eBGP Multihop Lab Configuration

[TariqMK]

Hi all,

I am building a basic eBGP lab to test out the concept of making 2 non-directly connected neighbours BGP peers.

The network the BGP routers will be going 'across' is an OSPF network.

The lab is below along with relevant configuration:

OSPF Config:

R4
router ospf 10
network 172.16.0.0 0.0.0.3 area 0
network 172.16.0.8 0.0.0.3 area 0

R5
router ospf 10
network 172.16.0.4 0.0.0.3 area 0
network 172.16.0.8 0.0.0.3 area 0

Unfortunately it doesn't seem to work, does anyone have some idea what I am doing wrong?

[Jon Marshall]

So are you trying to peer across the 172.16.x.x OSPF network ? 

What do the routing tables on R4 and R5 look like ie. do they have routes to each others IPs ? 

Also R4's neighbor IP cannot be 10.0.0.4  as that is a subnet address in your topology. 

Jon

[TariqMK]

Hi Jon,

Thanks for pointing that out, not sure how I missed that. I changed the neighbor to 10.0.0.5 instead.

As requested, the Routing Tables of R4 and R5 are below:

R4
Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 10.0.0.0/30 is directly connected, Ethernet0/0
L 10.0.0.2/32 is directly connected, Ethernet0/0
172.16.0.0/16 is variably subnetted, 5 subnets, 2 masks
C 172.16.0.0/30 is directly connected, Ethernet0/1
L 172.16.0.1/32 is directly connected, Ethernet0/1
O 172.16.0.4/30 [110/20] via 172.16.0.10, 00:02:31, Ethernet0/2
[110/20] via 172.16.0.2, 00:02:31, Ethernet0/1
C 172.16.0.8/30 is directly connected, Ethernet0/2
L 172.16.0.9/32 is directly connected, Ethernet0/2


R5
Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 10.0.0.4/30 is directly connected, Ethernet0/0
L 10.0.0.5/32 is directly connected, Ethernet0/0
172.16.0.0/16 is variably subnetted, 5 subnets, 2 masks
O 172.16.0.0/30 [110/20] via 172.16.0.9, 00:27:46, Ethernet0/2
[110/20] via 172.16.0.5, 00:27:36, Ethernet0/1
C 172.16.0.4/30 is directly connected, Ethernet0/1
L 172.16.0.6/32 is directly connected, Ethernet0/1
C 172.16.0.8/30 is directly connected, Ethernet0/2
L 172.16.0.10/32 is directly connected, Ethernet0/2

[Jon Marshall]

So R4 and R4 do not have routes to the IPs you have used for the neighbor IPs. 

You need to advertise the 10.0.0.x/30 subnets into OSPF.

Jon

[TariqMK]

So I need to redistribute BGP into OSPF? Or just add a static route for R4 and R5 pointing to the BGP neighbor addresses?

[Jon Marshall]

You could use statics although you would also need them on R3 as well or you can do - 

R4

router ospf 10
network 10.0.0.0 0.0.0.3 area 0
passive-interface e0/0

R5

router ospf 10
network 10.0.0.4 0.0.0.3 area 0
passive-interface e0/0

Jon

[Jon Marshall]

Apologies, got that the wrong way round. 

Have just edited previous post with correct details :) 

Jon