34. Debugging output takes priority over other network traffic. Also, the
debug all command generates more output than any other debug command, and it can
severely affect the router's performance. In practically all cases, it is best
to use more specific debug commands.
35. Default route is used when there is no other known route to a given IP
packet’s destination. Default route is also known as gateway of last resort.
36. Distance vector protocol depends only on Hop count to determine the
nearest next hop for forwarding a packet. One obvious disadvantage is that, if
you have a destination connected through two hops via T1 lines, and if the same
destination is also connected through a single hop through a 64KBPS line, RIP
assumes that the link through 64KBPS is the best path!
37. DOD Model maps to OSI model as below:
Process/ Application maps to OSI's Application, Presentation, Session layers
Host-to-Host maps to ISO's Transport layer (layer 4).
Internet maps to ISO's Network layer (layer 3).
Network Access maps to ISO's Data Link and Physical Layers (layers 2, 1).
38. During password recovery, the config register and NVRAM are modified. ROM
hold the bootstrap code to start up the router and Flash contain the IO image.
Each exclamation mark (!) represents that one UDP segment has been
successfully transferred. While erasing, you get 'e' displayed on screen.
39. EIGRP (as well as IGRP) uses Bandwidth and Delay as default criteria to
determine the best path. The description of the terms is given below:
1. Bandwidth: This is the smallest bandwidth between the source and destination.
2. Delay: This is the cumulative interface delay along the path.
3. Reliability: This is the worst case reliability between source and
destination based on keep alives.
4. Loading: This is the worst case load on a link between source and destination
based on bps.
5. MTU: Smallest MTU in path.
40. EIGRP uses multicasts to send queries to neighbor routers.
41. There are five different types of passwords:
- ENABLE PASSWORD - A global command that restricts access to privileged
exec mode. This is a non-encrypted password.
- 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.
- 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.
- Auxiliary Password: Auxiliary password is used to set password to the
auxiliary port. This port is used to access a router through a modem.
- Console Password: Console password is used to set the console port
Extended Service Set (ESS) is a set of two or more Basic Service Sets (BSSes)
working together to form a single wireless network. Stations are able to move
between BSS within a single ESS yet remain “connected” to the fixed network
and so continue to receive emails etc. As a Station moves into a new BSS, it
will carry out a re-association procedure with the new AP (Access Point).
42. For accessing a switch over IP network, you need to do some minimum
configuration tasks using Console port on the switch. In the given question, the
default gateway needs to be configured on the switch for accessing the
management interface (VLAN1) from HostA.
43. For communicating between two hosts directly, you need a cross cable.
Also, the subnet mask 255.255.255.192 cannot accommodate the given IP addresses.
Therefore, you need to change either the host IP addresses so that they are
within a given subnet, or change the subnet address itself so that both the
hosts are within the subnet.
44. For connecting a switch to another switch, a crossover cable is required.
For connecting a host to a switch, a straight-through cable is used. For
connecting a Cisco Router/Cisco Switch console port, a rollover cable is
45. For IGRP routing, you need to provide the AS (Autonomous System) number
in the command. Routers need AS number to exchange routing information. Routers
belonging to same AS exchange routing information.
46. For using full duplex Ethernet transmission, a switch is required. A Hub
cannot support full duplex transmission. In full duplex mode, there will not be
any frame collisions.
47. Frame tagging is a technique, where a unique identifier is tagged to each
frame as it is forwarded through the switch fabric.
48. FTP (File Transfer Protocol) is used for transferring files from and to a
client computer to a host. FTP is a connection oriented protocol. It uses TCP/IP
for file transfer. Compare this with UDP protocol used by TFTP.
49. Given below are the four important forms of NAT (Network Address
- Static NAT: It is a one-to-one mapping between an unregistered IP address
and a registered IP address.
- Dynamic NAT: Usually, Dynamic NAT is implemented, where a pool of public
IP addresses is shared by an entire private IP subnet. When a private host
initiates a connection, a public IP address is selected. The mapping of the
computer’s non-routable IP address matched to the selected IP address is
stored in the NAT Table. As long as the outgoing connection is maintained,
the private host can be reached by incoming packets sent to the specified
public address. When the binding expires, the address is returned to the
pool for reuse.
- Overloading: A variation of Dynamic NAT, also known as Network Address
Port Translation (NAPT) maps multiple unregistered IP addresses to a single
registered IP address by multiplexing streams differentiated by the TCP/UDP
- Overlapping: When Overlapping is employed, the IP addresses used on the
internal network are registered IP addresses utilized on another network. To
avoid conflict, a NAT Table is built to translate these redundant internal
addresses to a unique IP address. Vice versa, when sending packets into the
private network, the registered addresses must be translated to an address
unique in the network.
50. IANA (Internet Assigned Numbers Authority) is the organization under the
Internet Architecture Board (IAB) of the Internet Society that oversees the
allocation of Internet Protocol addresses to Internet service providers (ISPs).
ICANN (a non governmental organization) has now assumed responsibility for the
tasks formerly performed by IANA. ISPs in turn allot IP addresses to small
companies, and businesses.
51. ICMP (Internet Message Control Protocol) messages are used for basic
error reporting between host to host, or host to gateway. It is not used for
error reporting between Gateways. ICMP messages are encapsulated using the IP
protocol. For example, the command “ping” uses ICMP protocol. In the OSI
Reference model, ICMPs are generally considered part of the IP layer.
ICMP ( Internet Control Message Protocol) sends an ICMP message if the
destination is unreachable. Routers can make alternate route decisions based on
ICMP messages, if appropriate.
52. If no matching MAC entry is found in the MAC table of a switch, the frame
will be broadcast to all other ports except the port through which it had
- EIGRP update packet is sent every 90 seconds by default. This is 30 Sec
- IGRP, and OSPF use Autonomous System (AS) numbers. An IGRP AS is a complex
network that has diverse bandwidth and delay characteristics.
54. Important Network Address Translation (NAT) terms of inside local, inside
global, outside local, and outside global are explained below:
- Inside local: A private IP address assigned to a host on the inside
- Inside global: A public IP address that represents one or more inside
local IP addresses to the outside world.
- Outside local: The IP address of an outside host as it appears to the
inside network. Not necessarily a legitimate address, it is allocated from
an address space routable on the inside.
- Outside global: The IP address assigned to a host on the outside network.
The address is allocated from a globally routable address or network space.
55. In "ad-hoc" or Independent Basic Service Set (IBSS)
configuration there is no backbone infrastructure. An IBSS is one BSS or Basic
Service Set. Mobiles can talk to each other without the use of an Access Point
(AP). In the Extended Service Set (ESS) configuration, there will be two or more
Access Points (APs), and users can freely roam between the Access Points without
any disconnection or reconfiguration. BSS will use only one Access Point.
56. In Carrier Sense Multiple Access With Collision Detection (CSMA/CD), a
node transmits only after listening to the media, and ensuring that no
transmission is taking place. Further, sending nodes detect when a collision
occurs and stop transmitting immediately, backing off for a random amount of
time before trying again. This results in efficient use of the media since the
bandwidth of transmitting the entire frame is not wasted.
57. In Cisco routers, the interfaces are “administratively down” by
default. You need to enable an interface to use it.
58. In normal course, a DTE device is expected to communicated with a DCE
device. In such event, the connections between the DCE and DTE devices is
straight. However, if the communication need to happen between two DTEs or two
DCEs, the signals need to be rolled. This is achieved by rolling the pins in the
cable or in the DB-25 adapter. Typically, a DTE to DTE communication can be
- 1. By connecting DTE to a rolled RJ-45 cable to a straight DB-25 adapter
to DTE, OR
- By connecting a straight RJ-45 cable to a rolled DB-25 adapter to DTE.
Similarly, a DTE to DCE communication can be achieved by:
- Connecting a DTE to a straight RJ-45 cable to a straight DB-25 adapter to
- Connecting a rolled RJ-45 cable to a rolled DB-25 adapter to DCE.
Note that rolling the signals twice is same as using straight through cables
or adapters without any rolling at all.
59. In RIP, after route convergence, all routes are distributed to the
neighbors by a router.
60. Internet connectivity is normally achieved using a WAN connection.
Therefore, you need a serial port for connecting to the Internet. On the other
hand, a switch normally requires an Ethernet port for connectivity.
61. Inter-Switch Link (ISL) is one of the VLAN trunking protocols used for
switched VLAN networks. It uses frame tagging to identify the VLAN. ISL
encapsulates the original Ethernet frame, and a VLAN-ID is inserted into the ISL
Inter-Switch Link and 802.1Q are two VLAN Trunking Protocols used with Fast
Ethernet, that Cisco supports. LANE is associated with ATM and 802.10 is
associated with FDDI. Also, it is important to note that ISL, 802.1Q, and 802.10
use Frame Tagging to identify the VLANs.
62. IP addresses are written using decimal numbers separated by decimal
points. This is called dotted decimal notation of expressing IP addresses.
The different classes of IP addresses is as below:
Class Format Leading Bit Network address Maximum Maximum hosts
pattern Range networks / nodes
A N.H.H.H 0 0 - 126 127 16,777,214
B N.N.H.H 10 128 - 191 16,384 65,534
C N.N.N.H 110 192 - 223 2,097,152 254
Network address of all zeros means "This network or segment".
Network address of all 1s means " all networks", same as hexadecimal
of all Fs.
Network number 127 is reserved for loopback tests.
Host(Node) address of all zeros mean "This Host (Node)".
Host (Node) address of all 1s mean "all Hosts (Nodes) " on the
63. IP is the protocol that works at Internet layer. It forwards the packets
based on the network address(IP address) in the packets and the routing tables.
IP Packets are transported from source network to the destination network by
what is known as routing. Hop-by-hop routing model is used by the Internet for
delivery of packets. At each hop, the destination IP address is examined, the
best next hop is determined by the routing protocol (such as RIP, OSPF or BGP)
and the packet is forwarded by one more hop through this route. The same process
takes place at the next hop. During this process, the logical addresses remain
same. In an IP network, the logical addresses are IP addresses. The hardware
interface addresses, such as MAC address change with each hop.
64. IP RIP based networks send the complete routing table during update. The
default update interval is 30 seconds.
ISL, 802.1Q are the VLAN trunking protocols associated with Fast Ethernet.
The VLAN trunking protocol defined by 802.10 is associated with FDDI. LANE (LAN
Emulation) is associated with ATM.
65. ISP router is normally configured with static route.
66. It is important to know the difference between a collision domain and a
broadcast domain. When you use Hubs, all the nodes connected to the hub will be
in the same collision domain. However, when you use switches and implement VLANs,
each VLAN will be in a separate broadcast domain. The packet forwarding between
VLANs is achieved through the use of routing.