Cluster-Id

Scenario to verify BGP cluster-id parameter configuration for Route Reflectors.

In iBGP networks, the split-horizon rule prevents a router from re-announcing routes learned from one iBGP peer to another iBGP peer. This creates a full-mesh requirement that does not scale well in large networks. Route Reflectors (RR) solve this problem by reflecting routes between their clients, eliminating the need for a full mesh.

The cluster-id parameter identifies a cluster of Route Reflectors. By default, the cluster-id equals the router-id of the RR. When you have redundant Route Reflectors serving the same clients, you should configure them with the same cluster-id to prevent routing loops. The cluster-id is included in the CLUSTER_LIST attribute of reflected routes, and if a router receives a route with its own cluster-id in the list, it discards the route to prevent loops.

Test BGP Cluster ID

Description

This test demonstrates the effect of cluster-id and route reflection in iBGP. First, without route-reflector configuration, the iBGP split-horizon rule prevents DUT0 from re-announcing routes learned from DUT1 to DUT2. DUT1 has redistribute connected configured, so it announces its network 10.10.0.0/24. Then, after configuring DUT0 as a Route Reflector with cluster-id 10.10.10.1 and marking both neighbors as route-reflector-client, the route gets reflected and DUT2 receives it with the cluster-id in the attributes.

Scenario

Note

First we configure iBGP without route-reflector to observe the split-horizon rule.

Step 1: Set the following configuration in DUT0 :

set interfaces ethernet eth0 address 10.10.0.1/24
set interfaces ethernet eth1 address 20.20.0.1/24
set protocols bgp 100 neighbor client1 remote-address 10.10.0.2
set protocols bgp 100 neighbor client1 remote-as 100
set protocols bgp 100 neighbor client2 remote-address 20.20.0.2
set protocols bgp 100 neighbor client2 remote-as 100
set system login user admin authentication encrypted-password '$6$GSjsCj8gHLv$/VcqU6FLi6CT2Oxn0MJQ2C2tqnRDrYKNF8HIYWJp68nvXvPdFccDsT04.WtigUONbKYrgKg8d6rEs8PjljMkH0'

Step 2: Set the following configuration in DUT1 :

set interfaces ethernet eth0 address 10.10.0.2/24
set protocols bgp 100 neighbor rr remote-address 10.10.0.1
set protocols bgp 100 neighbor rr remote-as 100
set protocols bgp 100 redistribute connected
set system login user admin authentication encrypted-password '$6$GSjsCj8gHLv$/VcqU6FLi6CT2Oxn0MJQ2C2tqnRDrYKNF8HIYWJp68nvXvPdFccDsT04.WtigUONbKYrgKg8d6rEs8PjljMkH0'

Step 3: Set the following configuration in DUT2 :

set interfaces ethernet eth1 address 20.20.0.2/24
set protocols bgp 100 neighbor rr remote-address 20.20.0.1
set protocols bgp 100 neighbor rr remote-as 100
set system login user admin authentication encrypted-password '$6$GSjsCj8gHLv$/VcqU6FLi6CT2Oxn0MJQ2C2tqnRDrYKNF8HIYWJp68nvXvPdFccDsT04.WtigUONbKYrgKg8d6rEs8PjljMkH0'

Attention

Verify iBGP sessions establish between DUT0 and both clients.

Step 4: Run command protocols bgp show ip summary at DUT0 and check if output matches the following regular expressions:

10.10.0.2.*Established[\s\S]+20.20.0.2.*Established

Attention

Verify DUT0 receives route 10.10.0.0/24 from DUT1 via redistribute connected.

Step 5: Run command protocols bgp show ip at DUT0 and check if output matches the following regular expressions:

10.10.0.0/24.*10.10.0.2

Note

Without route-reflector, DUT2 does NOT receive the route due to iBGP split-horizon rule.

Step 6: Run command protocols bgp show ip at DUT2 and check if output does not match the following regular expressions:

10.10.0.0/24

Note

Now we configure DUT0 as Route Reflector with cluster-id and mark neighbors as clients.

Step 7: Modify the following configuration lines in DUT0 :

set protocols bgp 100 neighbor client1 route-reflector-client
set protocols bgp 100 neighbor client2 route-reflector-client
set protocols bgp 100 parameters cluster-id 10.10.10.1

Attention

Verify iBGP sessions remain established after configuration change.

Step 8: Run command protocols bgp show ip summary at DUT0 and check if output matches the following regular expressions:

10.10.0.2.*Established[\s\S]+20.20.0.2.*Established

Attention

Verify DUT2 now receives the reflected route 10.10.0.0/24.

Step 9: Run command protocols bgp show ip at DUT2 and check if output matches the following regular expressions:

10.10.0.0/24.*10.10.0.2

Attention

Verify the route on DUT2 contains the cluster-id 10.10.10.1 in attributes.

Step 10: Run command protocols bgp show ip 10.10.0.0/24 at DUT2 and check if output contains the following tokens:

Originator: 10.10.0.2, Cluster list: 10.10.10.1