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CCNA Cheatsheet – GeeksforGeeks

A CCNA certification proves you’ve the competencies wanted to navigate an ever-changing IT panorama. CCNA exams cowl community fundamentals, IP providers, safety fundamentals, automation, and programmability. Designed for agility and flexibility, CCNA proves you’ve the talents wanted to handle and optimize at this time’s most superior networks. CCNA coaching programs and exams are the inspiration for advancing your profession in any route. A Cisco certification resides proof of the requirements and rigor your group acknowledges and trusts to satisfy and exceed market calls for. Here’s a cheat sheet for CCNA Examination.

Community Fundamentals:

Networking Gadgets Utilized in CCNA: 

Names of gadgets use in CCNA Description

A router is a community machine that forwards information packets between laptop networks. A router receives a packet from an enter port, checks its header, performs  primary capabilities equivalent to checksum checking, seems to be up the suitable output port’s routing desk, drops the packet, and so forth. Ahead the packet to the output port.


A change is a community machine used to divide a community into completely different subnets referred to as subnets or LAN segments. Filters and forwards packets between LAN segments based mostly on MAC deal with. A change establishes a brief connection between a supply and vacation spot for communication and terminates the connection when the dialog ends. It additionally offers full bandwidth for community visitors going to and from gadgets on the identical time, lowering collisions.


A firewall is a {hardware} or software-based community safety machine that screens all incoming and outgoing visitors and accepts, denies, or drops particular visitors based mostly on an outlined set of safety guidelines.


Intrusion prevention programs are often known as intrusion detection and prevention programs. This can be a community safety utility that screens community or system exercise for malicious exercise. The primary perform of an intrusion prevention system is to establish malicious exercise, acquire and report details about that exercise,  and try to dam or cease it.

Entry factors

This can be a community machine that enables your machine to hook up with a wired community.  Entry factors are used to construct WLANs (Wi-fi Native Space Networks). It’s generally utilized in massive workplaces and buildings with rising companies.


the community controller is a centralized programmable automation level that lets you handle, configure, monitor, and troubleshoot your digital community infrastructure, along with manually configuring community gadgets. An extensible server function that gives Run the service. It acts as an interface between your retailer and your community infrastructure.


Endpoint Safety Management is a software program know-how that facilitates the popularity and operation of private laptops to achieve entry to the company neighborhood. This permits neighborhood admins to limit constructive web sites to particular clients, thus adhering to their group’s guidelines and necessities concerning the additive in query. Endpoint safety management buildings embrace digital personal VPN purchasers, working programs, and up-to-date antivirus software program.


Servers are computer systems devoted to a particular objective, and in contrast to desktop computer systems, these computer systems are constructed to be sturdy, long-lived, and long-running in comparison with desktop PCs.

Community Topology Architectures:

Traits of community topology Description

LAN stands for Native Space Community. That is a pc community that covers a comparatively small space. B. Inside a constructing or campus as much as a number of kilometers in dimension.


MAN stands for Metropolitan Space Community. It’s a pc community that connects many LANs into a bigger community in order that laptop assets could be shared. This kind of community covers a bigger space than a LAN however is smaller than a WAN  designed to span a whole metropolis.


WAN stands for Huge Space Community. It’s a pc community consisting of two or extra LANs or MANs overlaying a big geographical space.


A spine-leaf structure is a knowledge heart community topology that consists of two switching layers: backbone and leaf.

Small workplace/house workplace (SOHO)

SOHO stands for Small Workplace/Dwelling Workplace Community. Immediately, many aspiring entrepreneurs and small enterprise house owners want to make money working from home or keep a small workplace.

Cloud storage

Cloud storage merely shops information over the web on cloud-based servers. As soon as your information is saved within the cloud, you’ll be able to entry it anyplace over the web from a number of gadgets.

Bodily Interface and Cabling Varieties:

Interfaces and cabling Description
Single-mode fiber cable

SMF (Single-Mode Fibers) are fiber cables designed to hold solely single-mode gentle, which is the transverse mode. They’re used for long-distance transmission of alerts.

multi-mode fiber cable

Multimode fiber optic cable is a kind of fiber optic cable that transmits information via a bigger diameter core, permitting the typical single-mode transceiver to hold a number of modes of sunshine.

copper wire

Copper cables use electrical alerts to transmit information between networks. There are three forms of copper cable: coaxial cable, unshielded twisted pair, and shielded twisted pair. Coax degrades over lengthy distances


Ethernet is probably the most extensively used LAN know-how outlined by the IEEE 802.3 normal. The rationale for its large applicability is that Ethernet is simple to grasp, simple to implement and keep, and allows cheap community implementation. Moreover, Ethernet gives flexibility by way of allowed topologies.


Energy Over Ethernet (POE) is a method used for constructing wired Ethernet native space networks (LANs) which use Ethernet information cables as a substitute of regular electrical energy cords and wiring to hold {the electrical} present required to function every machine.

IP Addressing:

Courses of IP Addresses:

Class First 5 bits in binary First Octet vary
A 0xxxx 0-127 (truly 1-126 as a result of 0 and 127 are reserved
B 10xxx 128-191
C 110xx 192-223
D 1110x 224-239
E 1111x 240-254

Reserved IP Addresses:

Tackle What it represents The place can or not it’s used
Community deal with of all 0s

Stands for “this community”. For instance,

Ship a broadcast message to the community.

Community deal with of all 1s

Represents “all networks”.

Ship a broadcast message to all networks.

Node deal with of all 0s

Represents a community deal with or all hosts on a community. Instance or

Routers route visitors based mostly on community addresses.

Node deal with of all 1s

It represents all hosts on the community and can be referred to as the printed deal with. Instance or

Used to ship broadcasts to all hosts on the community.

Total deal with of 0s

Stands for “any community”.

Utilized by routers to set a default route.

Total IP set to all 1s.

Stands for all hosts in community.

Used to ship/broadcast messages

Stands for loopback deal with which is actually the host itself

Ship visitors from the host to itself. Use this deal with in your browser to hook up with the online server working on the host itself.

Legitimate Hosts Addresses in Every Subnet:

Variable Size Subnet Masks (VLSM):

Troubleshooting IP Addressing:

Troubleshooting Description
Packet Web Grouper (PING)

Ping is without doubt one of the mostly used utilities for troubleshooting addressing and connectivity issues. This utility is obtainable for many working programs, together with Cisco gadgets, and could be accessed via the command line interface utilizing the ping command. Checks if the goal host is up utilizing the ICMP protocol.


Traceroute is one other fashionable utility  out there on all working programs. On some working programs, the utility could be accessed utilizing the tracert or traceroute instructions within the CLI. It’s used to seek out every hop between a supply host and a vacation spot host, serving to to see the trail taken by a packet.

IP config

On Home windows machines, all this info is displayed within the output of the ipconfig /all command. On Unix-based programs, this info could be considered utilizing the ifconfig command.

ARP Tables

This desk comprises the MAC and IP deal with associations discovered by the system. On most working programs, the ARP desk could be considered with the arp –a command. On  Cisco gadgets, you’ll be able to view the arp desk  utilizing the present ip arp command.

Port Safety:

Switches be taught MAC addresses as frames are forwarded via change ports. Port safety permits you to restrict the variety of MAC addresses that may be discovered on a port, configure static MAC addresses, and set penalties if that port is utilized by unauthorized customers. Customers can limit, shutdown, or defend port safety instructions.

Port-Safety Phrases of Violation:

Time period Definition
defend To Drops packets with no alert
limit To Drops packets and increment security-violation rely
shutdown To Shuts down the port (default)

Troubleshooting Port Safety:

Command Description
# present port-security [interface g1/1] port standing, violation mode, max/whole MACs,…
# present port-security deal with Safe MACs on ports.
# present errdisable restoration Examine if auto restoration is enabled. Disabled by default.

Configure VLANs:

Digital LAN (VLAN) is an idea that enables gadgets to be logically partitioned at layer 2 (information hyperlink layer). Layer 3 gadgets usually share a broadcast area, however the idea of VLANs can be utilized to divide the printed area with switches.

Layer2 Swap VLAN Config:

Layer3 Swap VLAN Config:

Router (on a Stick) VLAN Config:

Troubleshoot VLANs on a Swap:


STP (Spanning Tree Protocol):

Spanning Tree Protocol (STP) prevents body loops by placing interfaces on a change right into a forwarding or blocking states.

Troubleshoot STP:


EtherChannel is a port hyperlink aggregation know-how that teams a number of bodily port hyperlinks into one logical hyperlink. Used to supply high-speed connectivity and redundancy. As much as eight hyperlinks could be aggregated into one logical hyperlink.

Troubleshoot Etherchannel:

Configure a Serial:

The pace of the Layer 1 connection is decided by the CSU/DSU. DTE (Knowledge Terminal Tools)  and DCE (Knowledge Communications Tools) cables are utilized in labs with out an exterior CSU/DSU.

Command Description
(config)# interface serial 1/0 To Configure interface serial 1/0
(config-if)# clock price 128000 To Set clock price for DCE router aspect to 128 kbps
(config)# present controllers serial 1/0 To Confirm clock price on serial interface 1/0

Entry Management Lists (ACLs):

Default masks for default ACL:

Interface ACLs:

Troubleshooting ACLs:

Community Tackle Translation (NAT):

Community Tackle Translation (NAT) is the method of translating a number of native IP addresses into a number of world IP addresses, or vice versa, to be able to present Web entry to native hosts. It additionally performs port quantity translation. H. Masks the host’s port quantity with one other port quantity in packets routed to the vacation spot.

Time period Definition
inside native IP addresses assigned to hosts within the community will not be routable
inside world A routable IP deal with assigned by your Community Info Middle or ISP
outdoors native The IP deal with of the distant host seen on the community will not be routable
outdoors world The owner-assigned IP deal with of the distant host, routable


SNAT, because the identify suggests, is a method for typically translating the supply IP deal with when connecting from a personal IP deal with to a public IP deal with. Maps the originating consumer IP deal with within the request to a remodel outlined on the BIG-IP machine. That is the most typical type of NAT and is used when inside hosts have to provoke classes with exterior or public hosts.


DNAT, because the identify proposes, is a method for largely translating vacation spot IP addresses when connecting from a public IP deal with to a personal IP deal with. It’s usually used to redirect packets destined for a particular IP deal with on one host or a particular port on an IP deal with to a different deal with (almost definitely one other host).

Port Tackle Translation (PAT):

Port deal with translation is carried out in routers. So the IP packet obtained by the router comprises a personal IP and a port quantity (supplied by the pc), so the router replaces the personal IP with the general public IP of the router and a particular port is assigned to this connecting machine.

DHCP (Dynamic Host Management Protocol):

Dynamic Host Configuration Protocol (DHCP) is an utility layer protocol used to supply:

  1. Subnet Masks (Possibility 1 – e.g.,
  2. Router Tackle (Possibility 3 – e.g.,
  3. DNS Tackle (Possibility 6 – e.g.,
  4. Vendor Class Identifier (Possibility 43 – e.g., ‘unifi’ = ##the place unifi = controller)

Troubleshooting DHCP:

HSRP (Sizzling Standby Router Protocol):

HSRP (Sizzling Standby Router Protocol) is a CISCO proprietary protocol that gives redundancy for an area subnet. In HSRP, two or extra routers create the phantasm of a digital router.

Troubleshooting HSRP:

Command Description
# present standby HSRP Teams, their VIPs, state, lively router, standby router, preemption.

Service Degree Agreements (SLAs):

Service Degree Agreements (SLAs) are efficiency constraints negotiated between the cloud service supplier and the shopper. Beforehand, in cloud computing, all service degree agreements had been negotiated between the shopper and the buyer of the service. Immediately, with the arrival of main utility-style cloud suppliers, most service degree agreements are standardized till clients turn out to be main shoppers of cloud providers. cloud.

Troubleshooting SLAs:

Telnet / Console:

TELNET stands for Terminal Community. It’s a kind of protocol that enables a pc to hook up with an area laptop. It’s used as the usual TCP/IP protocol for the digital terminal service supplied by ISO. The pc that initiates the connection known as the native laptop. 


SSH (Safe Shell) is an entry identifier used within the SSH protocol. In different phrases, it’s a cryptographic community protocol used to transmit encrypted information over a community. It permits you to hook up with a server or servers with out having to recollect or enter your password for every system that should join remotely from one system to a different.

TACACS+ Protocol:

TACACS+, which stands for Terminal Entry Controller Entry Management Server, is a safety protocol used throughout the AAA framework to supply centralized authentication for customers who want to entry the community.

Easy Community Administration Protocol (SNMP):

SNMP is an utility layer protocol that makes use of UDP port quantity 161/162. SNMP is used to watch the community, detect community failures, and typically even to configure gadgets remotely.

CDP – Cisco Discovery Protocol:

CDP permits customers to make use of plenty of show instructions that enable them to view linked machine info equivalent to native port info, distant port info, hostname, machine platform, and so on.

Hyperlink Layer Discovery Protocol (LLDP):

It’s an open layer 2 protocol compliant with the IEEE (802.1AB) normal. LLDP is an open supply various to CDP (Cisco Discovery Protocol), which can be a tool discovery protocol that runs solely on layer 2 (information hyperlink layer)  on Cisco-manufactured gadgets (routers). routers, bridges, entry servers, and switches).

Level-to-Level Protocol (PPP):

Level-to-Level Protocol (PPP) is mainly a set of uneven protocols for various connections or hyperlinks that don’t present frames, i.e., uncooked bit pipes. PPP additionally needs different protocols to ascertain connections, authenticate customers, and likewise transport community layer information. PPP will not be a single protocol, however a set of protocols consisting of easy protocols that deal with numerous elements of Layer 2 point-to-point communication.

Troubleshooting PPP:

Command Description
# present controllers S0/0/0 To Present interface, linked kind of cable, clock price
# present interfaces To Present encapsulation, logical bandwidth
# present ppp all To Present session state, auth kind, peer ip and identify
# debug ppp authentication To Debug PPP authentication


Routing Info Protocol (RIP) is a dynamic routing protocol that makes use of hop rely as a routing metric to seek out the perfect path between supply and vacation spot networks. It’s a distance vector routing protocol with an AD worth of 120 and operates on the community layer of the OSI mannequin. RIP makes use of port quantity 520.

Troubleshooting RIP:

Command Description
# present ip[v6] protocols Present rip timers, interfaces, networks,
# present ip rip database Routes discovered by rip had been used to compile the routing desk
# present ip route Present discovered routes
# clear ip route * Eliminate all routes


EIGRP (Enhanced Inside Gateway Routing Protocol) is a dynamic routing protocol used to seek out the perfect path between any two Layer 3 gadgets for packet supply. EIGRP works on prime of the community layer protocol of the OSI mannequin and makes use of protocol quantity 88. It makes use of metrics to seek out the perfect path between two Layer 3 gadgets (Layer 3 routers or switches). utilizing EIGRP.

Command Description
# present run | part eigrp To Present EIGRP settings.
# present interfaces g1/1 To Present configured/default bandwidth and delay.
(config-if)# bandwidth To Overwrite bandwidth used for eigrp metric.
(config-if)# delay To Overwrite show used for eigrp metric.
(config)# router eigrp 23 To Add and conf EIGRP AS#23
(config-router)# community To Announce routes to
(config-router)# no shutdown On some iOS variations, it’s off by default.
(config-router)# [no] eigrp router-id To Set Defaults to highest loopback ip
(config-router)# [no] passive-interface g1/2 To Disable EIGRP right here. Ignore incoming pkgs.
(config-router)# [no] passive-interface default To Disable EIGRP on all ifs by default.
(config-router)# maximum-paths To set Default 4, should match, the variety of load-balanced paths.
(config-router)# variance 4 To Set Default 1, Max 4:1 variance for unequal lb.
(config-router)# no auto-summary To Set Don’t summarize a smaller subnet route in a giant one.
# present ip[v6] eigrp neighbors To point out Neighbor deal with, if, maintain time, uptime, queued pkgs
# present ip[v6] eigrp interfaces [if-name] To Present If, Variety of friends, pending routes, queued pkgs
# present ip[v6] route [eigrp] To ShowRoutes beginning with D had been discovered by way of EIGRP
# present ip[v6] eigrp topology [all-links] Topology desk

EIGRP with ipv6:


Open Shortest Path First (OSPF) is a link-state routing protocol used to seek out the perfect path between supply and vacation spot router utilizing its personal shortest path first). OSPF was developed by the Web Engineering Job Drive (IETF) as one of many Inner Gateway Protocols (IGP), i.e., a protocol aimed toward shifting packets inside a big autonomous system or routing area.

Router Varieties:

Time period Definition
Inner Router Checklist All OSPF interfaces in a single space
Spine Router It has a number of OSPF interfaces within the spine
Space Boundary Router (ABR) It has at the very least one interface within the spine space and at the very least one in one other space
Autonomous System Boundary Router (ASBR) To Injects routes into OSPF by way of redistribution from different routing protocols

OSPF with ipv6 (OSPFv3):

Command Description
(config)# ipv6 unicast-routing To point out unicast routing via ipv6
(config)# ipv6 router OSPF To point out config of ipv6 on the router
(config-router)# router-id Required if we don’t have any v4 deal with configured.
(config-if)# ipv6 OSPF space Required for OSPFv3.

The community’s command doesn’t exist, and non talked about instructions are the identical.

Troubleshooting OSPF:

Command Description
# present run | sect ospf To run OSPF
# present ip(v6) protocols To point out ipv6 in OSPF
# present ipv6 ospf To point out reference bandwidth, router-id, networks, interface per space
# present ip(v6) ospf neighbor To point out neighbor IDs, IPs, and by way of the interface.
# present ip(v6) ospf neighbor element To point out dr, bdr, timers, and so on.
# present interface transient To point out admin downlink
# present ip(v6) ospf interface transient To point out OSPF enabled interfaces
# present ip(v6) ospf interface g1/1 To point out OSPF associated Infos for g1/1, passive?
# present ip(v6) route (ospf) To point out OSPF routes are marked O, present route advert and value 



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