Cisco BGP-4 Command and Configuration Handbook

3-6 bgp cluster-id 32-bit_id

Syntax Description:

32-bit_id ” Route reflector cluster ID entered as either a 32-bit number or an IP address.

Purpose: EBGP loop detection is based on the AS-path attribute. If a BGP router receives an update from an EBGP peer containing the local AS number, the update is ignored. The AS- path method of loop detection does not work when you're using route reflectors, because the reflector and the clients are in the same AS. A route reflector generates an originator ID assigned from the router ID. When you're using multiple route reflectors, the route reflectors in the same cluster must be configured with the same ID, called the cluster ID. A cluster consists of the router reflectors and their clients . The cluster IDs contained in the cluster list are used for loop detection within the local AS when route reflectors are being used.

Cisco IOS Software Release: 11.0

Configuration Example: Redundant Route Reflectors

Figure 3-6 shows a cluster consisting of two clients and two route reflectors. Two route reflectors are configured for redundancy and therefore must have the same cluster ID.

Router A interface Loopback0 ip address 172.16.88.3 255.255.255.224 ! interface Ethernet1/0 ip address 172.16.0.2 255.255.255.252 ! interface Ethernet1/1 ip address 172.16.0.9 255.255.255.252 ! router eigrp 1 network 172.16.0.0 no auto-summary ! router bgp 1 network 172.16.88.0 mask 255.255.255.224 neighbor 172.16.0.1 remote-as 1 neighbor 172.16.0.10 remote-as 1 ___________________________________________________________________________ Router B interface Ethernet1/0 ip address 172.16.0.1 255.255.255.252 ! interface Ethernet1/1 ip address 172.16.0.5 255.255.255.252 ! interface Ethernet1/2 ip address 172.16.0.17 255.255.255.252 ! router eigrp 1 network 172.16.0.0 network 193.16.0.0 no auto-summary ! router bgp 1 bgp cluster-id 1 neighbor 172.16.0.2 remote-as 1 neighbor 172.16.0.2 route-reflector-client neighbor 172.16.0.6 remote-as 1 neighbor 172.16.0.6 route-reflector-client neighbor 172.16.0.18 remote-as 1 ___________________________________________________________________________ Router C interface Ethernet1/0 ip address 172.16.0.14 255.255.255.252 ! interface Ethernet1/1 ip address 172.16.0.10 255.255.255.252 ! interface Ethernet1/2 ip address 172.16.0.18 255.255.255.252 ! router eigrp 1 network 10.0.0.0 network 172.16.0.0 network 193.16.0.0 no auto-summary ! router bgp 1 bgp cluster-id 1 neighbor 172.16.0.9 remote-as 1 neighbor 172.16.0.9 route-reflector-client neighbor 172.16.0.13 remote-as 1 neighbor 172.16.0.13 route-reflector-client neighbor 172.16.0.17 remote-as 1 ___________________________________________________________________________ Router D interface Ethernet2/0 ip address 172.16.0.6 255.255.255.252 ! interface Ethernet2/1 ip address 172.16.0.13 255.255.255.252 ! router eigrp 1 network 172.16.0.0 no auto-summary ! router bgp 1 neighbor 172.16.0.5 remote-as 1 neighbor 172.16.0.14 remote-as 1

Verification

Verify that Routers A and D are clients of Routers B and C:

rtrB# show ip bgp neighbor 172.16.0.2 BGP neighbor is 172.16.0.2, remote AS 1, internal link BGP version 4, remote router ID 172.16.88.3 BGP state = Established, up for 00:28:35 Last read 00:00:36, hold time is 180, keepalive interval is 60 seconds Neighbor capabilities: Route refresh: advertised and received Address family IPv4 Unicast: advertised and received Received 32 messages, 0 notifications, 0 in queue Sent 31 messages, 0 notifications, 0 in queue Route refresh request: received 0, sent 0 Minimum time between advertisement runs is 5 seconds For address family: IPv4 Unicast BGP table version 2, neighbor version 2 Index 3, Offset 0, Mask 0x8 Route-Reflector Client 1 accepted prefixes consume 36 bytes Prefix advertised 0, suppressed 0, withdrawn 0 rtrB# show ip bgp neighbor 172.16.0.6 BGP neighbor is 172.16.0.6, remote AS 1, internal link BGP version 4, remote router ID 172.16.2.1 BGP state = Established, up for 00:32:22 Last read 00:00:23, hold time is 180, keepalive interval is 60 seconds Neighbor capabilities: Route refresh: advertised and received Address family IPv4 Unicast: advertised and received Received 35 messages, 0 notifications, 0 in queue Sent 36 messages, 0 notifications, 0 in queue Route refresh request: received 0, sent 0 Minimum time between advertisement runs is 5 seconds For address family: IPv4 Unicast BGP table version 2, neighbor version 2 Index 1, Offset 0, Mask 0x2 Route-Reflector Client 0 accepted prefixes consume 0 bytes Prefix advertised 1, suppressed 0, withdrawn 0

Verify that the cluster ID has been configured:

rtrD# show ip bgp 172.16.88.0 BGP routing table entry for 172.16.88.0/27, version 3 Paths: (2 available, best #1, table Default-IP-Routing-Table) Not advertised to any peer Local 172.16.0.2 (metric 307200) from 172.16.0.5 (172.16.88.3) Origin IGP, metric 0, localpref 100, valid, internal, synchronized, best Originator: 172.16.88.3, Cluster list: 0.0.0.1 Local 172.16.0.9 (metric 307200) from 172.16.0.14 (172.16.88.3) Origin IGP, metric 0, localpref 100, valid, internal, synchronized Originator: 172.16.88.3, Cluster list: 0.0.0.1

Troubleshooting

Step 1. Verify that the BGP neighbors are in the Established state using the show ip bgp neighbors command.

If the neighbor relationship is not in the Established state, see section 8-23. For IBGP and loopbacks, see section 8-33.

Step 2. Verify that the route reflector clients have been configured using the show ip bgp neighbors command.

Step 3. Verify that the same cluster ID has been configured on each route reflector in the cluster.