In the following configuration, INTERNAL1 and INTERNAL4 are RR and INTERNAL2 and INTERNAL3 are clients. I am not able to see the routes 20.1.1.0 and 10.1.1.0 on INTERNAL3 and 30.1.1.0 and 40.1.1.0 on INTERNAL2. 10.1.1.0 is connected to fa0/0 of ISP1, 20.1.1.0 is connected to fa0/0 of ISP2, 30.1.1.0 is connected to fa0/0 of ISP3 and 40.1.1.0 is connected to fa0/0 of ISP4.
I am not able to under why RR is not advertising routes further to the other side from INTERNAL2 to INTERNAL3 and vice versa?
INTERNAL2(config)#do sh ip route
Gateway of last resort is not set
20.0.0.0/24 is subnetted, 1 subnets
B 20.1.1.0 [20/0] via 112.1.1.2, 00:06:58
112.0.0.0/24 is subnetted, 1 subnets
C 112.1.1.0 is directly connected, FastEthernet0/1
110.0.0.0/24 is subnetted, 1 subnets
C 110.1.1.0 is directly connected, FastEthernet0/0
111.0.0.0/24 is subnetted, 1 subnets
C 111.1.1.0 is directly connected, FastEthernet2/0
10.0.0.0/24 is subnetted, 1 subnets
B 10.1.1.0 [20/0] via 111.1.1.1, 00:06:58
150.1.0.0/24 is subnetted, 1 subnets
B 150.1.1.0 [200/0] via 110.1.1.1, 00:07:00
120.0.0.0/24 is subnetted, 1 subnets
C 120.1.1.0 is directly connected, FastEthernet1/0
INTERNAL3(config)#do sh ip route
Gateway of last resort is not set
140.1.0.0/24 is subnetted, 1 subnets
C 140.1.1.0 is directly connected, FastEthernet0/1
114.0.0.0/24 is subnetted, 1 subnets
C 114.1.1.0 is directly connected, FastEthernet1/0
113.0.0.0/24 is subnetted, 1 subnets
C 113.1.1.0 is directly connected, FastEthernet2/0
130.1.0.0/24 is subnetted, 1 subnets
C 130.1.1.0 is directly connected, FastEthernet0/0
40.0.0.0/24 is subnetted, 1 subnets
B 40.1.1.0 [20/0] via 114.1.1.2, 00:06:36
150.1.0.0/24 is subnetted, 1 subnets
B 150.1.1.0 [200/0] via 130.1.1.1, 00:06:38
30.0.0.0/24 is subnetted, 1 subnets
B 30.1.1.0 [20/0] via 113.1.1.1, 00:06:40
INTERNAL4(config)#do sh ip route
Gateway of last resort is not set
140.1.0.0/24 is subnetted, 1 subnets
C 140.1.1.0 is directly connected, FastEthernet0/1
114.0.0.0/24 is subnetted, 1 subnets
B 114.1.1.0 [200/0] via 140.1.1.1, 00:12:39
20.0.0.0/24 is subnetted, 1 subnets
B 20.1.1.0 [200/0] via 112.1.1.2, 00:12:33
40.0.0.0/24 is subnetted, 1 subnets
B 40.1.1.0 [200/0] via 114.1.1.2, 00:12:41
10.0.0.0/24 is subnetted, 1 subnets
B 10.1.1.0 [200/0] via 111.1.1.1, 00:12:39
30.0.0.0/24 is subnetted, 1 subnets
B 30.1.1.0 [200/0] via 113.1.1.1, 00:12:36
[ONLY RELEVANT CONFIGURATION DISPLAYED FOR INTERNAL4]
INTERNAL2#sh run | s bgp
router bgp 64100
no bgp default ipv4-unicast
bgp log-neighbor-changes
neighbor 110.1.1.1 remote-as 64100
neighbor 111.1.1.1 remote-as 64001
neighbor 112.1.1.2 remote-as 64002
neighbor 120.1.1.2 remote-as 64100
!
address-family ipv4
neighbor 110.1.1.1 activate
neighbor 111.1.1.1 activate
neighbor 112.1.1.2 activate
neighbor 120.1.1.2 activate
no auto-summary
no synchronization
network 110.1.1.0 mask 255.255.255.0
network 111.1.1.0 mask 255.255.255.0
network 112.1.1.0 mask 255.255.255.0
network 120.1.1.0 mask 255.255.255.0
exit-address-family
INTERNAL4#sh run | s bgp
router bgp 64100
no bgp default ipv4-unicast
bgp cluster-id 64100
bgp log-neighbor-changes
neighbor 120.1.1.1 remote-as 64100
neighbor 140.1.1.1 remote-as 64100
neighbor 150.1.1.1 remote-as 64100
!
address-family ipv4
neighbor 120.1.1.1 activate
neighbor 120.1.1.1 route-reflector-client
neighbor 140.1.1.1 activate
neighbor 140.1.1.1 route-reflector-client
neighbor 150.1.1.1 activate
no auto-summary
no synchronization
network 10.1.1.0 mask 255.255.255.0
network 20.1.1.0 mask 255.255.255.0
network 150.1.1.0 mask 255.255.255.0
exit-address-family
INTERNAL1#sh run | s bgp
router bgp 64100
no bgp default ipv4-unicast
bgp cluster-id 64100
bgp log-neighbor-changes
neighbor 110.1.1.2 remote-as 64100
neighbor 130.1.1.2 remote-as 64100
neighbor 150.1.1.2 remote-as 64100
!
address-family ipv4
neighbor 110.1.1.2 activate
neighbor 110.1.1.2 route-reflector-client
neighbor 130.1.1.2 activate
neighbor 130.1.1.2 route-reflector-client
neighbor 150.1.1.2 activate
no auto-summary
no synchronization
network 150.1.1.0 mask 255.255.255.0
exit-address-family
INTERNAL3#sh run | s bgp
router bgp 64100
no bgp default ipv4-unicast
bgp log-neighbor-changes
neighbor 113.1.1.1 remote-as 64003
neighbor 114.1.1.2 remote-as 64004
neighbor 130.1.1.1 remote-as 64100
neighbor 140.1.1.2 remote-as 64100
!
address-family ipv4
neighbor 113.1.1.1 activate
neighbor 114.1.1.2 activate
neighbor 130.1.1.1 activate
neighbor 140.1.1.2 activate
no auto-summary
no synchronization
network 113.1.1.0 mask 255.255.255.0
network 114.1.1.0 mask 255.255.255.0
network 130.1.1.0 mask 255.255.255.0
network 140.1.1.0 mask 255.255.255.0
exit-address-family
client-to-client reflection
and don't have conflicting RR cluster-ids (or if you do, that you understand why.) Be sure that the next-hops of your routes are reachable via your IGP as well. That is a common error that's not caused by your RR configuration; it would be apparent even if you had a normal IBGP session from, for example, INTERNAL2 to INTERNAL3. In fact, temporarily adding such a session is a good troubleshooting step. – Jeff Wheeler May 12 '20 at 23:53