In a recent discussion here we produced at least two issues with decentralized architecture.
#1. Mobility. One of the main attractions of the controller-based architecture (CBA) in the first place was to improve the experience for hand-held devices which don't hibernate between locations. The device can't know that it has changed subnets when it roams. So it either breaks or there is tunneling of some sort. It's not clear which approach, centralized or decentralized, has the more difficult scaling issue once mobile tunneling is taken into account. #2. IP space use. With centralized you create a pool of X number of subnets with some headroom. Quite efficient. With distributed, you first have to choose to have wireless traffic on the building vlan or not. If you put it on the building vlan wireless users are behind any existing departmental firewall or ACL. If that's unacceptable you have to create a new vlan in each building and allocate IP space for each, with headroom, which is a much less efficient use of IP space. Tom Zeller Indiana University ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.
