... Well, level 1 routers gives you pretty much the same isolation as areas. Unless you consider the relative size of the level 1 routing messages a problematic burden compared to level 2 routing messages. However, I'm not even sure you can make the system not transmit level 1 routing messages on all interfaces, meaning they will go out anyway, even if you only have another area at the other end of the line. I think if you have a point to point out of area link you won't see L1 routing messages, but you probably will see them on an Ethernet. The routing message size isn't an issue in Phase IV because the data can be sent in pieces. That was another important change from Phase III, which always sends the route data for all nodes (up to 255 of them) whether there is a change or not. 255 nodes just barely fits into a standard DDCMP packet, but 1023 nodes would not. (Nor in a standard Ethernet frame, for that matter.) And it's wasteful to send data that hasn't changed. So Phase IV has a way to send routing data for selected nodes. paul