We currently have about 15 remote sites and 2 data centers. Each remote site has an MPLS connection and a backup internet connection from the local ISP that routes internal traffic over a VPN tunnel and internet traffic straight out through the local connection. The data centers each have very large internet and MPLS connections.
Each branch is configured with a default route to go out the local ISP connection (ip route 0.0.0.0 0.0.0.0 gi0/1). I would like to advertise a default route via BGP so that we are only depending on ISPs as a tertiary backup.
So, my questions:
How do I advertise a default route via BGP?
If I do only that, will it override the locally configured default route? I'm thinking no, but just want to make certain.
How do I advertise a backup default route via BGP that points to the secondary data center?
How do I make the internet link be a backup to the backup default route?
On your DC routers you will need "default-information originate" under the router bgp section - this will tell them to advertise a default route into the MPLS cloud. You can use a route-map on the secondary DC to make the default route advertised from there appear less favourable than the primary.
On your spoke sites you should change your static route to be a floating static route so it will only come into effect if both DC routes are not available.