BGP Route Reflector with Single Cluster and Default Settings
Today I am going to talk about the BGP route reflector with single cluster and default settings. I already talk about the basics of the route reflector in my earlier article with the configuration example.
Now starting from the start a little bit, we need to take a snapshot on BGP route reflector. So the concept of BGP route reflectors resolves the expensive iBGP full meshed topology or you can say BGP route reflector are another solution for the explosion of iBGP peering within the AS. Now let's start with the scenario where i will talk about the single cluster and the default settings
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Fig 1.1- BGP RR with Single Cluster
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RR#show run | sec bgp
router bgp 1
bgp log-neighbor-changes
neighbor 10.0.10.2 remote-as 1
neighbor 10.0.10.2 route-reflector-client
neighbor 10.0.20.2 remote-as 1
neighbor 10.0.20.2 route-reflector-client
neighbor 10.0.40.2 remote-as 1
In this case, RouteXP_PE1 and RouteXP_PE3 are clients of RR while RouteXP_PE2 is non-client. In conventional designs, non-client router will be route reflector for routers in the next hierarchy level but in this example just another PE is used for simplicity.
RR#show ip bgp cluster-ids
Global cluster-id: 172.16.3.3 (configured: 0.0.0.0)
BGP client-to-client reflection: Configured Used
all (inter-cluster and intra-cluster): ENABLED
intra-cluster: ENABLED ENABLED
List of cluster-ids:
Cluster-id #-neighbors C2C-rfl-CFG C2C-rfl-USE
RR#sh ip bgp 172.16.1.1
BGP routing table entry for 172.16.1.1/32, version 2
Paths: (1 available, best #1, table default)
Advertised to update-groups:
1 2
Refresh Epoch 2
Local, (Received from a RR-client)
10.0.10.2 from 10.0.10.2 (172.16.1.1)
Origin IGP, metric 0, localpref 100, valid, internal, best
rx pathid: 0, tx pathid: 0x0
RR#show ip bgp update-group 1
BGP version 4 update-group 1, internal, Address Family: IPv4 Unicast
BGP Update version : 4/0, messages 0
Topology: global, highest version: 4, tail marker: 4
Format state: Current working (OK, last not in list)
Refresh blocked (not in list, last not in list)
Update messages formatted 2, replicated 2, current 0, refresh 0, limit 1000
Number of NLRIs in the update sent: max 1, min 0
Minimum time between advertisement runs is 0 seconds
Has 1 member:
10.0.40.2
RR#show ip bgp update-group 2
BGP version 4 update-group 2, internal, Address Family: IPv4 Unicast
BGP Update version : 4/0, messages 0
Route-Reflector Client
Topology: global, highest version: 4, tail marker: 4
Format state: Current working (OK, last not in list)
Refresh blocked (not in list, last not in list)
Update messages formatted 3, replicated 6, current 0, refresh 0, limit 1000
Number of NLRIs in the update sent: max 1, min 0
Minimum time between advertisement runs is 0 seconds
Has 2 members:
10.0.10.2 10.0.20.2
These outputs show that RR receives the 172.16.1.1/32 prefix from RouteXP_PE1 and reflects it to the client RouteXP_PE3 and non-client RouteXP_PE2. In this particular case, update is also sent back to S1PE1, but it happens because RouteXP_PE1 and RouteXP_PE3 have the same routing policy and, therefore, form the same update group.
