BGP Path Preference between two ISP

[Saeed Siddiqui]

Hello Wonderful People, would you please help me with this? the IPs and hostname are fictitious but design is real. please see attached VISIO.

i have two internet circuit coming in from two different providers ISP 1 and ISP 2, we are pairing with each provider via EBGP,  both circuits are being terminated into two different Cisco 3850 switches DCSW1 and DCSW2 respectively. both swtiches are also doing HSRP and IBGP peering.

both circuits are advertising default routes.

Question, how can make ISP1 is primary for all incoming traffic and outgoing traffic and ISP2 should only become active when ISP1 is down.

currently, HSRP is active on DCSW1 therefore we see incoming and outgoing traffic on DCSW1 but we also see incoming traffic via ISP2 coming into DCSW2.

please help

[MHM Cisco World]

Yes any L3 device can have more than one default route it depend on how you lean the defualt route the L3 will prefer which one.

[Richard Burts]

As MHM says it is quite possible for a layer 3 device (switch or router) to have multiple default routes. And how they are used does depend on how they are learned. In your case with connection on the switch to 2 ISP there will be 2 external BGP default routes. It is possible that both default routes will be active (some traffic on one and some traffic on the other = load sharing) or it is possible that one will be active/primary and the other will be secondary. If you want it to operate as primary/secondary the easy way to do this is to configure local preference in the configuration of both ISP.

[Richard Burts]

As I think about it I will change my suggestion and say that using weight rather than local preference might be a better option. Using weight will only have an effect on routes learned from ISP2 and ISP3 while local preference would also effect ISP1 routes.