BGP - secondary default route

[louis0001]

Hi,

we have 2 core sites (100 miles apart) connected via a 1gb leased line.

At both sites we have an internet breakout. However, in normal use, all traffic flows out of site A.

All of our remote sites connect to both sites via an MPLS network using BGP

Site A advertises the static default route 0.0.0.0/0 via SITE A firewall to SITE A internet
Site B has a static default route 0.0.0.0/0 to site A via 1gb leased line.

What I want to do is change Site B to advertise the static route 0.0.0.0/0 via SITE B firewall to SITE B internet. I'm wondering what effect this will have as it will inject a secondary 0.0.0.0/0 into the routing table? And if so, how do we make SITE A the preferred route for the remote (BGP) sites?

[Francesco Molino · Accepted solution]

Hi Louis

If you advertise a second default route, traffic will take the best path based on bgp attributes. If you want to control and always make SITE A default route preferred, you will need to configure the local preference like:

route-map SITEA permit 10

 set local-pref 200

Router bgp xxxxx

neighbor SITE-A-ROUTER-IP route-map SITEA in

The higher the local-pref value is the higher the path is preferred. If you want to make site A best path for default route only, you can also create a prefix-list and call it into your route-map like:

ip prefix-list default seq 5 permit 0.0.0.0/0

route-map SITEA permit 10

 set local-pref 200

 match ip address prefix default

route-map SITEA permit 20

Router bgp xxxxx

neighbor SITE-A-ROUTER-IP route-map SITEA in

This config will force site A as best path for default route only.

[louis0001]

Wow..... thank you very much for the quick reply. I shall look into that today. Thank you.

[Francesco Molino]

You're welcome. If you have any concerns or need help, don't hesitate.