managing network connections. networking cables

Managing Network connections

Networking Cables

Network Cabling

Ethernet Topology

• Bus topology– Connects each node in a line– Has no central connection point

• Star topology– Connects all nodes to a centralized hub– More popular; easier to maintain

Ethernet Topology

Ethernet Using Star Topology

Ethernet Hub

Ethernet Using Star Bus Topology

Repeaters

• Devices that amplify signals on a network• Help overcome limitations on the length of

cables that can be used• Two kinds

– Amplifier repeater– Signal-regenerating repeater (used by Ethernet)

Repeaters

Wireless LANs (WLANs)• Make connections using a wireless NIC• Communicate directly or connect to a LAN by way of

a wireless access point (AP)• Popular where cables are difficult to install• Slower than wired networks• Security is an issue• Standards

– 1999 IEEE 802.11b (Wi-Fi, AirPort)– Bluetooth

Token Ring

• Physical star; logical ring• Transmits data at 4 Mbps or 16 Mbps• Uses a centralized device called a MAU

(Multistation Access Unit)• Less popular than Ethernet

Network Cards

FDDI

Token ring

Network Cards

Ethernet

Wireless

How NIC (Network Interface Card) Works

• Network card– Sends and receives data to and from system bus in parallel– Sends and receives data to and from network in series– Uses a transceiver for signal conversion

• Network in use is transparent to applications software using it

• Network nodes are identified by a MAC (Media Access Control) address

Ethernet Combo Card

Considerations When Selecting a Network Card

• Speed and type of network• Type of cable (shielded twisted-pair, coaxial,

or fiber-optic) – except for wireless connections

• Type of slot (PCI or ISA)

Segmenting a Network

• Decreases amount of traffic on overall network

• Done through use of bridges and switches– More intelligent than hubs; make decisions about

whether or not to allow traffic to pass, or where to forward that traffic

– Use MAC addresses, which they store in routing tables, to determine where to send packets

Bridges

Bridges and Switches• Bridges

– Send broadcast messages; not good for large networks

– Effective at separating high-volume areas on a LAN

– Work best when used to connect LANs that usually do not communicate outside their immediate network

• Switches– Send a packet only to network

segment for which it is destined

Bridges and Switches

Bridges Compared with Switches

MAC Addresses

• Unique addresses that are permanently embedded in a NIC and identify a device on a LAN

• Expressed as six pairs of hexadecimal numbers and letters

• A local address• Used at the lowest (physical) networking level for

NICs and other devices on the same network to communicate

MAC and IP Addresses

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• TCP/IP Overview• Configuring TCP/IP Clients• Using TCP/IP Utilities

Network Address Translation

• Uses a single public IP address to access the Internet on behalf of all hosts on the network using other IP addresses

• Proxy server sometimes does double duty as a firewall

Proxy Server

Connecting Networks with Routers• Responsible for data

traveling across interconnected networks

• Use IP addresses to determine path for packet

• Stateless devices• Transmit data packet to a

remote network only if data packet is a routable protocol

Using Routers to Connect Networks Web browser in Chennai

Web server in Newyork

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TCP/IP Overview

• Transmission Control Protocol/Internet Protocol (TCP/IP) is an industry-standard suite of protocols used on local area networks (LANs) and wide area networks (WANs).

• Microsoft Windows supports TCP/IP.

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Architectural Overview of the TCP/IP

33

The TCP/IP Protocols

• The TCP/IP protocols – Provide networking connectivity support for

computers (called hosts) on LANs and WANs – Follow a set of standards for how computers

communicate and how networks are interconnected

– Follow the four-layer Department of Defense (DOD) model

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Application Layer • Software programs gain access to the network

through the application layer.• This layer maps roughly to the session,

presentation, and application layers of the Open Systems Interconnection (OSI) model.

• The following TCP/IP utilities and services run at the application layer:– Hypertext Transfer Protocol (HTTP)– File Transfer Protocol (FTP)– Simple Mail Transfer Protocol (SMTP)

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Application Layer (Cont.)

• TCP/IP utilities and services that run at the application layer (Cont.): – Telnet– Domain Name System (DNS)– Simple Network Management Protocol (SNMP)

• Microsoft TCP/IP provides two interfaces for applications to use:– WinSock– Network Basic Input/Output System (NetBIOS)

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Transport Layer

• Transport protocols – Provide communication sessions between computers – Define the type of transport service as either

connection-oriented or connectionless datagram-oriented

• This layer maps roughly to the transport layer in the OSI model.

• The transport layer protocols are– TCP: connection-oriented, reliable– UDP: connectionless, no guarantee of packet delivery

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Internet Layer • The Internet layer protocols encapsulate

transport layer data into units called datagrams, address them, and route them to their destinations.

• This layer maps roughly to the network layer in the OSI model.

• Windows implements three main protocols at this layer:– Internet Protocol (IP)– Address Resolution Protocol (ARP)– Internet Control Message Protocol (ICMP)

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Link Layer

• This layer sends and receives frames, which are packets of information transmitted on a network as a single unit.

• The link layer is equivalent to the data-link and physical layers of the OSI model.

• Two protocols often used for WAN connections are part of the TCP/IP suite:– Point-to-Point Protocol (PPP)– Serial Line Internet Protocol (SLIP)

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Transmission Control Protocol • Transmission Control Protocol (TCP) is a

reliable, connection-oriented delivery service.• TCP achieves reliability by using a system

called positive acknowledgment with retransmission.

• Many Internet client applications, such as Web browsers and FTP clients, rely on TCP to transmit files.

• Virtually every application that transmits large amounts of data over a network uses TCP.

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User Datagram Protocol (UDP)

• Provides a connectionless datagram service that does not guarantee delivery or correct sequencing of delivered packets

• Used by applications that – Do not require an acknowledgment of data receipt – Usually transmit small amounts of data at one time

• Used by – Broadcast transmissions – Services and applications such as DNS, Dynamic Host

Configuration Protocol (DHCP), and SNMP

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Internet Protocol

• Internet Protocol (IP) does the actual delivery of datagrams.

• IP adds the following header fields to each packet:

Source IP Address Destination IP Address Protocol

Checksum Time to Live (TTL)

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IP Addressing • Every host on a TCP/IP network must have a

unique IP address (a 32-bit number that identifies both the host and the network the host is located on).

• IP addresses are expressed in dotted-decimal format, such as 192.168.123.132.

• Each set of four dotted-decimal numbers represents eight bits of the binary address. – The addresses range from 00000000 to 11111111,

or, in decimal notation, from 0 to 255.

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IP Addressing (Cont.) • An IP address is accompanied by a subnet mask.• The subnet mask, when compared to the IP address,

identifies the part of the IP address that is the network identifier and the part that is the host identifier.– The 1s identify network bits and the 0s identify host bits.– In the subnet mask 255.255.0.0, the first 16 bits (2 octets)

are the equivalent of all ones in binary form.• The first two octets of the IP address are the network identifier.• The last two octets represent the host identifier.

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Why IP Address?• To communicate on the Internet, a computer must use an IP

address that is registered with the Internet Assigned Numbers Authority (IANA).– In practice, you obtain a valid network address from your Internet

service provider (ISP), not directly from the IANA.• The IANA assigns network identifiers only; the administrator

assigns a unique host identifier to each computer.• There are three primary classes of network addresses: A, B,

and C. – The actual class used is based on the size of the network.– Each address class has a different default subnet mask.

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IP Address Classes

47

IP Address Class Characteristics

• You can identify the class of an IP address by looking at the value of its first octet.

• Because a Class A address uses only eight bits for its network ID, only 126 possible Class A addresses exist.

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Guidelines for IP Address Assignments

• There are several general guidelines for how to assign IP addresses:– The first octet of the network ID cannot be 127.– The network and host ID bits cannot be all 1s.– The network and host ID bits cannot be all 0s.– The host ID for each computer must be unique.– A unique network ID is required for each network and

wide area connection. – A registered network ID is required for connecting to

the Internet.– All TCP/IP hosts require unique host IDs.– Each host requires a subnet mask.

49

Using Private Addresses

• Workstations protected by firewalls and computers that do not connect to the Internet can use unregistered, private IP addresses.

• When building a private network, you should use one of the special ranges of private IP addresses, rather than assigning IP addresses randomly.

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IP Address Ranges for Private Networks

Class Network Addresses

A 10.0.0.0 through 10.255.255.255

B 172.16.0.0 through 172.31.255.255

C 192.168.0.0 through 192.168.255.255

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Routing • Routing is the process of choosing a path over

which to send packets, which is the primary function of IP.

• A router (also called a gateway) is a device that forwards packets from one physical network to another.

• Routers match packet headers to a LAN segment and choose the best path for the packet, which optimizes network performance.

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Packet Routing Example

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IP Routing

• To make routing decisions, the IP layer consults a routing table, which consists of a series of entries, called routes.

• On a computer running Windows, a routing table is built automatically based on its TCP/IP configuration.

• To view a routing table on a computer running Windows, at a command prompt, type route print, and then press Enter.

CmdC:\> route print

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Static and Dynamic IP Routing • Static routing can only use fixed routing tables. • Static routers require building and updating routing

tables manually. • Use the Route.exe command to add static entries to the

routing table.• Dynamic routing

– Automatically updates routing tables – Uses routing protocols, such as Routing Information Protocol

(RIP) and Open Shortest Path First (OSPF), to periodically transmit the contents of their routing tables to the other routers on the network

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Installing TCP/IP • The Windows Xp setup program automatically installs

TCP/IP if it detects a network interface adapter in the computer.

• You need to manually install TCP/IP on a computer running Windows Xp only if– The default protocol selection was overridden during setup– You have deleted it from a connection

• In Windows Xp, TCP/IP is implemented as a single module called Internet Protocol (TCP/IP), which is installed from the Network And Dial-Up Connections application in Control Panel.

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Installing TCP/IP (Cont.)

• To manually install TCP/IP:1. Log on using an administrator account.2. Click Start, point to Settings, and then click

Network And Dial-Up Connections.

3. Right-click the Local Area Connection icon, and then select Properties to display the

LocalArea Connection Properties dialog box.

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Installing TCP/IP (Cont.)

• To manually install TCP/IP (Cont.): 4. Click Install. 5. In the Select Network Component Type dialog

box, select Protocol, and then click Add. 6. In the Select Network Protocol dialog box, select Internet Protocol (TCP/IP) in the Network Protocol list, and then click OK. 7. Click Close.

Type the following commands in cmd and write what it shows

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Using Ipconfig.exe • Use Ipconfig.exe to view the TCP/IP

configuration settings on a host, including IP address, subnet mask, and default gateway. – At the command prompt, type ipconfig or ipconfig

/all and then press Enter.– Use the /all parameter to display more

information.• Running Ipconfig is an easy way to view the IP

address and other parameters that the DHCP server has assigned to your computer.

61

Using Ping

• Ping is a command-line utility that uses Echo Request messages to determine if the TCP/IP stack of another computer on the network is functioning normally.

• From a command prompt, type ping target (where target is the IP address or the name [DNS or NetBIOS, Example ping www.google.co.in] of the computer you are trying to contact).– A successful ping results in several reply messages from the

target computer.– If the ping fails, one or both computers might have a

networking hardware or software problem.

– Example c:\> ping 192.168.1.2

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Using Traceroute

• Tracert.exe, a variant of Ping, displays the path that packets take to their destination.

• From a command prompt, type tracert target (where target is the IP address or the name [DNS or NetBIOS] of the target computer).

• Use Tracert.exe to isolate the location of a network communications problem, particularly when a router is suspected.

• Example C:\> tracert.exe 192.168.1.2

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Using Pathping • Pathping is a route tracing tool that

– Sends packets to each router on the way to a final destination over a period of time

– Computes results based on the packets returned from each hop• You can use Pathping.exe to isolate problems because it

shows the degree of packet loss at any given router or link.

• From the command line, type pathping target (where target is the IP address or the name [DNS or NetBIOS] of the target computer).

• Example C:\> pathping.exe 192.168.1.2

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Using Route.exe (Cont.)

• The ROUTE PRINT command displays the current contents of the routing table.

• To create a new entry, use ROUTE ADD with parameters that specify the values for the entry.

• Example C:\> route.exe 192.168.1.2

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Using Route.exe

• Use Route.exe to create, delete, or modify static routes in a routing table on a computer running Windows 2000.

• Route.exe uses the following syntax:ROUTE [-f] [-p][command[destination] [MASK netmask] [gateway] [METRIC metric] [IF interface]]

• The Route.exe command variable takes one of four values:

PRINT ADD

DELETE CHANGE

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Using Arp.exe

• IP uses ARP to discover the hardware address that each datagram is transmitted to.

• Resolved addresses are stored in an ARP cache.• Use Arp.exe to view or change the contents of the ARP

cache.• Arp.exe uses the following syntax:

ARP [-a {ipaddress}] [-n ipaddress] [-s ipaddress hwaddress {interface}] [-d ipaddress {interface}]

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Using Netstat.exe

• Netstat.exe is a Windows 2000 command-line utility that displays information about – The current network connections of a computer

using TCP/IP – The traffic generated by various TCP/IP protocols

• Netstat.exe uses the following syntax: NETSTAT [interval] [-a] [-p protocol] [-n] [-e] [-r] [-s]

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Using Nbtstat.exe • Nbtstat.exe is a Windows 2000 command-line

utility that displays information about the NetBIOS over TCP/IP connections used by Windows 2000 when communicating with other Windows computers on a TCP/IP LAN.

• Nbtstat.exe uses the following syntax:NBTSTAT [-a name] [-A ipaddress] [-c] [-n] [-r] [-R] [-s] [-S] [-RR]

• The parameters for Nbtstat.exe are case-sensitive.

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Using Nslookup.exe • Nslookup.exe is a Windows 2000 command-

line utility that enables you to generate DNS request messages and transmit them to a specific DNS server on the network.

• Nslookup.exe uses the following syntax:

NSLOOKUP DNSname DNSserver– DNSname specifies the DNS name you want to

resolve.– DNSserver specifies the DNS name (or IP address

of the DNS server) you want to query for the name you want to resolve.

DNS – Domain Name System

Domain Names• A domain name is the sequence of labels from a node to the root,

separated by dots (“.”s), read left to right– The name space has a maximum depth of 127 levels– Domain names are limited to 255 characters in length

• A node’s domain name identifies its position in the name space

d a ko ta

w e s t

to rna do

e a st w w w

n o m in um m e ta in fo

c om

b e rke ley n w u

e du g ov

n a to

in t

a rm y

m il

uu

n e t o rg

""

Subdomains

• One domain is a subdomain of another if its domain name ends in the other’s domain name– So sales.nominum.com is a subdomain of

• nominum.com & com

– nominum.com is a subdomain of com

Name Resolution

• Name resolution is the process by which resolvers and name servers cooperate to find data in the name space

• Closure mechanism for DNS?– Starting point: the names and IP addresses of the name

servers for the root zone (the “root name servers”)– The root name servers know about the top-level zones and

can tell name servers whom to contact for all TLDs

ping www.nominum.com.

The Resolution Process

• Let’s look at the resolution process step-by-step:

annie.west.sprockets.com

What’s the IP address of

www.nominum.com?

The Resolution Process• The workstation annie asks its configured name

server, dakota, for www.nominum.com’s address

ping www.nominum.com.annie.west.sprockets.com

dakota.west.sprockets.com

The Resolution Process• The name server dakota asks a root name server, m, for

www.nominum.com’s address


m.root-servers.net



www.nominum.com?

The Resolution Process• The root server m refers dakota to the com name servers• This type of response is called a “referral”


m.root-servers.net

dakota.west.sprockets.com Here’s a list of the com name servers.

Ask one of them.

The Resolution Process• The name server dakota asks a com name server,

f, for www.nominum.com’s address


m.root-servers.net



www.nominum.com?

f.gtld-servers.net

The Resolution Process• The com name server f refers dakota to the

nominum.com name servers


f.gtld-servers.net

m.root-servers.net


Here’s a list of the nominum.com name servers.

Ask one of them.

The Resolution Process• The name server dakota asks a nominum.com name

server, ns1.sanjose, for www.nominum.com’s address


f.gtld-servers.net

m.root-servers.net


ns1.sanjose.nominum.net


www.nominum.com?

The Resolution Process• The nominum.com name server ns1.sanjose

responds with www.nominum.com’s address


f.gtld-servers.net

m.root-servers.net


ns1.sanjose.nominum.netHere’s the IP address for

www.nominum.com

Here’s the IP address for

www.nominum.com

The Resolution Process• The name server dakota responds to annie with

www.nominum.com’s address


f.gtld-servers.net

m.root-servers.net



ping ftp.nominum.com.

Resolution Process (Caching)

• After the previous query, the name server dakota now knows:– The names and IP addresses of the com name servers– The names and IP addresses of the nominum.com name

servers– The IP address of www.nominum.com

• Let’s look at the resolution process again



What’s the IP address of ftp.nominum.com?

Resolution Process (Caching)• The workstation annie asks its configured name

server, dakota, for ftp.nominum.com’s address


f.gtld-servers.net

m.root-servers.net




What’s the IP address of ftp.nominum.com?

Resolution Process (Caching)• dakota has cached a NS record indicating ns1.sanjose is an

nominum.com name server, so it asks it for ftp.nominum.com’s address


f.gtld-servers.net

m.root-servers.net





ftp.nominum.com

Resolution Process (Caching)• The nominum.com name server ns1.sanjose

responds with ftp.nominum.com’s address


f.gtld-servers.net

m.root-servers.net





ftp.nominum.com

Resolution Process (Caching)• The name server dakota responds to annie with

ftp.nominum.com’s address


f.gtld-servers.net

m.root-servers.net



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