BGP OSPF - Next Hop Issue with IOS XE Router

[abhishekkumarrakeshkumarmishra]

Network Diagram brief

Please refer to the attachment or the following for the network diagram

Please note it is a lab diagram for learning and testing purposes.

-> There are 4 IOS XE Routers
-> The interface links are represented in the following format.
Example: For an interface IP - 155.1.146.X/24 - X denotes the Router nos (1,2,3 and so on)
-> All the routes have loopback on them.
Example: For R1 - 150.1.1.1/24
-> R1, R4 and R6 is running OSPF as usual.
The required network with the Router loopback's are advertised into it.
-> IBGP is running between R1, R4 and R6. It uses loopback for IBGP peering.
-> EBGP is running between R1, R4 (on 155.1.45.X/24) and R5. It uses interface ip for peering.

Issue:
1 -> R5 is not able to ping R6 loopback ip when the ping is sourced from R5's loopback.
2 -> R6 is not able to ping R5 loopback ip when the ping is sourced from R6's loopback.
No other ping related issues.

R6 and R5 are both able to reach R1 properly including the ping from their loopback as well.

The problem kind of appears to be specifically on R6 as traffic from R5 is able to reach R1.
There some to be some weird thing with CEF. Don't know why, but on R6 for 150.1.5.5 the nexthop is unusable.
Even though the route is in routing table.

Please have a look at the following for the CLI output's of Routers

CLI Outputs:
Please ignore the MPLS configs.
As removing it does not resolve's the issue.

CLI output - R1
R1#sh run | sec router
router ospf 1
router-id 1.1.0.0
network 150.1.1.0 0.0.0.255 area 0
network 155.1.146.0 0.0.0.255 area 0
router bgp 100
bgp router-id 1.1.0.0
bgp log-neighbor-changes
no bgp default ipv4-unicast
neighbor 150.1.4.4 remote-as 100
neighbor 150.1.4.4 update-source Loopback0
neighbor 150.1.6.6 remote-as 100
neighbor 150.1.6.6 update-source Loopback0
neighbor 155.1.0.5 remote-as 200
!
address-family ipv4
network 150.1.1.0 mask 255.255.255.0
network 155.1.0.0 mask 255.255.255.0
network 155.1.13.0 mask 255.255.255.0
network 155.1.146.0 mask 255.255.255.0
neighbor 150.1.4.4 activate
neighbor 150.1.4.4 send-community extended
neighbor 150.1.4.4 route-reflector-client
neighbor 150.1.4.4 send-label
neighbor 150.1.6.6 activate
neighbor 150.1.6.6 send-community extended
neighbor 150.1.6.6 route-reflector-client
neighbor 150.1.6.6 next-hop-self
neighbor 150.1.6.6 soft-reconfiguration inbound
neighbor 150.1.6.6 send-label
neighbor 155.1.0.5 activate
neighbor 155.1.0.5 soft-reconfiguration inbound
exit-address-family
mpls ldp router-id Loopback0 force
R1#show ip route
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, m - OMP
n - NAT, Ni - NAT inside, No - NAT outside, Nd - NAT DIA
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
H - NHRP, G - NHRP registered, g - NHRP registration summary
o - ODR, P - periodic downloaded static route, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR
& - replicated local route overrides by connected

Gateway of last resort is not set

150.1.0.0/16 is variably subnetted, 5 subnets, 2 masks
C 150.1.1.0/24 is directly connected, Loopback0
L 150.1.1.1/32 is directly connected, Loopback0
O 150.1.4.0/24 [110/2] via 155.1.146.4, 23:15:54, GigabitEthernet1.146
B 150.1.5.0/24 [20/0] via 155.1.0.5, 22:22:19
O 150.1.6.0/24 [110/2] via 155.1.146.6, 23:15:40, GigabitEthernet1.146
155.1.0.0/16 is variably subnetted, 8 subnets, 2 masks
C 155.1.0.0/24 is directly connected, GigabitEthernet3.10
L 155.1.0.1/32 is directly connected, GigabitEthernet3.10
B 155.1.5.0/24 [20/0] via 155.1.0.5, 22:22:19
C 155.1.13.0/24 is directly connected, GigabitEthernet2.20
L 155.1.13.1/32 is directly connected, GigabitEthernet2.20
B 155.1.45.0/24 [200/0] via 150.1.4.4, 23:02:55
C 155.1.146.0/24 is directly connected, GigabitEthernet1.146
L 155.1.146.1/32 is directly connected, GigabitEthernet1.146
R1#show ip ospf database

OSPF Router with ID (1.1.0.0) (Process ID 1)

Router Link States (Area 0)

Link ID ADV Router Age Seq# Checksum Link count
1.1.0.0 1.1.0.0 1528 0x8000002F 0x00C828 2
1.4.0.0 1.4.0.0 1584 0x80000030 0x00E9FA 2
1.6.0.0 1.6.0.0 1383 0x80000030 0x0008D4 2

Net Link States (Area 0)

Link ID ADV Router Age Seq# Checksum
155.1.146.6 1.6.0.0 1383 0x8000002B 0x003C85
R1#show ip bgp
BGP table version is 18, local router ID is 1.1.0.0
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
t secondary path, L long-lived-stale,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path
*> 150.1.1.0/24 0.0.0.0 0 32768 i
r>i 150.1.4.0/24 150.1.4.4 0 100 0 i
* i 150.1.5.0/24 150.1.4.4 0 100 0 200 i
*> 155.1.0.5 0 0 200 i
r>i 150.1.6.0/24 150.1.6.6 0 100 0 i
* 155.1.0.0/24 155.1.0.5 0 0 200 i
*> 0.0.0.0 0 32768 i
* i 150.1.4.4 0 100 0 i
* i 155.1.5.0/24 150.1.4.4 0 100 0 200 i
*> 155.1.0.5 0 0 200 i
*> 155.1.13.0/24 0.0.0.0 0 32768 i
* 155.1.45.0/24 155.1.0.5 0 0 200 i
*>i 150.1.4.4 0 100 0 i
Network Next Hop Metric LocPrf Weight Path
*> 155.1.146.0/24 0.0.0.0 0 32768 i
* i 150.1.4.4 0 100 0 i
* i 150.1.6.6 0 100 0 i
R1#

CLI Output - R4
R4#sh run | sec router
router ospf 1
router-id 1.4.0.0
network 150.1.4.0 0.0.0.255 area 0
network 155.1.146.0 0.0.0.255 area 0
router bgp 100
bgp router-id 1.4.0.0
bgp log-neighbor-changes
no bgp default ipv4-unicast
neighbor 150.1.1.1 remote-as 100
neighbor 150.1.1.1 update-source Loopback0
neighbor 155.1.45.5 remote-as 200
!
address-family ipv4
network 150.1.4.0 mask 255.255.255.0
network 155.1.0.0 mask 255.255.255.0
network 155.1.45.0 mask 255.255.255.0
network 155.1.146.0 mask 255.255.255.0
neighbor 150.1.1.1 activate
neighbor 150.1.1.1 send-community extended
neighbor 150.1.1.1 next-hop-self
neighbor 150.1.1.1 soft-reconfiguration inbound
neighbor 150.1.1.1 send-label
neighbor 155.1.45.5 activate
neighbor 155.1.45.5 send-community extended
neighbor 155.1.45.5 soft-reconfiguration inbound
neighbor 155.1.45.5 send-label
exit-address-family
mpls ldp router-id Loopback0 force
R4#show ip route
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, m - OMP
n - NAT, Ni - NAT inside, No - NAT outside, Nd - NAT DIA
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
H - NHRP, G - NHRP registered, g - NHRP registration summary
o - ODR, P - periodic downloaded static route, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR
& - replicated local route overrides by connected

Gateway of last resort is not set

150.1.0.0/16 is variably subnetted, 6 subnets, 2 masks
B 150.1.1.0/24 [200/0] via 150.1.1.1, 22:11:42
O 150.1.1.1/32 [110/2] via 155.1.146.1, 22:11:42, GigabitEthernet2.146
C 150.1.4.0/24 is directly connected, Loopback0
L 150.1.4.4/32 is directly connected, Loopback0
B 150.1.5.0/24 [20/0] via 155.1.45.5, 22:23:54
O 150.1.6.0/24 [110/2] via 155.1.146.6, 23:17:15, GigabitEthernet2.146
155.1.0.0/16 is variably subnetted, 9 subnets, 2 masks
C 155.1.0.0/24 is directly connected, GigabitEthernet3.10
L 155.1.0.4/32 is directly connected, GigabitEthernet3.10
B 155.1.5.0/24 [20/0] via 155.1.45.5, 22:23:54
B 155.1.13.0/24 [200/0] via 150.1.1.1, 23:04:29
C 155.1.45.0/24 is directly connected, GigabitEthernet4.40
L 155.1.45.4/32 is directly connected, GigabitEthernet4.40
C 155.1.45.5/32 is directly connected, GigabitEthernet4.40
C 155.1.146.0/24 is directly connected, GigabitEthernet2.146
L 155.1.146.4/32 is directly connected, GigabitEthernet2.146
204.12.1.0/24 is variably subnetted, 2 subnets, 2 masks
C 204.12.1.0/24 is directly connected, GigabitEthernet5.43
L 204.12.1.4/32 is directly connected, GigabitEthernet5.43
R4#show ip ospf database

OSPF Router with ID (1.4.0.0) (Process ID 1)

Router Link States (Area 0)

Link ID ADV Router Age Seq# Checksum Link count
1.1.0.0 1.1.0.0 1619 0x8000002F 0x00C828 2
1.4.0.0 1.4.0.0 1673 0x80000030 0x00E9FA 2
1.6.0.0 1.6.0.0 1473 0x80000030 0x0008D4 2

Net Link States (Area 0)

Link ID ADV Router Age Seq# Checksum
155.1.146.6 1.6.0.0 1473 0x8000002B 0x003C85
R4#show ip bgp
BGP table version is 52, local router ID is 1.4.0.0
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
t secondary path, L long-lived-stale,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path
*>i 150.1.1.0/24 150.1.1.1 0 100 0 i
*> 150.1.4.0/24 0.0.0.0 0 32768 i
* i 150.1.5.0/24 155.1.0.5 0 100 0 200 i
*> 155.1.45.5 0 0 200 i
r>i 150.1.6.0/24 150.1.6.6 0 100 0 i
* 155.1.0.0/24 155.1.45.5 0 0 200 i
* i 150.1.1.1 0 100 0 i
*> 0.0.0.0 0 32768 i
* i 155.1.5.0/24 155.1.0.5 0 100 0 200 i
*> 155.1.45.5 0 0 200 i
*>i 155.1.13.0/24 150.1.1.1 0 100 0 i
* 155.1.45.0/24 155.1.45.5 0 0 200 i
*> 0.0.0.0 0 32768 i
Network Next Hop Metric LocPrf Weight Path
* i 155.1.146.0/24 150.1.1.1 0 100 0 i
*> 0.0.0.0 0 32768 i
R4#

CLI Output - R5
R5#show run | sec router
router bgp 1015
bgp router-id 1.5.0.0
bgp log-neighbor-changes
bgp confederation identifier 200
bgp confederation peers 1012 1013
no bgp default ipv4-unicast
neighbor 155.1.0.1 remote-as 100
neighbor 155.1.45.4 remote-as 100
!
address-family ipv4
network 150.1.5.0 mask 255.255.255.0
network 155.1.0.0 mask 255.255.255.0
network 155.1.5.0 mask 255.255.255.0
network 155.1.45.0 mask 255.255.255.0
neighbor 155.1.0.1 activate
neighbor 155.1.0.1 send-community extended
neighbor 155.1.0.1 soft-reconfiguration inbound
neighbor 155.1.0.1 send-label
neighbor 155.1.45.4 activate
neighbor 155.1.45.4 send-community extended
neighbor 155.1.45.4 soft-reconfiguration inbound
neighbor 155.1.45.4 send-label
exit-address-family
mpls ldp router-id Loopback0 force
R5#sh ip route
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, m - OMP
n - NAT, Ni - NAT inside, No - NAT outside, Nd - NAT DIA
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
H - NHRP, G - NHRP registered, g - NHRP registration summary
o - ODR, P - periodic downloaded static route, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR
& - replicated local route overrides by connected

Gateway of last resort is not set

150.1.0.0/16 is variably subnetted, 5 subnets, 2 masks
B 150.1.1.0/24 [20/0] via 155.1.0.1, 22:25:40
B 150.1.4.0/24 [20/0] via 155.1.0.1, 22:25:40
C 150.1.5.0/24 is directly connected, Loopback0
L 150.1.5.5/32 is directly connected, Loopback0
B 150.1.6.0/24 [20/0] via 155.1.0.1, 22:25:40
155.1.0.0/16 is variably subnetted, 11 subnets, 2 masks
C 155.1.0.0/24 is directly connected, GigabitEthernet3.10
L 155.1.0.5/32 is directly connected, GigabitEthernet3.10
C 155.1.5.0/24 is directly connected, GigabitEthernet2.5
L 155.1.5.5/32 is directly connected, GigabitEthernet2.5
B 155.1.13.0/24 [20/0] via 155.1.0.1, 22:25:40
C 155.1.45.0/24 is directly connected, GigabitEthernet4.40
C 155.1.45.4/32 is directly connected, GigabitEthernet4.40
L 155.1.45.5/32 is directly connected, GigabitEthernet4.40
C 155.1.58.0/24 is directly connected, GigabitEthernet1.58
L 155.1.58.5/32 is directly connected, GigabitEthernet1.58
B 155.1.146.0/24 [20/0] via 155.1.0.1, 22:25:40
R5#show ip bgp
BGP table version is 12, local router ID is 1.5.0.0
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
t secondary path, L long-lived-stale,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path
*> 150.1.1.0/24 155.1.0.1 0 0 100 i
* 155.1.45.4 0 100 i
*> 150.1.4.0/24 155.1.0.1 0 100 i
* 155.1.45.4 0 0 100 i
*> 150.1.5.0/24 0.0.0.0 0 32768 i
*> 150.1.6.0/24 155.1.0.1 0 100 i
* 155.1.45.4 0 100 i
*> 155.1.0.0/24 0.0.0.0 0 32768 i
* 155.1.0.1 0 0 100 i
* 155.1.45.4 0 0 100 i
*> 155.1.5.0/24 0.0.0.0 0 32768 i
*> 155.1.13.0/24 155.1.0.1 0 0 100 i
* 155.1.45.4 0 100 i
Network Next Hop Metric LocPrf Weight Path
*> 155.1.45.0/24 0.0.0.0 0 32768 i
* 155.1.0.1 0 100 i
* 155.1.45.4 0 0 100 i
*> 155.1.146.0/24 155.1.0.1 0 0 100 i
* 155.1.45.4 0 0 100 i
R5#

CLI Ouput - R6
R6#show run | sec router
router ospf 1
router-id 1.6.0.0
network 150.1.6.0 0.0.0.255 area 0
network 155.1.146.0 0.0.0.255 area 0
router bgp 100
bgp router-id 1.6.0.0
bgp log-neighbor-changes
no bgp default ipv4-unicast
neighbor 150.1.1.1 remote-as 100
neighbor 150.1.1.1 update-source Loopback0
!
address-family ipv4
network 150.1.6.0 mask 255.255.255.0
network 155.1.146.0 mask 255.255.255.0
neighbor 150.1.1.1 activate
neighbor 150.1.1.1 send-community extended
neighbor 150.1.1.1 next-hop-self
neighbor 150.1.1.1 soft-reconfiguration inbound
neighbor 150.1.1.1 send-label
exit-address-family
mpls ldp router-id Loopback0 force
R6#show ip route
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, m - OMP
n - NAT, Ni - NAT inside, No - NAT outside, Nd - NAT DIA
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
H - NHRP, G - NHRP registered, g - NHRP registration summary
o - ODR, P - periodic downloaded static route, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR
& - replicated local route overrides by connected

Gateway of last resort is not set

54.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 54.1.1.0/24 is directly connected, GigabitEthernet3
L 54.1.1.6/32 is directly connected, GigabitEthernet3
150.1.0.0/16 is variably subnetted, 6 subnets, 2 masks
B 150.1.1.0/24 [200/0] via 150.1.1.1, 22:13:55
O 150.1.1.1/32 [110/2] via 155.1.146.1, 22:13:55, GigabitEthernet1.146
O 150.1.4.0/24 [110/2] via 155.1.146.4, 23:10:45, GigabitEthernet1.146
B 150.1.5.0/24 [200/0] via 150.1.1.1, 22:12:06
C 150.1.6.0/24 is directly connected, Loopback0
L 150.1.6.6/32 is directly connected, Loopback0
155.1.0.0/16 is variably subnetted, 8 subnets, 2 masks
B 155.1.0.0/24 [200/0] via 150.1.1.1, 23:06:43
B 155.1.5.0/24 [200/0] via 150.1.1.1, 22:12:06
B 155.1.13.0/24 [200/0] via 150.1.1.1, 23:06:43
B 155.1.45.0/24 [200/0] via 150.1.4.4, 23:06:43
C 155.1.67.0/24 is directly connected, GigabitEthernet1.67
L 155.1.67.6/32 is directly connected, GigabitEthernet1.67
C 155.1.146.0/24 is directly connected, GigabitEthernet1.146
L 155.1.146.6/32 is directly connected, GigabitEthernet1.146
R6#show ip ospf database

OSPF Router with ID (1.6.0.0) (Process ID 1)

Router Link States (Area 0)

Link ID ADV Router Age Seq# Checksum Link count
1.1.0.0 1.1.0.0 1750 0x8000002F 0x00C828 2
1.4.0.0 1.4.0.0 1805 0x80000030 0x00E9FA 2
1.6.0.0 1.6.0.0 1603 0x80000030 0x0008D4 2

Net Link States (Area 0)

Link ID ADV Router Age Seq# Checksum
155.1.146.6 1.6.0.0 1603 0x8000002B 0x003C85
R6#show ip bgp
BGP table version is 32, local router ID is 1.6.0.0
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
t secondary path, L long-lived-stale,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path
*>i 150.1.1.0/24 150.1.1.1 0 100 0 i
r>i 150.1.4.0/24 150.1.4.4 0 100 0 i
*>i 150.1.5.0/24 150.1.1.1 0 100 0 200 i
*> 150.1.6.0/24 0.0.0.0 0 32768 i
*>i 155.1.0.0/24 150.1.1.1 0 100 0 i
*>i 155.1.5.0/24 150.1.1.1 0 100 0 200 i
*>i 155.1.13.0/24 150.1.1.1 0 100 0 i
*>i 155.1.45.0/24 150.1.4.4 0 100 0 i
* i 155.1.146.0/24 150.1.1.1 0 100 0 i
*> 0.0.0.0 0 32768 i
R6#
R6#show ip cef 150.1.5.5
150.1.5.0/24
nexthop 155.1.146.1 GigabitEthernet1.146 unusable: no label
R6#show ip cef 150.1.5.5 detail
150.1.5.0/24, epoch 2, flags [rib defined all labels]
recursive via 150.1.1.1 label 16
nexthop 155.1.146.1 GigabitEthernet1.146 unusable: no label
R6#

[abhishekkumarrakeshkumarmishra]

It's really baffling me as I am not able to understand what I am missing. 

One thing, I remebered that there is some sort of path recursion max depth command thing as well.
But the thing is that command and it's application is on the XR series not on XE series.

[sagarjadhwani]

Since R4 is a route-reflector client to R1, configure next-hop-self to rewrite the BGP next-hop for routes learned from R5:

R4(config)# router bgp 100

R4(config-router)# address-family ipv4

R4(config-router-af)# neighbor 150.1.1.1 next-hop-self

This ensures that when R4 advertises 155.1.5.0/24 to R1, it sets its own Loopback0 (150.1.4.4) as next-hop, which is reachable via OSPF.

[paul driver]

Hello
No sure why you have a bgp confederation on rtr5 surely this should reside in ASN 200 with  two ebgp peers to R1 & R4 AS100 ? 
Also you using label unicast ( send label ) but i dont see any mpls interfaces (or your not showing them, either way as a result ipv4 AF are not consulted .

Try the following

All rtrs
router bgp x
address-family ipv4
no neighbor x.x.x. send-label
no neighbor x.x.x.x soft-reconfiguration inbound
no neighbor x.x.x. send-community extended

Rtrs  1,4,6
int lo0
ip ospf network point-to-point

Rtr1
int x/x
ip address 155.1.146.1/24
ip ospf 1 priority 150

router ospf 1
passive interface <facing R5>

Rtr4
int x/x
ip address 155.1.146.4/24
ip ospf 1 priority 100

router ospf 1
passive interface <facing R5>

Rtr6
int x/x
ip address 155.1.146.6/24
ip ospf 1 priority 0

rtr 5
router bgp 200
bgp router-id 1.5.0.0
bgp log-neighbor-changes
no bgp default ipv4-unicast
neighbor 155.1.0.1 remote-as 100
neighbor 155.1.45.4 remote-as 100
address-family ipv4
network 150.1.5.0 mask 255.255.255.0
network 155.1.0.0 mask 255.255.255.0
network 155.1.5.0 mask 255.255.255.0
network 155.1.45.0 mask 255.255.255.0
neighbor 155.1.0.1 activate
neighbor 155.1.45.4 activate
exit-address-family

[Harold Ritter]

Hi @abhishekkumarrakeshkumarmishra ,

The fact that 150.1.5.5 is considered unusable on R6 is due to the IGP and LDP not being in sync for prefix 150.1.1.1, which is the recursive next hop for prefix 150.1.5.0/24.

150.1.1.1 is received as 150.1.1.1/32 via OSPF and as 150.1.1.0/24 via LDP. 

You can fix it by configuring 150.1.1.1/32 on the loopback interface on R1 or as @paul driver recommended you can configure "ip ospf network point-to-point" on the loopback interface, which will force OSPF to advertise the prefix advertised the configured prefix length (by default the prefix is advertised as a /32, regardless of the prefix length configured).

It is normally recommended to configure the loopback interface address as a /32 though.

[abhishekkumarrakeshkumarmishra]

Thanks @sagarjadhwani for the config update recommendation.

Thanks @Harold Ritter and @paul driver for the solution. 

The fix was spot on.

Also, I was using /24 loopback and BGP confederations, just for learning purposes. I am following a mock lab workbook and tinkering with it for revising. 

But can you guys  @Harold Ritter and @paul driver explain, why exactly advertising /24 prefix in ospf solved the next hop problem.

As far as I know, The router should perform recursive checks to determine the actual exit interface and it was able to see the interface. 

So according to my understanding the recursive route exit interface determination will work like this

150.1.5.5/24 --> (Part of 150.1.5.0/24) --> 150.1.1.1 --> (Part of 150.1.1.0/24) --> Via 155.1.146.1 and interface Ge1.146

(Non working conditions output - Mentioned in the original questions)

R6#show ip cef 150.1.5.5
150.1.5.0/24
nexthop 155.1.146.1 GigabitEthernet1.146 unusable: no label

Based on that CEF should build the table and the route should be usable, I think so ???

And more over the route to 150.1.1.1/32  was present in the routing table (when ip ospf network point-to-point was not there).

The ping to 150.1.1.1 was successful from R6 during that time. 

What am I missing ??

And is it because, I was using MPLS (Something to do with it) as well in this scenario ???

[Harold Ritter]

Hi @abhishekkumarrakeshkumarmishra ,

> But can you guys  @Harold Ritter and @paul driver explain, why > exactly advertising /24 prefix in ospf solved the next hop           > problem.

The issue, as I previously mentioned, is due to the fact that OSPF advertises the loopback interface ip address as a /32 by default, despite the fact that you configured a /24.

This by itself would not be an issue if it wasn't that LDP will advertise the loopback interface ip address according to the configured mask (/24 in your case).

The fact that OSPF and LDP are out of sync causes the issue you are seeing in your lab.

Configuring a /32 fo the loopback interface ip address solves the issue, as both OSPF and LDP will be in sync.

The same goes with configuring "ip ospf network point-to-point", which forces OSPF to advertise the configured value (/24 in your case). This also solves the out of sync issue as both OSPF and LDP advertise a /24.

[paul driver]

Hello
You say you were doing a lab workbook, I do not know from which text your were working through but certain features applied stood out all of which for their various reasons didn't seem applicable in this topology 

Below are these features (Apart from R5 which was obviously running as a bgp confederation rtr for which i just suggested a simple ebgp rtr alternative)
  
- Ospf network types on loopbacks
- Bgp soft reconfiguration inbound 
- Send-Label
- Next-hop self on RRC

Ospf  loopback network type 
by default loopback interfaces in ospf are seen as stub interfaces as such anything ip address other than an host address would still as a host /32 unless that is the network type of the loopback is change to accommodate a larger ip address range

Bgp soft reconfiguration inbound 
This is an old way of bgp soft reset which when enabled has the rtr hold a table of unfiltered received policy’s which then processed can be applied to the rtr without any network disruption - however this unfiltered table is stored locally on the rtr thus its takes up memory resources 
Nowadays all rtrs should support Route Refresh (RR-dynamic soft reset) basically the same as soft reset but it doesn’t hold any unfiltered policies thus less resource intensive 

Send-Label -  due to the lack of any mpls, this wasn't required as it primary use is to send MPLS labels to its bgp peers

Next-hop self on “stub” RRC  R6 isn’t applicable- the rtr would have no other link that it would be necessary to advertise itself as a next hop for.