# &develguide;

One single tree (for both IPv4 and IPv6) is used. Each node contains a byte, the &ip; addresses stretching from root to the leafs.

## Tree of &ip; addresses

    	   / 193 - 175 - 132 - 164
    tree root /                  \ 142
    	  \ 195 - 37 - 78 - 163
    	   \ 79 - 134

To detect the whole address, step by step, from the root to the leafs, the nodes corresponding to each byte of the ip address are expanded. In order to be expended a node has to be hit for a given number of times (possible by different addresses; in the previous example, the node 37 was expended by the 195.37.78.163 and 195.37.79.134 hits).

For 193.175.132.164 with x= reqs_density_per_unit:

- After first req hits -> the 193 node is built.

- After x more hits, the 175 node is build; the hits of 193 node are split between itself and its child--both of them gone have x/2.

- And so on for node 132 and 164.

- Once 164 build the entire address can be found in the tree. 164 becomes a leaf. After it will be hit as a leaf for x times, it will become RED (further request from this address will be blocked).

So, to build and block this address were needed 3*x hits. Now, if reqs start coming from 193.175.132.142, the first 3 bytes are already in the tree (they are shared with the previous address), so I will need only x hits (to build node 142 and to make it RED) to make this address also to be blocked. This is the reason for the variable number of hits necessary to block an &ip;.

The maximum number of hits to turn an address red are (n is the address's number of bytes):

1 (first byte) + x (second byte) + (x / 2) * (n - 2) (for the rest of the bytes) + (n - 1) (to turn the node to red).

So, for IPv4 (n = 4) will be 3x and for IPv6 (n = 16) will be 9x. The minimum number of hits to turn an address red is x.