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MCITP MCSE and CCNA Certification Notes Series :
MCSE 2016 Boot Camp :
Azure Boot camp :
CCNA / CCNAX
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CCNA Boot Camp
Cisco Hierarchical Model:
For more information about this, please read our
separate tutorial titled "The
Cisco Hierarchical Model".
OSI Model:
The OSI model is a layered model and a
conceptual standard used for defining standards
to promote multi-vendor integration as well as
maintain constant interfaces and isolate changes
of implementation to a single layer. It is NOT
application or protocol specific. In order to
pass any Cisco exam, you need to know the OSI
model inside and out.
The OSI Model consists of 7 layers as follows:
Layer |
Description |
Device |
Protocol |
Application |
Provides network access for
applications, flow control and error
recovery. Provides communications
services to applications by identifying
and establishing the availability of
other computers as well as to determine
if sufficient resources exist for
communication purposes. |
Gateway |
NCP, SMB, SMTP, FTP, SNMP, Telnet,
Appletalk |
Presentation |
Performs protocol conversion, encryption
and data compression |
Gateway and redirectors |
NCP, AFP, TDI |
Session |
Allows 2 applications to communicate
over a network by opening a session and
synchronizing the involved computers.
Handles connection establishment, data
transfer and connection release |
Gateway |
NetBios |
Transport |
Repackages messages into smaller
formats, provides error free delivery
and error handling functions |
Gateway |
NetBEUI, TCP, SPX, and NWLink |
Network |
Handles addressing, translates logical
addresses and names to physical
addresses, routing and traffic
management. |
Router and brouter |
IP, IPX, NWLink, NetBEUI |
**Data Link |
Packages raw bits into frames making it
transmitable across a network link and
includes a cyclical redundancy check(CRC).
It consists of the LLC sublayer and the
MAC sublayer. The MAC sublayer is
important to remember, as it is
responsible for appending the MAC
address of the next hop to the frame
header. On the contrary, LLC sublayer
uses Destination Service Access Points
and Source Service Access Points to
create links for the MAC sublayers. |
Switch, bridge and brouter |
None |
Physical |
Physical layer works with the physical
media for transmitting and receiving
data bits via certain encoding schemes.
It also includes specifications for
certain mechanical connection features,
such as the adaptor connector. |
Multiplexer and repeater |
None |
Here is an easy way to memorize the order of the
layers:
All People Seem To Need Data Processing.
The first letter of each word corresponds to the
first letter of one of the layers. It is a
little corny, but it works.
Class |
Range |
Explanation |
A |
1-126 |
IP addresses can be class A, B or C.
Class A addresses are for networks with
a large number of hosts. The first octet
is the netid and the 3 remaining octets
are the hostid. Class B addresses are
used in medium to large networks with
the first 2 octets making up the netid
and the remaining 2 are the hostid. A
class C is for smaller networks with the
first 3 octets making up the netid and
the last octet comprising the hostid.
The later two classes aren’t used for
networks. |
B |
128-191 |
C |
192-223 |
D |
224-239 (Multicasting) |
E |
240-255 (Experimental) |
A subnet mask blocks out a portion of an IP
address and is used to differentiate between the
hostid and netid. The default subnet masks are
as follows:
Class |
Default Subnet |
# of Subnets |
# of Hosts Per Subnet |
Class A |
255.0.0.0 |
126 |
16,777,214 |
Class B |
255.255.0.0 |
16,384 |
65,534 |
Class C |
255.255.255.0 |
2,097,152 |
254 |
In these cases, the part of the IP address
blocked out by 255 is the Net ID.
3COM’s IP addressing tutorial is
just superior. It covers basic IP addressing
options as well as subnetting and VLSM/CIDR.
IPX/SPX:
IPX will also be an important issue to consider
in network management given the fact there many
companies still use Netware servers. There are
two parts to every IPX Network address - the
Network ID and the Host ID. The first 8 hex
digits represent the network ID, while the
remaining hex digits represent the host ID,
which is most likely the same as the MAC
address, meaning we do not need to manually
assign node addresses. Note that valid
hexadecimal digits range from 0 through 9, and
hexadecimal letters range from A through F.
FFFFFFFF in hexadecimal notation = 4292967295 in
decimal.
Sequenced Packet Exchange(SPX) belongs to the
Transport layer, and is connection-oriented. It
creates virtual circuits between hosts, and that
each host is given a connection ID in the SPX
header for identifying the connection. Service
Advertisement Protocol(SAP) is used by NetWare
servers to advertise network services via
broadcast at an interval of every 60 minutes by
default.
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