Question : ospf reference-bandwidth

1). changing ref-bw = does it require to be changed on complete ospf domain including all areas "must=?", or it could be any specfic area
2). and if its possible for specfic area, "Is it possible to change it only on non-backbone area"

Answer : ospf reference-bandwidth

It should be changed on all router of the ospf domain in order to have a common base of cost calculation

Regards