eBGP neighbours don't advertise

tstbj0001 · ‎05-10-2014

Hello

I've been trying to configure a WAN that uses eBGP in order to exchange routing data, but nothing seems to work.

The configuration is very basic and yet I can't receive any BGP packets.

router bgp 6774
no synchronization
bgp router-id 2.2.2.2
bgp log-neighbor-changes
network 2.2.2.2 mask 255.255.255.255
neighbor 1.1.1.1 remote-as 12666
neighbor 1.1.1.1 update-source Loopback0
neighbor 3.3.3.3 remote-as 9031
neighbor 3.3.3.3 ebgp-multihop 255
neighbor 3.3.3.3 update-source Loopback0
no auto-summary

Is there something blatantly wrong with my configuration?

Thank you for your help.

Nagendra Kumar Nainar · ‎05-10-2014

Hi,

You need to enable ebgp multihop on other routers which is missing.

On R2, enable ebgp multihop for 1.1.1.1

router bgp 6774
 no synchronization
 bgp router-id 2.2.2.2
 bgp log-neighbor-changes
 network 2.2.2.2 mask 255.255.255.255
 neighbor 1.1.1.1 remote-as 12666
 neighbor 1.1.1.1 update-source Loopback0
 neighbor 3.3.3.3 remote-as 9031
 neighbor 3.3.3.3 ebgp-multihop 255
 neighbor 3.3.3.3 update-source Loopback0

On R5 and R6 enable ebgp multihop for all neighbors,

router bgp 9031
 no synchronization
 bgp log-neighbor-changes
 neighbor 1.1.1.1 remote-as 12666
 neighbor 1.1.1.1 update-source Loopback0
 neighbor 2.2.2.2 remote-as 6774
 neighbor 2.2.2.2 update-source Loopback0

router bgp 12666
 no synchronization
 bgp router-id 1.1.1.1
 bgp log-neighbor-changes
 network 1.1.1.1 mask 255.255.255.255
 neighbor 2.2.2.2 remote-as 6774
 neighbor 2.2.2.2 update-source Loopback0
 neighbor 3.3.3.3 remote-as 9031
 neighbor 3.3.3.3 update-source Loopback0

By default, eBGP will expect from directly connected address. If it is between loopback, you need to enable multihop to bring the session up.

-Nagendra

tstbj0001 · ‎05-11-2014

Hello

Thank you for the fast response!

I've added multihop as you've requested along with some other config and it's working partially: the routers that are directly connected receive packets from each other, but the ones that aren't receive 0 packets (R2 and R6).

Neighbor        V    AS MsgRcvd MsgSent   TblVer InQ OutQ Up/Down State/PfxRcd
1.1.1.1         4 12666       8       7       15    0    0 00:00:32        4
3.3.3.3         4 9031       0       0        0    0    0 never    Active
10.10.10.10     4 12666       8       9       15    0    0 00:01:08        4
11.11.11.10     4 12666       0       0        0    0    0 never    Idle
11.11.11.20     4 9031       0       0        0    0    0 never    Idle

The configuration:

router bgp 6774
no synchronization
bgp log-neighbor-changes
network 2.2.2.2 mask 255.255.255.255
network 10.10.10.20 mask 255.255.255.255
neighbor 1.1.1.1 remote-as 12666
neighbor 1.1.1.1 ebgp-multihop 255
neighbor 1.1.1.1 update-source Loopback0
neighbor 3.3.3.3 remote-as 9031
neighbor 3.3.3.3 ebgp-multihop 255
neighbor 3.3.3.3 update-source Loopback0
neighbor 10.10.10.10 remote-as 12666
neighbor 11.11.11.10 remote-as 12666
neighbor 11.11.11.20 remote-as 9031
no auto-summary

router bgp 12666
no synchronization
bgp log-neighbor-changes
network 1.1.1.1 mask 255.255.255.255
network 10.10.10.0 mask 255.255.255.0
network 10.10.10.10 mask 255.255.255.255
network 11.11.11.0 mask 255.255.255.0
network 11.11.11.10 mask 255.255.255.255
neighbor 2.2.2.2 remote-as 6774
neighbor 2.2.2.2 ebgp-multihop 255
neighbor 2.2.2.2 update-source Loopback0
neighbor 3.3.3.3 remote-as 9031
neighbor 3.3.3.3 ebgp-multihop 255
neighbor 3.3.3.3 update-source Loopback0
neighbor 10.10.10.20 remote-as 6774
neighbor 11.11.11.20 remote-as 9031
no auto-summary

router bgp 9031
no synchronization
bgp log-neighbor-changes
network 3.3.3.3 mask 255.255.255.255
network 11.11.11.0 mask 255.255.255.0
network 11.11.11.20 mask 255.255.255.255
neighbor 1.1.1.1 remote-as 12666
neighbor 1.1.1.1 ebgp-multihop 255
neighbor 1.1.1.1 update-source Loopback0
neighbor 2.2.2.2 remote-as 6774
neighbor 2.2.2.2 ebgp-multihop 255
neighbor 2.2.2.2 update-source Loopback0
neighbor 10.10.10.10 remote-as 12666
neighbor 10.10.10.20 remote-as 6774
neighbor 11.11.11.10 remote-as 12666
no auto-summary

Could you also help me out with this one?

Thanks again.

milan.kulik · ‎05-12-2014

Hi,

are you able to Ping between the Lopopbacks you are using as BGP source/destinations?

Don't forget TCP connectivity is a prerequisite to establish a BGP session.

As I don't see any static routes in your configs, how do the routers know where to forward the packets with the other router's Loopback destination IP?

Best regards,

Milan