88. TCP and UDP work at transport layer of OSI model or the Host-to-Host
layer of DOD Model.
- Telnet command works at Layer 7 of your TCP/IP stack. If you are able to
Telnet to your remote router, you can be sure that the TCP/IP stack is
Other commands, such as Ping, trace, and ipconfig work at lower layers of
the TCP/IP stack.
- Telnet is used for terminal emulation that runs programs remotely.
FTP is used to transfer files.
- TCP/IP is the protocol used when you are Telnetting to a remote host. HTTP
is used for accessing the World Wide Web services.
90. The “no cdp enable” instruction has to be given at the interface
configuration mode, where CDP needs to be disabled. (in this case S0/0).
91. service password-encryption command:
Directs the router to encrypt passwords that are saved in the configuration
file. Service password encryption is applied to all passwords, including
username passwords, authentication key passwords, the privileged command
password, console and virtual terminal line access passwords. This command is
primarily useful for keeping unauthorized individuals from viewing your password
in your configuration file.
92. The address range and the corresponding binary values for the first octet
of IP classes are as given below:
Class A: 0-127 binary: 00000000-01111111
Class B: 128-191 binary: 10000000 – 10111111
Class C: 192-223 binary: 11000000 – 11011111
Class D: 224-239 binary: 11100000 – 11101111
Note that the IP address 188.8.131.52 belongs to class B, and hence the
applicable binary address range is 10000000 – 10111111.
93. The auxiliary password is used to set the password for the auxiliary
port. Assuming that you are at # prompt, the sequence of commands are:
- RouterA#config t
- RouterA(config)#line aux 0
- RouterA(config-line)#password <password>
Now you are set with a password <password>. Type "<ctrl>Z
" to take you to the # prompt or "exit" to go back to global
configuration "RouterA(config)#" prompt.
Similar procedure is applicable for setting vty and console passwords as
94. A banner is displayed whenever anyone logs in to your Cisco router. The
syntax for configuring the banner is
- "banner motd # " . MOTD stands for "Message Of The
# 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 msg has ended.
95. The Catalyst 1900 and 2820 series switches support three types of
- FastForward (Cut-through): In this type of switching, the packet is
forwarded as soon as the destination address is read. This has least
- FragmentFree ( Modified cut-through): This type of switching is useful
when your network is experiencing large number of collisions. FragmentFree
switching has a latency in between FastFoward and the Store-and_Forward.
- Store-and-Forward: This method stores the entire frame and checks for
errors before forwarding it on to another port. Store-and-forward has the
highest latency compared with both FastForward and FragmentFree.
The default switching method used by Catalyst 1900 series switches is
96. The Cisco router can be configured from many locations.
- Console port: During the initial installation, you configure the router
from a console terminal connected to the "Console port" of the
- 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 OpenView.
97. The command "ipx routing" selects IPX as a routing protocol and
starts the routing process. Some other important commands are:
- ipx maximum-paths 2: This command allows load sharing over parallel metric
paths to the destination. The parallel paths that can be used is limited to
- Interface ethernet 0.1 : Indicates the first sub interface on interface
98. The command "show CDP neighbors" displays all the neighboring
devices connected and their capability. Several capability codes are:
- R - Router H - Host
- T - Trans Bridge I - IGMP
- B - Source Route Bridge r - repeater
- S - Switch
This command displays the following:
1. Neighbor Device ID : The name of the neighbor device;
2. Local Interface : The interface to which this neighbor is heard
3. Capability: Capability of this neighboring device - R for router, S for
switch, H for Host etc.
4. Platform: Which type of device the neighbor is. (2500 router or anything
5. Port ID: The interface of the remote neighbor you receive CDP information
6. Holdtime: Decremental hold time in seconds
99. The command "terminal no editing" stops all advance editing
100. Important CDP Commands:
- The command “cdp run” in global configuration mode enables CDP
globally on the router.
- The command “cdp enable” is used to enable CDP on a particular
- The command used to disable CDP is “ no cdp enable”.
- The command “ip default-gateway 192.168.1.1” in global configuration
mode can be used to sets the default gateway on a Cisco switch/router.
101. Typical sequence of steps involved in password recovery (on 2501
- Power cycle the router by turning it OFF and ON.
- Press Break key (key configuration depends on the router type) within 60
seconds of power on.
- Use the rommon command o/r 0X2142
- Use rommon command INITIALIZE to load IOS
- Skip the setup mode (by choosing NO to configuration commands).
- Enter privileged mode
- After entering the privileged mode, you can view the passwords by issuing
appropriate config commands.
102. The command syntax for configuring RIP version1 on a router is:
- Router rip
Network <network number>
Note that the network numbers are specified as either class A, or Class B or
Class C; and contain no subnetting information.
The command to configure a static route to network 184.108.40.206/28 from
assuming that the default gateway is 220.127.116.11 is:
- ip route 18.104.22.168 255.255.255.240 22.214.171.124
Syntax: ip route <remote_network> <mask> <default_gateway>
103. The correct syntax for setting default route is:
- Router(config)#ip route 0.0.0.0 0.0.0.0 126.96.36.199
You can also set default route by specifying the interface as below:
- Router(config)#ip route 0.0.0.0 0.0.0.0 s0
The syntax is:
- ip route 0.0.0.0 0.0.0.0 <next_hop_address>.
104. The default administrative distances for various protocols are as below:
- Directly connected ------ 0
Static Route ------------- 1
External BGP ------------20
EIGRP ------------------ 90
IGRP ------------------ 100
OSPF ----------------- 110
ISIS ------------------- 115
RIP -------------------- 120
105. The default port numbers used for some important services are:
SSL:443 (Secure socket layer)
When you are accessing a Web page, the browser sends the request over the
default port number (For WWW, the default port number is 80). For any reason, If
you change the default port number that a Web server listens to, users need to
specify the port number in the URL.
106. The distinguishing characteristics of a TCP frame are Sequence Number,
Acknowledgment Number, and Window.
107. The following are frequently used OSI layer 2 (data link) protocols:
c. Frame Relay
f. Token Ring
108. The following are main features of route summarization in EIGRP:
- By default, EIGRP summarizes routes at the major network boundaries (classful
- To enable summarization at any level other than major network boundary,
you need to disable auto summarization using the command:
- The following command enables summarization at an arbitrary network
“Ip summary-address <as-number> <address-mask>”
- Note that you need to specify the IP address and routing mask of the
summary route. No need to specify the metrics.
109. The following are some important commands that can be used to edit and
review command history buffer. 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 "Down
<esc> B : Moves to beginning of previous word.
<esc> F : Moves to beginning of next word.
<ctrl>R : Creates new command prompt, followed by all the characters
typed at the last one.
110. The following are some Presentation Layer standards:
- Graphic and Visual Image: PICT, TIFF, JPEG
Movies and Sound: MIDI, MPEG, Quick Time
The following are Session layer standards:
111. The following are the important characteristics of SDM:
- SDM doesn’t use Telnet/SSH for communicating with the router. Actually,
a web server will be running on the router, and the client software will be
running on the host computer.
- SDM uses web interface on a PC, and the user needs to connect to the
router over an IP network and not through Console.
- The configuration will be written to the router’s running configuration
file only after the Finish button is pressed on the SDM wizard. Note that
the configuration is not written to the start-up configuration.
- SDM configuration wizard allows DHCP client services to be configured,
with an option to add PAT services or not.
112. The following are true about HDLC encapsulation over serial links:
a. HDLC encapsulation used on Cisco routers is proprietary (uses a Type field),
and may not be compatible with routers manufactured by other vendors
b. It is recommended to use other encapsulation schemes such as PPP when
connecting between a Cisco router and a non-Cisco router instead of HDLC
113. The following are true about the IP address 188.8.131.52/25
- Subnet mask: 255.255.255.128
- Subnet address: 184.108.40.206
- Broadcast address: 220.127.116.11
- Lowest valid host address in the given subnet: 18.104.22.168 (A host
address of all zeros cannot be used)
- Highest valid host address in the given subnet: 22.214.171.124 (A host
address of all ones cannot be used)
- Valid host address range: 126.96.36.199 - 188.8.131.52
114. The following precautions may be taken to harden network infrastructure:
- Use physical barriers such as room lock so that un-authorized persons do
not have access to the network devices.
- Use firewall so that outsiders cannot access network devices from outside
- Enable SSH so that passwords are transmitted in encrypted form
115. The four layers of DoD model from Top to Bottom are:
- Process Layer: Responsible for implementation of user-level aplications
such as mail delivery, file transfer, and remote login.
- Host-to-Host Layer: Responsible for flow control,and retransmission of
lost packets. TCP, and UDP protocols work at this layer.
- Internet Layer: Responsible for routing data across a network of networks.
Routed protocols such as IP work at this layer. Routing protocols are also
associated with this layer.
- Network Access Layer: Responsible for the delivery of data segments over a
given particular hardware media. Different protocols such as CSMA/CD work at
116. The Internet architecture provides an unregulated network path to attack
innocent hosts. Denial-of-service (DoS) attacks exploit this to target
mission-critical services. DoS attacks, are explicit attempts to block
legitimate users system access by reducing system availability. Any physical or
host-based intrusions are generally addressed through hardened security policies
and authentication mechanisms. Although software patching defends against some
attacks, it fails to safeguard against DoS flooding attacks, which exploit the
unregulated forwarding of Internet packets.
117. MAC sub-layer:
- The Mac sublayer specification 802.3z describes gigabit Ethernet over
fiber or shielded copper.
- The Mac sublayer specification 802.3ab (1000BaseT) describes gigabit
Ethernet over Category 5 UTP.
118. The MAC address contains 48 bits expressed as 12 hexadecimal digits.
Note that 2 hexadecimal digits represent a byte. Therefore, a MAC address
contains 6 bytes. The first 3 bytes represent the manufacturer identification
code. The next 3 bytes represent the interface number unique to a given
manufacturer. MAC address represents the hardware address and is usually burned
into the ROM. A typical MAC address looks like:
xx-xx-xx-xx-xx-xx, where x represents a hexadecimal digit.
Here, 00-00-0c represents the vendor address, and 12-14-33 typically
represents the interface serial number. The last 6 hex digits are administered
by respective vendors, and unique to a given vendor.
119. The MAC address table of a switch would be empty to begin with. However,
it builds the MAC table learning from the frames that arrive at its ports by
adding the MAC address and the corresponding port that it had arrived to the MAC
120. The maximum allowed cable lengths are as given below:
- 10Base5: 500 meters
- 10Base2: 185 meters
- 10BaseT: 100 meters
- 100BaseT: 100 meters
- 1000BaseT: 100 meters
121. The number of distinct IPs' required in an IP network are:
- One each per client computer
- One each per server computer
- One each per router interface.
122. TCP and UDP Protocol Characteristics:
- TCP is a full-duplex, connection-oriented protocol. It incorporates error
checking as well.
- UDP (User Datagram Protocol): UDP is a thin protocol. UDP is a
connectionless protocol. It doesn't contact the destination before sending
the packet and doesn't care whether the packet is reached at the
destination. UDP uses port number 6.
123. The port numbers used by different programs are as below:
- FTP : Port #21
Telnet: Port #23
SMTP: Port #25
SNMP: Port #161
- It is also worthwhile to know that FTP,Telnet,SMTP use TCP; whereas
TFTP,SNMP use UDP.
124. The purpose of port security is to prevent access to the LAN from
125. The range of numbers from 184.108.40.206 to 220.127.116.11 are used for
multicast packets. This is known as Class D address range.
126. The store and forward switch works by first receives the whole packet
before retransmission. Cut-through switch mode retransmits a frame as soon as it
reads the destination address. Fragment-free switch mode reads the first 64
bytes before retransmission. Therefore, the latency of cut-through and
fragment-free switch modes is constant, whereas that of store-and-forward varies
depending on the length of the packet.
127. The subnet Id of a host with IP address 18.104.22.168/20 is 22.214.171.124
The available host address range is 126.96.36.199 - 188.8.131.52
Broadcast address: 184.108.40.206
128. The syntax for ping command is : "ping <destination_address>"
The following are possible responses to "ping" command:
U destination Unreachable
C Congestion experienced
! Successful receipt of echo reply
. Time out
? Packet type unknown
& Packet time to live exceeded
Ping sends ECMP echo. Ping can be used with almost any type of Network layer
protocols including IPX, IP, VINES, AppleTalk etc.