Cisco Certified Network Associate CCNA
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31. Ethernet_II has a type field to identify the
upper-layer protocol. 802.3 has only a length field and
can't identify the upper-layer protocol.
32.To find valid hosts given an IP address (say
18.104.22.168) and a subnet mask (sat a 12-bit subnet). The
valid hosts are determined as below:
A 12-bit subnet mask gives us
255.255.255.240; 4094 subnets, each with 14 hosts. (Host
addresses of all zeros and all 1s can't be assigned). The
22.214.171.124 is in the 48 subnet range. The valid range is
through 49 - 62. 63 is a broadcast address.
Here is how you get the subnet range:
Find the subnet mask. In this case, default subnet mask for
Class B address is 255.255.0.0. There are additional; 12
bits in the subnet mask. Now the subnet mask looks like:
This is equal to 255.255.255.240.0.
Now, deduct the lowest value octet (Which is non zero), from
256. Here, (256-240)=16.
This is the value
that the subnets are incremented. Therefore, you will have
hosts with values from:
to 126.96.36.199 (All 0s and all 1s host addresses
can not be used)
188.8.131.52 and so on.
It is important to
know that subnets are incrementing here by a factor of 16.
33. The following are some important commands that can be
used to edit and review command history buffer on a Cisco
router. It will be useful to practice these commands.
<ctrl> A :
Move to the beginning of the command line
<ctrl> E :
Move to the end of the command line
<ctrl> F :
Move forward one character, same as using "Right
<ctrl> B :
Move backward one character, same as using "Left
<ctrl> P :
Repeat Previous command, same as using "Up
<ctrl> N :
Repeat Next (more recent) command, same as using
<esc> B :
Moves to beginning of previous word.
<esc> F :
Moves to beginning of next word.
Creates new command prompt, followed by all the characters
typed at the last one.
34. The following are some frequently used COPY commands:
COPY RUNNING-CONFIGURATION STARTUP-CONFIGURATION
(alternatively, you can use an older version of the
command, WRITE MEMORY): This command saves the current
configuration to NVRAM. Alternatively, we can issue the
command using short form: COPY RUNNING STARTUP - Copies
configuration from RAM to NVRAM
COPY STARTUP RUNNING - This command merges configuration from
NVRAM to RAM.
COPY FLASH TFTP - Copies current IOS from router flash memory
to TFTP server.
COPY TFTP FLASH - Copies image file from TFTP server to
flash. This is used to upgrade the IOS image file to a
newer version, or if your IOS image becomes corrupt.
35. The banner is displayed whenever
anyone logs in to your Cisco router. The syntax is
"banner motd # " . MOTD stands for "Message Of
# symbol signifies
the start of the banner message to the router. You will be
prompted for the message to be displayed. You need to
enter "#" symbol at the end of the message,
signifying that the message has ended.
36. Router modes of operation:
User EXEC mode (Prompt: Router>):- This is the
LOWEST level of access. This allows examination of
router status, see routing tables, and do some
diagnostics. However, you cannot change the router
configuration, view the configuration files, or control
the router in any way. The prompt in this mode is
Privileged (enable) EXEC mode (Prompt: Router#):- This mode
allows you to have all the privileges of EXEC (user) mode
plus commands that enable you to view configuration files,
change the router configuration, perform troubleshooting
that could potentially disrupt traffic. The default prompt
for this mode is "Router#".When you are working
in the privileged mode (at # prompt), you can get back to
user mode by typing "disable" at the
Configuration mode (Prompt:
Global configuration mode allows you to perform
tasks that affect the entire router, such as naming the
router, configuration of banner messages, enabling routed
protocols, and generally anything that affects the
operation of the entire router.
When you first switch on a router, you enter Setup
mode. Setup mode is different from configuration mode in
that setup mode appears when there is no configuration
file present. Upon entering setup mode, you can supply
some basic configuration parameters to Cisco router.
37. You can use "tab" to complete the command
that you are typing.
38. SHOW command is extensively used for seeing the status
and configuration information of the router.
Some of the frequently used commands
-This command displays the router's active
configuration file, passwords, system name, and interface
settings, interfaces IP addresses etc.
SHOW INTERFACE - Shows status and configuration information
of the local interfaces. The first line says something
like “TokenRing1 is up, line protocol is up”. The
first part “TokenRing1 is up” describes the physical
layer components such as electrical cabling and signaling
are OK. The second part “line protocol is up” means
that the router is detecting keep-alive messages. The
router may be put into administratively down status, at
which point the line would read, “TokenRing1 is
administratively down, line protocol is down.”
SHOW INTERFACE SERIAL 0 - Shows the serial 0 configuration.
SHOW INTERFACES - Displays statistics for all interfaces
configured on the switch.
SHOW PROCESS - Displays a router’s CPU utilization.
SHOW CONFIG - Displays information on the startup
SHOW VERSION - Displays information about the system hardware
(RAM/ROM), software version, names of configuration files,
and boot-images. This command will also show the current
configuration register value.
39. The Cisco router can be configured from many
Console port: During the initial installation, you configure
the router from a console terminal connected to the
"Console port" of the router.
Virtual Terminals (vty): A virtual terminal (vty) is
typically accessed through Telnet. A router can be
accessed through vty after it the initial installation in
the network. There are five virtual terminals, namely,
Auxiliary Port: you can configure a router through auxiliary
port. Typically, a modem is used to configure the modem
through aux port.
TFTP Server: Configuration information can be downloaded from
a TFTP server over the network.
NMS (Network Management Station): You can also manage router
configuration through NMS such as CiscoWorks or HP
40. There are five different types of passwords:
1. ENABLE PASSWORD - A global command that restricts
access to privileged exec mode. This is a non-encrypted
2. ENABLE SECRET - Assigns a one-way encryptographic
secret password, available in versions 10.3 and up. This
secret password is used instead of the enable password
when it exists.
3. Virtual Terminal Password (vty password): The virtual terminal
password is used for Telnet sessions into the router. The
password can be changed at any time. It can be set up when
you configure the router from the console. There can be
five distinct passwords corresponding to each vty (vty0 to
vty4) or there can be a single password for all vtys.
4. Auxiliary Password: Auxiliary password
is used to set password to the auxiliary port. This port
is used to access a router through a
5. Console Password: Console password is used to set the console port