BGP Path Selection question

[DW1]

Hi, i am just looking for some advice if i am looking at doing the correct thing.

Scenario - I have a Datacenter and a DR site, where they are both connected to 2 different ISPs. There are also sites that are on either of these ISPs.

The DR site is also a user site, so i need to make ISP1 the preferred path back to the datacenter and out to the internet. I also need the traffic to come back the same way.

I know i can prepend AS for ISP2 so ISP1 has less AS to get to the datacenter, but will the path back be the same? Ive tried setting this environment up in GNS3 but im having some issues that I'm working on.

I also want the sites hanging off that ISP, to go the more direct path to the DR site or back through the datacenter for accessing sites hanging off the other ISP. As well as going through DC for internet

Appreciate any help.

thanks

David 

[whitegrape]

Presuming all are using ibgp instead of internal routing protocol. Outgoing can use local preferences to control. It will work fine.

[Julio E. Moisa]

Hi

You can use weight and local preference for incoming traffic with higher metric and as prepend with lowest metric for outbound traffic. 

For example:

route-map ISP1-IN permit 5

set local-preference 1000

route-map ISP1-OUT permit 5

set as-path prepend 100

route-map ISP2-IN permit 5

set local-preference 500

route-map ISP2-OUT permit 5

set as-path prepend 100 100 100

router bgp 100

neighbor 1.1.1.1 remote 1

neighbor 1.1.1.1 route-map ISP1-IN in

neighbor 1.1.1.1 route-map ISP1-OUT out

neighbor 2.2.2.2 remote 2

neighbor 2.2.2.2 route-map ISP2-IN in

neighbor 2.2.2.2 route-map ISP2-OUT out

This example will be applied to every traffic, once implemented you can execute: clear ip bgp * soft

So you will have symmetric traffic. There are many ways to manipulate the traffic using BGP attributes. Also you can match networks through ACL or Prefix-list under the route-maps, if you want to do that for especific networks and the rest with default parameters, you must include empty route-map sequences to avoid any discard. 

Hope it is useful

:-)