The topology is like this: One central router C 3600 is connected with several other routers C 2800 In each 2800 router, several Level-1 NET elements are connected.AR28 use in every area
(please, check attachment for topology)
It is confirmed that AR28 don't support ISIS multi process. In customer's environment, this feature is necessary. but it will support
on some new router such as AR49 and also support on huawei high end router
All the routers (central & peripherals) are configured as Level-1, because if they are configured as Level-1-2 the NET elements cannot be managed by their NMS platform.
If a router has to support more than 80 NET elements, lets say for example 240, then these elements are going to be shared in 3 areas that each can support 80 elements. Then the router is running multi process ISIS. For example, if a router belong to areas A, B, and C then 3 process are configured for each area (ISIS process A, ISIS process B, ISIS process C).
Also, in order to have communication between the peripheral and the central router, for each ISIS process a GRE tunnel is configured.