CIDR represents the IP address and its subnet mask with a single number.
Each node j is connected to a subnet, and for each node j, there exists a rule-set r j that is used to filter the traffic directed to its own subnet, to itself, or to the Internet across the connection attached to its subnet.
In this scheme, when an MN changes its subnet and obtains a new CoA from the new FA, the new FA updates the new address to the MN's previous FA so that the new FA forms a new location management hierarchical level for that user.
With a smooth variation and quite a steep gradient, in particular near the optimal subnet count, E gives a sensitive measure of how well a particular network split performs in terms of its subnet count.
This solution has two drawbacks: it is impossible if R is made up of thousands of rules for the considerations introduced in Section 2.2, and it would be extremely easy to circumvent since, when the packet leaves its own subnet, it is not filtered anymore.
This takes into account that in our scenario, each node is a gateway for its own subnet, so the first hop is counted in its own subnet.
To solve this problem, one specific link-local multicast group is defined within the ITS station on every connected subnet.
