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                                    </span>
                                </blockquote>
<p align="left">
                                    <span class="resourceSectionTitle">Notes:</span>
                                </p>
                                <blockquote>
                                    <p class="smtext">
                                        <img border="0" src="../../../../../CHAPID=knet-v214aCH47510/RLOID=knet-v214aRLO47817/RIOID=knet-v214aRIO125374/knet/v214aclixsi144/line450.gif" width="450" height="1"></p>
                                    <p class="smtext">
                                        <img border="0" src="../../../../../CHAPID=knet-v214aCH47510/RLOID=knet-v214aRLO47817/RIOID=knet-v214aRIO125374/knet/v214aclixsi144/line450.gif" width="450" height="1"></p>
                                    <p class="smtext">
                                        <img border="0" src="../../../../../CHAPID=knet-v214aCH47510/RLOID=knet-v214aRLO47817/RIOID=knet-v214aRIO125374/knet/v214aclixsi144/line450.gif" width="450" height="1"></p>
                                </blockquote>
<p align="left">
                                    <span class="resourceSectionTitle"><span class="resourceRed">Step 1 - IP Address Basics.</span></span>
                                </p>
                                <blockquote>
                                    <p class="smtext">
                                        <b>Explanation:</b> IP network addresses are assigned by the Internet Network Information Center (InterNIC). If your organization has a class "A" IP network address, the first octet (8 bits) is assigned be InterNIC and your organization can use the remaining 24 bits to define up to 16,777,214 hosts on your network. This is a lot of hosts. It is not possible to put all of these hosts on one physical network without separating them with routers and subnets. A workstation may be on one network or subnet and a server may be on another network or subnet. When the workstation needs to retrieve a file from the server it will need to use its subnet mask to determine the network or subnet that the server is on. The purpose of a subnet mask is to help hosts and routers determine the network location where a destination host can be found. Refer to the following table to review IP address classes, default subnet masks and the number of networks and hosts that can be created with each class of network address.</p>
                                    <table border="1" cellpadding="2" cellspacing="0" width="592" bordercolor="#000000">
<tr>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="28"><b>Cls</b></td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="59"><b>1st Octet Decimal Range</b></td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="62"><b>1st Octet High Order Bits</b></td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="86"><b>Network / Host ID (N=Network, H=Host)</b></td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="90"><b>Default Subnet Mask</b></td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="135"><b>Number of Networks</b></td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="156"><b>Hosts per Network </b>(usable addresses)</td>
</tr>
<tr>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="28"><b>A</b></td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="59">1 - 126*</td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="62">0</td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="86">N.H.H.H</td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="90">255.0.0.0</td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="135">126 (2<sup>7</sup> - 2)</td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="156">16,777,214 (2 <sup>24</sup> - 2)</td>
</tr>
<tr>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="28"><b>B</b></td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="59">128 - 191</td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="62">1 0聽</td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="86">N.N.H.H</td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="90">255.255.0.0</td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="135">16,382 (2<sup>14</sup> - 2)</td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="156">65,534 (2 <sup>16</sup> - 2)</td>
</tr>
<tr>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="28"><b>C</b></td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="59">192 - 223</td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="62">1 1 0</td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="86">N.N.N.H</td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="90">255.255.255.0</td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="135">2,097,150 (2<sup>21</sup> - 2)</td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="156">254 (2 <sup>8</sup> - 2)</td>
</tr>
<tr>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="28"><b>D</b></td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="59">224 - 239</td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="62">1 1 1 0</td>
<td class="smtext" align="center" colspan="4" rowspan="1" valign="top" width="467">Reserved for Multicasting</td>
</tr>
<tr>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="28"><b>E</b></td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="59">240 - 254聽</td>
<td class="smtext" align="center" colspan="1" rowspan="1" valign="top" width="62">1 1 1 1 0</td>
<td class="smtext" align="center" colspan="4" rowspan="1" valign="top" width="429">Experimental, used for research</td>
</tr>
</table>
                                </blockquote>
<p align="left">
                                    <span class="resourceSectionTitle"><span class="resourceRed">Step 2 - The "ANDing" process.</span></span>
                                </p>
                                <blockquote>
                                    <p class="smtext">
                                        <b>Explanation:</b> Hosts and routers use the "ANDing" process to determine if a destination host is on the same network or not. The ANDing process is done each time a host wants to send a packet to another host on an IP network. If you want to connect to a server, you may know the IP address of the server you want to connect to or you may just enter the host name (for example, www.cisco.com) and a Domain Name Server (DNS) will convert the host name to an IP address. First the source host will compare (AND) its own IP address to its own subnet mask. The result of the ANDing is to identify the network where the source host resides. It will then compare the destination IP address to its own subnet mask. The result of the 2nd ANDing will be the network that the destination host is on. If the source network address and the destination network address are the same they can communicate directly. If the results are different then they are on different networks or subnets and will need to communicate through routers or may not be able to communicate at all.</p>
                                    <p class="smtext">ANDing depends on the subnet mask. A default subnet mask for a Class C network is 255.255.255.0 or 11111111.111111111.111111111.00000000. This is compared to the source IP address bit for bit. The first bit of the IP address is compared to the first bit of the subnet mask and the second bit to the second, and so on. If the two bits are both ones, then the <b>ANDing result is a ONE</b>. If the two bits are a zero and a one or two zeros then the <b>ANDing result is a ZERO</b>. Basically this means that a combination of 2 ones results in a ONE, anything else is a zero. The result of the ANDing process is the network or subnet number that the source or destination address is on.</p>
                                </blockquote>
<p align="left">
                                    <span class="resourceSectionTitle"><span class="resourceRed">Step 3 - Two Class C networks using the default subnet mask.</span></span>
                                </p>
                                <blockquote>
                                    <p class="smtext">
                                        <b>Explanation:</b> This example will show how a Class C default subnet mask can be used to determine which network a host is on. A default subnet mask does not break an address into subnets. If the default subnet mask is used then the network is not being "subnetted". Host X (source) on network 200.1.1.0 has an IP address of 200.1.1.5 and wants to send a packet to host Z (destination) on network 200.1.2.0 and has an IP address of 200.1.2.8. All hosts on each network are connected to hubs or switches and then to a router. Remember that with a Class C network address ARIN (American Registry for Internet Numbers) assigns the first 3 octets (24 bits) as the network address so these are two different class C networks. This leaves one octet (8 bits) for hosts so each class C network could have up to 254 hosts (2^8 power = 256 -- 2 = 254).</p>
                                    <img border="0" src="../../../../../CHAPID=knet-v214aCH47510/RLOID=knet-v214aRLO47817/RIOID=knet-v214aRIO125374/knet/v214alabimage1066/10_6_6.gif" width="600" height="184"><p class="smtext">The ANDing process will help the packet get from host 200.1.1.5 on network 200.1.1.0 to host 200.1.2.8 on network 200.1.2.0 using the following steps.</p>
                                    <span class="smtext">
                                        <ol type="a">
<li>
                                                <b>Host X compares its own IP address to its own subnet mask using the ANDing process</b>
<table border="0" cellpadding="2" width="65%" bordercolor="#000000">
<tr>
<td class="smtext" colspan="1" rowspan="1" width="52%"><b>Host X IP address 200.1.1.5</b></td>
<td class="smtext" colspan="1" rowspan="1" width="50%">11001000.00000001.00000001.00000101</td>
</tr>
<tr>
<td class="smtext" colspan="1" rowspan="1" width="52%"><b>Subnet Mask 255.255.255.0</b></td>
<td class="smtext" colspan="1" rowspan="1" width="50%">11111111.11111111.11111111.00000000</td>
</tr>
<tr>
<td class="smtext" colspan="1" rowspan="1" width="52%"><b>ANDing Result (200.1.1.0)</b></td>
<td class="smtext" colspan="1" rowspan="1" width="50%">11001000.00000001.00000001.00000000</td>
</tr>
</table>
<table cellpadding="0" cellspacing="0" border="0">
                                                    <tr>
                                                        <td width="100%"><img height="10" width="1" border="0" src="../../../../../images/ccna/common/transdot.gif"></td>
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                                                                                <td><span class="note"><b>NOTE:</b>
<p class="smtext">The result of step 3a of the ANDing process is the network address of host X which is 200.1.1.0</p>
</span></td>
                                                                            </tr>
                                                                        </table>
                                                                    </td>
                                                                </tr>
                                                            </table>
                                                        </td>
                                                    </tr>
                                                </table>
                                            </li>
<li>
                                                <b>Next host X compares the IP address of the Host Z destination to its own subnet mask using the ANDing process.</b>
<table border="0" cellpadding="2" width="65%" bordercolor="#000000">
<tr>
<td class="smtext" colspan="1" rowspan="1" width="52%"><b>Host Z IP address 200.1.2.8</b></td>
<td class="smtext" colspan="1" rowspan="1" width="50%">11001000.00000001.00000010.00001000</td>
</tr>
<tr>
<td class="smtext" colspan="1" rowspan="1" width="52%"><b>Subnet Mask 255.255.255.0</b></td>
<td class="smtext" colspan="1" rowspan="1" width="50%">11111111.11111111.11111111.00000000</td>
</tr>
<tr>
<td class="smtext" colspan="1" rowspan="1" width="52%"><b>ANDing Result (200.1.2.0)</b></td>
<td class="smtext" colspan="1" rowspan="1" width="50%">11001000.00000001.00000010.00000000</td>
</tr>
</table>
<table cellpadding="0" cellspacing="0" border="0">
                                                    <tr>
                                                        <td width="100%"><img height="10" width="1" border="0" src="../../../../../images/ccna/common/transdot.gif"></td>
                                                    </tr>
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                                                        <td width="100%">
                                                            <table bgcolor="#000000" bordercolor="#000000" cellspacing="0" bordercolorlight="#000000" width="100%" border="0">
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                                                                    <td width="100%">
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                                                                            <tr>
                                                                                <td><span class="note"><b>NOTE:</b>
<p class="smtext">The result of step 3b ANDing process is the network address of host Z which is 200.1.2.0.</p>
</span></td>
                                                                            </tr>
                                                                        </table>
                                                                    </td>
                                                                </tr>
                                                            </table>
                                                        </td>
                                                    </tr>
                                                </table>
<p class="smtext">Host X compares the ANDing results from step A and the ANDing result from step B and they are different. Host X now knows that host Z is not in its Local Area Network (LAN) and it must send the packet to its "Default Gateway" which is the IP address of the router interface of 200.1.1.1 on network 200.1.1.0. The router will then repeat the ANDing process to determine which router interface to send the packet out.</p>
                                            </li>
</ol>
                                    </span>
                                </blockquote>
<p align="left">
                                    <span class="resourceSectionTitle"><span class="resourceRed">Step 4 - One Class C network using a Custom subnet mask.</span></span>
                                </p>
                                <blockquote>
                                    <p class="smtext">
                                        <b>Explanation:</b> This example uses a single Class C network address (200.1.1.0) and will show how a class C custom subnet mask can be used to determine which subnetwork (or subnet) a host is on and to route packets from one subnetwork to another. Remember that with a class C network address ARIN assigns the first 3 octets (24 bits) as the network address. This leaves 8 bits (one octet) for hosts so each class C network could have up to 254 hosts (2^8 power = 256 -- 2 = 254).</p>
                                    <p class="smtext">Perhaps you want less than 254 host (workstations and servers) all on one network and you want to create 2 sub-networks and separate them with a router for security reason or to reduce traffic. This will create smaller independent broadcast domains and can improve network performance and increase security since these subnetworks will be separated by a router. Assume you will need at least 2 subnetworks and at least 50 hosts per subnetwork. Since you only have one Class C network address you have only 8 bits in the fourth octet available for a total of 254 possible hosts, you must create a Custom Subnet mask. You will use the custom subnet mask to "BORROW" bits from the host portion of the address. The following steps will help accomplish this:</p>
                                    <span class="smtext">
                                        <ol type="a">
<li>The first step to "subnetting" is to determine how many subnets are needed. In this case you will need 2 subnetworks. To see how many bits you should borrow from the host portion of the network address, add the bit values from right to left until the total (decimal value) is greater than the number of subnets you will need. Since we need 2 subnets, add the one bit and the two bit which equals three. This is over the number of subnets we need, so we will need to borrow at least two bits from the host address starting from the left side of the octet that contains the host address.
<table border="0" width="451" bordercolor="#000000">
<tr>
<td class="smtext" colspan="1" rowspan="1" width="225"><b>Network address: 200.1.1.0</b></td>
<td class="smtext" colspan="1" rowspan="1" width="23"></td>
<td class="smtext" colspan="1" rowspan="1" width="25"></td>
<td class="smtext" colspan="1" rowspan="1" width="25"></td>
<td class="smtext" colspan="1" rowspan="1" width="20"></td>
<td class="smtext" colspan="1" rowspan="1" width="22"></td>
<td class="smtext" colspan="1" rowspan="1" width="19"></td>