CCNP experiment: Router Reflector solution for BGP routing Black Hole

[Lab environment]

The C3640-IK9O3S-M Version 12.4 (10)

[PURPOSE]

Router Reflector is used to solve the BGP Route black hole problem caused by horizontal segmentation of IBGP.

[Experiment topology]

[Experiment description]

R1, R2, R4, and R5 run the BGP protocol, while R2, R3, and R4 run the OSPF protocol. The objective is to make 1.1.1.1 <-> 5.5.5.5 accessible to each other

The IBGP neighbor relationship is established using the loopback interface.

Use a direct connection interface between R1 <-> R2 and R4 <-> R5 to establish an EBGP relationship

Data-layer BGP routing black hole problem: Since R3 does not run BGP, R2 and R4 do not pass route entries to R3. Therefore, R3 does not have routes 1.1.1.1 and 5.5.5, resulting in a routing black hole. If BGP is run on R3 and an IBGP relationship is established with R2 and R4, the routes of R2 and R4 are not completely learned due to horizontal segmentation of IBGP.

Solution: Using route reflectors, R3 is used as the reflector (RR), and other IBGP routers are used as clients (C). Route reflectors and their clients form a Route Reflection cluster, the client only needs to establish a neighbor with the route reflector, and does not need to establish a neighbor with each IBGP router.

Rules for Route reflectors:

1. routes received by RR from EBGP are reflected to clients and non-clients;

2. routes received from the client are reflected to the client, non-client, and EBGP neighbors;

3. routes received from non-clients are only reflected to clients and EBGP peers, but not to other non-clients.

Lab procedure]

1. Basic configuration of R1, Port:

!
Interface Loopback0
Ip address 1.1.1.1 255.255.255.0
!
Interface Serial0/0
Ip address 12.0.0.1 255.255.255.0
Clock rate 64000
!

2. Basic R2 configuration, port, and OSPF:

!
Interface Loopback0
Ip address 2.2.2.2 255.255.255.0
!
Interface Serial0/0
Ip address 12.0.0.2 255.255.255.0
!
Interface Serial0/1
Ip address 23.0.0.1 255.255.255.0
Clock rate 64000
!
Router ospf 110
Router-id 2.2.2.2
Network 2.2.2.0 0.0.0.255 area 0
Network 23.0.0.1 0.0.0.0 area 0
!

3. R3 basic configuration, port, and OSPF:

!
Interface Loopback0
Ip address 3.3.3.3 255.255.255.0
!
Interface Serial0/0
Ip address 34.0.0.1 255.255.255.0
Clock rate 64000
!
Interface Serial0/1
Ip address 23.0.0.2 255.255.255.0
!
Router ospf 110
Router-id 3.3.3.3
Network 3.3.3.0 0.0.0.255 area 0
Network 23.0.0.2 0.0.0.0 area 0
Network 34.0.0.1 0.0.0.0 area 0
!

4. basic configuration of R4, port, and OSPF:

!
Interface Loopback0
Ip address 4.4.4.4 255.255.255.0
!
Interface Serial0/0
Ip address 34.0.0.2 255.255.255.0
!
Interface Serial0/1
Ip address 45.0.0.1 255.255.255.0
Clock rate 64000
!
Router ospf 110
Router-id 4.4.4
Network 4.4.4.0 0.0.0.255 area 0
Network 34.0.0.2 0.0.0.0 area 0
!

5. R5 basic configuration, Port:

!
Interface Loopback0
Ip address 5.5.5.5 255.255.255.0
!
Interface Serial0/1
Ip address 45.0.0.2 255.255.255.0
!

6. Configure EBGP between R1 and R2

// Configure AS 1 in R1
Router bgp 1
No synchronization
Bgp router-id 1.1.1.1
Network 1.1.1.0 mask 255.255.255.0
Neighbor 12.0.0.2 remote-as 3
No auto-summary

// R2 configure AS 3
Router bgp 3
No synchronization
Bgp router-id 2.2.2.2
Neighbor 12.0.0.1 remote-as 1
No auto-summary

7. Configure EBGP between R4 and R5

// Configure AS 3 on R4
Router bgp 3
No synchronization
Bgp router-id 4.4.4
Neighbor 45.0.0.2 remote-as 5
No auto-summary

// R5 configure AS 5
Router bgp 5
No synchronization
Bgp router-id 5.5.5
Network 5.5.5.0 mask 255.255.255.255.0
Neighbor 45.0.0.1 remote-as 3
No auto-summary

8. Use the loopback interface to configure the IBGP relationship between R2, R3, and R4

// R3 Configuration
Router bgp 3
No synchronization
Bgp router-id 3.3.3.3
Neighbor 2.2.2.2 remote-as 3
Neighbor 2.2.2.2 update-source Loopback0
Neighbor 4.4.4 remote-as 3
Neighbor 4.4.4 update-source Loopback0
No auto-summary

// R2 Configuration
Router bgp 3
Neighbor 3.3.3.3 remote-as 3
Neighbor 3.3.3.3 update-source Loopback0
Nei 3.3.3.3 next-hop-self

// R4 Configuration
Router bgp 3
Neighbor 3.3.3.3 remote-as 3
Neighbor 3.3.3.3 update-source Loopback0
Nei 3.3.3.3 next-hop-self

9. Enable route reflectors on R3 and specify the client

Router bgp 3
Neighbor 2.2.2.2 route-reflector-client
Neighbor 4.4.4.4 route-reflector-client

10. view the route table of R3

R3 # sh ip bgp
BGP table version is 3, local router ID is 3.3.3.3
Network Next Hop Metric LocPrf Weight Path
*> I1.1.1.0/24 2.2.2.2 0 100 0 1 I
*> I5.5.5.0/24 4.4.4.4 0 100 0 5 I

11. Verify the connectivity between R1 and R5 loopback ports

R1 # ping 5.5.5 so 1.1.1.1
Sending 5, 100-byte ICMP Echos to 5.5.5.5, timeout is 2 seconds:
Packet sent with a source address of 1.1.1.1
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 188/325/496 MS

12. view the reflection route entry 5.5.5.0/24 on R2

R2 # sh ip bgp 5.5.5.0/24
BGP routing table entry for 5.5.5.0/24, version 3
Paths: (1 available, best #1, table Default-IP-Routing-Table)

4.4.4.4 (metric 129) from 3.3.3.3 (3.3.3.3)
Origin IGP, metric 0, localpref 100, valid, internal, best
Originator: 4.4.4.4, Cluster list: 3.3.3.3

13. view the reflection route entry 1.1.1.0/24 on R4

R4 # sh ip bgp 1.1.1.0/24
BGP routing table entry for 1.1.1.0/24, version 3
Paths: (1 available, best #1, table Default-IP-Routing-Table)

2.2.2.2 (metric 129) from 3.3.3.3 (3.3.3.3)
Origin IGP, metric 0, localpref 100, valid, internal, best
Originator: 2.2.2.2, Cluster list: 3.3.3.3

14. Evaluation

Compared with the neighbor full interconnection, the route reflectors simplify the configuration and quantity, because the IBGP neighbor relationship only needs to be established between the client and the RR.