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CCNA 2.0 Study Guide

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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

Application

File, print, message, database, and applications

Determines availability of the target host.

www, email, ftp, telnet, edi, quake

Presentation

Data Encryption, compression, and translation services

Determines the syntax of the data transfer.

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

Session

Dialog control, coordinates the comunications

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

Transport

End-to-end communication

Responsible for hiding the communications from the higher layers.

TCP / UDP

Network

Routing

IP / ICMP, BootP, ARP, RARP

Routers

Data Link

Framing

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

WAN:

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

Physical

Wire…

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

Repeaters / Hubs

DOD Model

Process/application à application, presentation, session

Host-to-host à transport

Internet à network

Network access à Datalink / physical

LAN

Ethernet

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.

FDDI

100 Mbps

token passing with dual counter-rotating rings

Token-ring

802.5

4 / 14 Mbps

ATM

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

SWITCHING

Store – and – forward

Buffers whole frame before forwarding

Cut-Through

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 forwarded.

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.

TCP/IP

Port numbers:

TCP: protocol number 6

ftp: 21

telnet: 23

smtp: 25

UDP: protocol number 17

Dns: 53

Tftp: 69

Snmp: 141

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 110 192-223

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

NOTE:

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….

IPX

Protocl Stack:

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

Transport à IPX, SPX

Network à IPX

Data link à ODL Open Data Link

Physical à whatever

IPX

Connectionless, and communicates via sockets

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

Addressing:

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

SPX

Sequence Packet eXchange

Connection oriented protocol

Creates virtual circuits, with specific connection IDs

RIP

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

SAP

Service advertising protocol

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

Broadcast every 60 seconds

NLSP

NetWare Link Services Protocol

Link-state protcol to replace RIP and SAP someday…

NCP

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 servers

-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

Link-state

IGRP: Interior Gateway Routing Protocol (cisco proprietary)

Distance-vector

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

Link-state:

No-second hand info, and understands entire network

Uses LSP packets to build ‘personal’ copy of entire network structure to route from

LSP: link-state packets or “hello packets”

Chooses ‘best’ path based on: bandwidth, congestion, metrics, etc.

Update times can be set very lengthy as changes cause triggered udpates.

EXTERIOR routing protocols

EGP: Exterior Gateway Protocol

Polls neighbors

exchanges info about AS with neighbors

distance vector

very simple

BGP: Border Gateway Protocol

Can detect routing loops

Can work between AS

Other Random Cisco protocols

CDP: Cisco Discovery Protocol

Runs SNAP: SubNetwork Access Protocol at the datalink layer.

- this allows routers running different protocols to still communicate

- 60 second updates, 180 second hold time

Cisco IOS Commands

#show cdp interface

interface information, encapsulation info, and timing information

#show cdp entry <name or * for all>

shows detailed information about other routers on network

#show cdp neighbors

shows summary information that is being exchanged

#show cdp neighbor detail

extended listing of info for all routers

#show cdp traffic

shows packets sent / received amount neighbors

WAN:

POTS

Plain Old Telephone Service. (politely is: pstn: public switched telephone network)

Demarc: end of responsbility for provider, start for customer

CPE: customer premise equipment

Local loop: wire from CO to demarc

CO: Central Office: provider POP : point of presence

SDLC

Synchronous Data-Link Control

Used originally for SNA

Point –to-point or multipoint

Bounded or unbounded media, half or full duplex

Circuit or packet-switched networks

2 node types. Primay or Secondary (controlled by primary)

HDLC

High-Level Data-Link Control protocol

This is the default communication method for cisco routers of sync links, and is proprietary

This came after SDLC, and was modified into LAP and LAPB.

HDLC transfer modes:

NRM: Normal Response Mode: secondaries only speak when spoken to by pri

ARM: Async Response Mode: sec. can speak on own

ABM: Async Balanced Mode: nodes can be both pri and sec

LAPB:Link Access Procedure Balanced: built into x.25

DDR

Dial on demand Routing

· be sure and setup route as static, and with specified distance over 200 to make sure it is ‘last resort’

X.25

Point-to-point communication between DTE and DCE

DTE: Data Terminal Equipment (router or terminal, or whatever)

DCE: Data Circuit-Terminating Equipment (csu/dsi or modem)

PSE: Packet Switching Exchange: switches inside carriers network

Addresses defined by x.121 as a 14 digit number

DNIC:Data Network Identified Code is first 4 bits of address

Rest of address is assigned by the administrator

Full-duplex protocol

‘overbuilt’ with lots of error checking

Created SVC or PVC connections (switched or Permanent virtual circuits)

PLP

Packet layer protocol

x.25’s network layer protocol

modes: call setup, data transfer, idle, call clearing, restarting

LAPB

Link Access Procedure Balanced

Makes sure frames are error free and sequenced

Types of frames:

I information sequencing, flow control, error detect, recovery

S supervisory handles requests for, and suspension of transmittion

U unnumbered link setup and disconnections and error reporting

Setting up X.25 on Cisco

#interface <interface>

#encap x25

#x25 address <14 digit number>

to set the address

#x25 ips <bytes>

to configure Input Packet Size

#x25 ops <bytes>

to configure Output Packet Size

#x25 win <integer>

to configure Window Input Size

#x25 wout <integer>

to configure Window Output Size

Frame Relay

Shared Bandwidth

Can setup a CIR (Committed Information Rate)

Assumed error-checking is handled at another, higher, layer

PVCs are created at layer 2.

DLCIs: Data-link connection Identifiers : are used to identify virtual circuit connections.

DLCI address are assigned by the provider and then mapped to IP addresses by the router

LMI: Local management Interface

These are autodetected in current IOS versions….. however:

Keyword Meaning

Cisco: defined by industry group, and default

ANSI: Annex D defined by T1.617

Q933a: Defined by ITU-T Annex A Q.933A

LMI can be used to determine the global significance of the DLCI numbers.

Setup of Frame Relay on Cisco

#interface <interface>

#encapsulation frame-relay [ietf, or default is cisco]

use default to talk to other cisco routers, use ietf encapsulation to talk to non-cisco.

#frame-relay interface-dlci <dlci number>

to map dlci number to current interface, or subinterface

Then specify an IP address for that subinterface

Optionally you can hard-code the address on the other end.

#encap frame-relay [ietf]

#no inverse-arp

turns off auto addressing features

#ip address <ip address> <subnet mask>

#frame-relay map ip <address> <metric ? > [cisco] [broadcast]

this lets you mix encap types, and allow broadcast over interface

Monitoring Frame Relay

#show frame ?

ip ip statistics

lmi lmi stats

map map table

pvc pvc stats – this one displays the DLCI #

route route info

traffic protocol stats

PPP

Point to Point Protocol

Userfull for dial-up or sync links (ISDN)

Authenticate using PAP: password authentication protocol or

CHAP: Challenge Handshake Authentication Protocol

ISDN

Integrated Services Digital Network

Terminal equipment types:

TE1: understands ISDN

TE2: predates ISDN and needs a TA (terminal adapter) to work

ISDN reference points:

R: between non-isdn device and TA

S: between terminal and NT2 device

T: point between NT1 and NT2

U: point between NT1 and carrier line termination device

ISDN protocol codes:

E: existing telephone network

I: concepts, terms, and services

Q: switching and signaling

ISDN service levels:

Connect to lines with SPIDs (service Profile Identfiers) (phone numbers..)

BRI: Basic Rate Interface: 2B + 1D

B = 64kbs, D=14Kbps = 128kbs plus control

PRI: Primary Rate Interface: 23B + 1D

Total of 1.544Mbps

Configuring ISDN BRI

#isdn switch-type ?

tons of proprietary switch types

#interface <interface>

typicaly bri0, or something like that.

#encap ppp

ppp is method used to setup isdn phone calls

#isdn spid1 <spid1>

#isdn spid2 <spid2>

Configuring ISDN PRI

#controller <interface> <location>

typicaly something like #controller T1 1/0

#framing efs

sets Extended Super Framing, this is normal for T1/ PRI line

#linecode b8zs

line-conding mechanism to assist with timing by preventing strings of zeros

#pri-group timeslots <value from 1-24>

sets number of timeslots

Access lists:

Basics:

Access lists must be created, then applied to an interface

Access lists can filter incoming or outgoing from an interface

Packets are compared only until a match is made

Packets that do not meet any criteria on the list are discarded

Wildcard masking:

Nifty, acts like a reverse subnet mask:

Example: 0.0.0.255 would wildcard all hosts on class C network

0.0.0.0 would indicate no wildcarding

keywords:

host: 0.0.0.0 : just specified host

any: 255.255.255.255: absolutely anything

* when using keyword it comes before IP address, when using mask it comes after!!!!

List number scheme

List number range meaning

1-99 ip standard list

100-199 ip extended access list

800-899 ipx standard

900-999 ipx extended access list

1000-1099 IPX SAP access list

IP access list creation

#access-list <number of list> <permit | deny> <source address> [<mask>]

IP extended access list

#access-list <number> <permit |deny> <protocol> <source> <destination> <port>

source and destination can be masked

port can be ‘eq’ for equal, ‘neq’ not equal, ‘log’ logged, or assorted other things

port can also be keyworeded: www, smtp, finger, ftp, telnet, etc…..

ipx access list

#access-list <number> <permit|deny> <source network number> <destination network number>

no wildcarding needed with ipx

-1 is used to indicate ‘any network address’

extended ipx access lists

#access-list <number> <permit|deny> <protocol> <source> <socket> <destination> <socket>

-1 still indicates ‘any’ for socket or source address

IPX SAP access lists

#Access-list <number> <permit|deny> <source> <service type>

service type is numeric value

Applying Access list to Interface

#interface <interface>

#ip access-group <number of list> <in | out>

Monitoring:

#show access-list

shows the lists and how many matches for each line

#clear access-list counters <access list number>

clears statistics

Logging:

Keyword log can be placed at the end of extended access lists, and info will be logged to console by default, or could be re-directed to a error-log server

Logs include: access list number, source and destination port/address and number of packets.

Displaying access list info

#Show ip interface <interface>

displays which list is enabled for the interface, both incoming and outgoing

#show running-config

shows just about everything….including details of what makes up each access-list

CISCO Info:

Startup sequence

Bootstrap from Rom

Cisco IOS from Flash

From tftp

From Rom

Configuration File from NVRAM

From tftp server

From console

Editing commands

Toggle on/off: Terminal editing / terminal no editing

Control +

A move to beginning of line

E end

F forward

B back

P previous

N most recent

Show history

Terminal history size set buffer size

Arrow keys also work to edit and scroll through buffer

Passwords

Enable secret: one-way crypto password, has priority over ‘normal’ enable password

#config terminal

#enable secret <password>

Enable password: password to switch to priv mode

#config terminal

#enable password <password>

Virtual terminal password: password to allow telnet into router

#config terminal

#line vty 0 <max number of logins>

#login

#password <whatever password>

Banner

#banner motd <end Char>

yadda, yadda, yadda <end Char>

Hostname

#config t

#hostname <router hostname>

hostname resolution

#ip host <target hostname> <target host ip address>

this acts like a host file to allow static name resolution

#show hosts

displays configured hosts / ip addresses

#ip domain-lookup

#ip name-server <dns ip>

to configure DNS, use the 2 commands above. You can have up to 6 dns addresses

#no ip domain-lookup

disable dns lookkup

Interface Naming

S Serial

E Ethernet

T TokenRing

F Fiddi

Number as card/port or for 7000 series as VIP card/port (from 0) /interface (from 0)

Static Routing for IP

Config with:

#Ip route <network> <mask> <address|interface> [distance]

Display with:

#Show ip route

#Show ip route static

Remove ip routes with:

#No ip route <network>

Default route / route of last resort : (set network and mask to all 0s)

#Ip route 0.0.0.0 0.0.0.0 <address>

IP classless:

With IP classless ‘on’ packets are forward on a best-guess directly connected network instead of having them dropped.

- this is used with default routes

Testing:

#ping <address>

works with IP, ipx, appletalk, apollo, vines, and decnet

#ping <fill out info as prompted>

extended ping: works with ip, appletalk, and ipx to provide much more info

#trace <protocol> <address>

works with: ip, appletalk, clns, oldvines (cisco), vines (banyan).

- remember that TCP is not on any of these lists… it is a higher-level protocol.

Subinterfaces:

How to bind multiple conflicting commands to 1 interface… use subinterfaces.

Syntax is to place a period, then a integer after the device name.

Example: #int e0.100

Configuring Dynamic Routing for IP

RIP:

#router rip

#network <network we want to advertise>

-optional #passive <interface>

lets you run rip without advertising connection

-optional #neighbor <specific neighbor router>

lets info go over non-broadcast media (like WAN links)

-optional #debug ip rip or undebug ip rip

This shows all updates to the console (sent or received advertisements)

-optional #no router rip

Disables rip routing

IGRP

#router igrp <autonomous system number 1-65535>

turns on igrp and allows setting of AS number

#network <network we want to advertise>

-optional #debug ip igrp events #undebug ip igrp events

logs to console when/what events are done

-optional#debug ip igrp transactions #undebug ip igrp transactions

detailed log to console of what happens in each event

display routing info:

#show ip route

This displays all routes on the router, including how the route was ‘learned’

R = rip, C = connected, S = static, I = igrp, o = ospf, etc

#show ip route <protocol>

displays routes ‘learned’ from specified protocol only

#show ip protocol

displays protocol and detailed info on timing, sources of info, filters, etc.

#show ip interface

shows all lots of info on all interfaces

#show ip interface <interface>

shows info specific to the interface

IPX configuration

#ipx routing

to enable ipx routing

#interface <interface>

select an interface before providing specifc info for configuring ipx

#ipx network <ipx network address> [encapsulation <keyword for type>] [secondary]

- secondary indicates if more than one encapsulation type is used on 1 interface, recomened to use sub-interfaces

table of info for configuring encapsulation types

interface type frame type keyword

ethernet 802.3 novell-ether (default)

802.2 sap

ethernet_II arpa

ethernet_snap snap

token ring token-ring sap (default)

token-ring_snap snap

fddi fddi_snap snap (default)

802.2 sap

fddi_raw novell-fddi

Show IPX servers

#show ipx servers

this displays the contents of the SAP, listing all servers and services

show IPX route

#show IPX route

shows the IPX routing table

#ipx maximum paths <2-512>

enable multiple paths to 1 destination

#show ipx traffic

generates traffic statistics on ipx network usage

#show ipx interface <interface>

detailed info on specific interface

#debug ipx <all kinds of things>

lots of debug information available

Sources for IOS software:

Flash Memory

Default and normally good idea

#show flash

lists all versions stored in flash, but does not specify which is running

#show version

specifies which version of IOS you are running currently

Tftp server

Somewhat menu driven way to store and retrieve information to/from tftp server

#copy flash tftp –lets you backup your ios saved in flash

#copy tftp flash -lets you download new versions or restore over bad versions

tftp to backup / restore config info

#copy tftp running-config

#copy running-config tftp

Configuring fallback sources for IOS software

#boot system flash <ios_filename>

to boot from flash

#boot system tftp <ios_filename> <tftp_address>

to boot from remote tftp server

#boot system rom

to boot from hard-coded ios version, this is a ‘last resort’ kinda thing to do

IOS Commands that have little to do with routing

#show version

os version, uptime, how it was last started up, where ios was loaded from

hardware type and revision as well as detected interfaces

#show processes

shows pid, Queue priority, status (TY), runtime in milliseconds, stack space, proc name

#show memory

shows processor and I/O memory and watermarks / freespace

#show stacks

shows cause of last crash, and esoteric info

#show buffers

reveals size of buffers for small / middle / big / very big / large / huge

#show flash

reveals size and amount free, as well as what is stored.

#show running-config

shows the running configuration file

#show startup-config

shows the startup configuration file

#show interface

shows the hardware and their status, including usage stats

#show interface <interface>

shows hardware status and usage for specific interface

#show protocol

shows protocols enabled and routing info for each interface

#show ip protocol

shows more detail than show protocol

*Special thanks to THConsulting for compiling this information for these future CCNA Graduates

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