The CCNA Test
70 Questions
68% needed to Pass (must get 48 questions correct - can get 22 wrong)
90 minutes long (about 1 minute 20 seconds for each question)
Test said to Stress:
First, get some string and glue... er, Wires and Computers, that is!
Divide and Conquer - Cutting up your LAN
LANs can get too BIG, so "Segments" can be sliced off.
Repeaters work at the Physical Layer and do NOT segment networks!
(They take a message and shout it back out louder)
Hubs are glorified Repeaters that love to gossip.
They take in a message and repeat it to everyone.
Bridges work at the Datalink Layer and sort of help segment,
(but they pass on broadcasts)
Switches are basically Multiport Bridges.
Think of lots of little Bridges in a Box, all on Steroids
Can select which destination port to send stuff to...
Routers work at the Network Layer.
They examine the Destination IP address of a message.
Then send the message on to the next likely HOP,
headed towards it eventual goal.
Gateways act at the Application Layer,
Are usually computers that convert between different Protocols.
Good when you need to translate!
The Layers are as follows:
(most people use the silly phrase
"All People Seem To Need Data Processing to memorize these")
(I prefer the one I made up
"All Predators Start The Next Day Preying!")
Okay, here are the LAYERS of the OSI Standard...
in the usual Reverse Numeric Order.
Now we need to go over each Layer in detail:
3. Router Beginning Configuration
Starting Your Imaginary Cisco Router:
Step One - Remove From Imaginary Box
Step Two - Plug Imaginary Power Cord into Wall Socket
Step Three - Attach to the Imaginary Console Port on Back.
Step Four Connect Serial Cable from a PC
Use something like a VT-100 terminal program.
Step Five - Turn on Router with Imaginary Power Switch.
*The Router will Test it's Memory and Hardware (Power On Self-Test just like a PC)
*Next it will load it's "Bootstrap Program" from ROM
*Finally it will load a Cisco IOS image from it's FLASH memory.
*If the Router does not find a CONFIGURATION file in it's NVRAM
(that's Non-Volatile Random Access Memory, eh?)
*Then it will enter into it's Setup Dialog
(Hello, like to set me up?)
When it says "Would you like to enter the Initial Configuration Dialog?
You Say - "Yes!" (also say Yes if it asks if you are a god!!)
Hidden Behind the Scenes,
the Cisco Router has a 16 bit "Configuration Register"
16 Bits looks like this: 1111 0000 1111 0000
or maybe 0000 1111 1010 0011
Each bit is just a One or a Zero And is actually a little transistor switch.
It's just like a Light Switch
and can be off (zero)
or turned on (one)
This is called Binary, because it has only Two numbers, 1 and 0...
(from the Latin "Bi" meaning 2 and "Nary" meaning we lost the other numbers?)
Anyway, this Configuration Register holds the secrets of the Router!
Booting is the Process of the Route starting itself.
The Boot Field tells the Router how to Boot.
The Boot field is made up of the last 4 of the digits.
xxxx yyyy zzzz 1111 (or possibly 0000)
Actually this gives a range of 16 possible ones and zeroes.
Luckily we don't have to memorize all of them.
If the Boot field is 0000 - then enters ROM Monitor Mode.
If the Boot field is 0001 - then it boots from the ROM Image.
If the Boot field is between 0010 and 1111 then it Boots Normally.
Passwords For Your CISCO:
(this section not completed yet...)
Step 1 - User information is converted into data (type-itty type) - Upper Layers
Step 2 - Data is converted into segments (ok, you guys split up!) - Transport
Step 3 - Segments are converted into datagrams and packets (choose teams!) - Network
(Datagrams sent without prior circuit connection - head that way...)
(frames are sent with control info and proper introduction?)
Step 4 - Packets are put into logical frame. (Logical, Captain...) - Datalink
Step 5 - Frames are put into bits (I wouldn't give you 2 bits for this computer!)
User - Logon as peon, peasant, commoner...
You can Look but not Configure!
Enable - the command to enter the Command Executive Mode
(more commonly just called "enable" mode...)
Type the old "Config-T" at the prompt RouterBob#
End up with RouterBob(config)#
HELP - Cisco has On-line Context-sensitive Help Functions
SHOW [All kinds of different things] Commands:
SHOW "command" let's you see what's happening to whatever.
Commonly abbreviated to just SH or sh cause we're lazy...
SHOW INTERFACES - gives info on all the Router's Interfaces.
What is an Interface, you might ask?
An Interface is a place where two different things connect.
Specifically they refer to Where you Plug things IN.
Show IP Interfaces - gives info on all the Router's Interfaces that have IP on them.
Show IPX Interfaces - gives info on all the IPX Interfaces.
SHOW INTERFACE [name of individual Interface goes here}
- info on That Particular Interface.
SHOW ACCESS-LISTS - gives info on all the Access Lists
SHOW IP ACCESS-LISTS - gives info on all the IP Access Lists
SHOW IPX ACCESS-LISTS - gives info on all the IPX Access Lists
SHOW PROTOCOLS - shows info on all the Protocols that are Configured. also gives Network Layer Address info on each of the INTERFACES.
SHOW RUNNING-CONFIG - gives the current Router Configuration being used, which is stored in RAM.
SHOW STARTUP-CONFIG - gives the Router Configuration stored in the NVRAM (Non-Volatile RAM)
SHOW FLASH - gives the format and contents of the FLASH memory, including the Cisco IOS file's name.
SHOW VERSION -
shows the Configuration of System Hardware
shows the Software Version being used for Cisco IOS.
shows the names and sources of Configuration Files.
shows the Boot Images. (related to the IOS to be used)
SHOW BUFFERS - Shows vital info on the Router's Buffer Pools (small memory areas for send and receive)
SHOW MEMORY - Shows the memory statistics, including the Free Pool stats.
SHOW PROCESSES CPU - Shows the active Processes running on the computer. (a Process is part of a Computer Program that is does something)
SHOW STACKS - shows info about the Memory Stacks.
Includes Utilization of Processes
Includes Interrupt Routines
Shows reason for the Last Reboot of the router.
(cause of death - Kernal Mustard in the Library)
3. IP Addressing - particularly Subnetting
4. Access Lists
5. WAN technologies - especially ISDN
6. Networking Essentials
Flow Control
Controls the flow of information:
1. "Source Quench" messages
Come from Receiving computer to Sending Computer
Says "Buffer Full" don't send me no more til I'm ready!
Then later says "Segments Processed" - Send me More NOW!
2. "Windowing" (not TM by Microsoft)
Packets sent are acknowledged by Receiver.
If each one must be acked before the next one is Sent then that is a 1 to 1
or window size of ONE. (not really much of a window, eh?)
If only every second one must be acked then it is a Window Size of 2.
If 3 packets can be sent before an Ack is needed, then that's window Size 3.
3. Positive Acknowledgement with Re-Transmission
If a Window flow control system does not get an Ack signal after sending a series of packets.
Then it stops and resends the last set,
Waits for Acknowledgement before continuing sending.
STATIC ROUTING To configure a STATIC ROUTE:
IP ROUTE (to get to this DESTINATION NETWORK) (DEST. SUBNET MASK)
(use this IP ADDRESS) (and this name of INTERFACE) [and an optional ADMIN. Distance]
So it'd look like this:
"Remote Network" "Default Gateway"
IP ROUTE 10.1.1.0 255.0.0.0 10.1.2.1 S0 130 Go to this Network Subnet mask..... using this Address & this Interface Opt. admin. dist.
To configure a DEFAULT ROUTE
IP ROUTE 0.0.0.0 0.0.0.0 172.1.1.1
To go to any unknown Network Subnet Mask.... use this IP Address
IP CLASSLESS - a good command to install if you are doing Static Routing...
To configure router to send packets for unknown Routes to the best guess,
use the Global Configuration:
RouterA# config t
RouterA(config)# IP CLASSLESS
Then you need to create a "Default Route" to use with IP Classless
Where any packets with "destination unknown" will get sent.
A Static Route with the address 0.0.0.0 and Subnet mask 0.0.0.0
(according to the Longest Match Rule, all zeroes will match anything
See above for configuring Default Routes.
PING - May or may not stand for Packet Internetwork Groper. (the PING author says "No, really I just made it up!")
Sends an ICMP packet to a remote computer, gets an answering packet back
Ping Error Codes
I Interrupted
T Timeout
N ICMP Net Unreachable
H ICMP Host Unreachable
P ICMP Unknown Protocol
U ICMP Unreachable Port
A ICMP Administratively Prohibited (access-list refused)
? Anothing else that might come back
The Source Computer takes the Network Layer's PACKET
And the MAC Layer encapsulates (puts into a capsule) it into a FRAME.
The FRAME gets sent out as BITS across the Network Media (wires, etc)
A Router picks up the BITS
Recreates the FRAME with the PACKET inside. (not Intel inside, really)
Takes the FRAME off and looks at the Packet's
Network Layer Destination Address.
Then the Router figures out where to send the Packet next.
(the next HOP)
This is specifically the Port which leads to the best route toward the Destination.
The Router puts a new Encapsulation around the Packet (puts it in a FRAME) And sends it out as BITS to the Next HOP.
(Physical exercise)
Any Port in a Storm
Ports are how Upper Layers receive different types of info on one
connection.
Ports are Connection-oriented. (need to have TCP to work)
There are standard ports for many of the common Protocols.
FTP 21 - "files, to get one"
TFTP 69 (udp) - "needs no rhyme"
Telnet 23 - "tell it to go climb a tree"
SMTP 25 - "It's alive!"
HTTP 80 - "hat size 80"
DNS 53 - "lost at sea"
A Socket is a Port with an IP Address.
(Sort of like sending mail to specific Apartment in a big Apartment Building.)
Sockets allow more than one application to use one Internet connection
to send multiple types of things all at the same time.
WinSockets are a socket adopted by Microsoft (but not created by them)
Communications:
X.25
HDLC
Frame Relay
ISDN
BRI
PRI ATM
STP - an oil additive you put in your car...
(just kidding here, you don't have to memorize this one!)
LAN Types
Ethernet
Token Ring
Sneaker Net
Routing Protocols:
Static Routes
IP Route [destination network IP] [dest. net Subnet Mask] [send to this IP address]
Default Route
IP Default-Network [network IP number]
Or use a Router of the Last Resort
IP Route [dest. net = 0.0.0.0] [dest. subnet mask = 0.0.0.0]
[send to this IP address]
Basically means "If you don't know where to send it, send it here".
RIP - Routing Information Protocol
(distance vector - just uses Hops)
To cofigure RIP = ROUTER RIP
IGRP - Interior Gateway Routing Protocol
(distance vector)
To configure IGRP = ROUTER IGRP [Autonomous System #] NETWORK [network #]
EIGRP - Enhanced Interior Gateway Routing Protocol
(a distance vector protocol with enhanced superpowers)
Adds the following:
Automatic redistribution of IGRP routes into EIGRP interfaces & vice versa.
Increases Maximum Hop counts to 224
Neighbor discovery using "HELLO" system to find neighboring routers
Variable-Length SUBNET MASKING to increase available IP's
or redestribute them.
Sends out Partial Updates when it notes changes,
rather than entire routing table.
To Configure EIGRP - ROUTER EIGRP
OSPF - Open Shortest Path First
OSPF can set the best path by looking at the speed of the connection
as well as how many hops away it is,
OSPF does not send out it's entire routing table as a broadcast.
Instead when a change happens the entire network is told
To configure - ROUTER OSPF [put Autonomous System # here]
To add to Interface use - NETWORK [address] [mask] AREA [area ID #]
Areas are like Autonomous System's.
An Area is a contiguous portion of an Internetwork
Access Lists Permit or Deny All
Implicit "Deny All" is unspoken at the bottom of each list!
Access Groups assign Access Lists to Interfaces...
Cisco IOS Commands For Fun & Profit
IP ROUTE - used to send to a Destination Network with Subnet Mask,
using an IP Address.
Route of Last Resort use IP Route [netwk 0.0.0.0] [subnet 0.0.0.0] to IP Address.
IP Default-Network [network IP number] - Used to set up a Default Route.
SHOW ATM
SHOW X25
SHOW frame
ATM - Asynchronous Transfer Mode
VCC - Virtual Channel Circuit
VPI - Virtual Path Identifier ( one byte)
A VCD is a number assigned by Cisco.
Each Virtual Circuit in a Cisco system must have a VCD assigned... (really)
(a Link State Protocol - uses metrics like Cost, or Priority)
or what the "priority" the administrator sets is.
(it's callied flooding) about the new configuration immediately.
that does not share its Routing Table with other strange areas...
Determined by combining
and the VCI - Virtual Channel Identifier (two bytes)
(the VCI is like one or more of the VPI's)