Contents
- Introduction:
- Why do we need BGP Route Reflector
- BGP Route Reflector Configuration example:
Introduction:
According to the BGP Split Horizon rule, iBGP peers do not re-advertise routes that were learned from other iBGP peers. one of the workarounds is to design iBGP ASN in Full-mech topology, but the problem is that it doesn’t scale well.
you can check the Split horizon explanation from here:
BGP Split Horizon Explained [With Example]
Why do we need BGP Route Reflector
BGP requires that all iBGP peers have to be in a full-mesh topology. However, this requirement does not scale well when there are many iBGP peers. Instead of configuring a confederation, another way to reduce the iBGP mesh is to configure a route reflector.
See Also
What is BGP Route Reflector - Explanation & Discussion (Cisco Example)9815 Us Highway 98 W Unit 1501, MIRAMAR BEACH Property Listing: MLS® #950843With route reflectors, all iBGP peers don’t require a full mesh topology because there is a method to pass learned routes to neighbors. In this model, an iBGP peer is configured to be a route reflector responsible for passing iBGP learned routes to a set of iBGP neighbors.
BGP Route Reflector Configuration example:
The figure below illustrates a simple iBGP configuration with 4 iBGP speakers (Routers R1, R2, and R3 and R4) in the ASN 65001. With Route Reflector in place, when Router R2 receives a route from an external neighbor, it must advertise it to router R1 which is the Route Reflector.
The RR has formed an iBGP peer with all nodes in ASN 65001. So when a route comes to RR, it will be advertised to all Route Reflector Clients defined in the router R1 BGP configuration.
![BGP Route Reflector [Explained & Configuration] – Learn Duty (1)](https://i0.wp.com/learnduty.com/wp-content/uploads/2022/02/image-79.png "BGP Route Reflector [Explained & Configuration] – Learn Duty (1)")
Routers Configurations:
R1 Configuration:
hostname R1interface Ethernet0/0 ip address 172.16.1.9 255.255.255.252 half-duplex!interface Ethernet0/1 ip address 172.16.1.1 255.255.255.252 half-duplex!interface Ethernet0/2 ip address 172.16.1.5 255.255.255.252 half-duplex!router bgp 65001 no synchronization bgp log-neighbor-changes network 172.16.1.0 mask 255.255.255.252 network 172.16.1.4 mask 255.255.255.252 network 172.16.1.8 mask 255.255.255.252 neighbor 172.16.1.2 remote-as 65001 neighbor 172.16.1.2 route-reflector-client neighbor 172.16.1.6 remote-as 65001 neighbor 172.16.1.6 route-reflector-client neighbor 172.16.1.6 route-map CHANGE_NEXT_HOP1 out neighbor 172.16.1.10 remote-as 65001 neighbor 172.16.1.10 route-reflector-client no auto-summary!route-map CHANGE_NEXT_HOP1 permit 10 set ip next-hop 172.16.1.5R2 Configuration:
hostname R2interface Ethernet0/0 ip address 172.16.1.2 255.255.255.252 half-duplex!interface Ethernet0/1 ip address 172.16.1.13 255.255.255.252 half-duplex!router bgp 65001 no synchronization bgp log-neighbor-changes neighbor 172.16.1.1 remote-as 65001 neighbor 172.16.1.1 next-hop-self neighbor 172.16.1.14 remote-as 65002 no auto-summary!R3 Configuration:
hostname R3!interface Ethernet0/0 ip address 172.16.1.6 255.255.255.252 half-duplex!router bgp 65001 no synchronization bgp log-neighbor-changes neighbor 172.16.1.5 remote-as 65001 no auto-summaryR4 Configuration:
hostname R4interface Ethernet0/0 ip address 172.16.1.10 255.255.255.252 half-duplex!router bgp 65001 no synchronization bgp log-neighbor-changes neighbor 172.16.1.9 remote-as 65001 no auto-summaryR5 Configuration:
hostname R5!interface Loopback0 ip address 5.5.5.5 255.255.255.255!interface Ethernet0/0 ip address 172.16.1.14 255.255.255.252 half-duplex!router bgp 65002 no synchronization bgp log-neighbor-changes network 5.5.5.5 mask 255.255.255.255 neighbor 172.16.1.13 remote-as 65001 no auto-summaryVerifications:
R1:
R1#show ip bgpBGP table version is 18, local router ID is 172.16.1.9Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S StaleOrigin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path*>i5.5.5.5/32 172.16.1.2 0 100 0 65002 i*> 172.16.1.0/30 0.0.0.0 0 32768 i*> 172.16.1.4/30 0.0.0.0 0 32768 i*> 172.16.1.8/30 0.0.0.0 0 32768 iR1#show ip routeCodes: 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 routeGateway of last resort is not set 5.0.0.0/32 is subnetted, 1 subnetsB 5.5.5.5 [200/0] via 172.16.1.2, 01:52:02 172.16.0.0/30 is subnetted, 3 subnetsC 172.16.1.8 is directly connected, Ethernet0/0C 172.16.1.4 is directly connected, Ethernet0/2C 172.16.1.0 is directly connected, Ethernet0/1R1#R3:
R3#show ip bgpBGP table version is 10, local router ID is 172.16.1.6Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S StaleOrigin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path*>i5.5.5.5/32 172.16.1.5 0 100 0 65002 i*>i172.16.1.0/30 172.16.1.5 0 100 0 ir>i172.16.1.4/30 172.16.1.5 0 100 0 i*>i172.16.1.8/30 172.16.1.5 0 100 0 iR3#show ip roR3#show ip routeCodes: 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 routeGateway of last resort is not set 5.0.0.0/32 is subnetted, 1 subnetsB 5.5.5.5 [200/0] via 172.16.1.5, 00:22:54 172.16.0.0/30 is subnetted, 3 subnetsB 172.16.1.8 [200/0] via 172.16.1.5, 00:47:08C 172.16.1.4 is directly connected, Ethernet0/0B 172.16.1.0 [200/0] via 172.16.1.5, 00:47:02R3#ping 5.5.5.5Type escape sequence to abort.Sending 5, 100-byte ICMP Echos to 5.5.5.5, timeout is 2 seconds:!!!!!Success rate is 100 percent (5/5), round-trip min/avg/max = 88/130/172 msR3#R5:
R5#show ip bgpBGP table version is 5, local router ID is 172.16.1.14Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S StaleOrigin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path*> 5.5.5.5/32 0.0.0.0 0 32768 i*> 172.16.1.0/30 172.16.1.13 0 65001 i*> 172.16.1.4/30 172.16.1.13 0 65001 i*> 172.16.1.8/30 172.16.1.13 0 65001 iR5#show ip roR5#show ip routeCodes: 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 routeGateway of last resort is not set 5.0.0.0/32 is subnetted, 1 subnetsC 5.5.5.5 is directly connected, Loopback0 172.16.0.0/30 is subnetted, 4 subnetsC 172.16.1.12 is directly connected, Ethernet0/0B 172.16.1.8 [20/0] via 172.16.1.13, 00:45:52B 172.16.1.4 [20/0] via 172.16.1.13, 00:46:22B 172.16.1.0 [20/0] via 172.16.1.13, 00:45:52R5#![BGP Route Reflector [Explained & Configuration] – Learn Duty (2024)](data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mP8/h8AAvMB+NzmkbcAAAAASUVORK5CYII=)