Although the preceding example uses the entire third octet for a subnet address, note that you are not restricted to octet boundaries in subnetting. To create more network numbers, you need only shift some bits from the host address to the network address.
For instance, to partition a Class C network number The new netmask or subnet mask is The first subnet has network number Note: The number The number To use the table, write down the original class netmask and replace the 0 value octets with the dotted-decimal value of the additional subnet bits. For example, to partition your Class C network with subnet mask Netmask Notation Translation Table for One Octet Number of Bits Dotted-Decimal Value 1 2 3 4 5 6 7 8 The following table displays several common netmask values in both the dotted-decimal and the masklength formats.
Netmask Formats Dotted-Decimal Masklength In order for this scheme to work, all devices on the segment must agree on which bits comprise the host address. The DHCP server of the wireless router is preconfigured to automatically assign private addresses.
Regardless of your particular situation, do not create an arbitrary IP address; always follow the guidelines explained here. This type of Internet account is more costly than a single-address account typically used by a single user with a modem, rather than a router. This method allows several networked computers to share an Internet account using only a single IP address, which may be statically or dynamically assigned by your ISP. The router accomplishes this address sharing by translating the internal LAN IP addresses to a single address that is globally unique on the Internet.
All incoming inquiries are filtered out by the router. This filtering can prevent intruders from probing your system. However, using port forwarding, you can allow one computer for example, a Web server on your local network to be accessible to outside users. Each device on an Ethernet network has a unique MAC address, which is a bit number assigned to each device by the manufacturer. An ARP request is broadcast onto the network. All stations on the network receive and read the request.
The destination IP address for the chosen station is included as part of the message so that only the station with this IP address responds to the ARP request. All other stations discard the request.
The receiving station provides the transmitting station with the required destination MAC address. The next time data is sent, the address can be obtained from the address information in the table. Domain Name Server Many of the resources on the Internet can be addressed by simple descriptive names such as www. This addressing is very helpful at the application level, but the descriptive name must be translated to an IP address in order for a user to actually contact the resource.
When a computer accesses a resource by its descriptive name, it first contacts a DNS server to obtain the IP address of the resource. The computer sends the desired message using the IP address. Many large organizations, such as ISPs, maintain their own DNS servers and allow their customers to use the servers to look up addresses.
If the computers need to access the Internet, they should also be configured with a gateway address and one or more DNS server addresses. As an alternative to manual configuration, there is a method by which each computer on the network can automatically obtain this configuration information.
The DHCP server stores a list or pool of IP addresses, along with other information such as gateway and DNS addresses that it may assign to the other devices on the network. The wireless router has the capacity to act as a DHCP server.
Internet Security and Firewalls When your LAN connects to the Internet through a router, an opportunity is created for outsiders to access or disrupt your network. A NAT router provides some protection because by the very nature of the process, the network behind the router is shielded from access by outsiders on the Internet. However, there are methods by which a determined hacker can possibly obtain information about your network or at the least can disrupt your Internet access.
A greater degree of protection is provided by a firewall router. What is a Firewall? A firewall is a device that protects one network from another, while allowing communication between the two. A firewall incorporates the functions of the NAT router, while adding features for dealing with a hacker intrusion or attack. Several known types of intrusion or attack can be recognized when they occur.
When an incident is detected, the firewall can log details of the attempt, and can optionally send E-mail to an administrator notifying them of the incident. Using information from the log, the administrator can take action with the ISP of the hacker. Since user-level applications such as FTP and Web browsers can create complex patterns of network traffic, it is necessary for the firewall to analyze groups of network connection states.
Using Stateful Packet Inspection, an incoming packet is intercepted at the network layer and then analyzed for state-related information associated with all network connections. A central cache within the firewall keeps track of the state information associated with all network connections.
All traffic passing through the firewall is analyzed against the state of these connections in order to determine whether or not it will be allowed to pass through or rejected. Denial of Service Attack A hacker may be able to prevent your network from operating or communicating by launching a Denial of Service DoS attack. The method used for such an attack can be as simple as merely flooding your site with more requests than it can handle.
A more sophisticated attack may attempt to exploit some weakness in the operating system used by your router or gateway. Some operating systems can be disrupted by simply sending a packet with incorrect length information. Ethernet Cabling Although Ethernet networks originally used thick or thin coaxial cable, most installations currently use unshielded twisted pair UTP cabling. The UTP cable contains eight conductors, arranged in four twisted pairs, and terminated with an RJ45 type connector.
Table B Only 0. This rating will be printed on the cable jacket. A Category 5 cable will meet specified requirements regarding loss and crosstalk. Inside Twisted Pair Cables For two devices to communicate, the transmitter of each device must be connected to the receiver of the other device. The crossover function is usually implemented internally as part of the circuitry in the device. Computers and workstation adapter cards are usually media-dependent interface ports, called MDI or uplink ports.
Most repeaters and switch ports are configured as media-dependent interfaces with built-in crossover ports, called MDI-X or normal ports. Figure B-4 illustrates straight-through twisted pair cable.
However, using telephone cable results in excessive collisions, causing the attached port to be partitioned or disconnected from the network. In this wiring, the computer transmits on pins 1 and 2. At the hub, the perspective is reversed, and the hub receives on pins 1 and 2. When connecting a computer to a computer, or a hub port to another hub port, the transmit pair must be exchanged with the receive pair.
This exchange is done by one of two mechanisms. Most hubs provide an Uplink switch which will exchange the pairs on one port, allowing that port to be connected to another hub using a normal Ethernet cable. The second method is to use a crossover cable, which is a special cable in which the transmit and receive pairs are exchanged at one of the two cable connectors.
Crossover cables are often unmarked as such, and must be identified by comparing the two connectors. Since the cable connectors are clear plastic, it is easy to place them side by side and view the order of the wire colors on each. On a straight-through cable, the color order will be the same on both connectors. On a crossover cable, the orange and green pairs will be exchanged from one connector to the other.
This feature also eliminates the need to worry about crossover cables, as Auto UplinkTM will accommodate either type of cable to make the right connection. Note: If an ISP technician configured your computer during the installation of a broadband modem, or if you configured it using instructions provided by your ISP, you may need to copy the current configuration information for use in the configuration of your router. Write down this information before reconfiguring your computers. If the computer will connect to your network using an Ethernet NIC at Mbps, you must use a Category 5 Cat 5 cable such as the one provided with your router.
Use Internet Explorer 5. There are several ways you can gather the required Internet connection information. If you cannot locate this information, you can ask your Internet service to provide it or you can try one of the options below.
Record all the settings for each tab page. Once you locate your Internet configuration parameters, you may want to record them on the page below. Some ISPs use your full e-mail address as the login name. For example, Your ISP might call this your account, user, host, computer, or system name. In your IP network, each computer and the router must be assigned a unique IP addresses.
Each computer must also have certain other IP configuration information such as a subnet mask netmask , a domain name server DNS address, and a default gateway address. Double-click the Network icon. If you need to install a new adapter, follow these steps: a.
Select Adapter, and then click Add. Select the manufacturer and model of your Ethernet adapter, and then click OK. Select Protocol, and then click Add. Select Microsoft. Select Client, and then click Add. Restart your PC for the changes to take effect. The simplest way to configure this information is to allow the PC to obtain the information from a DHCP server in the network. The following steps will walk you through the configuration process for each of these versions of Windows.
Locate your Network Neighborhood icon. This will open the Network panel as shown below. If not selected, click in the radio button to the left of it to select it. Restart the PC. Repeat these steps for each PC with this version of Windows on your network.
Double-click the Internet Options icon. Proceed to the end of the Wizard. On the Windows taskbar, click the Start button, and then click Run. Type winipcfg, and then click OK. The IP Configuration window opens, which lists among other things , your IP address, subnet mask, and default gateway. From the drop-down box, select your Ethernet adapter. Double-click the Network and Dialup Connections icon. Double-click that entry. Select Properties. If not, select Install and add them.
Then, restart your PC. This will take you to the next step. The Connections List that shows all the network connections set up on the PC, located to the right of the window. This box displays the connection status, duration, speed, and activity statistics.
This will bring up a window called Network and Dial-up Connections. This will display Control Panel window. The Network panel will display. The Run window opens. Type cmd and then click OK. A command window opens 3. The default gateway is MacOS 8. Repeat this for each Macintosh on your network.
MacOS X 1. From the Apple menu, choose System Preferences, then Network. If not already selected, select Built-in Ethernet in the Configure list. Click Save. This modem must be a separate physical box not a card and must provide an Ethernet port intended for connection to a Network Interface Card NIC in a computer.
Your router does not support a USB-connected broadband modem. With a typical account, much of the configuration information is dynamically assigned when your PC is first booted up while connected to the ISP, and you will not need to know that dynamic information. The router then allows the PCs on the local network to masquerade as the single PC to access the Internet through the broadband modem. Are Login Protocols Used? Some ISPs require a special login protocol, in which you must enter a login name and password in order to access the Internet.
After your network and router are configured, the router will perform the login task when needed, and you will no longer need to run the login program from your PC. It is not necessary to uninstall the login program. What Is Your Configuration Information? More and more, ISPs are dynamically assigning configuration information. If any of these items are dynamically supplied by the ISP, your router automatically acquires them. These procedures are described next. Obtaining ISP Configuration Information for Windows Computers As mentioned above, you may need to collect configuration information from your PC so that you can use this information when you configure the wireless router.
Following this procedure is only necessary when your ISP does not dynamically supply the account information. To get the information you need to configure the router for Internet access: 1.
The Network window opens, which displays a list of installed components. Select the IP Address tab. If an IP address and subnet mask are shown, write down the information. If an address is present, your account uses a fixed static IP address. If no address is present, your account uses a dynamically-assigned IP address. Select the Gateway tab. Select the address and then click Remove to remove the gateway address. Select the DNS Configuration tab. If any DNS server addresses are shown, write down the addresses.
If any information appears in the Host or Domain information box, write it down. Click Disable DNS. You are returned to the Network window. Click OK. Reboot your PC at the prompt. You may also be prompted to insert your Windows CD. Obtaining ISP Configuration Information for Macintosh Computers As mentioned above, you may need to collect configuration information from your Macintosh so that you can use this information when you configure the wireless router.
In this case, close the Control Panel and skip the rest of this section. If an IP address appears under Router address, write down the address. If any Name Server addresses are shown, write down the addresses. If any information appears in the Search domains information box, write it down. Restart any computer that is connected to the firewall. On an The maximum data rate for the The This mode provides wireless connectivity to multiple wireless network devices within a fixed range or area of coverage, interacting with wireless nodes via an antenna.
In the infrastructure mode, the wireless access point converts airwave data into wired Ethernet data, acting as a bridge between the wired LAN and wireless clients. Connecting multiple Access Points via a wired Ethernet backbone can further extend the wireless network coverage. As a mobile computing device moves out of the range of one access point, it moves into the range of another.
As a result, wireless clients can freely roam from one Access Point domain to another and still maintain seamless network connection. There is no Access Point involved in this configuration. This mode enables you to quickly set up a small wireless workgroup and allows workgroup members to exchange data or share printers as supported by Microsoft networking in the various Windows operating systems.
Some vendors also refer to ad hoc networking as peer-to-peer group networking. In this configuration, network packets are directly sent and received by the intended transmitting and receiving stations. As long as the stations are within range of one another, this is the easiest and least expensive way to set up a wireless network. An SSID is a thirty-two character maximum alphanumeric key identifying the name of the wireless local area network.
Some vendors refer to the SSID as network name. For the wireless devices in a network to communicate with each other, all devices must be configured with the same SSID. This means the wireless station will try to associate with whichever access point has the stronger radio frequency RF signal, providing that both the access point and wireless station use Open System authentication.
Authentication and WEP Data Encryption The absence of a physical connection between nodes makes the wireless links vulnerable to eavesdropping and information theft. To provide a certain level of security, the IEEE With Open System authentication, a wireless computer can join any network and receive any messages that are not encrypted. With Shared Key authentication, only those PCs that possess the correct authentication key can join the network.
By default, IEEE Wired Equivalent Privacy WEP data encryption is used when the wireless devices are configured to operate in Shared Key authentication mode. The following events must occur before an Turn on the wireless station. The station listens for messages from any access points that are in range.
The station finds a message from an access point that has a matching SSID. The station sends an authentication request to the access point. The access point authenticates the station. The station sends an association request to the access point. The access point associates with the station. The station can now communicate with the Ethernet network through the access point. An access point must authenticate a station before the station can associate with the access point or communicate with the network.
The IEEE These two authentication procedures are described below. The station associates with the access point and joins the network. This process is illustrated below. The access point sends challenge text to the station. The station uses its configured bit or bit default key to encrypt the challenge text, and sends the encrypted text to the access point.
The access point compares the decrypted text with the original challenge text. If the decrypted text matches the original challenge text, then the access point and the station share the same WEP Key and the access point authenticates the station. The station connects to the network. If the decrypted text does not match the original challenge text the access point and station do not share the same WEP Key , then the access point will refuse to authenticate the station and the station will be unable to communicate with either the Typically, there are three WEP Encryption options available for For authentication purposes, the network uses Open System Authentication.
The receiving device decrypts the data using the same WEP Key. For authentication purposes, the wireless network uses Shared Key Authentication. Note: Some The bit WEP data encryption method allows for a five-character bit input. Additionally, 24 factory-set bits are added to the forty-bit input to generate a bit encryption key. The 24 factory-set bits are not user-configurable. Some vendors refer to the bit WEP data encryption as bit WEP data encryption since the user-configurable portion of the encryption key is 40 bits wide.
The bit WEP data encryption method consists of user-configurable bits. Similar to the forty-bit WEP data encryption method, the remaining 24 bits are factory set and not user configurable.
Some vendors allow passphrases to be entered instead of the cryptic hexadecimal characters to ease encryption key entry. When configured for bit encryption, Therefore, make sure that your In general, if your mobile clients will roam between access points, then all of the Note: Whatever keys you enter for an AP, you must also enter the same keys for the client adapter in the same order.
Wireless Channels The wireless frequencies used by IEEE Neighboring channels are 5 MHz apart. However, due to spread spectrum effect of the signals, a node sending signals using a particular channel will utilize frequency spectrum As a result, two separate wireless networks using neighboring channels for example, channel 1 and channel 2 in the same general vicinity will interfere with each other.
Applying two channels that allow the maximum channel separation will decrease the amount of channel cross-talk, and provide a noticeable performance increase over networks with minimal channel separation.
The radio frequency channels used in For example, Channels 1 to 11 are supported in the U. The preferred channel separation between the channels in neighboring wireless networks is 25 MHz 5 channels. This means that you can apply up to three different channels within your wireless network.
There are only 11 usable wireless channels in the United States. It is recommended that you start using channel 1 and grow to use channel 6, and 11 when necessary, as these three channels do not overlap. In response to this situation, the Wi-Fi Alliance announced a new security architecture in October that remedies the shortcomings of WEP. WEP is a data encryption method and is not intended as a user authentication mechanism.
WPA user authentication is implemented using Support for In the With A major problem with the If you do not update the WEP keys often, an unauthorized person with a sniffing tool can monitor your network for less than a day and decode the encrypted messages.
Products based on the For TKIP replaces WEP with a new encryption algorithm that is stronger than the WEP algorithm, but that uses the calculation facilities present on existing wireless devices to perform encryption operations. TKIP provides important data encryption enhancements including a per-packet key mixing function, a message integrity check MIC named Michael, an extended initialization vector IV with sequencing rules, and a re-keying mechanism. These features were either not yet ready for market or required hardware upgrades to implement.
The RADIUS server holds or has access to user credentials for example, user names and passwords and authenticates wireless users before they gain access to the network. This occurs at the Information in these elements includes the authentication method Possible authentication methods include Pre-shared key is an authentication method that uses a statically configured pass phrase on both the stations and the access point.
This obviates the need for an authentication server, which in many home and small office environments will not be available nor desirable. EAP over The supplicant in the station uses the authentication and cipher suite information contained in the information elements to decide which authentication method and cipher suite to use. For example, if the access point is using the pre-shared key method then the supplicant need not authenticate using full-blown Rather, the supplicant must simply prove to the access point that it is in possession of the pre-shared key.
If the supplicant detects that the service set does not contain a WPA information element then it knows it must use pre-WPA Keys are generated after successful authentication and through a subsequent 4-way handshake between the station and Access Point AP. TKIP includes a message integrity code MIC at the end of each plaintext message to ensure messages are not being spoofed. This framework enables using a central authentication server, which employs mutual authentication so that a rogue wireless user does not join the network.
It is important to note that When using Together, these technologies provide a framework for strong user authentication. Windows XP implements Information elements include the required authentication method Initial The client sends an EAP-start message. This begins a series of message exchanges to authenticate the client.
The access point replies with an EAP-request identity message. The client sends an EAP-response packet containing the identity to the authentication server.
The access point responds by enabling a port for passing only EAP packets from the client to an authentication server located on the wired side of the access point. The authentication server uses a specific authentication algorithm to verify the client's identity. This could be through the use of digital certificates or some other EAP authentication type. The authentication server will either send an accept or reject message to the access point. The access point sends an EAP-success packet or reject packet to the client.
If the authentication server accepts the client, then the access point will transition the client's port to an authorized state and forward additional traffic. As a result, you can update the EAP authentication type to such devices as token cards Smart Cards , Kerberos, one-time passwords, certificates, and public key authentication, or as newer types become available and your requirements for security change. Additionally, For the unicast encryption key, the Temporal Key Integrity Protocol TKIP changes the key for every frame, and the change is synchronized between the wireless client and the wireless access point AP.
For the global encryption key, WPA includes a facility the Information Element for the wireless AP to advertise the changed key to the connected wireless clients.
If configured to implement dynamic key exchange, the The access point uses the session keys to build, sign and encrypt an EAP key message that is sent to the client immediately after sending the success message. The client can then use contents of the key message to define applicable encryption keys. In typical The synchronized changing of the unicast encryption key for each frame. The determination of a unique starting unicast encryption key for each preshared key authentication.
Michael With Although the ICV is encrypted, you can use cryptanalysis to change bits in the encrypted payload and update the encrypted ICV without being detected by the receiver.
With WPA, a method known as Michael specifies a new algorithm that calculates an 8-byte message integrity check MIC using the calculation facilities available on existing wireless devices. Michael also provides replay protection. A new frame counter in the IEEE TKIP is a pragmatic compromise that allows organizations to deploy better security while AES capable equipment is being designed, manufactured, and incrementally deployed.
Specifically, it is susceptible to denial of service DoS attacks. If the access point receives two data packets that fail the message integrity code MIC within 60 seconds of each other, then the network is under an active attack, and as a result, the access point employs counter measures, which include disassociating each station using the access point.
This prevents an attacker from gleaning information about the encryption key and alerts administrators, but it also causes users to lose network connectivity for 60 seconds. More than anything else, this may just prove that no single security tactic is completely invulnerable. This is because WEP-based clients cannot support it. All other benefits to the WPA clients, such as integrity, are maintained.
For Windows wireless clients, you must obtain an updated network adapter driver that supports WPA. For wireless network adapter drivers that are compatible with Windows XP Service Pack 1 and Windows Server , the updated network adapter driver must be able to pass the adapter's WPA capabilities and security configuration to the Wireless Zero Configuration service.
The IEEE is an international organization that develops standards for hundreds of electronic and electrical technologies. The organization uses a series of numbers, like the Dewey Decimal system in libraries, to differentiate between the various technology families. The subgroup of the IEEE develops standards for local and wide area networks with the Wi-Fi , Another standard, The 5 GHz frequency band is not as crowded as the 2. These additional channels can help avoid radio and microwave interference.
This is a very commonly used frequency. Microwave ovens, cordless phones, medical and scientific equipment, as well as Bluetooth devices, all work within the 2. It will allow access points to communicate information on the permissible radio channels with acceptable power levels for client devices.
The devices will automatically adjust based on geographic requirements. The purpose of 11d is to add features and restrictions to allow WLANs to operate within the rules of these countries. Equipment manufacturers do not want to produce a wide variety of country-specific products and users that travel do not want a bag full of country-specific WLAN PC cards.
The outcome will be country-specific firmware solutions. It also operates in the 2. The standards are being defined to naturally co-exist with pre-RSN networks that are currently deployed. Current published ratification date is December As of February , no draft specification has been written - It is expected to use both the 2. The U. S government adopted the algorithm as its encryption technique in October , replacing the DES encryption it used.
AES works at multiple network layers simultaneously. Access points can also bridge to each other. There are various types of access points, also referred to as base stations, used in both wireless and wired networks. These include bridges, hubs, switches, routers and gateways. The differences between them are not always precise, because certain capabilities associated with one can also be added to another. For example, a router can do bridging, and a hub may also be a switch. Skip to main content.
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