Network Chapter 4

Start-of-Frame Delimiter (SFD)

(1 byte) the SFD identifies the beginning of the data field.

Destination Address (DA)

(6 bytes) This is the MAC address of the computer to which the frame is being transmitted; it can be a unicast, multicast, or broadcast.

10Base-FL

802.3j, Fiber, 2,000 (m)

10Base-F

802.3j, Fiber, 2000 (m)

10Base-FP

802.3j, Fiber, 500 (m)

100Base-T4

802.3u, CAT3, 4, or up to 5 UTP, 100 (m)

Network Controllers

Support large-scale interactive networks and communication between set-tops and application servers. Set-top is an information appliance device that contains a television-tuner input and displays output to a television set. Used in digital cable networks and enable such services as video-on-demand (VOD), catalog shopping, web browsing and email.

Bridge

computer networking device that creates a single aggregate network from multiple communication networks or network segments. This function is called network bridging. Bridging is distinct from routing, which allows multiple different networks to communicate independently while remaining separate

Ethernet Frames

data packet that has been encoded at the Data Link (Layer 2)for transmission from one node to another in an Ethernet network.

Small Form Factor Pluggable (SFP)

most commonly used in 2 Gbps and 4 Gbps Fiber Channel components to interconvert electrical signals and optical signals. Are similar to GBICs (gigabit interface converter) in their architecture. Allow higher port density that GBISs.

Gigabit Ethernet

technology that can transmit data at speeds of 1000 Mbps and primarily uses optical fibers for transmission. Ranging from 500 to 5000 meters depending on the type of optical fiber used. Ever expensive.

IEEE 802.3at

• Easier control over the power of remotely connected devices, which leads to better overall network power management. • Enables easy building-wide power back-up of critical systems; for example, all VoIP telephones, security cameras, etc. can be supplied with redundant power during power outages and brownouts via their network connections alone. • Lower cabling cost because no additional wiring is needed to support powering the remote device. • Lower installation costs because a licensed electrician is not needed to run data cable, nor must the installation be officially inspected. Power over Ethernet Plus (PoE+)

Frame Type

(2 bytes) This is the length of the entire Ethernet frame in bytes, or the frame type ID of the frame. This field can hold a value between 3 and 65,534, but the maximum value is usually less than 1,500.

Allows for a broader range of devices to be powered such as:

1) Cameras with pan/tilt/zoom capabilities 2) Door controllers 3) Point of sale terminals

10 Base-5

802.3, ThinNet coax, 500 (m)

10Base-2

802.3a, ThinkNet coax, distance 100 (M)

10Base-T

802.3i, CAT5 UTP, 100 (m)

10Base-FB

802.3j, Fiber, 2,000 (m)

100Base-TX

802.3u, CAT5 UTP or STP, 100 (m)

Partial Mesh

A variation of the mesh topology in which only a few nodes have direct links with all the other nodes. All nodes have direct links with others. Less complex, less expensive, contains fewer redundancies than a full mesh topology. sometimes referred to as a redundant star.

Extended-Star (Or star-of-Star)

Connecting the central nodes of two or more star networks with a new common node. To move data from one subnetwork to another, it must be forwarded through the new common node. Extended star topologies are commonly found in LANs.

Core Routers

Core routers located at the center of network backbone. They are used to connect multiple distribution routers located in different buildings to the backbone.

Forwarding

Data is sent and received on a port in this state. BPDUs are monitored to determine if the port should return to the blocked area.

IEEE 802.11

Describes Layer 1 and Layer 2 specifications for Wireless LANs in the 2.4-, 3.6-, 5- and 60-GHz frequency bands. Numerous amendments to the standards have been adopted as Wi-Fi technology has evolved.

Ethernet Frame Field

Description

NOTE

Routers are often referred to as default gateways or hops.

Distribution Routers

Routers that collect data from multiple access routers and redistribute them to an enterprise location such as a company's headquarters. The routing capabilities of a distribution router are greater then those of access routers.

MAC assresses

Use hexadecimal number system Positional numeral system with a base of 16 values 10 to 15 Broadcast MAC address notation is FF:FF:FF:FF:FF:FF. Each F in the hexadecimal notation represents four ones in the binary address.

Broadcast Domain

network segment on which broadcasts occur. Microsegmentation will not stop broadcasts. Switches flood broadcast out all ports by default, a single switch, or any number of switches connected together, comprise a single broadcast domain. Routers block broadcast by default. If the router has two Ethernet interfaces, network has two broadcast domains, one on either side of the router.

Access Routers

routers used in small office/home office (SOHO) networks. They are located at customer sites and are inexpensive.

PoE-Power over Ethernet

uses the IEEE 802.3af standard for transferring both electrical power and data to remote devices over twisted pair cable in an Ethernet network. Place device such as network switches, Voice over IP (VoIP) phones, wireless access points, and cameras in locations where it would be inconvenient or impossible to run electrical power for the device. Provides up to 15.4 W of power. Requires CAT5 or higher copper cable. IEEE 802.3at standard also know as Power over Ethernet + (PoE+), provides up to 25.5 W of power per port. backward compatible. Needed DC power onto the Ethernet cable that leads to the connected device.

Microsegmentation

which all nodes are logically separated from each other until there is a need to connect them. Switch listens to the transmissions of all of the nodes plugged into it ports. Learns MAC addresses of each of the nodes and puts those MAD addresses into a table in memory.

Source Address (SA)

(6 bytes) this is the MAC address of the computer transmitting data-the SA is always a unicast address.

Bus data transmitted sequence

*Each node on a bus listens passively to the channel until it receives a signal. Data signal passes by every node, but not through the node. *The node transmits data when the bud is free. First come, First serve *If two nodes try to transmit data at exactly the same time, a collision occurs on the wire. 32-bit jam signal is sent to indicate that a collision has occurred. Node waits random period of time before retransmission in order to avoid further collision. *Transmission fills the entire media of the bus, moving nearly instantaneously along the entire pathway. each node examines the destination MAC address to determine whether or not the transmission is intended for it and whether or not it should process the transmission. *The destination node picks up the transmission. *if none of the nodes accept the transmitted data, such as in the case of the destination node being switched off, the data packet is absorbed by the terminator.

NIC can be

1) Built into the motherboard of a computer or other network devices 2) Internally connected to a computer by using one of the expansion slots on the computer's motherboard. 3) Externally connected to a computer or other network device by using a USB, CompactFlash, or Firewire port

1000Base-T 1000Base-TX 1000Base-X 1000Base-CX 1000Base-SX 1000Base-LX 1000Base-LX 1000Base-LH 1000Base-LH

802.3ab, CAT5/CAT6 UTP, 100 Meters 802.3ab, CAT 6 UTP/CAT 7 UTP, 100 meters 802.3z, Shielded/Balanced coax, 25 to 5000 meters 802.3z, Shielded/Balanes coax, 25 meters 802.3z, Multimode fiber/Wavelength: 850, 550 in prictice (220 per specification) 802.3z, Single mode fiber/Wavelength: 1300 nm, 5000 meter 802.3z, Miltimode fiber/Wavelength:1300 nm, 550 meter 802.3z, Single mode fiber/ Wavelength: 1300 nm, 10000 Meters 802.3z, Multimode fiber/Wavelength: 1300 nm, 550 meter

10GBase-T 10GBase-SR 10GBase-SW 10GBase-LR 10GBase-LW 10GBase-ER 10GBase-EW 10GBase-T 10GBase-CX4

802.3ae, Multimode fiber/Wavelength: 850 nm, 9.9 GBps, 65 Meters 802.3ae, Multimode fiber/Wavelength: 850 nm, 10.3 Gbps, 300 meters 802.3ae, Multimode fiber/Wavelength: 85- nm, 9.9 Gbps, 300 meters 802.3ae, Single mode fiber/Wavelength: 1310nm, 10.3, 10000 meters 802.3ae, Single mode fiber/Wavelength: 1310 nm, Speed 10.3Gbps, 10,000 meters distance, Dark Fiber 802.3ae, Single mode fiber/Wavelength: 1550 nm, 10.3 Speed, Distance 40000 meters 802.3ae, Single Mode fiber, Wavelength: 1500 nm, fiber, 9.9 speed, 40000 distance 802.0an, CAT5e, 6, or 7 UTP, 10 speed, 100 meters Four thin twin-axial, cabled 4x2.5 speed, 25 meters

100Base-T

802.3u, CAT5 UTP, 100 (M)

100Base-FX

802.3u, Miltimode or single mode fiber, 412 (Half duplex), 2000 (Full duplex), 15000-20000 (Full duplex)

Spanning Tree

A Layer 2 protocol used to prevent switching loops. Redundant paths between switchs, where either two switches are connected using two different links or a ring of switches is connected to each other. Switching loop will occur. The first Address Resolution. Feedback loop will continue network utilization to go to near maximum manual intervention by an administrator.

Multilayer

A switch performs both routing and switching. Lauer 3 switch or a Layer 2-3 switch. Only limited routing functions. supports only Ethernet connections. Multilayer switches support the configuration of virtual local area networks (VLANs). Like partition.

Star-Ring

Connecting the central nodes of multiple star networks in a ring. The data flow between different subnetworks is through this ring. Data is sent in a circular pattern around the star configurations. Star-ring topologies are commonly found in metropolitan area networks (MANs)

Fast Ethernet

Ethernet technology that can transmit data at speeds of 100 Mbps. Use either coaxial cables or optical figers. Interconnected several LANs.

NOTE

Hybrid topologies are typically not designed as such. They usually arise when administrators connect existing network implementations independently by using different topologies.

Fragment-Free

LAN switches are characterized by the forwarding method that they support, such as a store-and-forward switch, cut-through switch, or fragment-free switch. In the store-and-forward switching method, error checking is performed against the frame, and any frame with errors is discarded

Content

Supports load balancing among server groups and firewalls, and web cache and application redirection. make intelligent decisions about data packets in real times, and understanding the criticality and type of the request.

switches

That acts as a common connection point for various nodes or segments. Working at Layer 2 of the OSI model. Switch reads the destination MAC address from the header and consults its table to determine which port to repeat the frame out of. Switches can keep conversations limited to only the nodes that are involved. 24-port switch can have 12 pairs of conversations going on at the same time.

ThickNet

ThickNet, also known as 10BASE5 or IEEE 802.3-1985, is an Ethernet standard that requires a specialized coaxial cable to transmit Ethernet frames at a rate of 10Mbps. It derives its nickname, which is a portmanteau of "Thick Ethernet," from the thick coaxial cable it uses, which is 0.375 inches in diameter. The designation 10BASE5, assigned to the ThickNet standard by the Institute of Electrical and Electronics Engineers, provides a quick summary of the characteristics of its physical medium: "10" denotes its maximum data transmission rate of 10Mbps; "BASE" is shorthand for "baseband transmission," meaning the medium exclusively transmits Ethernet signals; and "5" means that it can transmit data at a maximum length of 500 meters before it experiences signal degradation.

Common uses for VLANS

Traffic management, especially to impact of broadcasting, which is a natural and unavoidable part of Ethernet working. Transmits a Layer 2 broadcast. Separate nodes based on traffic types and then need for Quality of Service

10Base Standards

a number indicating media speed the signal type (Baseband or broadband) a code for either copper or fiber media

MAC address

also called a physical address, is a unique, hardware-level address assigned to every networking device by its manufacturer. 6 bytes long. First 3 bytes uniquely identify the manufacturer and are referred to as the Organizationally unique identifier (OUI)

Hybrid Topologies

any topology that exhibits the characteristics of more than one standard topology. can be complex to maintain because they typically incorporate a wide range of technologies.

NICs

called a network adapter or network card, is a device that serves as an interface between a network node and the network. Connect to a network, whether wired or wireless, a node must have a NIC installed

Ring Topology

in which each node is connected to the two nearest nodes; the upstream and downstream neighbors. Flow of data in a ring network is unidirectional to avoid collision. All nodes in the network are connected to form a cirle. each node handles all data packets that pass through it. data moves in one direction through each node that scans data packets, accepts packets, destined for it, and forwards packets destined for another node. Acts as a repeater and boots the signal when it re-transmits the data packet. Ensures that the signal quality is high. potentially unreliable. Failure of a single node can bring down the entire network.

VLANs Virtual LAN

logical grouping of ports on the switch. An administrator determines which ports are grouped together.

switches

make forwarding decisions based on Layer 2 (MAC) addresses.

Multiplexer

manages individual signals and enables them to share the media

Logical Bus Topology

network topology in which nodes receive the data transmitted all at the same times, regardless of the physical wiring layout of the network. Star data appears to flow in a single, continuous stream from the sending node to all other nodes through the switch. Only one node can transmit at a time.

Logical Star Topology

running on a physical star topology is the single most common implementation in modern LANs

ThinNet

the name given to Ethernet networking that uses RG58/U or RG58A/U cabling. Wire in bus configuration where segments can be up to 185 meters (607 feet) long. Made with BNC connectors Devices connect with T-connectors Each end of the cable must be terminated with a 50-ohm resistor.

Frame Check Sequence (FCS)

(4 bytes) The FCS checks the frame by using a 32-bit cyclic redundancy check (CRC) value. The FCS allows the receiving device to detect errors in the Ethernet frame and reject it if it appears damage.

Preamble (PRE)

(7 bytes) a pattern of ones and zeros used to signal the start of the frame and provide synchronization and timing information. The preamble notifies all nodes that there is data to follow.

Data

(n bytes) The payload of the frame (or the information being sent). It must be a minimum of 46 bytes long and can be a maximum of 1,500 bytes. If the length of data is less than 46 bytes, the data field must be extended by adding a filler to increase the length to a minimum of 46 bytes

Client Mode

A switch cannot modify VLANs but will receive configuration information from other swithews

Listening

BPDUs are processed by the switch. It does not forward frames. it waits for information to determine if it should return to the blocked state. It does not up date the MAC tables.

Disadvantages of Bus Topology

Can be unreliable Entire bus fails of there is a break in the network cables Transmits data more slowly than the other topologies, only two nodes can communicate at any time

Trunking

Combined to increase bandwidth and reliability in a process called trunking. Also known as link aggregation, port bonding, port teaming, EtherChannel, and NIC bonding. Manufacturer-implemented techniques exist, IEEE 802.1AX-2008 defines a standard for ling aggregation. Link Aggregation Control Protocol (LACP) provides a method to control the bundling of several physical ports together to form a single logical channel. Allows a network device to negotiate an automatic bundling of links by sending LACP packets to the peer. Allow redundant links to combine their bandwidth together without causing spannig tree loop. Linking two 1-Gbps ports on a switch can result in 2 Gbps aggregate throughput. Can result in a redundant connection in case one of the cables or ports fails.

Analog Modems

Device that modulates signals to encode digital information and demodulates signals to decode the transmitted information. Digital data of a device and turns it into modulated electrical signal for transmission over telephone lines.

Cut-through

In computer networking, cut-through switching is a method for packet switching systems, wherein the switch starts forwarding a frame (or packet) before the whole frame has been received, normally as soon as the destination address is processed. no error checking.

Repeater

In digital communication systems, a repeater is a device that receives a digital signal on an electromagnetic or optical transmission medium and regenerates the signal along the next leg of the medium. In electromagnetic media, repeaters overcome the attenuation caused by free-space electromagnetic-field divergence or cable loss. A series of repeaters make possible the extension of a signal over a distance

Transceivers

Is a device that has both a transmitter and a receiver integrated into it. Both send and receive data

NOTE

It is important not to confuse a gateway with the defauly gateway in TCP/IP, which just forwards IP data packets.

STP-Spanning Tree Protocol

Layer 2 Protocol used to prevent switching loops. Redundant paths between switches, where either two switches are connected using two different links or a ring of switches is connected to each other, a switching loop will occur. By thier name, flood broadcasts and multicasts out all ports, the first Address Resolution Protocol (ARP) frame sent by a client trying to find a neighbor or a router will cause a Layer 2 broadcast storm. Feedback loop will continue indefinitely until there is manual intervention by an administrator. Cause network utilization to go to near maximum capacity, CPU utilization of the switches to jump to 80 percent. replaced by spanning tree protocol.

Star-Bus Hybrid Topology

Linking the central nodes of several star networks by using a common bus, or network backbone. Inside each subnetwork, data flows as it would on a star network, and each of these star network is trated as a node on the larger bus network. To move data from one subnetwork to another, it must be placed on the common bus.

IEEE 802.2

Logical Link was developed to address the need for MAC sub-layer addressing in switches. The standard specifies the frame size and transmission rate. Frames can be sent over Ethernet and Token ring networks by using either copper or fiber media

Logical Ring Topology

Network Topology in which each node receives data only from its upstream neighbor and retransmits data only to its downstream neighbor, regardless of they physical layout of the network. been implemented as a physical star (Physical star-logical ring) Token ring, central hub would connect the devices in a star shape. Wiring was such that the electrical path was actually a never-ending loop, passing from the hub to a node, back to the hub, to another node, back to the hub, and so forth.

Physical Mesh Topology

Network topology in which each node is directly connected to every other node, similar to the physical point-to-point topology Allows each node to communicate with multiple nodes at the same time. Dedicated links with other nodes. data travel very fast extremely reliable provide reliable communication between independent networks.

NOTE

The OUI may also be called the block ID and the universal LAN MAC address may also be called the device ID.

Blocking

User data is not sent or received. BPDU data is received, but the port only goes into another state if other links are unavailable and the spanning tree algorithm determines that the port should change to the forwarding state.

Gateways

a generic term for any device or software that translates one network protocol to another. OSI Layer 3 or above. Stripping off the Layer 2 Ethernet encapsulation and replacing it with token ring encapsulation. Gateways can strip off entire protocol stacks. Transmission control Protocol/Internet Protocol (TCP/IP) stack and replacing it with Internetwork Packet eXchange/Sequenced Packet eXchange (IPX/SPX)

Hub

a network hardware device for connecting multiple Ethernet devices together and making them act as a single network segment. It has multiple input/output (I/O) ports, in which a signal introduced at the input of any port appears at the output of every port except the original incoming.[1] A hub works at the physical layer (layer 1) of the OSI model.[2] Repeater hubs also participate in collision detection, forwarding a jam signal to all ports if it detects a collision. In addition to standard 8P8C ("RJ45") ports, some hubs may also come with a BNC or Attachment Unit Interface (AUI) connector to allow connection to legacy 10BASE2 or 10BASE5 network segments.

Disable

a port that has been manually disabled.

Ethernet (IEEE 802.3)

a set of networking technologies and media access methods specified for LANs. Enables computers to communicate over small distances using a wired medium. Specifications for Ethernet including both OSI Layer 1 and Layer 2 Protocols.

Firewalls

a software program or a hardware device or a combination of both that protects a device or network from unauthorized data by blocking unsolicited traffic. Configured to block suspicious or unsolicited incoming traffic.

Transportation Mode

a switch receives configuration messages from other switches but does not process them.

Gigabit Interface Converter (GBIC)

a transceiver used to convert electrical signals into optical signals and vice versa. Used as an interface for high-speed networking and to upgrade the network, without needing to replace all components in the motherboard.

Dual Ring Topology

allows the use of two counter-rotating rings, in which each ring carries data in a opposite direction. Configuration are faster. in case of a breakage in the inner or outer ring, the two nodes on either side of the break connect the two rings together, closing the loop into a single ring. automatically reconfigured to a single-ring data flow. Reduce down time.

10 Gigabit Ethernet

currently the highest speed at which Ethernet operates. Achieve speeds of 10 Gbps, which is 10 times faster than Gigabite Ethernet.

Physical Topologies

describes a network's physical wiring layout or sharpe, whereas a logical topology describes the paths through which data moves. Common physical Topologies: Bus, ring, star, mesh

VLAN Pooling

is a mechanism whereby WAPs can choose among several different available VLANSs to assign to incoming client connections.

IEEE 802.1q

is the most commonly used trunk link protocol to addresss this issue 802.1q inserts a special tag in the Ethernet header identifying the VLAN for that frame.

Collision Domain

network segment in which a collision can happen. Nodes contend for access to the same physical medium. Occurs on a logical bus. Transmission of a single node is heard by all nodes. Logical Bus. Switch effectively eliminates collision. Port on the switch becomes its own collision domain because it will forward traffic to only the one recipient that is connected to it. 24-port switch will effectively have 24 collision domains.

Physical Bus Topology

network topology in which the nodes are arranged in a linear format. T-connector connects each node directly to the network cable Attachning a terminator at both ends of the network cable prevents a condition called signal bounce. Signal Bounce- signals endlessly move from one end of the wire to the other.

Physical Star Topology

network topology that uses a central connectivity device, such as a switch, with individual physical connections to each nodes. Send data to the connectivity device, and the device then forwards data to the appropriate destination node. single failed node does not bring down the whole network. If the central connectivity device fails, the entire network fails. Common in Client/server networks

Routers

networking device that connects multiple networks. Operating at Layer 3 of the OSI model. Layer 3 addresses, such as Internet Protocol (IP) addresses. Strip off the packet's layer 2 encapsulation and replace it with encapsulation that is appropriate for the outgoing transmission.

Learning

source addresses from received frames. Addresses are added to the Switching database. MAC address table is updates. No frames are forwarded.

IEEE 802.3af

standardizing existing practice for spare-pair (Alternative B) and common-mode data pair power (Alternative A) transmission, the IEEE PoE standards provide for signalling between the power sourcing equipment (PSE) and powered device (PD). This signaling allows the presence of a conformant device to be detected by the power source, and allows the device and source to negotiate the amount of power required or available. Up to 25.5 W is available for a device. Power over Ethernet or PoE describes any of several standardized or ad-hoc systems which pass electric power along with data on twisted pair Ethernet cabling. This allows a single cable to provide both data connection and electric power to devices such as wireless access points and IP cameras.

Termination

the application of a resistor or other device to the end of the cable. adding a terminator ensures that the ends or the cable do not represent an abrupt change in impedance. Match the impedance of all devices and cables to achieve proper signal flow.

Port Mirroring

the practice of duplication all traffic on one port in a switch to a second port. Effectively sending a copy of all the data to the node connect to the second port. Know as local port mirroring. Remote port mirroring implements port mirroring between multiple devices.

Store-and-Forward

the switch receives a frame on a port and stores the frame in it's memory buffer until the frame has been completely received. The switch analyzes the frame for information about its destination and uses CRC (cyclic redundancy check) a mathematical formula based on the number of 1 bits in the frame to decide whether the frame has an error. After confirming its integrity the frame is forward out the correct port and toward its destination. If a frame is corrupted the switch discards it and less bandwidth is wasted on the unusable frame. Some other useful information about store and forward switching is it is required for QoS (Quality of Service).

Server Mode

this is the default mode for VTP on a switch.

VTP- VALN Trunking Protocol (VTP)

tje messaging protocol that switches use of updated each other's VLAN databses

IEEE 802.3

working group and a collection of IEEE standards produced by the working group defining the physical layer and data link layer's media access control (MAC) of wired Ethernet. This is generally a local area network technology with some wide area network applications Most efficient in a physical Star-Logical bus topology.