CCNA Prep document

By Esther Flores,2014-06-17 08:16
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CCNA Prep document ...

CCNA Prep document

Supplied to you with best wishes from….. Chillnz

The two most significant things to study on the test are the OSI model and TCP/IP addressing and

    subnetting. If you know both of those very, very well, then you are guaranteed about 50% on the exam.

    The rest comes from this sheet.

The last bit of advice is that you didn‟t believe me on the importance of knowing the OSI model, learn it

    backwards, forwards, sideways, and be prepared to answer really nit-picky questions about it.

OSI Model


     File, print, message, database, and applications

     Determines availability of the target host.

     www, email, ftp, telnet, edi, quake


     Data Encryption, compression, and translation services

     Determines the syntax of the data transfer.

     Pict, tiff, jpet, midi, mpeg, quicktime, etc


     Dialog control, coordinates the comunications

     Nfs, sql, rpc, x windows, asp (appletalk session protocol), DNA SCP (digital whatzit)


     End-to-end communication

     Responsible for hiding the communications from the higher layers.

     TCP / UDP



     IP / ICMP, BootP, ARP, RARP


    Data Link


    Ethernet II, 802.5 (token ring), 802.3, 802.2 (802.3 with dsap and ssap logical link

    control fields)

    Media access control: MAC: 48 bits, 3 bytes vendor + 3 bytes serial number


    High-level datalink control HDLC (cisco default for serial links)

    Synchronous Data Link Control SDLC (uses polling)

    Link Access Procedure, Balanced LAPB

    x.25, slip, ppp, isdn, Frame Relay

    Bridges / Switches



     v.24, v.35, x.21, g.703, hssi, etc

     Repeaters / Hubs

DOD Model

     Process/application ; application, presentation, session

     Host-to-host ; transport

     Internet ; network

     Network access ; Datalink / physical



     802.3 CSMA/CD | Ethernet_II | 802.2

     10base2/thinnet: 185 meters

     10base5/thicknet: 500 meters

     10baseT: can run above 10Mbps 200ish meters

     5-4-3 rule: 5 segments, 4 repeaters, 3 segments populated

     100BaseTX: 100 meters, up to 2 repeaters. Packets between 512 and 1518.


     100 Mbps

     token passing with dual counter-rotating rings



     4 / 16 Mbps


     53-byte cells

     Flow Control

     Contention: CSMA/CD : Carrier Sense Multiple Access, Collision Detect

     Token Passing: Token Ring, Fiddi

     Polling: SDLC, some HDLC, some HP ethernet stuff


     Store and forward

     Buffers whole frame before forwarding


     Forward frame as soon as destination address is available

     Fragment Free

    Does Cut-Through after 64 bytes are received to stop collision packets from being


     802.1d Spanning-Tree Protocol STP

     detect and eliminates loops in routed network

     STA: Spanning Tree Algorithm

     Sends out BPDUs: Bridge protocol data units

     VLAN: Virtual Lans

     Create „logical‟ networks by location, function or department.. or protocol, or whatever.

    Done with a switch using Frame-Tagging (can be used between switches if you have ISL

    inter-switch link) Frame-Tagging uses unique user-defined identifiers while within the

    switch fabric, and is very scalable.


     Port numbers:

     TCP: protocol number 6

     ftp: 21

     telnet: 23

     smtp: 25

     UDP: protocol number 17

     Dns: 53

     Tftp: 69

     Snmp: 161

     0-255: public assigned

     256 1023: assigned to companies

     1023+ user defined / source addresses

     IP Addressing:

     Class leading bits decimal range of first byte

     A 0 1-127

     B 10 128-191

     C 100 192-223

     Learn the rest of the stuff…. Way out of scope of this.


    Cisco considers the mask to be the bits beyond what is „normal‟ for that class address, not

    the entire number of bits in the subnet mask, sometimes….


     Protocl Stack:

     Application, presentation, session ; RIP, SAP, NCP, NLSP, etc…

     Transport ; IPX, SPX

     Network ; IPX

     Data link ; ODL Open Data Link

     Physical ; whatever


     Connectionless, and communicates via sockets

     Each host runs its own internal ipx network in addition to any lan network


     10 byte address

     first 4 bytes are network need to be unique, otherwise whatever..

     last 6 bytes are node - usually just use the MAC address


     Sequence Packet eXchange

     Connection oriented protocol

     Creates virtual circuits, with specific connection IDs


     Routing information protocol

     Distance vector protocol that establishes routes between ipx networks

     Judges based on ticks (1/18 second units) and hops

     Broadcast every 60 seconds

     Used to provide each server with a complete network map


     Service advertising protocol

     Servers use it to advertise, clients use it to locate services

     Broadcast every 60 seconds


     NetWare Link Services Protocol

     Link-state protcol to replace RIP and SAP someday…


     NetWare Core Protocol

     Provides access to server resources

     Netware in a nutshell

     -Strict client-server model (nobody is both)

     -Servers provide files, printing, messaing, applications, and databases

    -Every netware server (or cisco router) creates a SAP table of all services offered by all


    -A client issues a GNS (GetNearestServer request) broadcast to find out what is on the

    local SAP

     Netware frame types Features

    802.3 default on NetWare <=3.11

    802.2 default on NetWare 3.12+

    ethernet_ii supports tcp/ip and ipx

    ethernet_SNAP appletalk, tcp/ip, and ipx

    --- all of these are incompatible… god love‟m

Routing Protocols

     RIP: Routing Information Protocol

     Distance vector routing protocol

     Updates every 30 seconds

     Route invalid timer 90 seconds: time before route considered invalid.

     Route flush timer: 240 seconds: route removed from table

     Can use metrics (1-15) to weight against some interfaces

     15 hop limit

    OSPF: Open Shortest Path First

     Link-state routing

     Very infrequent broadcast updates

     Extremely granular metrics

    NLSP: Novell‟s Link State Protocol


    IGRP: Interior Gateway Routing Protocol (cisco proprietary)


     Metrics and hop count from 1-255

     Measures delay in units of 10 milliseconds

     Measures bandwidth on serial connection this needs to be set, default is T1

     Measures reliability as 1-255 (255 optimal):

     Measures load: 0-255 (0 = no-load)

     Allows multi-path routing (dual links of equal bandwidth to 1 location)

     Implements hold-downs, split horizons, and poision reverse updates

     Update timer is 90 seconds, invalid timer is 270 seconds (3 times update)

     Hold down timer is 280 (3 times update +10 seconds)

    flush timer is 630 seconds (7 times update)

    administrative distances: (reliability of information)

    0 = direct connection, 1 = static, 100 = igrp, 110 =ospf, 120 = rip, 255 = unknown

    EIGRP: Enhanced IGRP

     Hybrid routing protocol

     Uses distance vectors, however they are triggered by changes, not timers.

     Faster convergence, multiprotocol support

     Distance- vector:

     Uses second-hand info

     Problems detecting /closing routing loops (counting to infinity)

     Judges „best‟ based on hop counts

     Convergence can get pretty lengthy

     Split horizion: enforces that inforation is not sent back in direction it came from

     Route poisoning: Helps prevent incorrect updates by setting route down explicitly

     Hold-downs: prevents routes from changing too quickly, to allow time for stabilization