Network Devices

Lecture 2

Cabling Computer to computer – crossover

cable Computer to hub – straight-through

cable Hub to switch or Hub to hub

MDI-X port to MDI port – straight-through MDI port to MDI-X port – straight-through MDI-X port to MDI-X port – cross-over

LEDs Light emitting diodes Present on both hubs, switches,

and routers Green – live connection at that

port on that piece of equipment Flashing green – activity (traffic) Amber – problem Red or no light – not working

Managed v. Unmanaged

Applies to both switches and hubs Has an interface that can be

configured Speed VLANS (switches)

Number of Ports

Hubs and Switches 8 16 24 32

Packet

Network Header Data

The protocol data unit that is transmitted over a WAN or between LANs when using a router.

IP Address Logical Address or Network

Address #.#.#.#

Routers Intelligent network device Has CPU built in Determines best path for

packet to get to destination Bases decision on IP address

Synonyms – logical address, network address

Refers to its routing table to make decisions about which port to send the packet

Configurable Can connect two LAN

segments Can connect a LAN to a WAN

AUI ports – notice the transceivers on the second router on the rack.

Serial ports to connect LAN to WAN

Routable (Routed) Protocols

Responsible for sending messages between nodes.

IP – Internet Protocol (part of the TCP/IP protocol suite

IPX/SPX – Novell – going away; replaced by IP

Appletalk – MacIntosh – replaced by IP

NetBeui

This network protocol is non-routable.

Routing Protocols Routing protocols route routable protocols Responsible for updating routing tables

between routers so they can know the topology of the network and determine best path. Routing tables – lists of networks and the

associated port to each network Routing can be dynamic (automatic) or

administrator can configure a static route.

Routing Table Example

Network Interface

192.5.5.0 E0

205.7.5.0 E1

201.100.11.0 S0

S0

Network201.100.11.1

E1

Network205.7.5.0

Network 192.5.5.0

E0

Routing Protocols

Distance Vector Link State

Distance Vector Routers send routing table updates to

each neighboring router periodically. Examples

RIP (Routing Information Protocol) IGRP (Interior Gateway Routing Protocol)

Movement from one router to the next is considered a “hop.”

DV metric (measurement) is “hops.” Lower number of hops is better – determines

best path

DV Disadvantage

Each router transmits its entire routing table every 30 seconds (RIP) creating a lot of network traffic.

Convergence

The amount of time needed for all routers in a network to have common knowledge – routing tables all have the same information in them.

Routing LoopsA

C

D

E

B

Network 1

At first, all routers have common routing tables.

Network 1 goes down. Router E sends its routing table without Network 1. Router A updates its routing table. At the next update (after 30 seconds), Router A sends its table to D and B. They have to update their tables. Meanwhile, Router C doesn’t have the update about Network 1 so it sends its table to D & B. D may assume that there’s another path through C -> B to Network 1 so it updates its table. Next round, it updates Router A. Router A assumes there is another path. Now they all have inaccurate information and the loop continues.

Split HorizonA

C

D

E

B

Network 1

Split horizon will not allow an update from the opposite direction of the first update. So, A notified D and B and they cannot send erroneous tables back to A thereby preventing routing loops.

Link State Protocols Examples

OSPF – Open Shortest Path First NLSP – Network Link State Protocol

When network is installed and OSPF configured as the routing protocol, OSPF uses LSAs (Link State Advertisements) to collect information about the network and build a database of the entire topology.

During the initial stage where it is learning the topology, the process causes a lot of activity on the network. After the database is built and best paths chosen, traffic is minimized because updates only occur when there is a topology change, (for example, a network goes down) and LSAs are exchanged to make the update in the database.

Disadvantage Requires more RAM to store the database than DV protocols.

Server-based Routers

Servers can have two NICS installed and act as a limited router.

Brouter

Device that can function as both a router and a bridge depending upon the protocol of the message. If it is a routable protocol, it routes it. If the message protocol is an Ethernet protocol, it either forwards it or blocks it (functions as a bridge).

Gateways

A device, system, or software that can perform the function of translating data from one protocol to another (TR to Ethernet), and one format to another.

Usually a server. Slows network traffic because of

translation time.

CSU/DSUs

Channel Service Unit/Digital Service Unit

Changes signal from one digital format to another.

ISDN Terminal Adapters

Translates digital signal between two digital formats.

Modem

Modulator/Demodulator Translates from digital to analog

and back. 56 kbps maximum connection

speed. Actual transfer speed is less – around 43 kbps.

Two Factors that Determine Modem Connection Speed

Maximum connection speed of the Universal Asynchronous Receiver/Transmitter (UART) chip

Actual modem speed

UART Chips & Speeds

Chip Speed bps 8250 9600 16450 115200 16550 115200 16650 430800 16750 921600 16950 921600

Modem Commands to Know

ATA – Answers incoming call ATH – Hangs up current connection ATZ – Resets the modem ATI3 – Displays modem id info