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20 Cards in this Set
- Front
- Back
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APIPA - Automatic Private IP Addressing
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A feature of Microsoft Windows, APIPA is a DHCP failover mechanism. With APIPA, DHCP clients can obtain IP addresses when DHCP servers are nonfunctional. APIPA exists in all popular versions of Windows except Windows NT.
When a DHCP server fails, APIPA allocates addresses in the private range 169.254.0.1 to 169.254.255.254. Clients verify their address is unique on the LAN using ARP. When the DHCP server is again able to service requests, clients update their addresses automatically. In APIPA, all devices use the default network mask 255.255.0.0 and all reside on the same subnet. APIPA is enabled on all DHCP clients in Windows unless the computer's Registry is modified to disable it. APIPA can be enabled on individual network adapters. |
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ARP - Address Resolution Protocol
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Definition: ARP converts an Internet Protocol (IP) address to its corresponding physical network address. ARP is a low-level network protocol, operating at Layer 2 of the OSI model.
ARP works on Ethernet networks as follows. Ethernet network adapters are produced with a physical address embedded in the hardware called the Media Access Control (MAC) address. Manufacturers take care to ensure these 6-byte (48-bit) addresses are unique, and Ethernet relies on these unique identifiers for message delivery. When any device wishes to send data to another target device over Ethernet, it must first determine the MAC address of that target given its IP address These IP-to-MAC address mappings are derived from an ARP cache maintained on each device. If the given IP address does not appear in a device's cache, that device cannot direct messages to that target until it obtains a new mapping. To do this, the initiating device first sends an ARP request broadcast message on the local subnet. The host with the given IP address sends an ARP reply in response to the broadcat, allowing the initiating device to update its cache and proceed to deliver messages directly to the target. |
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MAC Address (Media Access Control)
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In computer networking, the Media Access Control (MAC) address is every bit as important as an IP address. Learn in this article how MAC addresses work and how to find the MAC addresses being used by a computer... (see below)
More of this Feature Part 2: Finding MAC Addresses Part 3: Changing MAC Addresses Join the Discussion "I am just confused about why the router will respond with its own MAC address and not the MAC address of the destination host. "If the router keeps an ARP table of IP-to-MAC addresses, then why doesn't it respond to the source host with the MAC of the destination host, regardless of whether they're on the same subnet?" -TJRUGG Related Resources IP Tutorials Elsewhere on the Web Vendor/Ethernet MAC Address Lookup What Is a MAC Address? The MAC address is a unique value associated with a network adapter. MAC addresses are also known as hardware addresses or physical addresses. They uniquely identify an adapter on a LAN. MAC addresses are 12-digit hexadecimal numbers (48 bits in length). By convention, MAC addresses are usually written in one of the following two formats: MM:MM:MM:SS:SS:SS MM-MM-MM-SS-SS-SS The first half of a MAC address contains the ID number of the adapter manufacturer. These IDs are regulated by an Internet standards body (see sidebar). The second half of a MAC address represents the serial number assigned to the adapter by the manufacturer. In the example, 00:A0:C9:14:C8:29 The prefix 00A0C9 indicates the manufacturer is Intel Corporation. Why MAC Addresses? Recall that TCP/IP and other mainstream networking architectures generally adopt the OSI model. In this model, network functionality is subdivided into layers. MAC addresses function at the data link layer (layer 2 in the OSI model). They allow computers to uniquely identify themselves on a network at this relatively low level. MAC vs. IP Addressing Whereas MAC addressing works at the data link layer, IP addressing functions at the network layer (layer 3). It's a slight oversimplification, but one can think of IP addressing as supporting the software implementation and MAC addresses as supporting the hardware implementation of the network stack. The MAC address generally remains fixed and follows the network device, but the IP address changes as the network device moves from one network to another. IP networks maintain a mapping between the IP address of a device and its MAC address. This mapping is known as the ARP cache or ARP table. ARP, the Address Resolution Protocol, supports the logic for obtaining this mapping and keeping the cache up to date. DHCP also usually relies on MAC addresses to manage the unique assignment of IP addresses to devices. |
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winipcfg
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winipcfg is a utility program Microsoft has included with the Windows operating system beginning with Windows 95. With this utility you can quickly find your computer's network addresses and other useful TCP/IP settings. winipcfg also allows you to fix network connection problems in certain situations.
Related Resources Windows Networking Resources The winipcfg Interface To run the utility in Windows, click the Start button, then choose Run from the menu, type winipcfg in the box and click OK. If the command completes successfully, an IP Configuration window appears as illustrated below The fields contained in this window are: Adapter Name: name of the network card or cards known to Windows. If the computer has more than one network adapter installed, this drop-down field allows the user to view settings for each of the adapters individually. The adapter name is supplied by the manufacturer of the device. Adapter Address: the Media Access Control (MAC) address of the network card IP Address: the Internet Protocol (IP) address for the computer when using this network card Subnet Mask: the IP network mask for the computer when using this network card Default Gateway: the gateway address for the computer when using this network card Clicking the Release or Release All buttons cause the currently selected adapter (or all adapters) to discard their DHCP network settings by notifying the DHCP server, then disconnect from the network. Clicking the Renew or Renew All buttons cause the currently selected adapter (or all adapters) to request new network settings from the DHCP server. Note: The information displayed by winipcfg is static, meaning that it does not update automatically as the computer's IP address changes. One must exit and re-run winipcfg to pick up any dynamic address change. Note: A few versions of Windows, like Windows 2000 Server, do not include winipcfg in their normal installation. On these systems, an alternate command for retrieving IP address information is ipconfig /all |
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IP - Internet Protocol
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Definition: IP (Internet Protocol) is the primary network protocol used on the Internet, developed in the 1970s. On the Internet and many other networks, IP is often used together with the Transport Control Protocol (TCP) and referred to interchangeably as TCP/IP.
IP supports unique addressing for computers on a network. Most networks use the Internet Protocol version 4 (IPv4) standard that features IP addresses four bytes (32 bits) in length. The newer Internet Protocol version 6 (IPv6) standard features addresses 16 bytes (128 bits) in length. Data on an Internet Protocol network is organized into packets. Each IP packet includes both a header (that specifies source, destination, and other information about the data) and the message data itself. IP functions at layer 3 of the OSI model. It can therefore run on top of different data link interfaces including Ethernet and Wi-Fi. |
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TCP/IP - Transmission Control Protocol / Internet Protoco
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Definition: Transmission Control Protocol (TCP) and Internet Protocol (IP) are two distinct network protocols, technically speaking. TCP and IP are so commonly used together, however, that TCP/IP has become standard terminology to refer to either or both of the protocols.
IP corresponds to the Network layer (Layer 3) in the OSI model, whereas TCP corresponds to the Transport layer (Layer 4) in OSI. In other words, the term TCP/IP refers to network communications where the TCP transport is used to deliver data across IP networks. The average person on the Internet works in a predominately TCP/IP environment. Web browsers, for example, use TCP/IP to communicate with Web servers. |
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OSI Model - Open Systems Interconnection model
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Definition: The OSI model defines internetworking in terms of a vertical stack of seven layers. The upper layers of the OSI model represent software that implements network services like encryption and connection management. The lower layers of the OSI model implement more primitive, hardware-oriented functions like routing, addressing, and flow control.
In the OSI model, data communication starts with the top layer at the sending side, travels down the OSI model stack to the bottom layer, then traveses the network connection to the bottom layer on the receiving side, and up its OSI model stack. The OSI model was introduced in 1984. Although it was designed to be an abstract model, the OSI model remains a practical framework for today's key network technologies like Ethernet and protocols like IP. Also Known As: Open Systems Interconnection (OSI) reference model, OSI seven layer model Examples: Internet Protocol (IP) corresponds to the Network layer of the OSI model, layer three. TCP and UDP correspond to OSI model layer four, the Transport layer. Lower layers of the OSI model are represented by technologies like Ethernet. Higher layers of the OSI model are represented by application protocols like TCP and UDP. |
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Ethernet
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Definition: Ethernet is a physical and data link layer technology for local area networks (LANs). Ethernet was invented by engineer Robert Metcalfe.
When first widely deployed in the 1980s, Ethernet supported a maximum theoretical data rate of 10 megabits per second (Mbps). Later, so-called "Fast Ethernet" standards increased this maximum data rate to 100 Mbps. Today, Gigabit Ethernet technology further extends peak performance up to 1000 Mbps. Higher level network protocols like Internet Protocol (IP) use Ethernet as their transmission medium. Data travels over Ethernet inside protocol units called frames. The run length of individual Ethernet cables is limited to roughly 100 meters, but Ethernet networks can be easily extended to link entire schools or office buildings using network bridge devices. |
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7 - Application
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Provides an entrance point for programs to gain access to network services
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6 - Presentation
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Translates data between different computing systems on a network. This layer translates the data generated by the application layer from its own syntax to a common transport syntax suitable for transmission over a network
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5 - Session
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Enables two applications to create a persistent communications connection
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4 - Transport
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Ensures that data is delivered in the order in which it is sent and without loss or duplication
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3 - Network
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Determines the physical path of the data to be transmitted based on the network conditions, the priority of service and other factors
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2 - Data Link
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Provides error-free transfer of data frames from one computer to another over the physical layer
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1 - Physical
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Establishes the physical interface and mechanisms for placing a raw stream of data bits on to the wire
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TCP/IP Application Layer
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Provides services and utilities that enable applications to access network resources, including windows Sockets and Net BIOS, which provide standard application interfaces for programs to access network services.
OSI Layers: Application, Presentation, Session |
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TCP/IP Transport Layer
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Responsible for guaranteed delivery and end to end communication using one of two protocols, UDP or TCP
OSI Layer Transport |
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TCP/IP Internet Layer
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Encapsulates transport layer data into units called packets, addresses them, and routes them to their destination
OSI Layer Network |
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TCI/IP Link Layer
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Specifies the requirements for sending and receiving packets. The layer is responsible for placing data on and receiving data from the physical network
OSI Layer Data-Link, Physical |
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UDP - User Datagram Protocol
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UDP (User Datagram Protocol) is a communications protocol that offers a limited amount of service when messages are exchanged between computers in a network that uses the Internet Protocol (IP). UDP is an alternative to the Transmission Control Protocol (TCP) and, together with IP, is sometimes referred to as UDP/IP. Like the Transmission Control Protocol, UDP uses the Internet Protocol to actually get a data unit (called a datagram) from one computer to another. Unlike TCP, however, UDP does not provide the service of dividing a message into packets (datagrams) and reassembling it at the other end. Specifically, UDP doesn't provide sequencing of the packets that the data arrives in. This means that the application program that uses UDP must be able to make sure that the entire message has arrived and is in the right order. Network applications that want to save processing time because they have very small data units to exchange (and therefore very little message reassembling to do) may prefer UDP to TCP. The Trivial File Transfer Protocol (TFTP) uses UDP instead of TCP.
UDP provides two services not provided by the IP layer. It provides port numbers to help distinguish different user requests and, optionally, a checksum capability to verify that the data arrived intact. In the Open Systems Interconnection (OSI) communication model, UDP, like TCP, is in layer 4, the Transport Layer. |
