CCNA CheatSheet

Contents
1. Introduction - OSI and TCP/IP.......................1
2. Cisco IOS Essentials.....................................2
3. Router Password Recovery..........................3
4. IPv4 Addressing.............................................4
5. IPv6 Addressing.............................................6
6. Subnetting......................................................7
7. Routing Protocols - EIGRP ….....................10
8. Routing Protocols OSPF.............................12
9. Network Address Translation (NAT)..........14
10. Access Control Lists (ACLs)......................15
11. VLANs and VTP............................................16
12. Ether Channel..............................................17
13. Spanning Tree Protocol..............................18
14. Router Redundancy (VRRP/HSRP)............20
15. Frequently Used Commands......................22
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Cisco™ CCNA : OSI and TCP/IP
1
Application : Responsible for identifying and establishing the availability of desired
comm partner and verifying sufficient resources exist for comm. Ex: FTP, SMTP
Presentation : Responsible for presenting the data in standard formats. Some
Presentation layer standards are JPEG, MPEG, MIDI, PICT, Quick Time, TIFF.
Session : Responsible for co-ordinating communication between systems/nodes.
Some of the session layer protocols and interfaces: NFS, RPC, SQL, ASP, DNA SCP
OSI MODEL
Transport : Responsible for multiplexing upper-layer applications, session mgmt
tearing down of virtual circuits, flow control and to maintain data integrity.
TCP/IP MODEL
Application : Defines TCP/IP application protocols and how
host programs interface with transport layer services to use
the network. Ex: FTP, SMTP, Telnet
Transport : Provides communication session management between
host computers. Ex: TCP, UDP
Internet : Performs routing of IP datagrams.
Ex: IP, ARP, ICMP
Some important port numbers
FTP : Port 20-21 Telnet : Port 23 DHCP : Ports 67 and 68 POP3 : Port 110
TFTP : Port 69 SMTP : Port 25 DNS : Port 53 HTTP : Port 80
Network : Responsible for sending packets from the source network to the destination
network using routing methods. Routers work at network layer.
Datalink : Consists of LLC sublayer and MAC sublayer. LLC handles error control, flow
flow control, framing etc. MAC handles access to shared media such as ethernet.
Physical : Responsible for ultimate transmission of data over network communications
media. Some of the standard interfaces at physical layer are EIA/TIA-232, V.24,V.35, HSSI
Physical : Controls the hardware devices and media that make
up the network.
Port numbers used by TCP/UDP
0-255 : Used for public applications
255-1023 : Assigned to companies
Above 1023 : Used by upper layers to set up sessions with other hosts and by
TCP to use as source and destination addresses.

Cisco™ CCNA : IOS
2
Internal memory components of a cisco router
ROM : Memory containing micro-code for basic functions to start and maintain the router.
RAM/DRAM : Stores the running configuration, routing tables, and packet buffers.
NVRAM : Memory that does not lose information when power is lost. Stores the system’s
configuration file and the configuration register.
Flash Memory : Stores the compressed IOS image.
Router boot configuration commands
boot system ROM : boots from system ROM
boot system flash <IOS file name> : boots
IOS from flash memory
boot system tftp <IOS file name>
<tftp_addr> : boots IOS from a tftp server
Cisco router configurable locations
Console port, Virtual Terminals (vty), Auxiliary port, TFTP server and Network management station
Router modes of operation include
Mode---------------------------> Prompt
user exec---------------------> Router>
Privileged----------------------> Router #
global config------------------> Router(config)#
Interface config--------------> Router(config-if)#
Router passwords
Enable password
Console password
Enable Secret
Virtual terminal password (vty)
Auxiliary password
Three ways router learns to forward packets
1. Static routes : Configured by the administrator manually. Syntax : ip route <ip-addr><mask-addr><ip-addr>
Ex: R1(config)#ip route 192.168.200.0 255.255.255.0 192.168.1.2
2. Default routes : This is used when a route is not known or is infeasible. Syntax : ip route 0.0.0.0 0.0.0.0 <ip-addr>
Ex: R1(config)#ip route 0.0.0.0 0.0.0.0 192.168.1.2
3. Dynamic routes : In dynamic routing, the routing tables are automatically updated.
Dynamic routing uses broadcasts and multicasts to communicate with other routers.
Router Cursor 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 Arrow”
<ctrl> B: Move backward one character, same as using “Left Arrow".
<ctrl> P: Repeat Previous command, same as using “Up Arrow”
<ctrl> N: Repeat Next (more recent) command, same as using "Down Arrow"
<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.
More info
To enable the Cisco IOS to forward packets destined for
obscure subnets of directly connected networks onto the best
route, use "ip classless" command.
By default, Cisco routers support 5 simultaneous telnet sessions.
This number can be configured using IOS commands.
Router Default Boot Sequence for Cisco IOS
1. NVRAM 3. TFTP server
2. Flash (sequential) 4. ROM
The router first looks at Startup Config file in NV
RAM, if not available, it falls back to Flash, then
to TFTP and then to ROM.
Configuration Register Command
Router(config)# config-register 0x10x (where that last x is 0-F in hex), when the last x is: 0 = boot
into ROM Monitor mode; 1 = boot the ROM IOS; 2 - 15 = look in startup-config file in NVRAM.

Cisco™ CCNA : Password Recovery
3
Note : The given procedures are generic in nature, and for exact sequence of steps, please refer to product manual.
Procedure 1
Complete these steps in order to recover your password:
1. Attach a terminal or PC with terminal emulation to the console port of the router and
set terminal settings to 9600 baud rate, No parity, 8 data bits, 1 stop bit, No flow
control.
The configuration register is usually set to 0x2102 or 0x102. If you can no longer
access the router you can safely assume that your configuration register is set to
0x2102.
2. Use the power switch in order to turn off the router, and then turn the router back on.
3. Press Break on the terminal keyboard within 60 seconds of power up in order to put
the router into ROMmon.
4. Type confreg 0x2142 at the rommon 1> prompt in order to boot from Flash. This step
bypasses the startup configuration where the passwords are stored.
5. Type reset at the rommon 2> prompt.
The router reboots, but ignores the saved configuration.
6. Type no after each setup question, or press Ctrl-C in order to skip the initial setup
procedure.
7. Type enable at the Router> prompt.
You are in enable mode and should see the Router# prompt.
8. Type configure memory or copy startup-config running-config in order to copy
the nonvolatile RAM (NVRAM) into memory.
9. Type configure terminal.
The router(config)# prompt appears.
10. Type enable secret <password> in order to change the enable secret password.
For example:
router(config)#enable secret cisco
11. Issue the no shutdown command on every interface that you use.
12. Type write memory or copy running-config startup-config in order to commit the
changes.
Procedure 2
Complete these steps in order to recover your password:
1. Shut down the router.
2. Remove the compact flash that is at the back of the router.
3. Power on the router.
4. Once the Rommon1> prompt appears, enter this command:
confreg 0x2142
5. Insert the compact flash.
6. Type reset.
7. When you are prompted to enter the initial configuration, type No, and press Enter.
8. At the Router> prompt, type enable.
9. At the Router# prompt, enter the configure memory command, and press Enter in
order to copy the startup configuration to the running configuration.
10. Use the config t command in order to enter global configuration mode.
11. Use this command in order to create a new user name and password:
router(config)#username cisco password cisco
12. Use this command in order to change the boot statement:
config-register 0x2102
13. Use this commnd in order to save the configuration:
write memory
Reload the router, and then use the new user name and password to log in to the
router.

Cisco™ CCNA : IPv4 Addressing
4
Converting Binary to Decimal
Binary is a base 2 system with only two numbers 0 or 1.
The weightage of binary digits from right most bit position to the left most bit
position is given below.
Example :
Convert 10011101 into a decimal value.
There are eight bits in the binary number. The decimal value for each bit position
is given below:
To convert, you simply take a value from the top row wherever there is a 1 below,
and then add the values together.
i.e, 1*27 + 0*26 + 0*25 + 1*24 + 1*23 + 1*22 + 0*21 + 1*20
= 128 + 0 + 0 + 16 + 8 + 4 + 0 + 1
= 157 (decimal value)
Converting Decimal to Binary
Decimal is a Base 10 system with 10 possible values (0 to 9)
To convert decimal to binary, simply divide the decimal value by 2 and then write
down the remainder, repeat this process until you cannot divide by 2 anymore.
For example, take the decimal value 157:
157 ÷ 2 = 78 with a remainder of 1 78 ÷ 2 = 39  with a remainder of 0
To convert, write this remainder first----------->
Next write down the value of the remainders from bottom to top (in other words
write down the bottom remainder first and work your way up the list) which
gives:
10011101 = 157

5
IP Address Intro
1. An IP address (32 bit number, 4 bytes) consists of four octets seperated
by dots.
The octet is a binary number of eight digits, which equals the decimal numbers
from 0 to 255.
2. The internet protocol defines the special network address 127.0.0.1 as a
local loopback address.
IP Address Classes ( Public IP range)
Class Format Leading-bit-pattern Network-addr-range Max-netw Max-hosts
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
Class D addresses are used for multicasting, they begin with “1110” and the addr range is 224-239.
Class E addresses are reserved addresses that begin with “11110” and the range is 240-254.
IPV4 Header
Private addr range : Class A : 10.0.0.0 to 10.255.255.255, Class B : 172.16.0.0 to 172.31.255.255,
Class C : 192.168.0.0 to 192.168.255.255
Subnet Mask and CIDR notation
A Subnet mask is a 32-bit number that masks an IP address, and divides the IP address into network
address and host address.
Subnet Mask is made by setting network bits to all "1"s and setting host bits to all "0"s.
Default Subnet Masks
Class A : 255.0.0.0, Class B : 255.255.0.0, Class C : 255.255.255.0
CIDR Notation : Classless Inter Domain Routing (CIDR) is a method for assigning IP addresses without
using the standard IP address classes like Class A, Class B or Class C.
In CIDR notation, an IP address is represented as A.B.C.D /n, where "/n" is called the IP prefix or network
prefix. The IP prefix identifies the number of significant bits used to identify a network.
Ex: 216.3.128.12, with subnet mask of 255.255.255.128 may be written as 216.3.128.12/25 using
CIDR Notation.

IPv6 : Points to Remember
1. IPv6 address is 128 bits in length represented in hexadecimal
2. IPv6 Loopback address is 0:0:0:0:0:0:0:1, also expressed as ::1.
3. IPv6 reserves two special addresses. They are 0:0:0:0:0:0:0:0 and 0:0:0:0:0:0:0:1.
4. Three transition strategies for migration from ipv6 to ipv4 are dual stacking, 6-to-4 tunneling and NAT-PT
6
EUI-64 Format
MAC to EUI-64 conversion inserts hex “FFFE” in the middle of a MAC addr, Then flips
the U/L bit to 1, in order to create a 64-bit interface ID from a 48-bit Mac address.
IPv6 Communication Types
Unicast : used for one-to-one communication.
There are 3 types of unicast addresses namely
global, unique-local and link-local
Multicast : used for one-to-many communication
IPv6 multicast address begins with "FF"
Anycast : used for one-to-one-of-many
communication
IPv6 Address Scopes
::/0----------------> Default Route
::/128------------> Unspecified
::1/128-----------> Loopback
FC00::/7---------> Unique Local Unicast
FE80::/10--------> Link-Local Unicast
FEC0::/10-------> Site-Local Unicast
FF00::/8----------> Multicast
IPv6 Addressing
IPv6 address consists of 8 groups of four hexadecimal digits separated by colons and which mainly consists
of 3 segments called Global Prefix which is of 48 bits, subnet part with 16 bits and Interface ID called as Host
part with 64 bits.
The first 3 octets constitute Global Prefix, the fourth octet constitute subnet part and the last four form the
Interface ID.
Rules : a) One set of 0's in the address can be replaced by :: but this can be done only once
b) One or any number of consecutive groups of 0 value can be replaced with two colons (::)
IPv6 Header
Version (4 bits) : IP version number (6)
Traffic Class (8 bits) : Used for QoS
Flow Label (20 bits) : Used for packet labelling
Payload Length (16 bits) : Length of the IPv6 payload
Next Header (8 bits) : Identifies the type of header following the IPv6 header
Hop Limit (8 bits) : Number of hops until the packet gets discarded.
Source Address (128 bits) : Source IP address
Destination Address (128 bits) : Destination IP address

Cisco™ CCNA : Subnetting
7
Subnetting Scenario Question 1
You want X number of subnets, what is the subnet mask ? (Assume we need 10 subnets, i.e, X=10)
Tip : Convert X to binary, determine how many low order bits need to make the number, that many bits is number of high order bits that make up your subnet mask, convert high order bits to
decimal value.
Solution :
Consider the Class C address – N.N.N.H where N is the Network portion and H is the host portion. Host Portion is as shown ----->
Step 1: Convert 10 to binary. Binary equivalent of 10 is as shown --------->
Step 2: Number of low order bits required to make the number is 4 (from the figure shown above)
Step 3: Therefore 4 high-order bits make up the subnet mask, i.e, 128, 64, 32, 16
Add 4 high order bits to create subnet mask i.e. 128+64+32+16=240 (11110000). The subnet mask is 255.255.255.255.240
255.255.255.240 is represented as -------->
Requirement for IPv4 Subnetting
1. Efficient use of available IP address space
2. Network traffic isolation
3. Improved security
4. Limiting broadcast messages
Subnetting Scenarios
The subnetting scenarios may broadly be divided in to two categories:
1. Optimize for a given number of hosts
2. Optimize for a given number of subnets
Finally, determine the host address range for each available subnet.

8
Determine the range of valid IP Addresses for an X subnet mask ? (Assume X value to be 240 in this case)
Tip : Convert X to binary and determine the decimal value of lowest high order bit, start the range of addresses at that value, and increment the range by that value.
.
Solution :
Step 1: Convert 240 to binary. Binary equivalent of 240 is as shown --------->
Step 2: The decimal value of lowest high order bit is 16 (24) as seen from the figure above. Therefore, this number becomes the increment value to determine the IP address ranges.
Subnet Mask: 255.255.255.240
Subnet Bits: 28 Host Bits: 4
Number of Subnets: 16 Hosts per Subnet: 14
The range of addresses for the given mask is as shown ------>
Note: All zeros and all ones host addresses cannot be used.

9
How many subnet bits are required for X number of hosts ? (Assume X value to be 5 in this case)
Tip : Convert X (for the subnets) to binary, determine the number of bits needed for the host portion, additionally determine the subnet mask from the remaining bits, using formula 2ⁿ, find the
relevant number of subnets in this scenario.
.
Solution :
Step 1: Consider the Class C address N.N.N.H, where H is the host portion whose binary and decimal representation is as shown ---->
Convert 5 to binary. Binary equivalent of 5 is as shown --------->
Step 2: As shown in the figure above, the number of bits needed for the host portion are 3. Therefore, 2bits-2=23-2=6 (6>5)
3 bits are required for the host portion for 5 hosts.
Step 3 (Additional): To know the subnet mask , add the decimal value of the remaining 5 bits i.e, (128+64+32+16+8) = 248
Subnet Mask is 255.255.255.248 (11111111.11111111.11111111.11111000)
Number of subnet bits: 29, here 5 bits are used from the host portion of our subnet mask
Therefore number of subnets required is (2n), where 'n' is the number of bits being used from the host portion of our subnet mask i.e. 5
Therefore, 25=32 is the number of subnets

Important terms used in EIGRP
Successor: A route (or routes) selected as the primary route(s) used to
transport packets to reach destination. Note that successor entries are kept in
the routing table of the router.
Feasible successor: A route (or routes) selected as backup route(s) used
to transport packets to reach destination. Note that feasible successor entries
are kept in the topology table of a router.
DUAL (Diffusing Update Algorithm): Enhanced IGRP uses DUAL algorithm to
calculate the best route to a destination
Routing metrics used by IGRP
Bandwidth: This is represents the maximum throughput of a link.
MTU (Maximum Transmission Unit): This is the maximum message length that is acceptable to
all links on the path. The larger MTU means faster transmission of packets.
Reliability: This is a measurement of reliability of a network link. It is assigned by the
administrator or can be calculated by using protocol statistics.
Delay: This is affected by the band width and queuing delay.
Load: Load is based among many things, CPU usage, packets processed per sec
Cisco™ CCNA : EIGRP
10
EIGRP (Enhanced Interior Gateway Protocol)
Important Features of EIGRP
1. Unlike RIP and IGRP, EIGRP updates are not periodic. EIGRP updates are sent only when
there is a topological change in the network.
2. In EIGRP, the router doing the summarization will build a route to null0 for the summarized
address. This ensures that the packets that are not destined for any network are routed
to null and thus dropped.
3. EIGRP provides the option of disabling route summarization.The command no
auto-summary can be used for this purpose. This option is not available in RIP and IGRP.
4. You can summarize routes in EIGRP at any arbitrary bit boundary
Important Command in EIGRP
1. Show ip eigrp topology : To display entries in the EIGRP topology table, use the show ip
eigrp topology command in EXEC mode.
2. show ip eigrp neighbours : To display the neighbors discovered by EIGRP, use the
show ip eigrp neighbors command in EXEC mode. It shows when neighbors become
active and inactive. The neighbor parameters displayed include Address, Interface,
Holdtime, Uptime, Q, Seq Num, SRTT, and RTO.
3. show ip route eigrp : Displays the EIGRP routes installed in the route table.
4. Show ip eigrp interface: Use the show ip eigrp interfaces command to determine on which
interfaces EIGRP is active, and to find out information about EIGRP relating to those
interfaces. The details shown include interfaces on which EIGRP is configured, numbered
of directly connected EIGRP neighbours on each interface, Mean SRTT, etc.

CiscoTM
CCNA : EIGRP
11
Packet types used by EIGRP when communicating with its neighboring EIGRP routers
1. Hello Packets - EIGRP sends Hello packets once it has been enabled on a router for a
network. These messages are used to identify neighbors and once identified, serve or
function as a keep alive mechanism between neighbors. EIGRP Hello packets are sent to
the link local Multicast group address 224.0.0.10.Hello packets sent by EIGRP do not require
an Acknowledgment to be sent confirming that they were received.
2. Acknowledgment Packets - An EIGRP Acknowledgment (ACK) packet is simply an EIGRP
Hello packet that contains no data. Acknowledgment packets are used by EIGRP to confirm
reliable delivery of EIGRP packets. ACKs are always sent to a Unicast address, which is
the source address of the sender.
3. Update Packets - EIGRP Update packets are used to convey reachability of destinations. Update
packets contain EIGRP routing updates. When a new neighbor is discovered, Update packets
are sent via Unicast to the neighbor which the can build up its EIGRP Topology Table. It is
important to know that Update packets are always transmitted reliably and always require explicit
Acknowledgment.
4. Query Packet - EIGRP Query packets are Multicast and are used to reliably request routing
information. EIGRP Query packets are sent to neighbors when a route is not available and the
router needs to ask about the status of the route for fast convergence. If the router that sends
out a Query does not receive a response from any of its neighbors, it resends the Query
as a Unicast packet to the non-responsive neighbor(s). If no response is received in 16 attempts,
the EIGRP neighbor relationship is reset.
5. Reply Packets - EIGRP Reply packets are sent in response to Query packets. The Reply packets
are used to reliably respond to a Query packet. Reply packets are Unicast to the originator of the
Query.
6. Request Packets - Request packets are used to get specific information from one or more
neighbors and are used in route server applications. These packet types can be sent either via
Multicast or Unicast, but are always transmitted unreliably.
Different Tables Used by EIGRP
1. Neighbor table: The neighbor table stores information about neighboring EIGRP routers:
a. Network address (IP)
b. Connected interface
c. Holdtime - how long the router will wait to receive another HELLO before dropping
the neighbor; default = 3 * hello timer
d. Uptime - how long the neighborship has been established
e. Sequence numbers
f. Retransmission Timeout (RTO) - how long the router will wait for an ack before retransmitting
the packet; calculated by SRTT
g. Smooth Round Trip Time (SRTT) - time it takes for an ack to be received once a packet has
been transmitted
h. Queue count - number of packets waiting in queue; a high count indicates line congestion
2. Topology table: It contains only the aggregation of the routing tables gathered from all
directly connected neighbors (not the entire network!). This table contains a list of destination
networks in the EIGRP- routed network together with their respective metrics. Also for every
destination, a successor and a feasible successor are identified and stored in the table if they
exist. Every destination in the topology table can be marked either as "Passive", which is the
state when the routing has stabilized and the router knows the route to the destination, or
"Active" when the topology has changed and the router is in the process of (actively)
updating its route to that destination.
3. Routing table: Stores the actual routes to all destinations; the routing table is populated from the
topology table with every destination network that has its successor and optionally feasible
successor identified (if unequal-cost load-balancing is enabled using the variance command)
The successors and feasible successors serve as the next hop routers for these destinations.

Cisco™ CCNA : OSPF
12
OSPF and OSPF Area
OSPF is a link state technology that uses Dijkstra algorithm to compute routing
information.
An OSPF area is a collection of networks and routers that have the same area
identification.OSPF process identifier is locally significant.
OSPF router ID determination
1. Use the address configured by the ospf router-id command
2. Use the highest numbered IP address of a loopback
interface
3. Use the highest IP address of any physical interface
4. If no interface exists, set the router-ID to 0.0.0.0
DR and BDR Election
When two or more routers are contending to be a DR (designated Router) on a network segment, the router with the highest OSPF priority will become the DR for that segment. The same process is
repeated for the BDR. In case of a tie, the router with the highest RID will win.
OSPF Area Types
Standard Area : Default OSPF area type
Stub Area : External link (type 5) LSAs are replaced with a default route
Totally Stubby Area : Type 3, 4, and 5 LSAs are replaced with a default route
Not So Stubby Area (NSSA) : A stub area containing an ASBR; type 5 LSAs are
converted to type 7 within the area
OSPF Priority
The ip ospf priority command is
used to set manually which router
becomes the DR. The range is 0-
255 and the default is 1. 0 means
it will never be DR or BDR.
Router Types
Internal Router : All interfaces reside within the same area
Backbone Router : A router with an interface in area 0 (the backbone)
Area Border Router (ABR) : Connects two or more areas
AS Boundary Router (ASBR) : Connects to additional routing domains; typically located in
the backbone

Cisco™ CCNA : OSPF
13
OSPF LSA Types
a. LSA 1 (Router LSA): Generated by all routers in an areato describe their directly attached
links (Intra-area routes).These do not leave the area.
b. LSA 2 (Network LSA): Generated by the DR of a broadcast or Nonbroadcast segment to
describe the neighbors connected to the segment. These do not leave the area.
c. LSA 3 (Summary LSA): Generated by the ABR to describe a route to neighbors outside the
area(Inter-area routes).
d. LSA 4 (Summary LSA): Generated by the ABR to describe a route to an ASBR to neighbors
outside the area.
e. LSA 5 (External LSA): Generated by ASBR to describe routes redistributed into the area.
These routes appear as E1 or E2 in the routing table. E2 (default) uses a static cost
Throughout the OSPF domain as it only takes the cost into account that is reported at
redistribution. E1 uses a cumulative cost of the cost reported into the OSPF domain at
Redistribution plus the local cost to the ASBR.
f. LSA 6 (Multicast LSA): Not supported on Cisco routers.
g. LSA 7 (NSSA External LSA): Generated by an ASBR inside a NSSA to describe routes
redistributed into the NSSA. LSA 7 is translated into LSA 5 as it leaves the NSSA.
These routes appear as N1 or N2 in the ip routing table inside the NSSA. Much like LSA 5
N2 is a static cost while N1 is a cumulative cost that includes the cost up to the ASBR.
LSAs used by different OSPF Areas
a. Area backbone LSAs: The LSAs generated by Area Backbone Routers are LSA1,
LSA2, LSA3, LSA4, and LSA5. Note that LSA6 is not supported by Cisco, and
LSA7 is generated by NSSA router.
b. Stub area LSAs: The Stub area router generates LSA types 1, 2, and 3. i.e.
Router LSA, Network LSA, and Summary LSA.
c. Totally Stubby LSAs: The Totally Stubby area routers generate LSA types 1 and 2
NSSA LSAs: A NSSA (Not So Stubby Area) router generates LSA types 1, 2, and 7.
LSA 7 is translated into LSA 5 as it leaves the NSSA
Default Route Advertisement in OSPF
A default route can be advertised into OSPF domain by an ASBR
router in one of two ways:
1.By using “default-information originate” command: This command
can be used when there is a default route(0.0.0.0/0) already existing.
This command will advertise a default route into OSPF domain.
2. By using “default-information originate always” command: This
command can be used when there is a default route (0.0.0.0/0) is
present or not. This command is particularly useful when the
default route is not consistent. An inconsistent default route may
result in flippingof the route advertised into the OSPF domain,
resulting in instability of the OSPF domain routing information.
Therefore,it is recommended to use “always” keyword.
Important Features of Stub Area
1. A stub area reduces the size of the link-state database to be maintained in an
area,which in turn result in less overhead in terms of memory capacity,
computational power, and convergence time.
2. The routing in Stub and totally Stubby areas is based on default gateway.
A default route (0.0.0.0) needs to be configured to route traffic outside the area.
3. The stub areas suited for Hub-Spoke topology.
4. Area 0 is not configured as Stubby or totally Stubby. This is because stub areas
are configured mainly to avoid carrying external routes, whereas Area 0 carries
external routes.
External Routes
The cost of external route depends on the configuration of ASBR.
There are two external packet types possible.
1. Type 1 (E1) - Here the metric is calculated by adding the external cost to the internal
cost of each link that the packet crosses.
2. Type 2 (E2) - This type of packet will only have the external cost assigned,
irrespective of where in the area it crosses. Type 2 packets are preferred over
Type1packets unless there are two same cost routes existing to the destination.

Cisco™ CCNA : NAT
14
Overloading
A special case of dynamic NAT that maps multiple unregistered IP addresses to a single registered (globally
unique) IP address by using different port numbers.
Dynamic NAT with overloading is also known also as PAT (Port Address Translation).
Static NAT
Maps an unregistered IP address to registered IP (globally unique) addresses on one-to-one basis.
The command, ip nat inside source static <local ip> <global ip> configures address translation for
static NAT.
Configuring NAT
When configuring NAT, NAT should be enabled on at least
one inside and one outside interface.
1. The command for enabling NAT on inside interface is:
R1(config-if)#ip nat inside
2. The command for enabling NAT on the outside interface
is:
R1(config-if)#ip nat outside
Remember to enter into appropriate configuration modes
before entering the commands.
Usually, the inside NAT will be configured on an Ethernet
interface, whereas the outside NAT is configured on a
serial interface.
Address Classification
Inside Local : An actual address assigned to an inside host
Inside Global : An inside address seen from the outside
Outside Global : An actual address assigned to an outside host
Outside Local : An outside address seen from the inside
NAT Pool : A pool of IP addresses to be used as inside global or
outside local addresses in translations
Defining an IP NAT Pool
1. Defining an IP NAT pool for the inside network using the command:
ip nat pool <pool-name> <start-ip> <end-ip> {netmask <net-mask> | prefix-length <prefix-length>} [type-
rotary] Ex: ip nat pool pool1 200.200.200.3 200.200.200.4 netmask 255.255.255.0
Note that type-rotary is optional command. It indicates that the IP address range in the address pool identifies
hosts among which TCP load is distributed.
2. Mapping the access-list to the IP NAT pool by using the command:
ip nat inside source list <access-list-number> pool <pool-name> Ex: ip nat inside source list 1 pool pool1
Dynamic NAT
Maps an unregistered IP address to a registered (globally unique) IP address from a group of registered
(globally unique) IP addresses.
The command, ip nat inside source list <access-list-number> pool <name>
is used to map the access-list to the IP NAT pool during the configuration of Dynamic NAT.
Overlapping
This occurs when your internal IP addresses belong to global IP address range that belong to another
network.

Cisco™ CCNA : Access-Lists
15
Access Lists
IP access lists are a sequential list of permit and deny conditions that apply to IP addresses or upper
layer protocols. Access Control Lists are used in routers to identify and control traffic.
Purpose of Access Lists
1. Controlling traffic through a router, and
2. Controlling VTY access to a router’s VTY
ports
3. Filter incoming and outgoing packets
4. Restrict contents of routing updates
5. Trigger dial-on-demand routing (DDR) calls
Types of IP Access Lists
Standard IP Access Lists
Extended IP Access Lists
Named Access Lists
Wild Card Masking
Wild card masking is used to permit or deny a group of addresses.
For example, if we have a source address 185.54.13.2 and want all the
hosts on the last octet to be considered, we use a wild card mask,
185.54.13.255.
The 32 bit wildcard mask consists of 1’s and 0’s
1 = ignore this bit
0 = check this bit
Special Case: Host 185.54.13.2 is same as 185.54.13.2 with a wild card
mask of 0.0.0.0, considers only specified IP.
Any is equivalent to saying 0.0.0.0 with a wild card mask of
255.255.255.255. This means none of the bits really matter. All IP
addresses need to be considered for meeting the criteria.
Standard Access List
1. These have the format, access-list [number] [permit or deny] [source_address]
Ex: access-list 1 permit 192.168.2.0 0.0.0.255
2. Place standard access lists as near the destination as possible and extended access lists
as close to the source as possible.
3. Access lists have an implicit deny at the end of them automatically. Because of this, an
access list should have at least one permit statement in it; otherwise the access list will
block all remaining traffic.
4. Access lists applied to interfaces default to outbound if no direction is specified.
Extended Access Lists and Named Access Lists
Extended Access lists have the format,
access-list {number}{permit or deny} {protocol} {source}source-wildcard [operator
[port]]{destination} destination-wildcard [operator [port]]
With extended IP access lists, we can act on any of the following:
- Source address - Port information (WWW, DNS, FTP, etc.)
- Destination address
- IP protocol (TCP, ICMP, UDP, etc.)
Ex: access-list 101 permit icmp host 192.168.3.2 any
Named Access lists have the format, ip access-list {standard /extended} name
Ex: ip access-list extended denyping
Permitted numbers for access-lists
1-99: IP standard access list 100-199: IP extended access list 800-899: IPX standard access list
1000-1099: IPX SAP access list 1100-1199: Extended 48-bit MAC address access list 900-999: IPX extended access list

Cisco™ CCNA : VLANs and VTP
14
VLANs – Points to Remember
1. VLAN 1 is the management VLAN.
2. Static VLAN : VLAN is statically assigned to the physical port and never changes.
3. Dynamic VLAN : VMPS automatically assigns VLAN based on MAC
4. Access Link : An access link can carry only one VLAN (used between host and switch port)
5. Trunk Link : A trunk link can carry multiple VLANs. Used to connect to other switches,
routers, or servers
6. Two types of Trunk framing: ISL (Cisco only) and 802.1.q
7. Trunk links can carry 1 to 1005 VLANs
8. Switchport modes are trunk, dynamic desirable, dynamic auto, access.
VLAN configuration
Creating VLANs
SW1#vlan database
SW1(vlan)#vlan 10 name firstvlan
SW1(vlan)#vlan 20 name secondvlan
VTP – Points to Remember
1. VTP is a Layer 2 messaging protocol. It carries configuration information throughout a
single domain
2. VTP Modes are
Server : Create, modify, or delete VLANs (This is the deafult vtp mode on a switch)
Client : Can't create, change, or delete VLANs
Transparent : Used when a switch is not required to participate in VTP, but only pass
the information to other switches
3. VTP domain is common to all switches participating in VTP
4. Pruning is a technique where in VLANs not having any access ports on an end switch
are removed from the trunk to reduce flooded traffic
5. Configuration revision number is a 32-bit number that indicates the level of revision
for a VTP packet. Each time the VTP device undergoes a VLAN change, the config
revision is incremented by one.
Access Port configuration
SW1(config-if)#switchport mode access
SW1(config-if)#switchport access vlan 10
Trunk Port configuration
SW1(config-if)#switchport mode trunk
SW1(config-if)#switchport trunk encapsulation dot1q
VTP Configuration
SW1#vlan database
SW1(vlan)#vtp mode (Server/Client/Transparent)
SW1(vlan)#vtp domain <name>
SW1(vlan)#vtp password <password>
SW1(vlan)#vtp pruning
Troubleshooting commands
1. show vlan
2. show vlan-membership
3. show vtp status
4. show interfaces trunk
5. show interface <interface-name> switchport
Access port config to a range of interfaces
SW1(config)#interface range fa 0/2 - 5
SW1(config)#interface range fa 0/6 - 10

Cisco™ CCNA : EtherChannel
17
EtherChannel
EtherChannel is a port link aggregation technology used primarily on Cisco
networking devices.It allows grouping of several physical Ethernet links to
create one logical Ethernet link for the purpose of providing fault-tolerance
and high-speed links between switches, routers and servers.
Features of EtherChannel that is running PagP
1. PAgP helps in the automatic creation of Fast EtherChannel.
2. PAgP does not group ports configured for dynamic VLANs. PagP requires
that all ports in a channel must belong to the same VLAN or should be
configured as trunk ports.
3. PAgP does not group ports that work at different speeds or port duplexes.
4. The load distribution algorithm in EtherChannel can use source IP,
destination IP, a combination of source and destination IPs, Source MAC,
destination MAC, or TCP.UDP port numbers for decision process. If there
are only two links in the EtherChannel, only 1 bit in the IP are required.
If there are 4 links in the EtherChannel, 2 bits are required.An XOR on
2 bits can have 4 possible outcomes. Similarly,for an 8 link EtherChannel,
3 bits are required.Conventionally, rightmost bits are always used
for XOR operation.
Important Features of Bundled Ports Using EtherChannel
1. EtherChannel can support from two to 8 links to be bundled into one logical link.
Therefore, if Gigabit Ethernet links are bundled, 8 links represents 8 Gbps of
one-way bandwidth, and 16 Gbps for full-duplex operation.
2. The bundled ports must have identical Spanning Tree settings
3. The bundled ports must have the same speed, duplex, and Ethernet media.
4. The bundled ports must belong to the same VLAN if not used as VLAN trunk.
5. If the bundled ports represent a VLAN trunk, then they must have same native
VLAN,and each port should have same set of VLANs in the trunk.
6. The EtherChannel also provides link redundancy. If one of the bundled links
fail,the traffic through the failed link is distributed to other working links in the
channel.The failover is transparent to the end user. Similarly traffic again flows
through the restored link, as and when a link is restored.
7. Note that the load balancing can be done based on source IP, destination IP,
both source and destination IP (XOR), source and destination MAC
addresses or TCP/UDP port numbers.
PAgP modes and the corresponding action
1. ON mode does not send or receive PAgP packets. Therefore, both ends
should be set to ON mode toform an EtherChannel.
2. Desirable mode tries to ask the other end in order to bring up the EtherChannel.
3. Auto mode participates in the EtherChannel only if the for end asks for
participation. Two switches in auto mode will not form an EtherChannel.
Important Commands
1. switch# show etherchannel port
Used for verifying the channel negotiation mode of an EtherChannel.
2. Switch# show etherchannel summary
Shows each port in the channel along with the status flag.
3. Switch(config)# port-channel load-balance src-ip
Will configure load balancing on EtherChannel switch links using source IP address.
PagP (Short for Port Aggregation Protocol)
PagP helps in the automatic creation of Fast EtherChannel links. PagP is
protocol is Cisco proprietary link aggregation protocol used in Cisco switches
routers, and servers.
LACP (Short for Link Aggregation Control Protocol)
LACP is different from PAgP. LACP is a standards based protocol and conforms
to IEEE standard 802.3ad, whereas PAgP is a Cisco proprietary protocol.

CiscoTM
CCNA : Spanning Tree Protocol
18
STP – Points to Remember
1. STP is a layer 2 protocol that runs on switches and bridges, the purpose of STP is to remove
switching loops. By default, STP is enabled on cisco switches.
2. All switches participating in STP exchange info with other switches in the network
Through messages known as BPDUs (Sent out at a frequency of 2 sec on every port)
3. STP port states are Blocked, Listen, Learn, Forward, Disabled
4. The command “show spanning-tree” includes the following info
i. VLAN number
ii. Root bridge priority, MAC address
iii. Bridge timers (Max Age, Hello Time, Forward Delay)
Selection Criteria
Root Bridge Selection
The switch with the lowest Bridge ID is chosen as
root.
Bridge ID is a combination of switch priority (32768
by default and the range is 0 to 65535 with
increments of 4096) and switch's MAC address
STP Port Roles
1. Root : A bridge can have only one root port. The root port is the port that leads to the root
bridge. All bridges except the root bridge will have a root port. the root port is in the STP
forwarding state.
2. Designated : One designated port is elected per link (segment). The designated port is
the port closest to the root bridge. Each designated port is in the STP forwarding state
3. Alternate : Alternate ports lead to the root bridge, but are not root ports. The alternate
ports maintain the STP blocking state.
4. Backup: This is a special case when two or more ports of the same bridge (switch) are
connected together, directly or through shared media. In this case, one port is designated,
and the remaining ports block. The role for this port is backup.
Root Port Selection
i . If there are 2 or more paths to reach the Root Bridge, select the bridge port associated with
the lowest accumulated path cost. OR
ii. If the path cost to reach the root bridge over 2 or more bridge ports is same, then: select the
neighboring switch with the lowest Switch ID value to reach the Root Bridge OR
iii. If there are two or more ports on the same bridge with the lowest path cost, then:
* Select the port with the lowest Port Priority value, if you have multiple paths to reach the
Root Bridge via same neighbor switch. OR
* If all the ports are configured with same priority number (32 by default), select the lowest
port number on the switch.
Designated Bridge Selection
i. In a LAN segment, the bridge with the lowest
path cost to the Root Bridge will be the DB OR
ii. If there are two bridges in the LAN segment
with equal path cost to the Root Bridge, then the
Bridge with the lowest Bridge ID becomes the
DB.
Designated Port Selection
i. The switch port (associated with the DB) on the LAN segment with the lowest accumulated path
cost to the Root Bridge will be selected as DP for the given segment. OR
ii. If a switch has redundant connections to the network segment, the switch port with the lowest
port priority (32 by default) is selected. OR
iii. If there is again a tie (it can happen if the priorities of the ports on this switch are the same), then
the lowest numbered port on the switch is selected.
Default Timers
Hello-----------------> 2s
Forward Delay-----> 15s
Max Age-------------> 20s
Link Costs
Bandwidth Cost
10 Mbps-----------> 100
100 Mbps----------> 19
1 Gbps---------------> 4
10 Gbps-------------> 2

CiscoTM
CCNA : Spanning Tree Protocol
19
Spanning Tree Protocols
a. Rapid Spanning Tree Protocol (RSTP) is based on the IEEE standard 802.1w. The standard has evolved from its
predecessor 802.1D. 802.1w has the advantage of faster convergence over 802.1D.RSTP defines port states
according to what the port does with the incoming frames. The allowed port states are as given below:
1. Discarding: The incoming frames are discarded. No MAC addresses are learned.
2. Learning: The incoming frames are dropped, but MAC addresses are learned.
3. Forwarding: The incoming frames are forwarded according to the learned MAC addresses.
b. PVST (Per VLAN Spanning Tree) implementation has one instance of STP running for each VLAN. Therefore, whe there are 32 VLANs in the bridge network, there
will be 32 instances of STP running. Also, each VLAN has a unique root, path cost etc. corresponding to that VLAN.
Protection against sudden loss of BPDUs
1.BPDU Skew Detection 2.Root Guard 3.BPDU Guard 4.UDLD 5.Loop Guard
1. Root Guard - When configured at the interface level, BPDU Guard shuts the port down as
soon as the port receives a superior BPDU. To enable root guard, use the command:
switch(config-if)# spanning-tree guard root
If the superior BPDUs are no more received, the port is restarts the normal STP states to return
to normal use.
2. BPDU Guard - Here if any BPDU (superior or not) is received on a port configured with BPDU
guard, the port is immediately put into errdisable state. The port is effectively shutdown.
To enable BPDU guard use the command at interface configuration mode:
switch(config-if)# spanning-tree bpduguard enable
A port that is shutdown will continue to be in errdisable state even if the BPDUs are no longer
received.It is recommended to use bpdu guard on all ports that have portfast enabled. The
protection is useful for access layer nodes where the end user computers are expected to be
Connected.
3. BPDU Skew Detection -It measures the amount of time that elapses from the expected time of
arrival of a BDPU to the actual time of arrival of the BDPU. The arrival skew time condition is
reported via syslog messages.
4. Loop Guard - The loop guard is intended to provide additional protection against L2 forwarding
Loops (STP loops). For example, an STP loop is created when a blocking port in a redundant
topology erroneously transitions to forwarding state. The loop guard needs to be enabled on the
non-designated ports to effectively prevent STP loops. Non-designated ports are the root port,
alternate root ports,and ports that are normally blocking. The command used to enable loop
guard is: Switch(config-if)# spanning-tree guard loop
The command is used at port level, loop guard is disabled by default on all switch ports.
5. Unidirectional Link Detection (UDLD) - The UDLD protocol allows devices connected through
media such as fiber-optic or twisted-pair Ethernet to monitor the physical configuration of
the cables and detect when a unidirectional link exists. If a unidirectional link is detected,
UDLD shuts down the affected port and send out an alert.
Spanning Tree Port States
The ports on a switch with enabled Spanning Tree Protocol (STP) are in one of the following
five port states.
1. Blocking 2. Listening 3. Learning 4. Forwarding 5.Disabled
A switch does not enter any of these port states immediately except the blocking state. When the
Spanning Tree Protocol (STP) is enabled, every switch in the network starts in the blocking state and
later changes to the listening and learning states.
Blocking - During blocking state, the port is listening to and processing BPDUs After 20 seconds,
the switch port changes from the blocking state to the listening state.
Listening - After blocking, a root port or a designated port will move to a listening state. During the
listening state the port discards frames received from the attached network segment it also discards
frames switched from other ports for forwarding. At this state, the port receives BPDUs from the
network segment and directs them to the switch system module for processing. After 15 seconds,
the switch port moves from the listening state to the learning state.
Learning - A port moves into the learning state after the listening state. During the learning state,
the port is listening for and processing BPDUs. In the listening state, the port starts to process user
frames and starts updating the MAC address table. Userframes are not forwarded to the destination.
After 15 seconds, the switch port moves from learning to forwarding.
Forwarding - Once in the forwarding state the port sends traffic. In a forwarding state, the port will
process BPDUs, update its MAC Address table with frames that it receives, and forward user traffic
through the port Forwarding State is the normal operational state.
Disabled - A port in the disabled state does not participate in frame forwarding and is
considered non-operational

Cisco™ CCNA : Router Redundancy
20
Important Features of HSRP
1. HSRP authentication is carried out in clear text.
2. The hosts served by HSRP router use the IP address of virtual router as the default IP address.
3. When an Active router fails in HSRP environment, Standby router assumes the Active router role.
This new Active router will remain as Active router even if the failed Active router comeback to service,
irrespective of the priority levels.
4. The default HSRP standby priority is 100. If the standby priorities of routers participating in HSRP are
same, the router with the highest IP address becomes the Active router.
5. Within the standby group of routers, the router with the highest standby priority in the group becomes
the active router. For example, a router with a priority of 100 will become active router over a router with
a priority of 50. The active router forwards packets sent to the virtual router. It maintains its active state
by using Hello messages.
6. Each router in a standby group can be assigned a priority value. The range of priority values is between
0 and 255 (including 0 and 255). The default priority assigned to a router in a standby group is 100. The
router with numerically higher priority value will become Active router in the HSRP standby group.
7. All routers in an HSRP standby group can send and/or receive HSRP message. Also, HSRP
protocol packets are addressed to all-router address (224.0.0.2) with a TTL of 1.
Note that the HSRP messages are encapsulated in the data portion of UDP packets.
8. In HSRP, the MAC address used by virtual router is made up of the following three components:
a. Vendor ID: The first three bytes of the MAC address correspond to the vendor ID.
b. HSRP ID: The next two bytes of the MAC address correspond to HSRP code. It is always 07.ac.
Therefore, the virtual router MAC address will have 07.ac in the fourth and fifth bytes.
c. Group ID: The last byte of the MAC address is the group's identification number.
Router Redundancy Protocols
1. Hot Standby Router Protocol (HSRP): HSRP is a Cisco proprietary protocol that offers router
redundancy. Here one router is elected as active router, and another router is elected as
standby router. All other routers are put in listen HSRP state. HSRP messages are exchanges
using multicast destination address 244.0.0.2 to keep a router aware of all others in the group.
2. Virtual Router Redundancy Protocol (VRRP): VRRP is very similar to HSRP. VRRP is a
standards based protocol and defined in RFC 2338. VRRP sends advertisements to multicast
destination address 244.0.0.18 using IP protocol.
3. Gateway Load Balancing Protocol (GLBP): GLBP overcomes some of the limitations of
HSRP/VRRP. Here, instead of just one active router, all routers in the group can participate
and offer load balancing.
4. Server Load Balancing (SLB): SLB provides a virtual server IP address to which client
machines can connect. The virtual server, in turn, is a group of real physical servers arranged
in a server farm.
Members of HSRP Group
1. Virtual router: virtual router is what is seen by the end user device. The virtual router has its
own IP and MAC addresses.
2. Active router: Forwards packets sent to the virtual router.An active router assumes the IP
and MAC addresses of the virtual router.
3. Standby router: Standby router monitors the state of HSRP by using Hello massages. It
assumes the role of Active router, should the current Active router fail.

CiscoTM
CCNA : Router Redundancy
21
Virtual Router Redundancy protocol (VRRP) – Important Features
1. VRRP will have one master router, and all other routers are in the backup state.
2. VRRP router priorities range from 1 to 254. By default, the priority is set to 100. 254 is
the highest priority.
3. The MAC address of the virtual router is of the form 0000.5e00.01xx, where xx is the
VRRP group number in the range 0 to 255 or 0 to ff hex.
4. The interval for VRRP advertisements is 1 second by default.
5. All VRRP routers are configured to preempt the current master router by default.
The router priority should be highest for the preemption to occur.
GLBP (Gateway Load Balancing Protocol) Load Balancing Methods
1. Round robin: Here the traffic load is distributed evenly across all routers.
2. Weighted: A higher weighting results in more ARP replies containing the virtual
MAC address of the router with higher weight.
3. Host-dependent: Here each client that generates an ARP always receives the same
virtual MAC. In other words, the MAC address is dependent on the host.
HSRP - Important Commands
RouterA# show standby
- Displays the HSRP router status. The command displays the router priority, state (active/standby), group
Number among other things.Also, to enable HSRP debugging, used the command:
RouterA# debug standby
- Enables HSRP debugging. To disable debugging, use the command “no debug standby”
R(config-if)# standby <group-number> priority <priority-value>.
- Sets the router’s priority in the standby group.
standby <group-number> preempt
- is used to force an interface to resume Active router state. Note that the priority of the router should be higher
than the current Active router.
R(config-if)# standby <group-number> ip <virtual-ip-address>
- Configures a router as a member of an HSRP standby group.
R(config-if)#standby 45 ip 192.32.16.5
- Sets group number 45 with a virtual IP address of 192.32.16.5
Syntax: R(config-if)# standby <group-number> ip <virtual-ip-address>
R(config-if)# standby <group-number> preempt
- Enables the previous Active router to resume its activity as Active router by taking over the role from
lower priority Active router.
standby <group-number> preempt
- Used to force an interface to resume Active router state. Note that the priority of the router
should be higher than the current Active router.

CiscoTM
CCNA : Configuration Commands
A. Setting Passwords
Sl. No. Task Commands
1 Configure router console password as "ciscocs"
R1(config)#line console 0
R1(config-line)#login
R1(config-line)#password ciscocs
2 Configure router vty password as "ciscovty"
R1(config)#line vty 0 4
R1(config-line)#password ciscovty
3 Configure router auxiliary password as "ciscoaux"
R1(config)#line aux 0
R1(config-line)#password ciscoaux
4 Set the encrypted enable password as "cisco" R1(config)#enable secret cisco
5 Set the unencrypted enable password as "ccna" R1(config)#enable password ccna
B. Router Copy Commands
6 Copy the running-configuration to startup-configuration (DRAM to NVRAM) R1#copy running-config startup-config (copy run start)
7 Copy the startup-configuration to running-configuration (NVRAM to DRAM) R1#copy startup-config running-config (copy start run)
8 Copy the startup-configuration to a TFTP server R1#copy startup-config tftp (copy start tftp)
9 Copy the running-configuration to a TFTP server R1#copy running-config tftp (copy run tftp)
10 Save a backup of the IOS to a TFTP server R1#copy flash tftp
11 Upgrade the IOS from a TFTP server R1#copy tftp flash
C. Routing Commands
12 Enable RIP version1 on all 192.168.x.x interfaces
R1(config)#router rip
R1(config-router)#network 192.168.0.0
13 Enable RIP version 2
R1(config)#router rip
R1(config-router)#version 2
15 Enable EIGRP with an AS number of 1, to all interfaces in the network 19.168.x.x
R1(config)#router eigrp 1
R1(config-router)#network 192.168.0.0
16
Enable OSPF on any local interface which starts with IP address
10.1.x.x , note the inverted mask and area.
R1(config)#router ospf 1
R1(config-router)#network 10.1.0.0 0.0.255.255 area 0
22

CiscoTM
CCNA : Show Commands
Router Show commands
Sl. No. Command Explanation
1. show access-list Displays all accesslists from all protocols present in a specified router.
2. show banner Displays the banner set on the router.
3. show cdp Shows the status of CDP such as holdtime value,no.of packets for every 60sec.
4. show cdp interface It tells the CDP configuration on an interface-by-interface basis.
5. show cdp neighbor|detail Displays info on directly connected neighbors.
6. show cdp traffic Displays the CDP traffic info.
7. show clock Displays the clock (time, date).
8. show flash Used to view all IOS images and file stored in flash(Default location of IOS images is in flash).
9. show frame-relay lmi Shows the detailed statistics regarding LMI.
10. show frame-relay map Displays the frame relay inverse ARP table.
11. show frame-relay pvc <dlci_num> Shows all the frame relay PVC's terminated and their statistics at a specified router.
12. show history Shows the previously executed commands.IOS device stores the last ten commands that are executed.
13. show hosts Displays the host table.
14. show interfaces To view interfaces,status,and statistics for an interface.If u don't lists a specific interface,all of the interfaces on the router are listed.
15. show ip eigrp neighbors Shows the list of eigrp neighbors that a specified router has.
16. show ip eigrp topology Displays the list of successor and feasible successors,as well as other types of routes.
17. show ip eigrp traffic It shows the information about trafiic statistics for eigrp.
18. show ip interfaces Displays status and global parameters associated with the interfaces on the router.
19. show ip interface brief Displays the interface operational status and IP addresses for all router interfaces.
20. show ip nat statistics Displays NAT statistics.
21. show ip nat translations Displays the NAT translations.
22. show ip ospf Displays general information about OSPF routing processes.
23. show ip ospf database Displays lists of information related to the OSPF database for a specific router.
24. show ip ospf interface If adjacent router's dont become neighbors, then use the command to check if the local router interface is configured correctly.
25. show ip ospf neighbor Displays the OSPF neighbour information.
26. show ip ospf neighbor detail Displays all OSPF neighbors in detail.
27. show ip route Displays the IP routing table.
28. show protocols Displays the routing protocols that have been configured and running on a specified router.
29. show running-config Shows the current config stored in RAM.
30. show sessions Shows the telnet sessions that are currently suspended.
31. show startup-config Shows the configuration stored in NVRAM.
23

CiscoTM
CCNA : Show Commands
32. show version Display version information for the hardware and firmware.
33. show arp Displays entries in the ARP table.
34. show ip protocols Displays parameters and current state of the active routing protocol process.
35. show users Displays users connected to the router.
36. show ipv6 interface <interface-name> Displays ipv6 interface configuration information.
37. show ipv6 rip Displays information about all current IPV6 RIP processes.
38. show ipv6 ospf Displays general information about OSPF routing processes.
39. show ipv6 route Displays routes in the IPV6 routing table.
40. show ipv6 protocols Displays parameters and current state of the active IPV6 routing protocol processes.
41. show ip dhcp binding Displays IP addresses assigned to the clients.
Switch Show commands
Sl. No. Command Explanation
1. show banner Displays the banner.
2. show flash Displays the file contents of the flash.
3. show history Displays the last 10 commands entered.
4. show interfaces To view interfaces,status,and statistics for an interface.
5. show interfaces vlan 1 Displays the VLAN status and the IP address of VLAN 1.
6. show ip interface brief Verifies the IP configuration.
7. show running-config Displays the config held in DRAM.
8. show startup-config Displays the NVRAM config.
9. show users Displays the users currently logged on.
10. show version Display IOS version information for the hardware and firmware.
11. show vlan Displays vlan information.
12. show vlan-membership Displays vlan membership information.
13. show mac-address-table Displays mac-address-table information.
14. show vtp status Displays vtp status information such as vtp mode, vtp domain etc.
15. show spanning-tree Displays spanning-tree statistics,including information about root bridge and port status.
16. show spanning-tree summary Displays summary of port states.
17. show spanning-tree vlan <vlan-id> Displays STP information for the specified VLAN.
24

CCNA CheatSheet

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