How to pass traffic from BGP routing to a VPN destination.

[Chin]

Dear All,

I having a difficulty on the BGP routing issue. I have 2 routers, router A1 and router A2 are running in BGP for routing connection. Currently we setup a site to site VPN from router A2 to router B. Once the VPN connection establish, how to i connect to router B from router A1?

I have attached the diagram and wish anyone can help me answer for it.

Many thanks.

[John Blakley]

Are you running a routing protocol between the two vpn endpoints? If not, you can simply create statics pointing from Router Office B to Office A1 via Office A2. You can Then redistribute the static into BGP so Office A1 knows how to get to Router Office B.

Another way would be to run a routing protocol between A2 and B over the vpn tunnel, and then perform a mutual redistribution on A2.

HTH,
John

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[Chin]

Hi John

Thanks your suggestion. I try to draft a configuration on these routers. Please correct me if i am wrong on it.

Let assume the site to site VPN is connected.

Office A1:

router bgp 65022

no synchronization

bgp log-neighbor-changes

network 172.16.152.0

timers bgp 15 20

redistribute connected

redistribute static

neighbor xx.xx.xx.xx remote-as 8805

neighbor xx.xx.xx.xx weight 100

neighbor xx.xx.xx.xx route-map ADVERTISE-WAN out

no auto-summary

ip prefix-list ADVERTISE-WAN seq 5 permit 172.16.152.0/24

Office A2:

router bgp 65021

no synchronization

bgp log-neighbor-changes

network 172.16.153.0

network 192.168.110.0

timers bgp 15 20

redistribute connected

redistribute static

neighbor xx.xx.xx.xx remote-as 8804

neighbor xx.xx.xx.xx weight 100

neighbor xx.xx.xx.xx route-map ADVERTISE-WAN out

no auto-summary

ip prefix-list ADVERTISE-WAN seq 5 permit 172.16.153.0/24

ip prefix-list ADVERTISE-WAN seq 10 permit 192.168.110.0/23

Once the 192.168.110.0/23 is advertised in the WAN routing, Office A1 able to access to office B via WAN cloud. It is possible to access it. Am i correct?

[John Blakley · Accepted solution]

It looks right. From this config, you'll be able to get to the shared subnet between A2 and B, but what's on the LAN side for B? You'll need to have a static address for that unless you're going to run a routing protocol. On Router B, you'll need a static route for A1 to point to A2 in order to get return traffic from A1 to B and back.

For example, if your lan subnet on Router B is 192.168.5.0/24, on A2 you would create a static route:

ip route 192.168.5.0 255.255.255.0

On Router A2, you're redistributing statics, so A1 would know how to get to B since A2 knows and is advertising that to A1.

HTH,
John

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[Chin]

Hi John,

Thanks for your help. Later I will try it after my office hour and I get back to you for the result.

Thank you very much and appreciate your help.

[Chin]

Hi John,

I have tried it and it working prefect to me. Thanks for your solution.