Solved: BGP Route Reflector

manish priyadarshi · ‎05-12-2020

In the following configuration, INTERNAL1 and INTERNAL4 are RR and INTERNAL2 and INTERNAL3 are clients. I am not able to see the routes 20.1.1.0 and 10.1.1.0 on INTERNAL3 and 30.1.1.0 and 40.1.1.0 on INTERNAL2. 10.1.1.0 is connected to fa0/0 of ISP1, 20.1.1.0 is connected to fa0/0 of ISP2, 30.1.1.0 is connected to fa0/0 of ISP3 and 40.1.1.0 is connected to fa0/0 of ISP4. I am not able to under why RR is not advertising routes further to the other side from INTERNAL2 to INTERNAL3 and vice versa?

INTERNAL2(config)#do sh ip route
Gateway of last resort is not set

     20.0.0.0/24 is subnetted, 1 subnets
B       20.1.1.0 [20/0] via 112.1.1.2, 00:06:58
     112.0.0.0/24 is subnetted, 1 subnets
C       112.1.1.0 is directly connected, FastEthernet0/1
     110.0.0.0/24 is subnetted, 1 subnets
C       110.1.1.0 is directly connected, FastEthernet0/0
     111.0.0.0/24 is subnetted, 1 subnets
C       111.1.1.0 is directly connected, FastEthernet2/0
     10.0.0.0/24 is subnetted, 1 subnets
B       10.1.1.0 [20/0] via 111.1.1.1, 00:06:58
     150.1.0.0/24 is subnetted, 1 subnets
B       150.1.1.0 [200/0] via 110.1.1.1, 00:07:00
     120.0.0.0/24 is subnetted, 1 subnets
C       120.1.1.0 is directly connected, FastEthernet1/0

INTERNAL3(config)#do sh ip route
Gateway of last resort is not set

     140.1.0.0/24 is subnetted, 1 subnets
C       140.1.1.0 is directly connected, FastEthernet0/1
     114.0.0.0/24 is subnetted, 1 subnets
C       114.1.1.0 is directly connected, FastEthernet1/0
     113.0.0.0/24 is subnetted, 1 subnets
C       113.1.1.0 is directly connected, FastEthernet2/0
     130.1.0.0/24 is subnetted, 1 subnets
C       130.1.1.0 is directly connected, FastEthernet0/0
     40.0.0.0/24 is subnetted, 1 subnets
B       40.1.1.0 [20/0] via 114.1.1.2, 00:06:36
     150.1.0.0/24 is subnetted, 1 subnets
B       150.1.1.0 [200/0] via 130.1.1.1, 00:06:38
     30.0.0.0/24 is subnetted, 1 subnets
B       30.1.1.0 [20/0] via 113.1.1.1, 00:06:40


   INTERNAL4(config)#do sh ip route
    Gateway of last resort is not set

         140.1.0.0/24 is subnetted, 1 subnets
    C       140.1.1.0 is directly connected, FastEthernet0/1
         114.0.0.0/24 is subnetted, 1 subnets
    B       114.1.1.0 [200/0] via 140.1.1.1, 00:12:39
         20.0.0.0/24 is subnetted, 1 subnets
    B       20.1.1.0 [200/0] via 112.1.1.2, 00:12:33

         40.0.0.0/24 is subnetted, 1 subnets
    B       40.1.1.0 [200/0] via 114.1.1.2, 00:12:41
         10.0.0.0/24 is subnetted, 1 subnets
    B       10.1.1.0 [200/0] via 111.1.1.1, 00:12:39

         30.0.0.0/24 is subnetted, 1 subnets
    B       30.1.1.0 [200/0] via 113.1.1.1, 00:12:36

[ONLY RELEVANT CONFIGURATION DISPLAYED FOR INTERNAL4]

INTERNAL2#sh run | s bgp
router bgp 64100
 no bgp default ipv4-unicast
 bgp log-neighbor-changes
 neighbor 110.1.1.1 remote-as 64100
 neighbor 111.1.1.1 remote-as 64001
 neighbor 112.1.1.2 remote-as 64002
 neighbor 120.1.1.2 remote-as 64100
 !
 address-family ipv4
  neighbor 110.1.1.1 activate
  neighbor 111.1.1.1 activate
  neighbor 112.1.1.2 activate
  neighbor 120.1.1.2 activate
  no auto-summary
  no synchronization
  network 110.1.1.0 mask 255.255.255.0
  network 111.1.1.0 mask 255.255.255.0
  network 112.1.1.0 mask 255.255.255.0
  network 120.1.1.0 mask 255.255.255.0
 exit-address-family

INTERNAL4#sh run | s bgp
router bgp 64100
 no bgp default ipv4-unicast
 bgp cluster-id 64100
 bgp log-neighbor-changes
 neighbor 120.1.1.1 remote-as 64100
 neighbor 140.1.1.1 remote-as 64100
 neighbor 150.1.1.1 remote-as 64100
 !
 address-family ipv4
  neighbor 120.1.1.1 activate
  neighbor 120.1.1.1 route-reflector-client
  neighbor 140.1.1.1 activate
  neighbor 140.1.1.1 route-reflector-client
  neighbor 150.1.1.1 activate
  no auto-summary
  no synchronization
  network 10.1.1.0 mask 255.255.255.0
  network 20.1.1.0 mask 255.255.255.0
  network 150.1.1.0 mask 255.255.255.0
 exit-address-family

INTERNAL1#sh run | s bgp
router bgp 64100
 no bgp default ipv4-unicast
 bgp cluster-id 64100
 bgp log-neighbor-changes
 neighbor 110.1.1.2 remote-as 64100
 neighbor 130.1.1.2 remote-as 64100
 neighbor 150.1.1.2 remote-as 64100
 !
 address-family ipv4
  neighbor 110.1.1.2 activate
  neighbor 110.1.1.2 route-reflector-client
  neighbor 130.1.1.2 activate
  neighbor 130.1.1.2 route-reflector-client
  neighbor 150.1.1.2 activate
  no auto-summary
  no synchronization
  network 150.1.1.0 mask 255.255.255.0
 exit-address-family

INTERNAL3#sh run | s bgp
router bgp 64100
 no bgp default ipv4-unicast
 bgp log-neighbor-changes
 neighbor 113.1.1.1 remote-as 64003
 neighbor 114.1.1.2 remote-as 64004
 neighbor 130.1.1.1 remote-as 64100
 neighbor 140.1.1.2 remote-as 64100
 !
 address-family ipv4
  neighbor 113.1.1.1 activate
  neighbor 114.1.1.2 activate
  neighbor 130.1.1.1 activate
  neighbor 140.1.1.2 activate
  no auto-summary
  no synchronization
  network 113.1.1.0 mask 255.255.255.0
  network 114.1.1.0 mask 255.255.255.0
  network 130.1.1.0 mask 255.255.255.0
  network 140.1.1.0 mask 255.255.255.0
 exit-address-family

Giuseppe Larosa · ‎05-12-2020

Hello @manish priyadarshi ,

the problem are the BGP next-hops : in iBGP the BGP next-hop is left unchanged but in your case this creates some issues.

If you look at INTERNAL2 router we can see in its routing table that there is no entry for network 140.1.1.0 and for network 130.1.1.0 that are the subnets connecting to INTERNAL3 the other client.

You need to run an IGP like OSPF on all internal links and you can also need to use the command

neighbor xx.x.x.x next-hop self under router bgp.

Once you enable OSPF you can configure and advertise in OSPF a loopback interface for each INTERNALx node and you can configure your iBGP sessions using the loopbacks as endpoints that is the best practice for iBGP and does not require any special command because iBGP has a TTL of 255 ( eBGP by default has a TTL =1).

Hope to help

Giuseppe

View solution in original post

Giuseppe Larosa · ‎05-12-2020