IBGP uses the split horizon rule to avoid loops within an AS, when an IBGP router receives a route from another IBGP peer, it does not advertise that route to other IBGP peers.

In a network with multiple IBGP peerings, we need to find a solution to ensure full connectivity within the network. There are main mechanisms used to achieve full connectivity:

1. Full mesh topology: Every router establishes IBGP peering with every other router. This is not an ideal solution for a Network with many routers, it’s not scalable and hence not commonly used.
2. Route Reflector: An RR is a designated router that reflects routes learned from one IBGP peer to all other peers. All routers only establish peering with the RR. It’s recommended to have multiple RRs in a large network to avoid a single point of failure.
3. BGP confederation: Divides the AS into sub-ASes to reduce the number of required IBGP peering. The nested AS also form EBGP peering between themselves.

This lab simulates how to configure router reflectors on Huawei routers. As shown in the topology above topology, we have two clusters. R2 is the RR of cluster 1 while R3 is the RR for cluster 2. R5 and R6 are RR clients of R2 while R4, R7, and R8 are RR clients of R3. R1 is a non-client. We simulate route exchange by creating a network 100.100.100.100/32 on R1 and advertise it in BGP.

**********************************R1
sys
#
sysname R1
#
interface GigabitEthernet0/0/0
 undo shutdown
 ip address 30.30.30.2 255.255.255.254
#
interface GigabitEthernet0/0/1
 undo shutdown
 ip address 30.30.30.0 255.255.255.254
#
interface Loopback100
 ip address 100.100.100.100 255.255.255.255
#
bgp 64000
 router-id 1.1.1.1
 peer 30.30.30.1 as-number 64000
 peer 30.30.30.3 as-number 64000
 #
 ipv4-family unicast
  undo synchronization 
  network 100.100.100.100 255.255.255.255
  peer 30.30.30.3 enable
  peer 30.30.30.1 enable
#

******************************R2
#
sysname R2
#
interface GigabitEthernet0/0/0
 undo shutdown
 ip address 30.30.30.3 255.255.255.254
#
interface GigabitEthernet0/0/1
 undo shutdown
 ip address 40.40.40.0 255.255.255.254
#
interface GigabitEthernet0/0/2
 undo shutdown
 ip address 10.10.10.4 255.255.255.254
#
interface GigabitEthernet0/0/3
 undo shutdown
 ip address 10.10.10.0 255.255.255.254
#
bgp 64000
 router-id 2.2.2.2
 peer 30.30.30.2 as-number 64000
 peer 40.40.40.1 as-number 64000
 group RR_PEER internal
 peer 10.10.10.5 as-number 64000
 peer 10.10.10.5 group RR_PEER
 peer 10.10.10.1 as-number 64000
 peer 10.10.10.1 group RR_PEER
 #
 ipv4-family unicast
  undo synchronization 
  undo reflect between-clients
  reflector cluster-id 2.2.2.2
  peer 30.30.30.2 enable
  peer 40.40.40.1 enable
  peer RR_PEER enable
  peer RR_PEER reflect-client
  peer 10.10.10.1 enable
  peer 10.10.10.1 group RR_PEER
  peer 10.10.10.5 enable
  peer 10.10.10.5 group RR_PEER  
#
commit

****************************R3
sys
#
sysname R3
#
interface GigabitEthernet0/0/0
 undo shutdown
 ip address 40.40.40.1 255.255.255.254
#
interface GigabitEthernet0/0/1
 undo shutdown
 ip address 30.30.30.1 255.255.255.254
#
interface GigabitEthernet0/0/2
 undo shutdown
 ip address 20.20.20.4 255.255.255.254
#
interface GigabitEthernet0/0/3
 undo shutdown
 ip address 20.20.20.2 255.255.255.254
#
interface Ethernet0/0/0
 undo shutdown
 ip address 20.20.20.0 255.255.255.254
#
bgp 64000
 router-id 2.2.2.2
 peer 30.30.30.0 as-number 64000
 peer 40.40.40.0 as-number 64000
 group RR_PEER internal
 peer 20.20.20.1 as-number 64000
 peer 20.20.20.1 group RR_PEER
 peer 20.20.20.5 as-number 64000
 peer 20.20.20.5 group RR_PEER
 peer 20.20.20.3 as-number 64000
 peer 20.20.20.3 group RR_PEER
 #
 ipv4-family unicast
  undo synchronization 
  undo reflect between-clients
  reflector cluster-id 2.2.2.2
  peer 30.30.30.0 enable
  peer 40.40.40.0 enable
  peer RR_PEER enable
  peer RR_PEER reflect-client
  peer 20.20.20.1 enable
  peer 20.20.20.1 group RR_PEER
  peer 20.20.20.5 enable
  peer 20.20.20.5 group RR_PEER  
  peer 20.20.20.3 enable
  peer 20.20.20.3 group RR_PEER 
#
commit

************************************R4
#
sysname R4
#
interface Ethernet0/0/0
 undo shutdown
 ip address 20.20.20.1 255.255.255.254
#
bgp 64000
 router-id 4.4.4.4
 peer 20.20.20.0 as-number 64000
 #
 ipv4-family unicast
  undo synchronization 
  peer 20.20.20.0 enable
#
return

**************************************R5
#
sysname R5
#
interface GigabitEthernet0/0/0
 undo shutdown
 ip address 10.10.10.5 255.255.255.254
#
interface GigabitEthernet0/0/1
 undo shutdown
 ip address  10.10.10.2 255.255.255.254
#
bgp 64000
 router-id 5.5.5.5
 peer 10.10.10.4 as-number 64000
 #
 ipv4-family unicast
  undo synchronization 
  peer 10.10.10.4 enable
#
return

*******************************R6
#
sysname R6
#
interface GigabitEthernet0/0/0
 undo shutdown
 ip address 10.10.10.1 255.255.255.254
#
interface GigabitEthernet0/0/1
 undo shutdown
 ip address  10.10.10.3 255.255.255.254
#
bgp 64000
 router-id 6.6.6.6
 peer 10.10.10.0 as-number 64000
 #
 ipv4-family unicast
  undo synchronization 
  peer 10.10.10.0 enable
#
return

***********************************R7
#
sysname R7
#
interface GigabitEthernet0/0/0
 undo shutdown
 ip address 20.20.20.5 255.255.255.254
#
bgp 64000
 router-id 7.7.7.7
 peer 20.20.20.4 as-number 64000
 #
 ipv4-family unicast
  undo synchronization 
  peer 20.20.20.4 enable
#
return

***********************************R8
#
sysname R8
#
interface GigabitEthernet0/0/0
 undo shutdown
 ip address 20.20.20.3 255.255.255.254
#
bgp 64000
 router-id 8.8.8.8
 peer 20.20.20.2 as-number 64000
 #
 ipv4-family unicast
  undo synchronization 
  peer 20.20.20.2 enable
#
return

Verify BGP peering status on the RR routers.

Verify BGP routing table for RR clients.