NETGEAR CG814M manual Netmask, Equals

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Reference Manual for the Model CG814M Wireless Cable Modem Gateway

Class C

Class C addresses can have 254 hosts on a network. Class C addresses use 24 bits for the network address and eight bits for the node. They are in this range:

192.0.1.x to 223.255.254.x.

Class D

Class D addresses are used for multicasts (messages sent to many hosts). Class D addresses are in this range:

224.0.0.0 to 239.255.255.255.

Class E

Class E addresses are for experimental use.

This addressing structure allows IP addresses to uniquely identify each physical network and each node on each physical network.

For each unique value of the network portion of the address, the base address of the range (host address of all zeros) is known as the network address and is not usually assigned to a host. Also, the top address of the range (host address of all ones) is not assigned, but is used as the broadcast address for simultaneously sending a packet to all hosts with the same network address.

Netmask

In each of the address classes previously described, the size of the two parts (network address and host address) is implied by the class. This partitioning scheme can also be expressed by a netmask associated with the IP address. A netmask is a 32-bit quantity that, when logically combined (using an AND operator) with an IP address, yields the network address. For instance, the netmasks for Class A, B, and C addresses are 255.0.0.0, 255.255.0.0, and 255.255.255.0, respectively.

For example, the address 192.168.170.237 is a Class C IP address whose network portion is the upper 24 bits. When combined (using an AND operator) with the Class C netmask, as shown here, only the network portion of the address remains:

11000000 10101000 10101010 11101101 (192.168.170.237)

combined with:

11111111 11111111 11111111 00000000 (255.255.255.0)

Equals:

11000000 10101000 10101010 00000000 (192.168.170.0)

B-4

Networks, Routing, and Firewall Basics

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Contents NETGEAR, Inc Trademarks World Wide Web Page Contents USB Appendix a Appendix C Contents Contents Typographical Conventions About This ManualAudience Special Message Formats Technical SupportAbout the CG814M Gateway Key FeaturesChapter Introduction Built-in Cable Modem802.11b Standards-based Wireless Networking Powerful, True FirewallContent Filtering Protocol Support Configurable Auto Uplink Ethernet ConnectionUSB Port Easy Installation and Management What’s in the Box? Firewall’s Front PanelLED Descriptions Gateway’s Rear Panel CG814M Gateway Rear PanelIntroduction LAN Hardware Requirements Connecting the Gateway to the InternetWhat You Will Need Before You Begin Computer RequirementsWhere Do I Get the Internet Configuration Parameters? LAN Configuration RequirementsInternet Configuration Requirements Connecting the Gateway to the Internet Record Your Internet Connection Information Connecting the CG814M Gateway Connecting to Your ComputerEthernet USBConnecting to your Cable Service Provider WirelessConnecting the Power Adapter Log in to the GatewayLogin window opens as shown in -3below Connect to the Internet Connecting the CG814M Gateway to the Internet ConfigurationConnecting the Gateway to the Internet Connecting the Gateway to the Internet Connecting the Gateway to the Internet Security Chapter Wireless ConfigurationConsiderations For a Wireless Network Wireless Settings Placement and RangeWireless Settings Restricting Wireless Access by MAC AddressConfiguring Wired Equivalent Privacy WEP Wireless Configuration Wireless Configuration Chapter Protecting Your Network Protecting Access to Your CG814M GatewayChanging the Built-In Password Blocking Keywords, Sites, and Services Set Password menuBlock Keywords and Domains Click on the Block Sites link of the Content Filtering menu Blocking Services ProxyPort Blocking CookiesPort Forwarding Port Blocking menuTo forward inbound traffic Port Triggering Considerations for Port ForwardingTo configure Port Triggering Setting Up a Default DMZ Host Respond to Ping on Internet WAN PortProtecting Your Network Chapter Managing Your Network Network Status InformationViewing Gateway Status This screen shows the following parametersMenu 3.2 Router Status Fields Connection Status Connection screenCurrent System Time Configuring LAN IP SettingsLAN IP Setup Dhcp Use router as Dhcp serverViewing and Emailing Logged Information Logs menuErasing Configuration Enabling Logs Event E-mail NotificationRunning Diagnostic Utilities Diagnostics menuManaging Your Network Chapter Troubleshooting Basic FunctionsLocal Link LEDs Not On Power LED Not OnTest LED Stays On Troubleshooting the Web Configuration Interface Cable Link LED Not OnTesting the LAN Path to Your Gateway Troubleshooting the ISP ConnectionTroubleshooting a TCP/IP Network Using a Ping Utility Testing the Path from Your PC to a Remote Device Troubleshooting Appendix a Technical Specifications TCP/IPTechnical Specifications Appendix B Networks, Routing, and Firewall Basics Related Publications Basic Router ConceptsIP Addresses and the Internet What is a Router?Routing Information Protocol Three Main Address Classes Netmask EqualsSubnet Addressing Example of Subnetting a Class B AddressNetmask Notation Translation Table for One Octet Private IP Addresses Single IP Address Operation Using NAT Single IP Address Operation Using NATMAC Addresses and Address Resolution Protocol Related DocumentsDomain Name Server IP Configuration by DhcpInternet Security and Firewalls Stateful Packet Inspection What is a Firewall?Denial of Service Attack Ad-hoc Mode Peer-to-Peer Workgroup Wireless NetworkingWireless Network Configuration Infrastructure ModeExtended Service Set Identification Essid Authentication and WEP EncryptionWireless Channel Selection Table B-1 802.11b Radio Frequency ChannelsUplink Switches and Crossover Cables Ethernet CablingCable Quality Appendix C Preparing Your Network Preparing Your Computers for TCP/IP NetworkingConfiguring Windows 95, 98, and ME for TCP/IP Networking Install or Verify Windows Networking ComponentsPreparing Your Network Enabling Dhcp to Automatically Configure TCP/IP Settings Selecting Windows’ Internet Access MethodConfiguring Windows NT, 2000 or XP for IP Networking Verifying TCP/IP PropertiesConfiguring the Macintosh for TCP/IP Networking MacOS 8.6 orMacOS Verifying TCP/IP Properties for Macintosh Computers What Is Your Configuration Information? Verifying the Readiness of Your Internet AccountMail.xxx.yyy.com Preparing Your Network Restarting the Network Glossary Networks See Network Address Translation Connection