Route Redundancy via HSRP over BGP cloud

[dedra_live]

Hello,

Please find attached the site to site connectivity diagram over MPLS L3.

If the HSRP is configured on both sites at the router inside interface, how can the routers be configured in a way that if an active link on the other or local site goes down, how will the routes get converged in a BGP cloud. The route redundancy should be active passive and not active active.

Thanks.

[milan.kulik]

Hi,

you can configure one of the routers on the site as primary - advertising the site prefixes to the backbone with better BGP attributes (lower MED, e.g., or the secondary router could prepend the AS number several times).

Then you can configure HSRP on the primary router to track the status of the WAN interface and to decrement HSRP priority on the LAN interface in a case the tracked WAN interface goes down.

(You could even configure some more sophisticated tracking like checking the PE router reachability, e.g., but WAN interface status tracking is the easiest one.)

HTH,

Milan

[nihit-tandon]

How can you track when the WAN interface is Ethernet !!!

[milan.kulik]

In that case, you need to find something more sophisticated to track.

Like one specific route received from a BGP neighbor, or something else depending on your network.

See  http://www.cisco.com/en/US/customer/docs/ios/ipapp/configuration/guide/ipapp_eot.html#wp1054818

or http://www.cisco.com/en/US/docs/ios/ipapp/configuration/guide/ipapp_eot.pdf

for details.

HTH,

Milan

[dedra_live]

Hi Milan,

Could you please provide a configuration example for the following

"you can configure one of the routers on the site as primary - advertising the site prefixes to the backbone with better BGP attributes (lower MED)"

Thanks.

[milan.kulik]

Hi,

you can use:

router bgp xxx

nei yyy route-map bgp_out out

Where

route-map bgp_out permit 10

set metric 10

on your primary router

while

route-map bgp_out permit 10

set metric 100

on your secondary router.

This way your primary router will advertise the prefixes with MED=10  to the backbone while your secondary router will advertise the same prefixes with a worse MED=100.

Or you can use

route-map bgp_out permit 10

set  as-path prepend xxx xxx xxx xxx xxx

on your secondary router which will then advertise the prefixes with a longer AS_PATH.

HTH,

Milan