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New Member

eBGP neighbours don't advertise

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.

3 REPLIES
Cisco Employee

Hi,

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

New Member

HelloThank you for the fast

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.

 

 

Hi, are you able to Ping

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
 

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