Problems of BGP routes Advertisement

[AnonyKwan]

 

I am new to Advance BGP.

In the AS 65002, R2 and R4 do not have full BGP routes that R3 has.

The R2 and R4 are the Router reflector Client.

what should i do to make

R4 have the BGP route to 172.16.1.0 (R1 g0/1) and route from R1 to R4

R1 BGP Config

router bgp 65001
bgp log-neighbor-changes
neighbor 2.2.2.2 remote-as 65002
neighbor 2.2.2.2 ttl-security hops 2
neighbor 2.2.2.2 update-source Loopback1
!
address-family ipv4
network 1.1.1.1 mask 255.255.255.255
network 172.16.1.0 mask 255.255.255.0
network 192.168.1.0 mask 255.255.255.252
neighbor 2.2.2.2 activate
exit-address-family

R1 Routes

Gateway of last resort is not set

1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback1
2.0.0.0/32 is subnetted, 1 subnets
S 2.2.2.2 is directly connected, GigabitEthernet0/0
3.0.0.0/32 is subnetted, 1 subnets
B 3.3.3.3 [20/0] via 2.2.2.2, 00:23:47
172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C 172.16.1.0/24 is directly connected, GigabitEthernet0/1
L 172.16.1.1/32 is directly connected, GigabitEthernet0/1
192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.1.0/30 is directly connected, GigabitEthernet0/0
L 192.168.1.1/32 is directly connected, GigabitEthernet0/0
192.168.2.0/30 is subnetted, 1 subnets
B 192.168.2.0 [20/0] via 2.2.2.2, 00:36:17
192.168.3.0/30 is subnetted, 1 subnets
B 192.168.3.0 [20/0] via 2.2.2.2, 00:23:47

R2 BGP Config

router bgp 65002
bgp log-neighbor-changes
neighbor 1.1.1.1 remote-as 65001
neighbor 1.1.1.1 ttl-security hops 2
neighbor 1.1.1.1 update-source Loopback1
neighbor 3.3.3.3 remote-as 65002
neighbor 3.3.3.3 update-source Loopback1
!
address-family ipv4
network 2.2.2.2 mask 255.255.255.255
network 192.168.1.0 mask 255.255.255.252
network 192.168.2.0 mask 255.255.255.252
neighbor 1.1.1.1 activate
neighbor 3.3.3.3 activate
neighbor 3.3.3.3 next-hop-self
exit-address-family

R2 Routes

Gateway of last resort is not set

1.0.0.0/32 is subnetted, 1 subnets
S 1.1.1.1 is directly connected, GigabitEthernet0/0
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback1
3.0.0.0/32 is subnetted, 1 subnets
S 3.3.3.3 is directly connected, GigabitEthernet0/1
172.16.0.0/24 is subnetted, 1 subnets
B 172.16.1.0 [20/0] via 1.1.1.1, 00:39:10
192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.1.0/30 is directly connected, GigabitEthernet0/0
L 192.168.1.2/32 is directly connected, GigabitEthernet0/0
192.168.2.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.2.0/30 is directly connected, GigabitEthernet0/1
L 192.168.2.1/32 is directly connected, GigabitEthernet0/1
192.168.3.0/30 is subnetted, 1 subnets
B 192.168.3.0 [200/0] via 3.3.3.3, 00:26:40

R3 BGP Config

router bgp 65002
bgp log-neighbor-changes
neighbor 2.2.2.2 remote-as 65002
neighbor 2.2.2.2 update-source Loopback1
neighbor 4.4.4.4 remote-as 65002
neighbor 4.4.4.4 update-source Loopback1
!
address-family ipv4
network 3.3.3.3 mask 255.255.255.255
network 192.168.2.0 mask 255.255.255.252
network 192.168.3.0 mask 255.255.255.252
neighbor 2.2.2.2 activate
neighbor 2.2.2.2 route-reflector-client
neighbor 4.4.4.4 activate
neighbor 4.4.4.4 route-reflector-client
exit-address-family

R3 Routes

Gateway of last resort is not set

1.0.0.0/32 is subnetted, 1 subnets
B 1.1.1.1 [200/0] via 2.2.2.2, 00:28:33
2.0.0.0/32 is subnetted, 1 subnets
S 2.2.2.2 is directly connected, GigabitEthernet0/1
3.0.0.0/32 is subnetted, 1 subnets
C 3.3.3.3 is directly connected, Loopback1
4.0.0.0/32 is subnetted, 1 subnets
S 4.4.4.4 is directly connected, GigabitEthernet0/2
172.16.0.0/24 is subnetted, 1 subnets
B 172.16.1.0 [200/0] via 2.2.2.2, 00:28:33
172.17.0.0/24 is subnetted, 1 subnets
B 172.17.1.0 [200/0] via 4.4.4.4, 00:29:05
192.168.1.0/30 is subnetted, 1 subnets
B 192.168.1.0 [200/0] via 2.2.2.2, 00:28:33
192.168.2.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.2.0/30 is directly connected, GigabitEthernet0/1
L 192.168.2.2/32 is directly connected, GigabitEthernet0/1
192.168.3.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.3.0/30 is directly connected, GigabitEthernet0/2
L 192.168.3.1/32 is directly connected, GigabitEthernet0/2

R4 BGP Config

router bgp 65002
bgp log-neighbor-changes
neighbor 3.3.3.3 remote-as 65002
neighbor 3.3.3.3 update-source Loopback1
!
address-family ipv4
network 4.4.4.4 mask 255.255.255.255
network 172.17.1.0 mask 255.255.255.0
network 192.168.3.0 mask 255.255.255.252
neighbor 3.3.3.3 activate
exit-address-family

R4 Routes

Gateway of last resort is not set

3.0.0.0/32 is subnetted, 1 subnets
S 3.3.3.3 is directly connected, GigabitEthernet0/2
4.0.0.0/32 is subnetted, 1 subnets
C 4.4.4.4 is directly connected, Loopback1
172.17.0.0/16 is variably subnetted, 2 subnets, 2 masks
C 172.17.1.0/24 is directly connected, GigabitEthernet0/3
L 172.17.1.1/32 is directly connected, GigabitEthernet0/3
192.168.2.0/30 is subnetted, 1 subnets
B 192.168.2.0 [200/0] via 3.3.3.3, 00:30:47
192.168.3.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.3.0/30 is directly connected, GigabitEthernet0/2
L 192.168.3.2/32 is directly connected, GigabitEthernet0/2

[Giuseppe Larosa · Accepted solution]

Hello @AnonyKwan ,

within AS65002 you should use also an IGP like OSPF to advertise the loopback addresses and also all the 192.168.x.0 subnets.

In addition to this R2 should use next-hop self towards R3 3.3.3.3 to avoid issues with unknown BGP next-hop 1.1.1.1

eBGP routes will keep the BGP next-hop unchanged when propagated into iBGP in AS 65002 but BGP next-hop 1.1.1.1 is not known on R3.

This is a general rule a BGP router cannot accept a BGP advertisement if the BGP next-hop is not known = not in the IP routing table.

The same concept applies for R2's loopback when seen from R4.

Hope to help

Giuseppe

[AnonyKwan]

Hi @Giuseppe Larosa 

Many Thanks, it solved my problems.

Is it the reason why people implemented full mesh in a small IBGP, right?

In the real world scenario,

Are people implement another IGP with IBGP or full mesh? Something like BGP + MPLS (Not quite understand this concept yet)?

Thanks a lot

[Giuseppe Larosa]

Hello @AnonyKwan ,

I am happy you have solved your issues.

Using an IGP to advertise the loopbacks is the common way to build the network, the use of BGP Route Reflector is common too but it is rather difficult to build a network using iBGP without an underlying IGP.

Your understanding is correct the use of an IGP + MP BGP over loopbacks and LDP is the basis for MPLS enabled networks.

In the case of MPLS networks the iBGP sessions must use loopbacks as endpoints of sessions  to make the MPLS services to work.

Hope to help

Giuseppe