# A kind data structure and arithmetic for subnetting

Discussion in 'Cisco' started by Hell, May 1, 2006.

1. ### HellGuest

A kind data structure and arithmetic for subnetting
Written by www.softsession.com

This document describes a kind data structure and arithmetic for
subnetting. With this arithmetic, the required subnet can be quickly
located in a network with complicated hiberarchy.
Because network segment is identified by IP address and mask, such as
Binary. The binary tree can be used to describe the net structure and
Eg. A organization has the network segment 192.168.0.0/22, and there
are two departments( Department A and Department B) under this
organization. Department A was assigned subnet 192.168.0.0/25 and B was
assigned subnet 192.168.1.0/25,the network structure chart is as
following:
http://www.softsession.com/resource/images/network4.gif

Below is the IP address management information structure chart
represented by binary tree :
http://www.softsession.com/resource/images/network3.gif

The data structure of each node is as below:
struct SNetdata
{
string sIP; //subnet ID, identified by IP address and mask, such as
192.168.0.0/24
int iNodeType;
string sLeftIP; // left subtree node, left subtree subnet ID
string sRightIP; //right subtree node, right subtree subnet ID
string sParentIP; //parent node, parent subnet ID
};
There are four types of node: used, unused, middle node, root node, as
below:
enum NODE_TYPE
{
USEDNODE=1, //used node
UNUSEDNODE=2, //unused node
MIDDLENODE=3, //middle node, which is generated during the course of
subnetting
ROOTNODE=4, //root node
};

IP address management information is saved in these nodes. All these
nodes can be linked by double linked list. Considering the subnet ID
will be frequently used to perform searching in the IP address
management dataset, thus the map of STL is used to save each node and
subnet ID is used as index key in order to quicken the searching speed.
typedef map<string,SNetdata,less<string> > MAPNetData;
MAPNetData NetDatas;

Assumed that the organization is newly added Department C and
Department D. C is needed to assign a 25-bits mask subnet and D is
needed to assign a 24-bits mask subnet.
The ordinary IP address management software and subnet calculator can't
solve this problem. With the binary tree data structure, the problem
can be solved easily. For the first problem, to assign a 25-bits mask
subnet for Department C, we preorder traversal the binary tree
beginning from the root node 192.168.0.0/22, to find the leaf node of
unused type and the mask less or equal 25. In this example, we can find
192.168.0.128/25, which is the subnet assigned for Department C.

Traversal arithmetic is as below:
int TraversalTree(string StartIP, int iTarMask, string& ResIP)
/*
StartIP: represents the subnet ID of the beginning node when preorder
traversalling the binary tree. In this example it is root
node192.168.0.0/22.
iTarMask: represents the mask of the target node we are searching for
ResIP: represents the subnet ID of the target node we have found
*/
{
MAPNetData::iterator MyIterator;
SNetdata NetData;
the tree
int iRes,k;
string tmpstr;

MyIterator=NetDatas.find(StartIP);
if(MyIterator==NetDatas.end())
return -1;
NetData=(*MyIterator).second;

tmpstr=StartIP.substr(StartIP.find("/",0)+1,2);

return 3;

if(NetData.LeftIP==""&&NetData.RightIP=="")
{
if(NetData.iNodeType==UNUSEDNODE)
{
ResIP=NetData.IP;
return 1; // Have found it
}
else
return 2;
}

if(iRes<0||iRes==1)
return iRes;

if(iRes<0||iRes==1)
return iRes;

return 0;
}

Then for the second problem, to assign a 24-bits mask subnet for
Department D. Following the above mentioned arithmetic to traversal the
binary tree, we can find 192.168.2.0/23. Cause the assigned subnet is
24-bits mask, we need to perform subnetting under this node. Then we
will get 192.168.2.0/24, which is the subnet we needed. After the
assigning, the IP address management information structure chart
represented by binary tree is as below:
http://www.softsession.com/resource/images/network2.gif

For the details, see http://www.softsession.com/resource/ref1.htm

Hell, May 1, 2006