BGP - [Part 21] - ROUTE REFLECTOR CONFIGURATION

There are 3 IBGP routers. As per Split Horizon rule Router R1 can send a route to R2, and R2 will receive the route from R1 but it will not send to R3. We can break the rule via Route Reflector.

Please check the below configuration.

Without Route Reflector 

Configuration - 

R1 Configuration -
interface Loopback1
 ip address 10.10.10.10 255.255.255.0
!
interface FastEthernet1/0
 ip address 192.167.23.1 255.255.255.0
 duplex auto
 speed auto
!
router bgp 200
 no synchronization
 bgp log-neighbor-changes
 network 10.10.10.0 mask 255.255.255.0
 neighbor 192.167.23.2 remote-as 200
 no auto-summary

R2 Configuration -
interface FastEthernet1/0
 ip address 192.167.23.2 255.255.255.0
 duplex auto
 speed auto
!
interface FastEthernet2/0
 ip address 192.167.24.1 255.255.255.0
 duplex auto
 speed auto
!
router bgp 200
 no synchronization
 bgp log-neighbor-changes
 neighbor 192.167.23.1 remote-as 200
 neighbor 192.167.24.2 remote-as 200
 no auto-summary

R3 Configuration -
interface FastEthernet2/0
 ip address 192.167.24.2 255.255.255.0
 duplex auto
 speed auto
!
router bgp 200
 no synchronization
 bgp log-neighbor-changes
 neighbor 192.167.24.1 remote-as 200
 no auto-summary

Verification - 

R2#show ip bgp 10.10.10.10
BGP routing table entry for 10.10.10.0/24, version 6
Paths: (1 available, best #1, table Default-IP-Routing-Table)
  Not advertised to any peer
  Local
    192.167.23.1 from 192.167.23.1 (192.167.23.1)
      Origin IGP, metric 0, localpref 100, valid, internal, best

now verify it, you can see in above output, Router R2 was received a route from 192.167.23.1 (R1).
now check, it will be advertise this route to R3 or not ?

R2#show ip bgp neighbors 192.167.24.2 advertised-routes
Total number of prefixes 0

now you can see in above output, R2 is not advertising this route to R3, we can do this via route reflector.

With Route Reflector

we will configure Route Reflector Client on Router R2 -

Configuration - 

R2 Configuration - 
interface FastEthernet1/0
 ip address 192.167.23.2 255.255.255.0
 duplex auto
 speed auto
!
interface FastEthernet2/0
 ip address 192.167.24.1 255.255.255.0
 duplex auto
 speed auto
!
router bgp 200
 no synchronization
 bgp log-neighbor-changes
 neighbor 192.167.23.1 remote-as 200
 neighbor 192.167.23.1 route-reflector-client
 neighbor 192.167.24.2 remote-as 200
 neighbor 192.167.24.2 route-reflector-client
 no auto-summary

Verification -

Now check again, R2 will be advertise to R3 or not ?

R2#show ip bgp neighbors 192.167.24.2 advertised-routes
BGP table version is 8, local router ID is 192.167.24.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network                 Next Hop            Metric LocPrf Weight Path
*>i10.10.10.0/24    192.167.23.1             0    100      0 i

Total number of prefixes 1

Now you can see in above output, R2 is advertising to R3

R3#show ip bgp 10.10.10.10

BGP routing table entry for 10.10.10.0/24, version 0

Paths: (1 available, no best path)

  Not advertised to any peer

  Local

    192.167.23.1 (inaccessible) from 192.167.24.1 (192.167.24.1)

      Origin IGP, metric 0, localpref 100, valid, internal

      Originator: 192.167.23.1, Cluster list: 192.167.24.1

Now R3 is receiving route from 192.167.24.1 (R2)

Originator ID  - 

• It is set by RR, we can see, this is the IP address of R1. 
• If any IBGP router will receive an update with its own originator ID, then it will be discarded. 

Cluster list - 

• It is the router ID of the RR.  
• In a large topology, may be multiple RR will be available, so between the route reflectors we still have to configure full mesh IBGP. It is possible that a loops between these route reflectors, so when a route reflector find its own cluster ID in update, then update will be discarded.

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Anubhav Upadhyay

Hello and welcome to networktopic Blog. My name is Anubhav. I am a Senior Network Egineer. I have created this blog specially to serve interview questions and answer on Network Routing and Switching, I will try my best to serve correct and updated networking knowledge for you as per my corporate experience.

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