When I need to connect a number of branch sites to one another for a customer, I typically recommend an MPLS VPN through a trusted carrier. The CE at each site speaks BGP with its upstream PE and each site is numbered with its own private ASN. This is very convenient for us as BGP provides myriad traffic engineering tools and our adjacencies are limited to n+1 for n sites (the +1 being our colo environment).
Lately, however, I've noticed increasing customer interest in Metro Ethernet solutions. Many of our customers have branch sites within a common metro area and MetroE quotes are coming in at several hundred dollars (USD) less than MPLS service for circuits of the same speeds. While this is appealing, I'm not sure how to best establish routing across a layer two backbone while avoiding turning a mesh topology into hub-and-spoke.
BGP would necessitate a full mesh of adjacencies among branch sites in order to maintain mesh connectivity, which obviously is undesirable from a scalability perspective. The other option is to deploy an IGP, namely OSPF, and have all sites form adjacencies across the WAN. I'd like to address each site as its own area, which seems like overkill but I want to preserve the ability to summarize routes advertised from each site and this can only be done on area borders.
Does this make sense? Are there any caveats to watch out for when deploying OSPF in this manner (for example, should I consider disabling LSA flooding)? Or is there another solution I've overlooked?