Computer Networks UNISA - Chap 6 – Network Hardware

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After reading this you should be able to

• Identify the functions of LAN connectivity hardware
• Install, configure, and differentiate between network devices such as NAIC’s, hubs, bridges, switches, routers, and gateways
• Explain the advanced features of a switch and understand popular switching techniques, including VLAN management
• Explain the purposes and properties of routing
• Describe common IPv4 and IPv6 routing protocols

NICs (Network Interface Cards)

• Are connectivity devices that enable a workstation, server, printer, etc. to receive and transmit data over the network media
• Most NICs contain a data transceiver (the device the transmits and receives data)
• NIC’s belong to both the Physical and Data Link layer of the OSI model because they issue signals to a wire or into the atmosphere and they receive data frames
• They perform the routines that determine which node has the right to transmit data over a network at any given instant – e.g. CSMA/CD on Ethernet
• Many NICs can also perform prioritization, network management, buffering, and traffic-filtering functions
• NICs do not analyse information added by the protocols in Layer 3 through to Layer 7 of the OSI model

Types of NICs

NICs come in a variety of types depending on the following…

• The access method  (Ethernet vs. token ring)
• Network transmission speed (100 Mbps, vs. 1 Gbps)
• Connector interfaces (RJ-45 vs. SC)
• Type of compatible motherboard or device (PCI)
• Manufacturer (3Com, Adaptec, etc.)

NICs that are installed on expansion slots

NICs can be installed via internal or external bus

Internal Bus (In order of speeds)

• ISA
• PCI (Peripheral Component Interconnect)
• PCIe (Peripheral Component Interconnect Express)

Peripheral (External) Bus

• PCMCIA (Personal Computer Memory Card International Association) – two flavours, CardBus or ExpressCard
• USB (Universal Serial Bus) – USB1, USB2 & USB3
• FireWire – old version supports up to 400 Mbps, new version supports up to 3 Gbps
• CompactFlash – slower than the rest, not common, more for smaller devices such as camera’s or PDA’s

On-board NICs

• Some devices are connected directly to the motherboard, this is common with laptops and new computers
• The advantage to using an on-board NIC is that it saves space and frees  expansion slots for additional peripherals

Wireless NICs

• NICs are designed for use with either wired or wireless networks. Wireless NICs contain antennas to send and receive signals
• One disadvantage to using wireless NICs is that they are more expensive than wired NICs

Installing NICs

Note – this is quite an in depth section in the book, however I am not sure on its appropriateness for the subject, so I am excluding it from my summary. That said, check on the exam outline if it is necessary to study.

Repeaters and Hubs

Repeaters

• The simplest type of connectivity devices that regenerate a digital signal
• Repeaters operate in the Physical layer of the OSI model thus have no means to interpret data the retransmit
• A repeater is limited not only in function, but also in scope – it contains one input port and one output port so it is capable of receiving a single data stream
• Repeaters are suited only to bus topology networks
• Advantage to repeaters is that it allows you to extend the range of a network inexpensively
• They are becoming less common as other devices that provide the same functionality and more become more affordable (i.e. switches)

Hubs

• A hub is a repeater with more than one output port
• It typically contains multiple data ports into which patch cables for network nodes are connected
• Hubs operate at the physical layer of the OSI model
• Most hubs also contain an uplink port that allows the hub to connect to another hub or connectivity device
• On Ethernet networks, hubs can serve as the central connection point for branches of a star or star-based hybrid topology
• Simplest types of hubs are known as passive hubs – do nothing but repeat signals
• More advanced hubs are called intelligent or managed hubs and can perform additional functions like filter data, provide diagnostic information, etc.
• Standalone hubs (workgroup hubs) are hubs that serve a group of computers that are isolated from the rest of the network or form their own small network
• One issue with hubs is that by merely repeating signals increases collisions and so most networks have replaced hubs with switches

Bridges

• A bridge is a device that connects two network segments by analysing incoming frames and making decisions about where to direct them based on each frame’s MAC address
• They operate at the Data link layer of the OSI model
• Bridges look like repeaters – they have a single input and a single output
• They differ from repeaters in that they can interpret physical addressing information
• Big advantage over hubs and repeaters is that they are protocol independent
• Bridges take longer to transmit data than hubs or repeaters because they examine the data being fed through
• Another advantage of bridges is that they extend the network without extending the collision domain
• Bridges can help improve network performance because they can be programmed to filter out certain types of frames
• To translate between two segment types, a bridge reads a frame’s destination MAC address and decides to either forward or filter it
• As nodes transmit data through the bridge, the bridge establishes a a filtering database (AKA forwarding table) of known MAC addresses and their locations on the network
• Bridges are almost extinct as the price of other technologies has decreased

Switches

• Switches are connectivity devices that subdivide a network into smaller logical pieces or segments
• Traditional switches operate on the Data Link layer of the OSI model
• More modern switches operate at Layer 3 or Layer 4 of the OSI model
• Switches interpret MAC address information
• Switches vary greatly in size and function
• Because switches have multiple ports, switches can make better use of limited bandwidth and prove more cost effective than bridges
• Each port on a switch acts like a bridge
• Switches provide at least two advantages over routers – better security (by isolating network segments) and better performance (by isolating one devices traffic from another)
• A disadvantage of switches if there is to much data being transferred, they can run out of buffer space

Switching Methods

Two basic switching methods exist

1. Cut-Through Mode – simply reads the MAC address in the header of the frame and decides whether to pass it through, does not examine any other data of the frame. Advantage is speed.
2. Store-and-Forward Mode – Reads entire data frame into memory and checks it for accuracy before transmitting it on. Store-and-Forward are more appropriate for larger LANs because they do not propagate errors however they are slower than cut through mode. Store-and-Forward mode is preferable in mixed speed environments

VLANs and Trunking

• Switches can also create VLANs (virtual local area networks) or logically separate networks within networks by grouping a number of ports into a broadcast domain
• A broadcast domain is a combination of ports that make up a Layer 2 segment. Ports in a broadcast domain rely on a Layer 2 device (like a switch) to forward broadcast frames among them
• In the context of a TCP/IP network, a broadcast domain is also known as a subnet

VLANs can link geographically distant users over a WAN, and create small workgroups with LANs. Reasons for VLANs include…

• Separating groups of users who need special security or network functions
• Isolating connections with heavy or unpredictable traffic patterns
• Identifying groups of devices whose data should be given priority handling
• Containing groups of devices that rely on legacy protocols incompatible with the majority of the network’s traffic

Trunking

• One switch’s interface can carry the traffic of multiple VLANs thanks to trunking
• A trunk is a single physical connection between devices through which many logical VLANs can transmit and receive data
• To keep data to each VLAN separate, each frame is identified with a VLAN identifier added to its header
• Trunking allows switches to make efficient use of their processing capabilities
• VLAN configuration can be complex, it requires careful planning to ensure all devices can exchange data that need to exchange data

STP (Spanning Tree Protocol)

• STP is used to eliminate the possibility of traffic loops, switches and bridges
• STP operates at the Data Link layers of the OSI model
• RSTP (Rapid Spanning Tree Protocol) is a new version of STP that is optimized compared to older slower versions
• STP is typically auto configured and does not need manual setup but can be customized

Content and Multilayer Switches

• Switches that operate anywhere from layer 4 and layer 7 are known as content switches or application switches
• There are few standards for these switches currently
• Higher layer switches cost substantially more than lower layer switches and are typically used on backbones and not in small contained LANs

Routers

• A router is a multiport connectivity device that directs data between nodes on a network
• Routers can integrate LANs and WANs running at different transmission speeds and using a variety of protocols
• Traditional standalone routers are being replaced by layer 3 switches

Characteristics

• A routers strength lies in its intelligence
• Routers can determine the shortest, fastest path between two nodes
• A typical router has an internal processor, an operating system, memory, input and output jacks for different types of networks
• A modular router (modem) is typically simple and inexpensive

All routers can do the following

• Connect dissimilar networks
• Interpret Layer 3 addressing and other information
• Determine the best path for data to follow from point A to point B
• Reroute traffic if a primary path is down but another path is available

• Interior routers – direct data between nodes on an autonomous LAN
• Border routers – connect an autonomous LAN with a WAN
• Static routing is a technique in which a network administrator programs a router to use specific paths between nodes

• Static routing is not optimal
• Dynamic routing automatically calculates the best path between two nodes and accumulates this information in a routing table
• Most networks use dynamic routing

Routing Protocols

Finding the best route for data to take across the network is one of the most valued and sophisticated functions performed by a router. There are various algorithms to determine the best path..

• Distance-Vector: RIP. RIPv2, BGP
• Link-State : OSPF, IS-IS
• Hybrid: EIGRP

It may be a good idea to add additional notes on these different algorithms from the book

Gateways and Other Multifunction Devices

Gateway is a term that can refer to one of many similar kinds of devices or interfaces in networking, so it is important to understand the context in which it is used.

• In broad terms, gateways are a combination of networking hardware and software that connect two dissimilar kinds of networks
• Gateways actually repackage information so that it can be read by another system
• Gateways can reside on servers, microcomputers, connectivity devices or mainframes

The following is a list of some common gateways

• Email gateway – translates messages from one type of email system to another
• Internet gateway – allows and manages access between LANs and the Internet
• LAN gateway – allows segments of a LAN running different protocols or different network models to communicate with each other
• Voice/data gateway – connects part of a network that handles data traffic with the part of the network that handles voice traffic
• Firewall – selectively blocks or filters traffic between networks