Cisco Certified Network Associate CCNA
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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
Internal memory components of a Cisco router:
1. ROM (Read Only Memory); Memory containing micro-code for basic
functions to start and maintain the router. ROM is not
typically used after the IOS is loaded.
2. RAM/DRAM : stores the
running configuration, routing tables, and packet buffers.
Some routers, such as the 2500 series, run IOS from Flash,
3. NVRAM (Non-Volatile Ram): Memory that does not lose information
when power is lost. Stores the system’s configuration
file and the configuration register. NVRAM uses a battery
to maintain the data when power is turned off.
4. Flash Memory: Stores the compressed IOS (IOS stands for Cisco
Internetwork Operating System)
image. Flash memory is either EEPROM or PCMCIA
card. Flash memory enables you to copy multiple versions
of IOS software. This allows you to load a new level of
the operating system in every router in your network and
then, to upgrade the whole network to that version at an
42. While a packet travels through an Internetwork, it
usually involves multiple hops. Note that the logical
address (IP address) of source (that created the packet)
and destination (final intended destination) remain
constant, the hardware
(Interface) addresses change with each hop.
43. Default administrative distances some important
routing protocols are as below:
Directly connect Interface
An administrative distance of 0 represents highest trustworthiness
of the route.
An administrative distance of 255 represents the lowest
trustworthiness of the route.
Routed and Routing protocols:
Routing protocols job is to maintain routing tables and route
packets appropriately. Examples of routing protocols are
RIP, IGRP, EIGRP, OSPF. Routers can support multiple
independent routing protocols and can update and maintain
routing tables for each protocol independently.
Routed protocols are used to transport user traffic from
source node to destination node. Examples of routed
protocols are IP, IPX, AppleTalk.
44. There are three ways a router learns how to
forward a packet:
1. Static Routes - Configured by the administrator manually. The
administrator must also update the table manually every
time a change to the network takes place. Static routes
are commonly used when routing from a network to a stub (a
network with a single route) network.
The command is
ip route network
mask address/interface [distance]
ex: ip route
22.214.171.124 255.255.255.0 126.96.36.199
Here, 188.8.131.52 is
the destination network or subnet
255.255.255.0 is the
184.108.40.206 is the
2. Default Routes - The default route (gateway of last resort) is used
when a route is not known or is infeasible. The command is
ip route 0.0.0.0
The default gateway
is set to 220.127.116.11
3. Dynamic Routes - In dynamic routing, the routing tables
are automatically updated. Dynamic routing uses broadcasts
and multicasts to communicate with other routers.
The commands to enable rip are:
45. To enable the Cisco IOS to forward packets
destined for obscure subnets of directly connected
networks onto the best route, you use "ip
46. There are broadly three types of routing
1. Distance Vector (Number of hops) - Distance vector
routing determines the direction (vector) and distance to
any link in the internetwork. Typically, the smaller the
metric, the better the path. EX: Examples of distance
vector protocols are
RIP and IGRP. Distance vector routing is useful for
smaller networks. The limitation is that any route which
is greater than 15 hops is considered unreachable.
Distance vector protocols listen to second hand
information to learn routing tables whereas, Link state
protocols build routing tables from first hand
information. Routers with distance vector protocols send
its entire routing table to each of its adjacent
2. Link State Routing: Link State algorithms are also
known as Shortest Path First (SPF) algorithms. SPF
generates the exact topology of the entire network for
route computation, by listening to the first hand
information. Link State protocols take bandwidth into
account using a cost metric. Link State protocols only
send updates when a change occurs, which makes them more
efficient for larger networks.
Bandwidth and delay are the most widely used
metrics when using Link-State protocols. EX: OSPF and NLSP.
Benefits of Link State protocols:
Allows for a larger scalable network
Reduces convergence time
3. Balanced Hybrid - Balanced Hybrid combines some aspects
of Link State and Distance Vector routing protocols.
Balanced Hybrid uses distance vectors with more accurate
metrics to determine the best paths to destination
networks. EX: EIGRP.
47. 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!
48. RIP (and IGRP) always summarizes routing information
by major network numbers. This is called classfull
49. Convergence is the term used to describe the state at
which all the internetworking devices,
running any specific routing protocol, are having
identical information about the internetwork in their
routing tables. The time it takes to arrive at identical
information of the internetwork is called Convergence
50. RIP,RIP2, and IGRP use distance vector algorithms.
RIP2 transmits the subnet mask with each
route. This feature allows VLSM (Variable Length Subnet
Masks) by passing the mask along with each route so that
the subnet is exactly defined.