Backup Path via : 30.30.30.144, eth3
FRR Metric : 20
Protection Provided : LP NP BP DP
R1#show ip route fast-reroute
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 ,p - stale info
* - candidate default
IP Route Table for VRF "default"
i L1 40.40.40.0/24 [115/10] via 10.10.10.141, eth1, 00:18:01
[FRR-NH] via 30.30.30.144, eth3
i L1 50.50.50.0/24 [115/15] via 20.20.20.143, eth2, 00:18:14
[FRR-NH] via 10.10.10.141, eth1
i L1 60.60.60.0/24 [115/15] via 10.10.10.141, eth1, 00:18:01
[FRR-NH] via 30.30.30.144, eth3
It is not mandatory that for all primary paths, there exists an LFA backup path only if inequality equation satisfies according to attributes configured on routers, backup path will be calculated.
To prohibit an interface from being used as a repair path, disable fast reroute calculation on the interface:
R1(config-if)#interface eth1 | Enter interface. |
(config-if)# isis fast-reroute per-prefix candidate disable level-1 | Disable fast reroute calculation on the interface. |
(config-if)#end | Exit. |
Verify that the eth1 interface is not used for backup path calculation.
R1#show ip isis route fast-reroute
Tag : 1 VRF : default
Codes : L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area,
D - discard, LP - Link Protecting, NP - Node Protecting,
BP - Broadcast Interface Disjoint, Pri - Primary Path,
Sec - Secondary Path, DP - Downstream Path
L1 40.40.40.0/24
Primary Path via : 10.10.10.141, eth1
FRR Backup Path via : 30.30.30.144, eth3
FRR Metric : 25
Protection Provided : LP NP BP
L1 50.50.50.0/24
Primary Path via : 20.20.20.143, eth2
FRR Backup Path via : 30.30.30.144, eth3
FRR Metric : 30
Protection Provided : LP NP BP
L1 60.60.60.0/24
Primary Path via : 10.10.10.141, eth1
FRR Backup Path via : 30.30.30.144, eth3
FRR Metric : 20
Protection Provided : LP NP BP DP
R1#show ip route fast-reroute
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 ,p - stale info
* - candidate default
IP Route Table for VRF "default"
i L1 40.40.40.0/24 [115/10] via 10.10.10.141, eth1, 00:20:22
[FRR-NH] via 30.30.30.144, eth3
i L1 50.50.50.0/24 [115/15] via 20.20.20.143, eth2, 00:20:35
[FRR-NH] via 30.30.30.144, eth3
i L1 60.60.60.0/24 [115/15] via 10.10.10.141, eth1, 00:20:22
[FRR-NH] via 30.30.30.144, eth3
R1#
Last modified date: 10/16/2023