Local preference for network.( outbound path selection)

[zapappindia]

Hello,

I have three sites in a HUB and spoke MPLS design (Site A is HUB)  (network diagram attached).

We have 2 MPLS providers and each site connected to both MPLS providers for load sharing and backup.

EBGP is running between the sites and both MPLS providers from all sites.

Site A(HUB) - 10.10.10.0/24

                     10.10.11.0/24

Site B - 172.16.31.0/24

            172.16.32.0/24

Site C - 10.10.12.0/24

            10.10.13.0/24

Question -  I want the inbound traffic to Site A from Site B (172.16.31.0/24 through MPLS provider A )

                                                                                     ( 172.16.32.0/24 through MPLS provider B )

                 I want the inbound traffic to Site A from Site C (10.10.12.0/24 through MPLS provider A )

                                                                                     (10.10.13.0/24 through MPLS provider B )

I cannot use the AS path prepend for this.  Can i use Local preference or weight attribute to control the inbound traffic for specific network with the help of route map? if yes can you provide any config example ?

Thanks

[Giuseppe Larosa]

Hello Zapappindia,

in order to be able to forward traffic to other sites based on source address you need to use Policy Based Routing.

BGP has a lot of tools but it is still a destination based dynamic protocol.

You could use BGP weight or local preference if you would like to implement something like:

use SP A to reach other sites, if SP A provided route is missing using SP B that is a primary/secondary strategy.

PBR requires the use of route-maps that are used to divert traffic and these are applied on internal LAN interfaces.

access-list 111 permit ip 172.16.32.0 0.0.0.255 10.10.10.0 0.0.1.255

route-map pbr-rule-siteB permit 10

match ip address 111

set ip next-hop

at the same time you can prefer ISP A so that 172.16.31.0/24 will use ISP A

router bgp yourASN

neigh weight 500

A similar setup should be done on site C. using an ACL like

access/list 121 permit ip 10.10.13.0 0.0.0.255 10.10.10.0 0.0.1.255

route-map pbr-rule-siteC permit 10

match ip address 111

set ip next-hop

at the same time you can prefer ISP A so that other SiteC IP subnet will use ISP A

router bgp yourASN

neigh weight 500

Hope to help

Giuseppe

[zapappindia]

Hello Giuseppe,

                           Thanks for the replay.  I need to have the traffic rerouted to SP A incase SP B fails and vice versa. When i specify the next hope to SP B  with route map (access-list 111 permit ip 172.16.32.0 0.0.0.255 10.10.10.0 0.0.1.255) to reach site A and what if SP B fails? will the traffic get rerouted through SP A to Site A ?

My requirement is to load share the traffic between both provider an incase if a provider fails all traffic needs to rerouted through other provider.

Thanks

[Giuseppe Larosa]

Hello Zapappindia,

>> My requirement is to load share the traffic between both provider an incase if a provider fails all traffic needs to rerouted through other provider.

your original requirements look like different and I have tried to answer to them

In PBR if the specified next-hop is unreachable standard destination based routing is used.

The question may become if this detection is quick enough for your needs.

Configuration for load balancing outbound can be performed, but it requires a different configuration with no use of PBR

you would need under process BGP

router bgp yourASN

maximum-paths 2

+

hidden command

bgp bestpath as-path multipath-relax

for performing load balancing you cannot provide a better weight or local preference to one eBGP peer over the other one!

Hope to help

Giuseppe