Problem with BGP adjacency

[sakatzidisgiwrgos]

Hello community,

I am trying several BGP configurations in a GNS3 lab and i have some issues.

BGP adjacencies do not seem to work, as i can not ping several ip address in the network and also they do not exist as BGP entries in the routing tables in some devices. To be more specific, i can not ping the loopback 0 in R4 from R3 and R2.

I do not know what i do wrong, but i do not think i miss something.

I am uploading the topology in GNS3 and also some basic configurations i have done in the routers.

Any help is appreciated.

Thanks in advance.

[MHM Cisco World]

Your bgp neighbor is not reachable

Run

ospf

between four routers and check again.

[sakatzidisgiwrgos]

Ah ok. So BGP works only when

OSPF

is also configured ?

[MHM Cisco World]

Bgp not need

ospf

but need rechability' you must ping IP you use in

bgp neighbor

command.

I Suggest use

ospf

to make each router reachable to each other.

[Harold Ritter]

Hi @sakatzidisgiwrgos ,

There is no need for

ospf

in your scenario, as all your bgp sessions use directly connected addresses.

Regards,

[MHM Cisco World]

two way he can solve issue 
as you mention using

next-hop

self in R1 
or using OSPF make

next-hop of 3.3.3.3

is reachable by other routers

[Harold Ritter]

That is absolutely right @MHM Cisco World . 

If

ospf

is not used the

next-hop-self all

needs to be configured on R1, so that the

next hop

is changed for reflected iBGP routes as well.

Regards,

[MHM Cisco World]

thanks a lot 

[Harold Ritter · Accepted solution]

Hi @sakatzidisgiwrgos ,

R2 and R4 can't reach

3.3.3.3/32

as the

next hop

received from R1 is not reachable. You need to configure the following on R1, so that it changes the

next hop

to itself:

router bgp 12

neighbor 10.1.1.99 next-hop-self all

neighbor 192.168.12.2 next-hop-self all

The other thing is that

12.12.12.0/24

is not advertised from R1 to R2, as routes received from an iBGP neighbor can't be advertised to another iBGP neighbor, unless you make R1 a route reflector as follow:

router bgp 12

neighbor 10.1.1.99 route-reflector-client

neighbor 192.168.12.2 route-reflector-client

Regards,