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| Layered Model | Layers divide the aspects of network operation into less complex elements. |
| Layer 1 | This layer provides the electrical, mechanical, procedural, and functional means for activating and maintaining the physical link between systems. This layer uses such physical media as twisted-pair, coaxial, and fiber-optic cable. |
| Layer 2 | This layer provides physical transmission across the medium. It handles error notification, network topology, and flow control. This layer uses Media Access Control (MAC) addresses, which also are referred to as physical or hardware addresses. |
| Layer 3 | This layer determines the best way to move data from one place to another. The router operates at this layer. This layer uses logical addressing schemes that can be managed by an administrator. This layer uses the Internet Protocol (IP) addressing scheme, along with Apple-Talk, DECnet, VINES, and IPX addressing schemes. |
| Layer 4 | This layer segments and reassembles data into a data stream. The transport layer has the potential to guarantee a connection and offer reliable transport. |
| Layer 5 | This layer establishes, maintains, and manages sessions between applications. |
| Layer 6 | This layer provides data representation and code formatting, along with the negotiation of data transfer syntax. It ensures that the data that arrives from the network can be used by the application, and it ensures that information sent by the application can be transmitted on the network. |
| Layer 7 | This layer provides network services to user applications. For example, a word processing application is serviced by file transfer services at this layer. |
| Peer Layers | Each layer's protocol exchanges information, called protocol data units (PDUs), between peer layers. Data; Segments; Packets; Frames; Bits. |
| 5 conversion sets of Data Encapsulation | Step 1 |
| Ethernet Standards | Ethernet and IEEE 802.3--LAN specifications, which operate at 10 Mbps over coaxial and twisted-pair cable. |
| Ethernet defined wiring standards | 10BASE2--Known as thin Ethernet, 10BASE2 allows network segments up to 185 meters on coaxial cable. |
| DoD Protocols | IP provides connectionless, best-effort delivery routing of datagrams. It is not concerned with the content of the datagrams (packets); instead, it looks for a way to move the datagrams (packets) to their destinations. |
| Subnet Definition | Subnets use unique 32-bit subnet addresses that are created by borrowing bits from the host field. Subnet addresses are visible to other devices on the same network, but they are not visible to outside networks. Subnetworks are not visible to outside networks because the outside networks can only reference the subnet's whole network address. |
| Network Layer: Path Determination | The network layer connects to networks and provides best-effort end-to-end packet delivery services to its user, the transport layer. The network layer sends packets from the source network to the destination network based on the IP routing table. After the router determines which path to use, it can proceed with switching the packet. Switching involves taking the packet the router accepted on one interface and forwarding it to another interface or port that reflects the best path to the packet's destination. |
| Layer 3 address explanation | The network address contains both a path and a host portion. The path portion identifies a path part used by the router within the network cloud; the host portion identifies a specific device on the network. By using consistent end-to-end addressing to represent the path of media connections, the network layer can find a path to the destination without unnecessary use of devices or links on the network. |
| Types of ICMP Messages | Destination unreachable |
| PING | a router receiving a packet that it is unable to deliver to its ultimate destination; because of this the router sends an ICMP host unreachable message to the source. The message might be undeliverable because there is no known route to the destination. On the other hand, an echo reply that is a successful reply to a ping command. |
| ARP | If the MAC address is not known, the source must send out an ARP request. To determine a destination address for a datagram, the ARP table on the router is checked. If the address is not in the table, ARP sends a broadcast looking for the destination station. Every station on the network receives the broadcast. |
| 2 basic operations of Router | a path determination function and a switching function. |
| Static Route | Static routing is administered manually. A network administrator enters route into the router's configuration. The administrator must manually update this static route entry whenever a network topology change requires an update. Static routing reduces overhead because routing updates are not sent (in the case of RIP, every 30 seconds). |
| Dynamic Route | Dynamic routing works differently. After the network administrator enters configuration commands to start dynamic routing, route knowledge is updated automatically by a routing process whenever new information is received from the network. Changes in dynamic knowledge are exchanged between routers as part of the update process. |
| Stub Network | When a network is accessible by only one path, a static route to the network can be sufficient. This type of partition is called a stub network. Configuring static routing to a stub network avoids the overhead of dynamic routing because routing updates are not sent. |
| Default Route | The default route can be reached by any unknown destination by directing the packet to the Internet. |
| Routed Protocol | Any network protocol that provides enough information in its network layer address to allow a packet to be forwarded from host to host based on the addressing scheme. Routed protocols define the format and use of the fields within a packet. Packets generally are conveyed from end system to end system. IP is an example of a routed protocol. |
| Routing Protocol | A protocol that supports a routed protocol by providing mechanisms for sharing routing information. Routing protocol messages move between the routers. A routing protocol allows the routers to communicate with other routers to update and maintain tables. TCP/IP examples of routing protocols are Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP), Enhanced Interior Gateway Routing Protocol (Enhanced IGRP), and Open Shortest Path First (OSPF) protocol. |
| Successful Dynamic Routing | Maintenance of a routing table |
| Routing Protocols Define | The set of rules used by a router when it communicates with neighboring routers. For example, a routing protocol describes: |
| Types of Routing Protocols | RIP-A distance-vector routing protocol |
| Autonomous System | Collection of networks under a common administration sharing a common routing strategy. Autonomous systems are subdivided by areas. An autonomous system must be assigned a unique 16-bit number by the IANA. Sometimes abbreviated AS. |
| Distance Vector | Distance vector routing algorithms call for each router to send its entire routing table in each update, but only to its neighbors. Distance vector routing algorithms can be prone to routing loops, but are computationally simpler than link state routing algorithms. |
| Link State | (also called the shortest path first [SPF] protocol) approach re-creates the exact topology of the entire network (or at least the partition in which the router is situated). |
| Convergence | The speed and ability of a group of internetworking devices running a specific routing protocol to agree on the topology of an internetwork after a change in that topology. |
| Ethernet Problems | The data frame broadcast delivery nature of Ethernet/802.3 LANs |
| Latency | 1. Delay between the time a device requests access to a network and the time it is granted permission to transmit. |
| Half-Duplex | Each Ethernet host checks the network to see whether data is being transmitted before it transmits additional data. If the network is already in use, the transmission is delayed. Despite transmission deferral, two or more Ethernet hosts can transmit at the same time, which results in a collision. |
| Network Congestion | As more people utilize a network to share large files, access file servers, and connect to the Internet, network congestion occurs. This can result in slower response times, longer file transfers, and network users becoming less productive due to network delays. |
| Bandwidth | The difference between the highest and lowest frequencies available for network signals. The term is also used to describe the rated throughput capacity of a given network medium or protocol. |
| Transmission Times | Transmission time equals the number of bits being sent times the bit time for a given technology. Another way to think about transmission time is as the time it takes a frame to actually be transmitted (small frames take a shorter amount of time, large frames take a longer amount of time to be transmitted). |
| Attenuation | attenuation means that the signal weakens (that is, attenuates) as it travels through the network. Attenuation is caused by the resistance in the cable, or medium. An Ethernet repeater is a physical-layer device on the network that boosts or regenerates the signal on an Ethernet LAN. |
| Collision Domains | In Ethernet, the network area within which frames that have collided are propagated. Repeaters and hubs propagate collisions; LAN switches, bridges and routers do not. |
| Broadcast Domains | The set of all devices that will receive broadcast frames originating from any device within the set. Broadcast domains are typically bounded by routers because routers do not forward broadcast frames. |
| Segmentation | 1.) Section of a network that is bounded by bridges, routers, or switches. |
| Segmenting with Bridges | Bridges "learn" a network's segmentation by building address tables that contain the address of each network device and which segment to use to reach that device. Bridges are Layer 2 devices that forward data frames according to the frames' Media Access Control (MAC) addresses. In addition, bridges are transparent to the other devices on the network. |
| Segmenting with Routers | Routers create the highest level of segmentation by forwarding data to the hub, to which workstations are connected. A router makes forwarding decisions to segments by examining the destination address on the data packet and looking in its routing table for forwarding instructions. A router must examine a packet to determine the best path for forwarding that packet to its destination. This process takes time. |
| Segmenting with Switches | A switch can segment a LAN into microsegments, which are single host segments. This creates collision-free domains from one larger collision domain. Although the LAN switch eliminates collision domains, all hosts connected to the switch are still in the same broadcast domain. |
| 2 basic operations of a switch | Switching data frames-This happens when a frame arrives on an input media and is transmitted to an output media. |
| 2 switching methods | There are two methods of switching data frames-Layer 2 and Layer 3 switching. Switching is the process of taking an incoming frame from one interface and delivering it out through another interface. Routers use Layer 3 switching to route a packet; switches (Layer 2 switches) use Layer 2 switching to forward frames. |
| Microsegmentation | Division of a network into smaller segments, usually with the intention of increasing aggregate bandwidth to network devices. (ie: hubs and switches) |
| Symmetric switching | Symmetric switching is one way to characterize a LAN switch according to the bandwidth allocated to each port on the switch. A symmetric switch provides switched connections between ports with the same bandwidth, such as all 10-Mbps ports or all 100-Mbps ports. |
| Asymmetric switching | Asymmetric switching makes the most of client/server network traffic flows where multiple clients are communicating with a server at the same time, requiring more bandwidth dedicated to the switch port that the server is connected to in order to prevent a bottleneck at that port. |
| Buffering | The area of memory where the switch stores the data is called the memory buffer. This memory buffer can use two methods for forwarding packets--port-based memory buffering and shared memory buffering. |
| Store and Forward | Store-and-forward-The entire frame is received before any forwarding takes place. The destination and/or the source addresses are read and filters are applied before the frame is forwarded. Latency occurs while the frame is being received; the latency is greater with larger frames because the entire frame takes longer to read. Error detection is high because of the time available to the switch to check for errors while waiting for the entire frame to be received. |
| Cut Through | The switch reads the destination address before receiving the entire frame. The frame is then forwarded before the entire frame arrives. This mode decreases the latency of the transmission and has poor LAN Switching error detection. Fast-forward and fragment-free are two forms of cut-through switching |
| VLAN | A VLAN is a logical grouping of network devices or users that are not restricted to a physical switch segment. The devices or users in a VLAN can be grouped by function, department, application, and so on, regardless of their physical segment location. A VLAN creates a single broadcast domain that is not restricted to a physical segment and is treated like a subnet. VLAN setup is done in the switch by software. |
| Spanning Tree Protocol | to allow duplicate switched/bridged paths without incurring the latency effects of loops in the network. Bridges and switches make their forwarding decisions for unicast frames based on the destination MAC address in the frame. If the MAC address is unknown, the device floods the frame out all ports in an attempt to reach the desired destination. |
| Spanning Tree Protocol States | Blocking-No frames forwarded, BPDUs heard |
