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Training On Networking Concepts


... data and network information are communicated from applications on one computer, ... model is responsible for managing communications between network applications. ... – PowerPoint PPT presentation

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Title: Training On Networking Concepts

Training On Networking Concepts
Presentation by Anand Mewalal
  • Topics
  • Communication Terms
  • OSI Reference Model and Layered Communication
  • Ethernet networking
  • TCP/IP
  • IP Subnetting
  • Networking Terms
  • Networking Devices
  • Common Networking commands
  • Troubleshooting Tools and Techniques
  • Common Problems

Communication Terms
  • Protocol For a network to work, the computers
    running on it need to agree on a set of rules.
    Such a set of rules is known as a protocol. It is
    similair to a language. One person speaking in
    Japanese to another who cannot understand it.
  • Open Systems interconnection (OSI) When
    networks first came into being, computers could
    typically communicate only with computers from
    the same manufacturer. Every Vendor has their Own
    protocol. For example, companies ran either a
    complete DECnet solution or an IBM solutionnot
    both together. In the late 1970s, the OSI (Open
    Systems Interconnection) model was created by the
    International Organization for Standardization
    (ISO) to break this barrier. The OSI model is the
    primary architectural model for networks. It
    describes how data and network information are
    communicated from applications on one computer,
    through the network media, to an application on
    another computer. The OSI reference model breaks
    this approach into layers
  • Connection oriented Protocols -establish a
    channel between the source and destination
    machines before any data is transmitted. The
    protocol ensures that packets arrive at the
    receiving station in the same sequence in which
    they were transmitted. If a packet is lost in
    transit, it is retransmitted by the source. The
    destination host acknowledges data sent from the
    source to the destination
  • Connectionless oriented protocols -provide no
    assurance that data sent from the source will
    reach the destination. They provide best-effort
    delivery. There is no guarantee that a packet
    will reach its destination or that it will be in
    order. However they require less overhead and are
    generally faster than connection-oriented
  • Encapsulation A layer in the OSI model provides
    services to the layer above it and, in turn,
    relies on the services provided by the layer
    below it. Encapsulation is the process by which
    information from an upper layer of the model is
    inserted into the data field of a lower layer. As
    a message leaves a networked station, it travels
    from Layer 7 to Layer 1. Data created by the
    application layer is passed down to the
    presentation layer. The presentation layer takes
    the data from the application layer and adds its
    own header and trailer to it. This data is then
    passed down to the session layer, which adds its
    own header and trailer and passes it down to the
    transport layer. The process repeats itself until
    the data reaches the physical layer. The physical
    layer does not care about the meaning of the
    data. It simply converts the data into bits and
    places it on the transmission media.
  • Decapsulation When the data arrives at its
    destination, the receiving stations physical
    layer picks it up and performs the reverse
    process (also known as decapsulation). The
    physical layer converts the bits back into frames
    to pass on to the data link layer. The data link
    layer removes its header and trailer and passes
    the data on to the network layer. Once again,
    this process repeats itself until the data
    reaches all the way to the application layer.

Ethernet Networking
Ethernet networking uses what is called Carrier
Sense Multiple Access with Collision Detect
(CSMA/CD), which helps devices share the
bandwidth evenly without having two devices
transmit at the same time on the network medium
to avoid collision of packets When a host wants
to transmit over the network, it first checks for
the presence of a digital signal on the wire. If
all is clear (no other host is transmitting), the
host will then proceed with its transmission. And
it doesnt stop there. The transmitting host
constantly monitors the wire to make sure no
other hosts begin transmitting. If the host
detects another signal on the wire, it sends out
an extended jam signal that causes all nodes on
the segment to stop sending data. The nodes
respond to that jam signal by waiting a while
before attempting to transmit again. Backoff
algorithms determine when the colliding stations
retransmit. If after 15 tries collisions keep
occurring, the nodes attempting to transmit will
then time-out. Ethernet frames The Data Link
layer is responsible for combining bits into
bytes and bytes into frames. Frames are used at
the Data Link layer to encapsulate packets handed
down from the Network layer for transmission on a
type of media access. Ethernet Frame
Preamble An alternating 1,0 pattern provides a
5MHz clock at the start of each packet, which
allows the receiving devices to lock the incoming
bit stream. The preamble uses either an SFD
(Start Field Delimiter) or synch field to
indicate to the receiving station that the data
portion of the message will follow. Frame Check
Sequence (FCS) FCS is a field at the end of the
frame that is used to store the cyclic redundancy
check (CRC).
OSI Layers
  • Application Layer
  • Provide interface to End user
  • Provides standardized services to Applications
  • Presentation Layer
  • Specifies Architecture Independant Data
    Transfer format
  • Encodes and Decodes Data, compress data
  • Session Layer
  • Manages user Sessions
  • Reports Upper layer Errors
  • Transport Layer
  • Manages network layer connections
  • Provides Reliable packet delivery mechanism
  • Network Layer
  • Addresses and routes packets
  • Data Link Layer
  • Frames Packets
  • Controls Physical layer data flow
  • Physical Layer
  • Interface between network medium and network

Physical Layer
  • Physical Layer
  • Interface between network medium and network
  • Defines electrical and mechanical characteristics
  • Physical layer This layer defines connectors,
    wiring, and the specifications on how voltage and
    bits pass over the wired (or wireless) media.
    Devices at this layer include repeaters,
    concentrators, and hubs. Devices that operate at
    the physical layer do not have an understanding
    of paths.

Ethernet V.2 - Ethernet 50 Ohm Coax , Thin Wire
50 Ohm Coax, Broadband 75 Ohm Coax, IEEE 802.3
(Ethernet) - 10 Base 5 Star LAN, 10 Base T
(Twister Pair), 10 Base 5, 10 Base 2, 10 Base F
(Fiber), 100 Base T / X, 1000 Base X (802.3),
1000 Bast T (802.3ae), IEEE 802.11 - IEEE
802.11a (52 Mbps), IEEE 11b WLAN (upto 11 Mbps),
IEEE 11g (WLAN 54 Mbps) IEEE 802.5 (Token Ring)
Fibre optic, Shielded Twisted pair (4/16 Mbps),
Unshielded twister pair (UTP 4/16) FDDI Fibre
optic IEEE 802.6 (MAN) SNI (Subscriber Network
interface, DSO (64 bps), DS1 T1 (1.544 Mbps),
E1 (2.048 Mbps), DS3 T3 (44.736 Mbps), E3
34.368 Mbps) - Communicates to ATM, HDLC, PPP,
SMDS, Frame Relay ISDN Q921 ISDN BRI (2b_at_64
kbps) / 1D_at_16kbps), ISDN Pri ( 30b _at_63kbps, 1D
_at_64kbps, 1 OAM _at_64kbps) PPP Frame Relay Serial
Interface EIA RS232D or V.24, V.35, X.21 (V.10,
V.10), RS-449, RS-530, HSSI
Data link Layer
  • Data Link Layer
  • Frames Packets
  • Controls Physical layer data flow
  • Data link layer This layer is concerned with the
    linkages and mechanisms used to move data about
    the network, including the topology, such as
    Ethernet or Token Ring, and deals with the ways
    in which data is reliably transmitted. This layer
    is responsible for delivering frames between
    network interface cards (NICs) on the same
    physical segment. Communication at the data link
    layer is generally based on hardware addresses.
    The data link layer wraps data from the network
    layer inside a frame. Examples of data link layer
    protocols include Ethernet, Token Ring, and
    Point-to-Point Protocol (PPP). Devices that
    operate at this layer include bridges and

Ethernet V.2 - Ethernet Data Link Control ATM
Layer ( Asynchronous Transfer Mode) ATM
Adaption layer (AAL1, AAL2, AAL3/4 AAL 5)
Frame Relay Link Access procedure for frame
mode bearer service LAPF
IEEE 802.2 - SNAP (Sub Network Access Protocol)
Type 1 (Connectionless service ) IEEE 802.3
CSMA/CD Media Access Ctrl, IEEE
802.11 WLAN Direct Sequence) Type 2
(Connection Service) IEEE 802.5 (Token Passing
Ring) Type 3 (ACK w/ Connectionless Service)
IEEE802.6 (MAN)
Internetwork- Virtual LAN IEEE Protocol -
802.1Q VLAN Tagging, GVRP, GMRP HDLC Serial
Interfaces PPP Serial interaces SMDS
(Switched Multi Megabit Data Service)-SMDS
interface protocol Frame Relay Link Access
procedure for frame mode bearer service LAPF
Upper layer protocol Communication ARP / RARP,
IP, IPX (Novell), NetBEUI (IBM) Cisco Protocols
CDP (Cisco Discover protocol), CGMP (Cisco group
Management Protocol) This is on DLL itself
Network Layer
  • Network Layer
  • Addresses and routes packets
  • Network layer This layer is responsible for
    addressing and delivering packets from the source
    node to the destination node. This is the layer
    on which routing takes place. It defines the
    processes used to route data across the network
    and the structure and use of logical addressing.
    The network layer takes data from the transport
    layer and wraps it inside a packet or datagram.
    Logical network addresses are generally assigned
    to nodes at this layer. Examples of network layer
    protocols include IP and IPX.

IP (Internet Protocol) ICMP (Internet Control
messaging Protocol), SLIP (Serial Line IP), CSLIP
(Compressed SLIP), IP Based Routing Protocols
EGP (Exterior based protocol), NHRP (Next hop
routing protocol), GGP (gateway to Gateway
Protocol), OSPF (Open shortest path first), RSVP
(Resource reservation protocol), VRRP (Virtual
router redundancy protocol) Cisco protocols
IGRP (Interior gateway routing protocol, EIGRP
(enhanced IGRP) VPN Tunnelling IPSEC (Internet
IP Security), IP in IP (IP Encapsulation in IP),
SCTP (Stream Control Transmission Protocol), GRE
(Generic Routing Protocol This communicates to
upper layer protocol PPTP Upper layer
Communication TCP , UDP
IPX ( Internet Packet Exchange) RIP (Routing
information Protocol, NLSP (Netware Link State
protocol) Upper layer Communication SPX, SAP
Service Access Point, NCP, Burst Mode
IGMP Internet Group Management protocol
Frame relay Q933, SVC, LMI CLLM
Transport layer
  • Transport Layer
  • Manages network layer connections
  • Provides Reliable packet delivery mechanism
  • Transport layer This layer provides reliable
    transmission of data segments, as well as the
    disassembly and assembly of the data before and
    after transmission. Port or socket numbers are
    used to identify these unique processes. Examples
    of transport layer protocols include Transmission
    Control Protocol (TCP), User Datagram Protocol
    (UDP), and Sequence Packet Exchange (SPX).

TCP (Transmission Control Protocol) It
Communicates with Netbios, DSI, SMB, MSRPC, SSL,
TLS, LDAP, TCP/IP Services (HTTP, Https, FTP,
Gopher, POP3, Telnet, NNTP), Xwindow, HP network
Services, LDP, LPP, Runix, RPC, DNS, Cisco
Routing Protocol TCP Based UDP (User Datagram
Protocol) - It communicates with Muticast Routing
protocols, Routing protocols UDP Based, UDP/IP
Datagram Protocol Services, DNS, RUNIX (Remote
Unix), LDP, SNMP, RPC, Cisco HSRP Hot Standby
Router VPN Tunnelling PPTP (Point to Point
Tunnelling Protocol, L2TP (Layer 2 Tunelling
Protocol), L2FP (Layet2 Forwarding protocol). It
Communicates to PPP, SLIP, and Radius Remote
Authentication / Kerberos
Session layer
  • Session Layer
  • Manages user Sessions
  • Reports Upper layer Errors
  • Session layer The session layer establishes,
    maintains, and manages the communication session
  • end systems. The session layer protocol is often
    unused in many protocols. Examples of session
    layer protocols are LDAP ( Lightweight Directory
    Access protocol), SSL, Secure Socket layer, TLS
    (Transport layer Protocol), RPC (Remote procedure
    call), RTP

Presentation Layer
  • Presentation Layer
  • Specifies Architecture Independant Data
    Transfer format
  • Encodes and Decodes Data, compress data
  • Presentation layer This layer is responsible for
    data presentation, encryption, and compression.
    I.e. data representation and code formatting.

TCP Services Http (Hyper text transfer
protocol), Https (Http secure), FTP (File
Transfer protocol), Gopher, POP3 (Post office
protocol), Telnet (Virtual terminal), NNTP
(Network News Transfer protocol), Other
protocols LPP (lightweight Presentation
protocol, DNS (Domain name Service) SNMP (Simple
Network management Protocol, NetBIOS, Citrix ICA,
NCP (Netware Core protocol) Netware 5.0
Application Layer
  • Application Layer
  • Provide interface to End user
  • Provides standardized services to Applications
  • Application layer This topmost layer of the OSI
    model is responsible for managing communications
    between network applications. This layer is not
    the application itself, although some
    applications may perform application layer
    functions. In other words, programs such as
    Microsoft Word or Corel are not at this layer,
    but browsers, FTP clients, and mail clients are.

Muticast Routing Protocols IP Based - Multicast
OSPF, DVMRP (Distance vector Multicast Routing
Protocol, PGM (Pragmatic General Multicast
Protocol), PIM (Protocol Independent Muticast),
IGMP (Internet Group Management protocol) Routing
protocols TCP Based MSDP (Multicast source
discovery Protocol), BGP (Border gateway
Protocol), MBGP (Multi Protocol BGP, DCAP (Data
link Switching Client Access protocol) Routing
Protocol UDP Based DHCP (Dynamic host
Configuration protocol), Bootp (Bootstrap
protocol), NTP ( Network time protocol), TFTP
(Trival File transfer protocol), ICP (Internet
Cache protocol), RUDP (Reliable Udp), GDP
(gateway Discovery Protocol), RIP, Other
Protocols SMTP (Simple Mail transfer Protocol),
IMAP Internet Message Access protocol), Xwindow
System (X10/X11), HP Network Service, RUNIX
remote Service, Sun Network Service, ND (Network
Disk), Cisco Protocols CISCO HSRP (Hot Standby
router UDP Based), Cisco STUN, RSRB, XOT (TCP
based) Microsoft Application Services WINS,
Browser, Netlogon, Spoolss, Exchange, Citix
Application Service ICA Browser Novell
Application Service DHCP, NDS (Network
Directory Services)
There are many protocols related to VOIP, ORACLE,
IBM, Storage. Which could not be covered in this
The IEEE (Institute of Electrical and Electronics
Engineers) 802 Specifications zoom in on the
lower layers of the OSI Reference Model. The 802
Project was started in February 1980, hence the
name. The 802 specs have 12 categories covering
network topologies, interface cards, and
  • 802.1 Internetworking.
  • 802.2 LLC (Logical Link Control).
  • 802.3 Ethernet LANs (Local Area Network), i.e.
    CSMA/CD (Carrier-Sense Multiple Access with
    Collision Detection) or 10BASE-T. See also my
    definition of Ethernet.
  • 802.3z 1000BASE-T or gigabit Ethernet.
  • 802.4 Token Bus LAN.
  • 802.5 Token Ring LAN. See also my definition of
    Token Ring.
  • 802.6 MAN (Metropolitan Area Network).
  • 802.7 Broadband Technical Advisory Group.
  • 802.8 Fiber Optic Technical Advisory Group.
  • 802.9 Integrated Voice and Data Networks.
  • 802.10 Network Security.
  • 802.11 Wireless Networks.
  • 802.12 Demand Priority Access LAN, 100.

Protocol Data Unit Application -
Data Presentation - Data Session -
Data Transport - Segment Network - Packet Data
Link - Frame Physical - Bits
OSPF (Open Shortest Path First) Used by TCP/IP
routers to determine the best path through a
network. RIP (Routing Information Protocol)
Helps TCP/IP routers to use the most efficient
routes to nodes on the network ICMP (Internet
Control Message Protocol) A Network layer
protocol that carries control messages, such as
error or confirmation messages.
TCP / IP Model
OSI Model
DOD Model
Protocol Data Unit
Application Presentation Session
Process / Application
Telnet / FTP / LPD / SNMP TFTP / NFS / SMTP / X
Network Access
Data Link Physical
Ethernet / Fast Ethernet Token Ring / FDDI
TCP (Transmission control protocol) developed
by the Defense Advanced Research Projects Agency
(DARPA), is the most widely used routed protocol
today. The upper layers just send a data stream
to the protocols in the Transport layers, TCP
segments a data stream and prepares it for the
Network layer The Network layer then routes the
segments as packets through an Internetwork TCP
and UDP uses port no to communicate with upper
layer. Eg TCP user port 21 for FTP, port 23 for
telnet, port 53 for DNS TCP Segment
Format UDP Segment Format
IP (Internet protocol) - This is where the
routing takes place. IP receives segments from
the Host-to-Host layer and fragments them into
(packets). Each router (layer-3 device) that
receives a packet makes routing decisions based
upon the packets destination IP address. IP
uses port 6 for TCP and port 17 for UDP IP packet
IP Addressing (Subnetting)
The current IP addressing scheme (IPv4) defines
an IP address as a 32-bit binary number 11000111
00011010 10101100 01010011 To make it more
convenient for us, the IP address is divided into
four 8-bit octets (bytes) 11000111.00011010.10101
100.01010011 These octets are then converted
from binary to decimal numbers (four decimal
digits separated by periods) When
this number is entered into a computer, the
machine automatically converts it to a 32-bit
binary number, with no regard for the individual
octets or the decimals. An IP address has two
portions, a network ID and a host ID. The
network ID is shared amongst all the stations on
a segment and must be unique across the entire
network. The host ID identifies a specific
device (host) within a segment and must be unique
on a particular segment. Classes When the
original IP routing scheme was developed, IP
addresses were divided into five classes. IP
addresses most commonly come as Class A, B, or C.
Class D addresses are used for multicasting, and
Class E addresses are reserved for experimental
and future use. Please note that in the table, N
Network and H Host.
  • x x x x x x x
  • 64 32 16 8 4 2 1
  • --------------------------------------------------
  • Class A addresses are one byte long, with the
    first bit of that byte reserved and the seven
    remaining bits available for manipulation. As a
    result, the maximum number of Class A networks
    that can be created is 128 because each of the
    seven bit positions can either be a 0 or a 1,
    thus 27 or 128.
  • 00000000 and is reserved so actual no
    of class A addresses are 128-2 126 network
    Nodes. We have 24 bits available for node
    address. There are 224 or 16777216, since 0 and 1
    are reserved. The actual no of usable nodes is
    16777216 2 16777214
  • - All host bits off is the network
  • - All host bits on is the
    broadcast address.
  • The valid hosts are the number in between the
    network address the broadcast address
  • Class B With a network address being two bytes
    (eight bits each), there would be 216 unique
    combinations. But the Internet designers decided
    that all Class B network addresses should start
    with the binary digit 1, then 0. This leaves 14
    bit positions to manipulate, therefore 16,384
    (214) unique Class B network addresses.
  • Class B address uses two bytes for node
    addresses. This is 216 minus the two reserved
    patterns (all 0s and all 1s), for a total of
    65,534 possible node addresses for each Class B
  • - All host bits turned off is the
    network address.
  • - All host bits turned on is the
    broadcast address.
  • The valid hosts would be the numbers in between
    the network address the broadcast address to
  • Class C network address, the first three bit
    positions are always the binary 110. The
    calculation is such 3 bytes, or 24 bits, minus 3
    reserved positions, leaves 21 positions. Hence,
    there are 221, or 2,097,152
  • Class C network has one byte to use for node
    addresses. This leads to 28 or 256, minus the two
    reserved patterns of all 0s and all 1s, for a
    total of 254 node addresses for each Class C
  • - All host bits turned off is the
    network ID.
  • - All host bits turned on is the
    broadcast address.
  • The valid hosts would be the numbers in between
    the network address the broadcast address to

IP Subnetting
Class D addresses are used to support IP
multicasting , Class E addresses are reserved
for experimental purpose We learned how to define
and find the valid host ranges used in a Class A,
Class B, and Class C network address by turning
the host bits all off and then all on. However,
you were defining only one network. What happens
if you wanted to take one network address and
create six networks from it? You would have to
perform what is called subnetting, which allows
you to take one larger network and break it into
many smaller networks. Benefits Reduced network
traffic, Optimised network performance,
Simplified Management, To create subnetworks,
you take bits from the host portion of the IP
address and reserve them to define the subnet
address. This means fewer bits for hosts, so the
more subnets, the fewer bits available for
defining hosts. Subnet Design Consideration How
many total subnets does the organization needs
today How many total subnets will the
organization need in the future How many hosts
are on the organizations largest subnet
today How many hosts will be on the organization
largest subnet need in the future In a Class C
address, only 8 bits is available for defining
the hosts. Remember that subnet bits start at the
left and go to the right, without skipping bits.
This means that subnet masks can be
10000000128, 11000000192, 11100000224,
11110000240, 11111000248, 11111100252,
11111110254, You cannot have only one bit for
subnetting, since that would mean that the bit
would always be either off or on, which would be
illegal. So, the first subnet mask you can
legally use is 192, and the last one is 252,
since you need at least two bits for defining
IP Subnetting
  • How many subnets? 2x2amount of subnets. X is
    the amount of masked bits, or the 1s. For
    example, 11000000 is 222. In this example, there
    are 2 subnets.
  • How many hosts per subnet? 2x2amount of hosts
    per subnet. X is the amount of unmasked bits, or
    the 0s. For example, 11000000 is 262. In this
    example, there are 62 hosts per subnet.
  • What are the valid subnets? 256subnet maskbase
    number. For example, 25619264. which is the
    first subnet and our base number or variable.
    Keep adding the variable to itself until you
    reach the subnet mask. 6464128. 12864192,
    which is invalid because it is the subnet mask
    (all subnet bits turned on). Our two valid
    subnets are, then, 64 and 128.
  • What are the valid hosts? Valid hosts are the
    numbers between the subnets, minus all 0s and all
  • What is the broadcast address for each subnet?
    Broadcast address is all host bits turned on,
    which is the number immediately preceding the
    next subnet.
  • Practice Example 1
  • In this example, you will subnet the network
    address and subnet mask
  • address / mask
  • How many subnets? 224 is 11100000, so our
    equation would be 2326.
  • How many hosts? 25230.
  • What are the valid subnets? 25622432. 323264.
    643296. 9632128. 12832160. 16032192.
    19264224, which is invalid because it is our
    subnet mask (all subnet bits on). Our subnets are
    32, 64, 96, 128, 160, and 192.
  • What are the valid hosts?
  • What is the broadcast address for each subnet?

IP Subnetting
Class B - possible Class B subnet
masks The Class B network address has
16 bits available for hosts addressing. This
means we can use up to 14 bits for subnetting
since we must leave at least two bits for host
addressing. Use Subnet Calculator
IP Subnetting
  • Practice Example 1
  • address
  • mask
  • 2222.
  • 214216,382.
  • 25619264. 6464128.
  • First find the broadcast addresses in step 5,
    then come back and perform step 4 by filling in
    the host addresses.
  • Find the broadcast address of each subnet, which
    is always the number right before the next
  • Practice Example 2
  • 21021022 subnets.
  • 26262 hosts.
  • 25619264 and 128. However, as long as all the
    subnet bits on the third are not all off, then
    subnet 0 in the fourth octet is valid. Also, as
    long as all the subnet bits in the third octet
    are not all on, 192 is valid in the fourth octet
    as a subnet.
  • First find the broadcast addresses in step 5,
    then come back and perform step 4 by filling in
    the host addresses.
  • Find the broadcast address of each subnet, which
    is always the number right before the next subnet.

Networking terms
IP to Name Resolution Network Basic
Input/Output System (NetBIOS) is used as their
primary name to IP resolution method for Windows
NT 3.51, and NT 4.0. system Windows Internet
Naming Service (WINS) Maps IP addresses to
workstation names. A Windows name resolution
service for network basic input/output system
(NetBIOS) names. WINS is used by hosts running
NetBIOS over TCP/IP (NetBT) to register NetBIOS
names and to resolve NetBIOS names to Internet
Protocol (IP) addresses. WINS is a database that
is intended to receive client name registrations
with their identifying IP addresses, cache those
credentials, and reply with those cached names
and IPs when queried against. WINS works in the
same manner as do DNS servers when they resolve
hosts names to IP addresses, except that WINS
substitutes NetBIOS names. Domain Name System
(DNS). Maps IP addresses into user friendly
Internet domain names. DNS servers are distribute
throughout the Internet that share their
information so that users can access virtually
any domain name. DNS is a hierarchical division
of the network into groups and subgroups, with
names reflecting this structure. It was designed
to store data in a distributed fashion to
facilitate decentralized control and efficient
operation, and included flexible and extensible
mechanisms for name registration and resolution.
Dynamic Host Configuration Protocol (DHCP)
Dynamically leases IP address to different users
and computers on a network as needed. DHCP comes
with the NT OS. It is used for easy TCP/IP
configuration of hosts within the network. The
DHCP server selects appropriate configuration
parameters (IP address with appropriate subnet
mask and other optional parameters, such as IP
address of the default gateway, addresses of DNS
servers, domain name, etc.) for the client
stations. DHCP server assigns clients IP
addresses, Lease, reservation, Exclusions,
DHCP allows you to automatically assign IP
addresses, subnet masks, and other configuration
information to client computers on the local
network. When a DHCP server is available,
computers that are configured to obtain an IP
address automatically request and receive their
IP configuration from that DHCP server upon
Networking Devices
HUB A hub is a device that runs at the physical
layer of the OSI model and allows Ethernet
networks to be easily expanded. A group of
connected hubs is called a collision
domain Bridges and switches are both intelligent
devices that divide a network into collision
domains. Bridges operate at the data link layer
of the OSI model and forward frames based on the
source and destination addresses in the frame.
Bridges learn about the presence of end stations
by listening to all traffic. By listening to all
the traffic on a network, a bridge is able to
build a database of the end stations that are
attached to it. The bridge creates a mapping of
each stations MAC address and the port of the
bridge to which it connects. When the bridge
receives a frame, it checks the frames
destination address against its database. If the
destination address is on the same port that the
frame came from, the bridge does not forward the
frame. If the destination address is on another
port, it forwards the frame only to the port to
which it is destined. If the destination address
is not present in the bridges database, it
floods the frame out all ports except the source
port. Switches are generally much faster than
bridges because switching is generally done in
hardware, and bridges are normally software
based. Switches also offer higher port densities
than bridges. Furthermore, although bridges
always use store-and-forward technology, some
switches support cut-through switching, which
allows them to reduce latency in the network.
Cut-through switching allows a switch to start
forwarding a frame as soon as the destination
address is received Virtual LAN (VLAN) is a group
of network stations that behave as though they
were connected to a single network segment, even
though they might not be. VLANs provide a
logical, rather than a physical, grouping of
devices attached to a switch or a group of
switches Router is a device that routes packets
between different networks based on the network
address located in the packet header (IP, IPX,
AppleTalk, and so on). Routers operate at Layer 3
(the network layer) of the OSI model and are
therefore protocol dependent. Routers have the
ability to connect two or more similar or
dissimilar networks. Gateways operate up to the
application layer of the OSI model and convert
from one protocol to another.
Networking Diagrams
Common Networking Commands
PING (Packet internet Gopher) A TCP/IP utility
that is used to test the 'reachability' of
destinations by sending them an ICMP echo and
waiting for a reply. Nslookup Displays
information that you can use to diagnose Domain
Name System (DNS) infrastructure. This will tell
you the current address or the name an IP
Address or site is registered to Tracert The
tracert command is used to visually see a network
packet being sent and received and the amount of
hops required for that packet to get to its
destination. Netstat Displays active TCP
connections, ports on which the computer is
listening, Ethernet statistics, the IP routing
table, IPv4 statistics Ipconfig This command is
used to display the network settings currently
assigned and given by a network
Identify the need for Networking Tools Are all
servers giving a good ping response Reporting
should be easy Alerting if there is a
problem. Proactive management tools Real Time
Alerting. Network Security Port Scanning to check
Vulnerablity Web Monitoring Bandwidth Utilization
/ Network Health Protocol Utilization Centralized
Monitoring Hard Disc free space, Processor
utilization Is okay
Duplicate Network layer Addresses Because
network layer addresses are assigned through
software and are not burned in hardware, two
stations might accidentally be assigned the same
network layer address.Local Routing This
happens when two networked stations on the same
segment are communicating with each other through
a router instead of talking to each other
directly. This is usually caused by a
misconfiguration of the network settings on one
or both hostsPing of Death is the name given to
a Denial of service exploit that was widely used
in conjunction with the ping utility. The exploit
required the transmission of an illegal packet
size that is, a packet greater than 65536 bytes.
This often led to a buffer overflow on the
receiving system - with sometimes disastrous and
often unpredictable results system crashes,
reboots, kernel dumps and so on.Denial of
Service Attack An attack that is specifically
designed to prevent the normal functioning of a
system, and thereby to prevent lawful access to
that system and its data by its authorized users.
DoS can be caused by the destruction or
modification of data, by bringing down the
system, or by overloading the system's servers
(flooding) to the extent that service to
authorized users is delayed or prevented.Routing
  Routing is a process preformed by a router
which moves packets of data around the Internet.
A router makes sure that a message is sent and
recieved and is part of what makes TCP/IP such a
useful protocol suite. To be able to successfully
start routing a router uses headers and a
forwarding table to find the destinations for
packets. A router uses the ICMP protocol section
of the TCP/IP protocol suite.
Common problems