BGP traffic engineering
The process of optimizing and controlling traffic flow within a network based on the BGP protocol is called BGP traffic engineering. It is possible with various techniques to achieve very granular manipulation of traffic. For example, you can approach a 80/20 split of traffic across two links.
There are several ways you can approach this. The simplest is using AS-Path prepending.
You can configure a primary and secondary BGP peering with two neighbors, create a Route-map that will prepend the local AS number multiple times, and apply the route-map to the secondary BGP peering. Now the traffic behavior will depend upon how many times you prepend your own AS. If you prepend it four times, the secondary path will appear less preferable to other ASes, and they will prefer the primary path. The result is an approximation to an 80/20 split of traffic.
Keep in mind that BGP traffic engineering depends on the routing decisions of other ASes, so it’s not possible to guarantee an exact 80/20 split. You’ll need to monitor the traffic and adjust the configuration as needed to achieve the desired distribution. Additionally, always coordinate with your neighboring ASes to make sure your traffic engineering policies are effective and aligned.