BGP Prepending

jucpci001 · ‎07-05-2015

Hi - I have LAN connected to ISP MPLS CE router (AS 65002) and LAN subnets are advertised via BGP from this CE into ISP MPLS network.

Remote end(1) – ISP MPLS CE1 (AS 65000) is connected to my (VPN) router1 (AS 65064), BGP is configured and my (VPN) router1 learns the routes for LAN subnets.

Remote end(2) – ISP MPLS CE2(AS 65000) is connected to my (VPN) router2 (AS 65064), BGP is configured and my (VPN) router2 too learns the routes for LAN subnets.

Note: my (VPN) router1 & my (VPN) router2 are not inter-connected.

Further,

my (VPN) router1 (AS65000) is connected to customer network (AS 65054), BGP configured and customer network learns routes for LAN subnets.

my (VPN) router2 (AS65000) is connected to customer network (AS 65054), BGP configured and customer network learns routes for LAN subnets.

i.e. Customer network has two route paths and prefers the one towards my (VPN) router1.

So current flow of traffic is, Forwards path: LAN->ISP-> my (VPN) router1-> Customer Network and Return Path Customer Network-> my (VPN) router1->ISP->LAN.

Here I want to make use of my (VPN) router2 i.e. Return Path should be Customer Network-> my (VPN) router2->ISP->LAN.

How can I achieve this, will BGP prepending gives a correct solution ? If so at which router I need to prepend AS path – at my (VPN) router1 so that customer network learns prepended route updates from my (VPN) router1 and prefers routes of my (VPN) router2 or I Should prepend somewhere on ISP routers ?

Regards, Jr.J

Peter Paluch · ‎07-07-2015

Hi,

I believe you have posted the same thread here:

https://supportforums.cisco.com/discussion/12549846/bgp-prepending

Please delete it first so that the eventual answers don't get spread between these two threads.

Understanding your situation just from the verbal description is somewhat difficult. It would be very helpful if you created a simple diagram of your network setup, depicting the autonomous systems and their numbers, the way they are interconnected, the individual BGP peerings that are in place, and please try to describe how the routing runs now and how you want it to run. Would you be able to create it and upload here? Please be as accurate as possible.

Best regards,
Peter

jucpci001 · ‎07-07-2015

Hi - Attached diagram. Could you pls check and help me out ?

Regards, Jr.J

Robert Falconer · ‎07-07-2015

So you are purposely trying to introduce asymmetric traffic flows? Not all applications and network devices like asymmetry, though it shouldn't be a problem if everything is shown on your drawing.

How is the customer network deciding to use Rtr1 for the return traffic? What is the routing mechanism that chooses that path?

jucpci001 · ‎07-08-2015

Hi - Not really asymmetric traffic flow. I have IPsec tunnel for Customer subnets traffic from the router behind CE to My Rtr1 & My Rtr2. I will start using the tunnel to My Rtr2 instead of present one i.e. My Rtr1 and that would need return via My Rtr2. Customer network uses AS-path attribute to select best route.

Regards, Jr.J

Robert Hillcoat · ‎08-18-2015

Robert Falconer is correct you are trying to route the traffic asymmetrically. Why you want to do this is beyond me.

What your better doing is having R2 as a backup router. Use HSRP and have them as iBGP neighbors.