CSR1#sh ip route ospf
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, 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, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR
Gateway of last resort is not set
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 [110/2] via 192.168.13.3, 00:00:58, GigabitEthernet3
O 192.168.23.0/24 [110/2] via 192.168.13.3, 00:00:58, GigabitEthernet3
[110/2] via 192.168.12.2, 00:04:05, GigabitEthernet1
O 192.168.34.0/24 [110/2] via 192.168.14.4, 00:01:38, GigabitEthernet2
[110/2] via 192.168.13.3, 00:00:58, GigabitEthernet3
CSR1#sh ip cef 3.3.3.3/32
3.3.3.3/32
nexthop 192.168.13.3 GigabitEthernet3
router ospf 1
fast-reroute per-prefix enable area 0 prefix-priority high
CSR1#sh ip cef 3.3.3.3/32
3.3.3.3/32
nexthop 192.168.13.3 GigabitEthernet3
repair: attached-nexthop 192.168.12.2 GigabitEthernet1
Let us try to shut down the link between CSR1 and CSR3 (which is the preferred path):
CSR1#sh ip route ospf
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, 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, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR
Gateway of last resort is not set
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 [110/3] via 192.168.14.4, 00:00:01, GigabitEthernet2
[110/3] via 192.168.12.2, 00:00:01, GigabitEthernet1
O 192.168.13.0/24 [110/3] via 192.168.14.4, 00:00:01, GigabitEthernet2
[110/3] via 192.168.12.2, 00:00:01, GigabitEthernet1
O 192.168.23.0/24 [110/2] via 192.168.12.2, 00:06:29, GigabitEthernet1
O 192.168.34.0/24 [110/2] via 192.168.14.4, 00:04:02, GigabitEthernet2
CSR1#show ip cef 3.3.3.3/32
3.3.3.3/32
nexthop 192.168.12.2 GigabitEthernet1
repair: attached-nexthop 192.168.14.4 GigabitEthernet2
nexthop 192.168.14.4 GigabitEthernet2
repair: attached-nexthop 192.168.12.2 GigabitEthernet1
CSR1#sh ip route 3.3.3.3
Routing entry for 3.3.3.3/32
Known via "ospf 1", distance 110, metric 3, type intra area
Last update from 192.168.12.2 on GigabitEthernet1, 00:00:25 ago
Routing Descriptor Blocks:
* 192.168.14.4, from 3.3.3.3, 00:00:25 ago, via GigabitEthernet2
Route metric is 3, traffic share count is 1
Repair Path: 192.168.12.2, via GigabitEthernet1
192.168.12.2, from 3.3.3.3, 00:00:25 ago, via GigabitEthernet1
Route metric is 3, traffic share count is 1
Repair Path: 192.168.14.4, via GigabitEthernet2
CSR1#sh ip route repair-paths 3.3.3.3
Routing entry for 3.3.3.3/32
Known via "ospf 1", distance 110, metric 3, type intra area
Last update from 192.168.12.2 on GigabitEthernet1, 00:00:51 ago
Routing Descriptor Blocks:
* 192.168.14.4, from 3.3.3.3, 00:00:51 ago, via GigabitEthernet2
Route metric is 3, traffic share count is 1
Repair Path: 192.168.12.2, via GigabitEthernet1
192.168.12.2, from 3.3.3.3, 00:00:51 ago, via GigabitEthernet1
Route metric is 3, traffic share count is 1
Repair Path: 192.168.14.4, via GigabitEthernet2
Brining back the link online:
CSR1#sh ip route ospf
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, 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, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR
Gateway of last resort is not set
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 [110/3] via 192.168.14.4, 00:03:15, GigabitEthernet2
[110/3] via 192.168.12.2, 00:03:15, GigabitEthernet1
O 192.168.23.0/24 [110/2] via 192.168.12.2, 00:09:43, GigabitEthernet1
O 192.168.34.0/24 [110/2] via 192.168.14.4, 00:07:16, GigabitEthernet2
Changing all costs to 10 and investigating needed outputs:
CSR1#sh ip route ospf
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, 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, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR
Gateway of last resort is not set
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 [110/11] via 192.168.13.3, 00:03:22, GigabitEthernet3
O 192.168.23.0/24 [110/20] via 192.168.13.3, 00:02:36, GigabitEthernet3
[110/20] via 192.168.12.2, 00:02:36, GigabitEthernet1
O 192.168.34.0/24 [110/20] via 192.168.14.4, 00:02:10, GigabitEthernet2
[110/20] via 192.168.13.3, 00:02:10, GigabitEthernet3
CSR1#sh ip cef 3.3.3.3
3.3.3.3/32
nexthop 192.168.13.3 GigabitEthernet3
repair: attached-nexthop 192.168.14.4 GigabitEthernet2
CSR1#sh ip ospf rib 3.3.3.3
OSPF Router with ID (1.1.1.1) (Process ID 1)
Base Topology (MTID 0)
OSPF local RIB
Codes: * - Best, > - Installed in global RIB
LSA: type/LSID/originator
*> 3.3.3.3/32, Intra, cost 11, area 0
SPF Instance 33, age 00:02:21
Flags: RIB, HiPrio
via 192.168.13.3, GigabitEthernet3
Flags: RIB
LSA: 1/3.3.3.3/3.3.3.3
repair path via 192.168.14.4, GigabitEthernet2, cost 21
Flags: RIB, Repair, IntfDj, BcastDj
LSA: 1/3.3.3.3/3.3.3.3
repair path via 192.168.12.2, GigabitEthernet1, cost 21
Flags: Ignore, Repair, IntfDj, BcastDj, SRLG
LSA: 1/3.3.3.3/3.3.3.3
As can be seen from the output above , the primary path is via the direct link between CSR1 and CSR3
And the repair path is via the link between CSR1 and CSR4
CSR1#sh ip route 3.3.3.3 255.255.255.255
Routing entry for 3.3.3.3/32
Known via "ospf 1", distance 110, metric 11, type intra area
Last update from 192.168.13.3 on GigabitEthernet3, 00:08:33 ago
Routing Descriptor Blocks:
* 192.168.13.3, from 3.3.3.3, 00:08:33 ago, via GigabitEthernet3
Route metric is 11, traffic share count is 1
Repair Path: 192.168.14.4, via GigabitEthernet2
Let us now shut down the backup link and check if R2 satisfies the link protection inequality
The link protection inequality which is similar in terminology to EIGRP feasiable successor
D(N,D) < D(N,S) + D(S,D)
Where
D : Distance (Cost) (D outside parentheses)
S : Source
D : Destination
N : Candidate
Enter configuration commands, one per line. End with CNTL/Z.
CSR1(config)#int g2
CSR1(config-if)#shut
CSR1#sh ip route 3.3.3.3 255.255.255.255
Routing entry for 3.3.3.3/32
Known via "ospf 1", distance 110, metric 11, type intra area
Last update from 192.168.13.3 on GigabitEthernet3, 00:00:27 ago
Routing Descriptor Blocks:
* 192.168.13.3, from 3.3.3.3, 00:00:27 ago, via GigabitEthernet3
Route metric is 11, traffic share count is 1
Repair Path: 192.168.12.2, via GigabitEthernet1
Let us bring back the link and try to modify the costs through R2 in order to be not elected for backup:
Adjusting the cost on the link between R2 and R3 to be 30
CSR1#sh ip ospf rib 3.3.3.3
OSPF Router with ID (1.1.1.1) (Process ID 1)
Base Topology (MTID 0)
OSPF local RIB
Codes: * - Best, > - Installed in global RIB
LSA: type/LSID/originator
*> 3.3.3.3/32, Intra, cost 11, area 0
SPF Instance 38, age 00:12:55
Flags: RIB, HiPrio
via 192.168.13.3, GigabitEthernet3
Flags: RIB
LSA: 1/3.3.3.3/3.3.3.3
repair path via 192.168.14.4, GigabitEthernet2, cost 21
Flags: RIB, Repair, IntfDj, BcastDj
LSA: 1/3.3.3.3/3.3.3.3
As can be seen , the backup path through R2 is missing , now let us shut down the link between CSR1 and CSR4 (the existing backup)
CSR1#sh ip ospf rib 3.3.3.3
OSPF Router with ID (1.1.1.1) (Process ID 1)
Base Topology (MTID 0)
OSPF local RIB
Codes: * - Best, > - Installed in global RIB
LSA: type/LSID/originator
*> 3.3.3.3/32, Intra, cost 11, area 0
SPF Instance 41, age 00:14:34
Flags: RIB, HiPrio
via 192.168.13.3, GigabitEthernet3
Flags: RIB
LSA: 1/3.3.3.3/3.3.3.3
CSR1#sh ip route 3.3.3.3
Routing entry for 3.3.3.3/32
Known via "ospf 1", distance 110, metric 11, type intra area
Last update from 192.168.13.3 on GigabitEthernet3, 00:04:18 ago
Routing Descriptor Blocks:
* 192.168.13.3, from 3.3.3.3, 00:04:18 ago, via GigabitEthernet3
Route metric is 11, traffic share count is 1
CSR1#sh ip cef 3.3.3.3/32
3.3.3.3/32
nexthop 192.168.13.3 GigabitEthernet3
Now , no backup path is availabe
By default , OSPF treats /32 routes as high priority routes , let us check the output for abother route:
CSR1#sh ip ospf rib 192.168.23.0
OSPF Router with ID (1.1.1.1) (Process ID 1)
Base Topology (MTID 0)
OSPF local RIB
Codes: * - Best, > - Installed in global RIB
LSA: type/LSID/originator
*> 192.168.23.0/24, Intra, cost 40, area 0
SPF Instance 44, age 00:32:22
Flags: RIB
via 192.168.12.2, GigabitEthernet1
Flags: RIB
LSA: 2/192.168.23.2/2.2.2.2
via 192.168.13.3, GigabitEthernet3
Flags: RIB
LSA: 2/192.168.23.2/2.2.2.2
Let us try to make the route 192.168.23.0/24 of high priority
ip prefix-list MSSK seq 5 permit 192.168.23.0/24
route-map MAP permit 10
match ip address prefix-list MSSK
router ospf 1
prefix-priority high route-map MAP
CSR1#sh ip ospf rib 192.168.23.0
OSPF Router with ID (1.1.1.1) (Process ID 1)
Base Topology (MTID 0)
OSPF local RIB
Codes: * - Best, > - Installed in global RIB
LSA: type/LSID/originator
*> 192.168.23.0/24, Intra, cost 40, area 0
SPF Instance 45, age 00:36:38
Flags: RIB, HiPrio
via 192.168.12.2, GigabitEthernet1
Flags: RIB
LSA: 2/192.168.23.2/2.2.2.2
repair path via 192.168.13.3, GigabitEthernet3, cost 40
Flags: RIB, Repair, IntfDj, BcastDj, PrimPath, NodeProt, Downstr
LSA: 2/192.168.23.2/2.2.2.2
repair path via 192.168.14.4, GigabitEthernet2, cost 50
Flags: Ignore, Repair, IntfDj, BcastDj, NodeProt
LSA: 2/192.168.23.2/2.2.2.2
via 192.168.13.3, GigabitEthernet3
Flags: RIB
LSA: 2/192.168.23.2/2.2.2.2
repair path via 192.168.12.2, GigabitEthernet1, cost 40
Flags: RIB, Repair, IntfDj, BcastDj, PrimPath, NodeProt, Downstr
LSA: 2/192.168.23.2/2.2.2.2
repair path via 192.168.14.4, GigabitEthernet2, cost 50
Flags: Ignore, Repair, IntfDj, BcastDj
LSA: 2/192.168.23.2/2.2.2.2
Now as there is an explicit deny , 3.3.3.3/32 is no longer high priority:
CSR1#sh ip ospf rib 3.3.3.3
OSPF Router with ID (1.1.1.1) (Process ID 1)
Base Topology (MTID 0)
OSPF local RIB
Codes: * - Best, > - Installed in global RIB
LSA: type/LSID/originator
*> 3.3.3.3/32, Intra, cost 11, area 0
SPF Instance 45, age 00:50:46
Flags: RIB
via 192.168.13.3, GigabitEthernet3
Flags: RIB
LSA: 1/3.3.3.3/3.3.3.3
ip prefix-list MSSK seq 10 permit 3.3.3.3/32
CSR1#sh ip ospf rib 3.3.3.3
OSPF Router with ID (1.1.1.1) (Process ID 1)
Base Topology (MTID 0)
OSPF local RIB
Codes: * - Best, > - Installed in global RIB
LSA: type/LSID/originator
*> 3.3.3.3/32, Intra, cost 11, area 0
SPF Instance 46, age 00:51:39
Flags: RIB, HiPrio
via 192.168.13.3, GigabitEthernet3
Flags: RIB
LSA: 1/3.3.3.3/3.3.3.3
We can exclude an interface from being elected as a candidate for backup using the below command:
interface gig2
ip ospf fast-reroute per-prefix candidate disable
CSR1#sh ip ospf rib 3.3.3.3
OSPF Router with ID (1.1.1.1) (Process ID 1)
Base Topology (MTID 0)
OSPF local RIB
Codes: * - Best, > - Installed in global RIB
LSA: type/LSID/originator
*> 3.3.3.3/32, Intra, cost 11, area 0
SPF Instance 48, age 00:55:13
Flags: RIB, HiPrio
via 192.168.13.3, GigabitEthernet3
Flags: RIB
LSA: 1/3.3.3.3/3.3.3.3
repair path via 192.168.14.4, GigabitEthernet2, cost 21
Flags: RIB, Stale, Repair, IntfDj, BcastDj
LSA: 1/3.3.3.3/3.3.3.3
CSR1#sh ip ospf rib 3.3.3.3
OSPF Router with ID (1.1.1.1) (Process ID 1)
Base Topology (MTID 0)
OSPF local RIB
Codes: * - Best, > - Installed in global RIB
LSA: type/LSID/originator
*> 3.3.3.3/32, Intra, cost 11, area 0
SPF Instance 48, age 00:55:20
Flags: RIB, HiPrio
via 192.168.13.3, GigabitEthernet3
Flags: RIB
LSA: 1/3.3.3.3/3.3.3.3
Now , let us configure loopback 0 interface on CSR4 and advertise it in OSPF
CSR4:
interface loopback0
ip address 4.4.4.4 255.255.255.255
ip ospf 1 area 0
and revert back all costs to 10 on all links and checking from CSR2 (S) for outputs:
CSR2#sh ip route ospf
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, 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, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/11] via 192.168.12.1, 00:02:53, GigabitEthernet1
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 [110/11] via 192.168.23.3, 00:01:55, GigabitEthernet2
4.0.0.0/32 is subnetted, 1 subnets
O 4.4.4.4 [110/21] via 192.168.23.3, 00:01:55, GigabitEthernet2
[110/21] via 192.168.12.1, 00:02:53, GigabitEthernet1
O 192.168.13.0/24 [110/20] via 192.168.23.3, 00:01:56, GigabitEthernet2
[110/20] via 192.168.12.1, 03:44:05, GigabitEthernet1
O 192.168.14.0/24 [110/20] via 192.168.12.1, 03:00:56, GigabitEthernet1
O 192.168.34.0/24 [110/20] via 192.168.23.3, 00:01:56, GigabitEthernet2
CSR2#sh ip route 4.4.4.4
Routing entry for 4.4.4.4/32
Known via "ospf 1", distance 110, metric 21, type intra area
Last update from 192.168.23.3 on GigabitEthernet2, 00:02:07 ago
Routing Descriptor Blocks:
192.168.23.3, from 4.4.4.4, 00:02:07 ago, via GigabitEthernet2
Route metric is 21, traffic share count is 1
Repair Path: 192.168.12.1, via GigabitEthernet1
* 192.168.12.1, from 4.4.4.4, 00:03:05 ago, via GigabitEthernet1
Route metric is 21, traffic share count is 1
Repair Path: 192.168.23.3, via GigabitEthernet2
CSR2#sh ip ospf rib 4.4.4.4
OSPF Router with ID (2.2.2.2) (Process ID 1)
Base Topology (MTID 0)
OSPF local RIB
Codes: * - Best, > - Installed in global RIB
LSA: type/LSID/originator
*> 4.4.4.4/32, Intra, cost 21, area 0
SPF Instance 40, age 00:02:21
Flags: RIB, HiPrio
via 192.168.23.3, GigabitEthernet2
Flags: RIB
LSA: 1/4.4.4.4/4.4.4.4
repair path via 192.168.12.1, GigabitEthernet1, cost 21
Flags: RIB, Repair, IntfDj, BcastDj, PrimPath, NodeProt, Downstr
LSA: 1/4.4.4.4/4.4.4.4
via 192.168.12.1, GigabitEthernet1
Flags: RIB
LSA: 1/4.4.4.4/4.4.4.4
repair path via 192.168.23.3, GigabitEthernet2, cost 21
Flags: RIB, Repair, IntfDj, BcastDj, PrimPath, NodeProt, Downstr
LSA: 1/4.4.4.4/4.4.4.4
Two backup paths are installed as inequality for link protection is passed
Now , what we want to examine is node protection
CSR2#sh ip route repair 4.4.4.4
Routing entry for 4.4.4.4/32
Known via "ospf 1", distance 110, metric 21, type intra area
Last update from 192.168.23.3 on GigabitEthernet2, 00:04:54 ago
Routing Descriptor Blocks:
192.168.23.3, from 4.4.4.4, 00:04:54 ago, via GigabitEthernet2
Route metric is 21, traffic share count is 1
Repair Path: 192.168.12.1, via GigabitEthernet1
* 192.168.12.1, from 4.4.4.4, 00:05:52 ago, via GigabitEthernet1
Route metric is 21, traffic share count is 1
Repair Path: 192.168.23.3, via GigabitEthernet2
Now , let us adjust the cost on the links between R2 and R3 to 30 , and between R1 and R4 to 15 and check the outputs
CSR2# sh ip ospf rib 4.4.4.4
OSPF Router with ID (2.2.2.2) (Process ID 1)
Base Topology (MTID 0)
OSPF local RIB
Codes: * - Best, > - Installed in global RIB
LSA: type/LSID/originator
*> 4.4.4.4/32, Intra, cost 26, area 0
SPF Instance 44, age 00:00:48
Flags: RIB, HiPrio
via 192.168.12.1, GigabitEthernet1
Flags: RIB
LSA: 1/4.4.4.4/4.4.4.4
repair path via 192.168.23.3, GigabitEthernet2, cost 41
Flags: RIB, Repair, IntfDj, BcastDj, NodeProt, Downstr
LSA: 1/4.4.4.4/4.4.4.4
We can see the flag of NodeProt , which means that R3 will be able to provide backup in case of the primary node (R1) failure
This was satisfied by passing Inquality of node protection:
D(N,D) < D(N,E) + D(E,D)
Where in our case:
N : CSR3
E : CSR1
D : CSR4
D(N,D) = 10
D(N,E) = 10
D(E,D) = 15
10 < 10 + 15 --> 10 < 25 Passed
Let us try to modify the costs again in order to make the inquality fails
CSR2# sh ip ospf rib 4.4.4.4
OSPF Router with ID (2.2.2.2) (Process ID 1)
Base Topology (MTID 0)
OSPF local RIB
Codes: * - Best, > - Installed in global RIB
LSA: type/LSID/originator
*> 4.4.4.4/32, Intra, cost 26, area 0
SPF Instance 52, age 00:00:11
Flags: RIB, HiPrio
via 192.168.12.1, GigabitEthernet1
Flags: RIB
LSA: 1/4.4.4.4/4.4.4.4
repair path via 192.168.23.3, GigabitEthernet2, cost 56
Flags: RIB, Repair, IntfDj, BcastDj
LSA: 1/4.4.4.4/4.4.4.4
As can be seen from the output above , the NodeProt disappeared
LFA Route Selection Criteria
Below are the backup prefix selection criteria with their preference in decreasing order. In the event of two backup routes available for a protected primary prefix, only one would be selected based on below mentioned ordered list of attributes they carry. Below is a brief explanation about these attributes.
Repair path selection policy tiebreaks (built-in default policy)
10 srlg
20 primary-path
30 interface-disjoint
40 lowest-metric
50 linecard-disjoint
60 node-protecting
70 broadcast-interface-disjoint
256 load-sharing
Shared risk link group (SRLG): Default LFA policy tries to avoid a path that carries same SRLG as primary path.Assume multiple routers are using the same switch ,so they all be sharing the same risk .
Primary-path: This helps in eliminating candidates that are not equal cost multiple path links or ECMPs.
Interface-Disjoint: This means that repair path is over a different interface as compared to the interface used to reach destination via primary path. In case of point-to-point links, this condition is always met.
Lowest-metric: Select a backup path with minimum cost to reach destination.
Linecard-disjoint: This prefers a backup route from an interface that is on another line card. This is also a special case of SRLG however; this does not require any special configuration and is handled automatically.
Node-protecting: Repair path all together bypasses primary path next-hop router. This ensures complete traffic protection even in the event of primary next-hop router failure.
Broadcast-interface-disjoint : This attributes helps to ensure that repair path does not make use of same broadcast network used by primary path.
Load-sharing: Traffic is load shared amongst candidate back up routes when all other checks discussed above fail to provide a unique back up path.
Let us try to modify the default built-in policy , but before that let us check outputs again and check inequality
CSR1#sh ip ospf rib 3.3.3.3
OSPF Router with ID (1.1.1.1) (Process ID 1)
Base Topology (MTID 0)
OSPF local RIB
Codes: * - Best, > - Installed in global RIB
LSA: type/LSID/originator
*> 3.3.3.3/32, Intra, cost 11, area 0
SPF Instance 76, age 00:27:28
Flags: RIB, HiPrio
via 192.168.13.3, GigabitEthernet3
Flags: RIB
LSA: 1/3.3.3.3/3.3.3.3
repair path via 192.168.12.2, GigabitEthernet1, cost 41
Flags: RIB, Repair, IntfDj, BcastDj, CostWon
LSA: 1/3.3.3.3/3.3.3.3
repair path via 192.168.14.4, GigabitEthernet2, cost 51
Flags: Ignore, Repair, IntfDj, BcastDj
LSA: 1/3.3.3.3/3.3.3.3
CSR1#sh ip route repair-paths 3.3.3.3
Routing entry for 3.3.3.3/32
Known via "ospf 1", distance 110, metric 11, type intra area
Last update from 192.168.13.3 on GigabitEthernet3, 00:05:29 ago
Routing Descriptor Blocks:
* 192.168.13.3, from 3.3.3.3, 00:05:29 ago, via GigabitEthernet3
Route metric is 11, traffic share count is 1
Repair Path: 192.168.12.2, via GigabitEthernet1
[RPR]192.168.12.2, from 3.3.3.3, 00:05:29 ago, via GigabitEthernet1
Route metric is 41, traffic share count is 1
As can be seen from the above output , R1 best path to reach R3 is via the direct link between them
Checking the inequality for link protection:
D(N,D) < D(N,S) + D(S,D)
If we considered first backup link to be R1 - R2
D : R3
S : R1
N : R2
D(N,D) = 20
D(N,S) = 20
D(S,D) = 10
Passed!
If we considered second backup link to be R1 - R4
D : R3
S : R1
N : R4
D(N,D) = 20
D(N,S) = 30
D(S,D) = 10
Passed!
CSR1#sh ip ospf fast-reroute
OSPF Router with ID (1.1.1.1) (Process ID 1)
Loop-free Fast Reroute protected prefixes:
Area Topology name Priority Remote LFA Enabled
0 Base High No
Repair path selection policy tiebreaks (built-in default policy):
10 srlg
20 primary-path
30 interface-disjoint
40 lowest-metric
50 linecard-disjoint
60 node-protecting
70 broadcast-interface-disjoint
256 load-sharing
OSPF/RIB notifications:
Topology Base: Notification Disabled, Callback Not Registered
Last SPF calculation started 00:00:25 ago and was running for 0 ms.
fast-reroute per-prefix tie-break lowest-metric index 10
fast-reroute per-prefix tie-break srlg index 20
CSR1#sh ip ospf fast-reroute
OSPF Router with ID (1.1.1.1) (Process ID 1)
Loop-free Fast Reroute protected prefixes:
Area Topology name Priority Remote LFA Enabled
0 Base High No
Repair path selection policy tiebreaks:
10 lowest-metric
20 srlg
256 load-sharing
OSPF/RIB notifications:
Topology Base: Notification Disabled, Callback Not Registered
Last SPF calculation started 00:00:56 ago and was running for 1 ms.
CSR1:
interface gig1
srlg gid 20
interface gig3
srlg gid 20
CSR1#sh ip ospf rib 3.3.3.3
OSPF Router with ID (1.1.1.1) (Process ID 1)
Base Topology (MTID 0)
OSPF local RIB
Codes: * - Best, > - Installed in global RIB
LSA: type/LSID/originator
*> 3.3.3.3/32, Intra, cost 11, area 0
SPF Instance 86, age 00:55:42
Flags: RIB, HiPrio
via 192.168.13.3, GigabitEthernet3
Flags: RIB
LSA: 1/3.3.3.3/3.3.3.3
repair path via 192.168.12.2, GigabitEthernet1, cost 41
Flags: RIB, Repair, IntfDj, BcastDj, SRLG, CostWon
LSA: 1/3.3.3.3/3.3.3.3
repair path via 192.168.14.4, GigabitEthernet2, cost 51
Flags: Ignore, Repair, IntfDj, BcastDj
LSA: 1/3.3.3.3/3.3.3.3
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