Watch the Simmerin' online guitar lesson by Andrew Ford from Focus On: Reggae Bass
Check out the performance. Here is a ska groove inspired by the Wailers song "Simmer Down". It is basically a walking bass line played over a 1-6-2-5 progression in Bb. There is a bridge that goes to the 3-minor chord and then 2-minor for 8 bars where the walking breaks up slightly, but a classic ska type bass line, let's try it.