CCNA Cheatsheet
Last Updated :
07 Oct, 2022
A CCNA certification proves you have the competencies needed to navigate an ever-changing IT landscape. CCNA exams cover network fundamentals, IP services, security fundamentals, automation, and programmability. Designed for agility and versatility, CCNA proves you have the skills needed to manage and optimize today’s most advanced networks. CCNA training courses and exams are the foundation for advancing your career in any direction. A Cisco certification is living proof of the standards and rigor your organization recognizes and trusts to meet and exceed market demands. Here is a cheat sheet for CCNA Examination.
Network Fundamentals:
Networking Devices Used in CCNA:
| Names of devices use in CCNA |
Description |
| Routers |
A router is a network device that forwards data packets between computer networks. A router receives a packet from an input port, checks its header, performs basic functions such as checksum checking, looks up the appropriate output port’s routing table, drops the packet, and so on. Forward the packet to the output port.
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| switches |
A switch is a network device used to divide a network into different subnets called subnets or LAN segments. Filters and forwards packets between LAN segments based on MAC address. A switch establishes a temporary connection between a source and destination for communication and terminates the connection when the conversation ends. It also provides full bandwidth for network traffic going to and from devices at the same time, reducing collisions.
|
| Firewalls |
A firewall is a hardware or software-based network security device that monitors all incoming and outgoing traffic and accepts, denies, or drops specific traffic based on a defined set of security rules.
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| IPS |
Intrusion prevention systems are also known as intrusion detection and prevention systems. This is a network security application that monitors network or system activity for malicious activity. The main function of an intrusion prevention system is to identify malicious activity, collect and report information about that activity, and attempt to block or stop it.
|
| Access points |
This is a network device that allows your device to connect to a wired network. Access points are used to build WLANs (Wireless Local Area Networks). It is commonly used in large offices and buildings with growing businesses.
|
| Controllers |
the network controller is a centralized programmable automation point that enables you to manage, configure, monitor, and troubleshoot your virtual network infrastructure, in addition to manually configuring network devices. An extensible server role that provides Run the service. It acts as an interface between your store and your network infrastructure.
|
| Endpoints |
Endpoint Security Control is a software technology that facilitates the recognition and operation of personal laptops to gain access to the corporate community. This allows community admins to restrict positive websites to specific customers, thus adhering to their organization’s rules and requirements regarding the additive in question. Endpoint security control structures include digital private VPN clients, operating systems, and up-to-date antivirus software.
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| Servers |
Servers are computers dedicated to a specific purpose, and unlike desktop computers, these computers are built to be durable, long-lived, and long-running compared to desktop PCs.
|
Network Topology Architectures:
| Characteristics of network topology |
Description |
| LAN |
LAN stands for Local Area Network. This is a computer network that covers a relatively small area. B. Inside a building or campus up to several kilometers in size.
|
| MAN |
MAN stands for Metropolitan Area Network. It is a computer network that connects many LANs into a larger network so that computer resources can be shared. This type of network covers a larger area than a LAN but is smaller than a WAN designed to span an entire city.
|
| WAN |
WAN stands for Wide Area Network. It is a computer network consisting of two or more LANs or MANs covering a large geographical area.
|
| Spine-leaf |
A spine-leaf architecture is a data center network topology that consists of two switching layers: spine and leaf.
|
| Small office/home office (SOHO) |
SOHO stands for Small Office/Home Office Network. Today, many aspiring entrepreneurs and small business owners prefer to work from home or maintain a small office.
|
| Cloud storage |
Cloud storage simply stores data over the internet on cloud-based servers. Once your data is stored in the cloud, you can access it anywhere over the internet from multiple devices.
|
Physical Interface and Cabling Types:
| Interfaces and cabling |
Description |
| Single-mode fiber cable |
SMF (Single-Mode Fibers) are fiber cables designed to carry only single-mode light, which is the transverse mode. They are used for long-distance transmission of signals.
|
| multi-mode fiber cable |
Multimode fiber optic cable is a type of fiber optic cable that transmits data through a larger diameter core, allowing the average single-mode transceiver to carry multiple modes of light.
|
| copper wire |
Copper cables use electrical signals to transmit data between networks. There are three types of copper cable: coaxial cable, unshielded twisted pair, and shielded twisted pair. Coax degrades over long distances
|
| Ethernet |
Ethernet is the most widely used LAN technology defined by the IEEE 802.3 standard. The reason for its wide applicability is that Ethernet is easy to understand, easy to implement and maintain, and enables inexpensive network implementation. Additionally, Ethernet offers flexibility in terms of allowed topologies.
|
| PoE |
Power Over Ethernet (POE) is a technique used for building wired Ethernet local area networks (LANs) which use Ethernet data cables instead of normal electrical power cords and wiring to carry the electrical current required to operate each device.
|
IP Addressing:
Classes of IP Addresses:
| Class |
First 5 bits in binary |
First Octet range |
| A |
0xxxx |
0-127 (actually 1-126 because 0 and 127 are reserved |
| B |
10xxx |
128-191 |
| C |
110xx |
192-223 |
| D |
1110x |
224-239 |
| E |
1111x |
240-254 |
Reserved IP Addresses:
| Address |
What it represents |
Where can it be used |
| Network address of all 0s |
Stands for “this network”. For example, 0.0.0.120
|
Send a broadcast message to the network.
|
| Network address of all 1s |
Represents “all networks”.
|
Send a broadcast message to all networks.
|
| Node address of all 0s |
Represents a network address or all hosts on a network. Example 10.0.0.0 or 172.16.0.0
|
Routers route traffic based on network addresses.
|
| Node address of all 1s |
It represents all hosts on the network and is also called the broadcast address. Example 172.16.255.255 or 192.168.10.255
|
Used to send broadcasts to all hosts on the network.
|
| Entire address of 0s |
Stands for “any network”.
|
Used by routers to set a default route.
|
| Entire IP set to all 1s. |
Stands for all hosts in network.
|
Used to deliver/broadcast messages
|
| 127.0.0.1 |
Stands for loopback address which is essentially the host itself
|
Send traffic from the host to itself. Use this address in your browser to connect to the web server running on the host itself.
|
Valid Hosts Addresses in Each Subnet:
Variable Length Subnet Mask (VLSM):
Troubleshooting IP Addressing:
| Troubleshooting |
Description |
| Packet Internet Grouper (PING) |
Ping is one of the most commonly used utilities for troubleshooting addressing and connectivity problems. This utility is available for most operating systems, including Cisco devices, and can be accessed through the command line interface using the ping command. Checks if the target host is up using the ICMP protocol.
|
| Traceroute |
Traceroute is another popular utility available on all operating systems. On some operating systems, the utility can be accessed using the tracert or traceroute commands in the CLI. It is used to find each hop between a source host and a destination host, helping to see the path taken by a packet.
|
| IP config |
On Windows machines, all this information is displayed in the output of the ipconfig /all command. On Unix-based systems, this information can be viewed using the ifconfig command.
|
| ARP Tables |
This table contains the MAC and IP address associations learned by the system. On most operating systems, the ARP table can be viewed with the arp –a command. On Cisco devices, you can view the arp table using the show ip arp command.
|
Port Security:
Switches learn MAC addresses as frames are forwarded through switch ports. Port security allows you to limit the number of MAC addresses that can be learned on a port, configure static MAC addresses, and set penalties if that port is used by unauthorized users. Users can restrict, shutdown, or protect port security commands.
Port-Security Terms of Violation:
| Term |
Definition |
| protect |
To Drops packets with no alert |
| restrict |
To Drops packets and increment security-violation count |
| shutdown |
To Shuts down the port (default) |
Troubleshooting Port Security:
| Command |
Description |
| # show port-security [interface g1/1] |
port status, violation mode, max/total MACs,… |
| # show port-security address |
Secure MACs on ports. |
| # show errdisable recovery |
Check if auto recovery is enabled. Disabled by default. |
Configure VLANs:
Virtual LAN (VLAN) is a concept that allows devices to be logically partitioned at layer 2 (data link layer). Layer 3 devices typically share a broadcast domain, but the concept of VLANs can be used to divide the broadcast domain with switches.
Layer2 Switch VLAN Config:
Layer3 Switch VLAN Config:
Router (on a Stick) VLAN Config:
Troubleshoot VLANs on a Switch:
VTP:
STP (Spanning Tree Protocol):
Spanning Tree Protocol (STP) prevents frame loops by putting interfaces on a switch into a forwarding or blocking states.
Troubleshoot STP:
Etherchannel:
EtherChannel is a port link aggregation technology that groups multiple physical port links into one logical link. Used to provide high-speed connectivity and redundancy. Up to eight links can be aggregated into one logical link.
Troubleshoot Etherchannel:
Configure a Serial:
The speed of the Layer 1 connection is determined by the CSU/DSU. DTE (Data Terminal Equipment) and DCE (Data Communications Equipment) cables are used in labs without an external CSU/DSU.
| Command |
Description |
| (config)# interface serial 1/0 |
To Configure interface serial 1/0 |
| (config-if)# clock rate 128000 |
To Set clock rate for DCE router side to 128 kbps |
| (config)# show controllers serial 1/0 |
To Verify clock rate on serial interface 1/0 |
Access Control Lists (ACLs):
Default mask for default ACL: 0.0.0.0
Interface ACLs:
Troubleshooting ACLs:
Network Address Translation (NAT):
Network Address Translation (NAT) is the process of translating one or more local IP addresses into one or more global IP addresses, or vice versa, in order to provide Internet access to local hosts. It also performs port number translation. H. Mask the host’s port number with another port number in packets routed to the destination.
| Term |
Definition |
| inside local |
IP addresses assigned to hosts in the network are not routable |
| inside global |
A routable IP address assigned by your Network Information Center or ISP |
| outside local |
The IP address of the remote host seen on the network is not routable |
| outside global |
The owner-assigned IP address of the remote host, routable |
SNAT:
SNAT, as the name suggests, is a technique for generally translating the source IP address when connecting from a private IP address to a public IP address. Maps the originating client IP address in the request to a transform defined on the BIG-IP device. This is the most common form of NAT and is used when internal hosts need to initiate sessions with external or public hosts.
DNAT:
DNAT, as the name proposes, is a technique for mostly translating destination IP addresses when connecting from a public IP address to a private IP address. It is typically used to redirect packets destined for a specific IP address on one host or a specific port on an IP address to another address (most likely another host).
Port Address Translation (PAT):
Port address translation is implemented in routers. So the IP packet received by the router contains a private IP and a port number (provided by the computer), so the router replaces the private IP with the public IP of the router and a specific port is assigned to this connecting device.
DHCP (Dynamic Host Control Protocol):
Dynamic Host Configuration Protocol (DHCP) is an application layer protocol used to provide:
- Subnet Mask (Option 1 – e.g., 255.255.255.0)
- Router Address (Option 3 – e.g., 192.168.1.1)
- DNS Address (Option 6 – e.g., 8.8.8.8)
- Vendor Class Identifier (Option 43 – e.g., ‘unifi’ = 192.168.1.9 ##where unifi = controller)
Troubleshooting DHCP:
HSRP (Hot Standby Router Protocol):
HSRP (Hot Standby Router Protocol) is a CISCO proprietary protocol that provides redundancy for a local subnet. In HSRP, two or more routers create the illusion of a virtual router.
Troubleshooting HSRP:
| Command |
Description |
| # show standby |
HSRP Groups, their VIPs, state, active router, standby router, preemption. |
Service Level Agreements (SLAs):
Service Level Agreements (SLAs) are performance constraints negotiated between the cloud service provider and the customer. Previously, in cloud computing, all service level agreements were negotiated between the customer and the consumer of the service. Today, with the advent of major utility-style cloud providers, most service level agreements are standardized until customers become major consumers of cloud services. cloud.
Troubleshooting SLAs:
Telnet / Console:
TELNET stands for Terminal Network. It is a type of protocol that allows a computer to connect to a local computer. It is used as the standard TCP/IP protocol for the virtual terminal service provided by ISO. The computer that initiates the connection is called the local computer.
SSH:
SSH (Secure Shell) is an access identifier used in the SSH protocol. In other words, it is a cryptographic network protocol used to transmit encrypted data over a network. It allows you to connect to a server or servers without having to remember or enter your password for each system that needs to connect remotely from one system to another.
TACACS+ Protocol:
TACACS+, which stands for Terminal Access Controller Access Control Server, is a security protocol used within the AAA framework to provide centralized authentication for users who wish to access the network.
Simple Network Management Protocol (SNMP):
SNMP is an application layer protocol that uses UDP port number 161/162. SNMP is used to monitor the network, detect network failures, and sometimes even to configure devices remotely.
CDP – Cisco Discovery Protocol:
CDP allows users to use a number of display commands that allow them to view connected device information such as local port information, remote port information, hostname, device platform, etc.
Link Layer Discovery Protocol (LLDP):
It is an open layer 2 protocol compliant with the IEEE (802.1AB) standard. LLDP is an open source alternative to CDP (Cisco Discovery Protocol), which is also a device discovery protocol that runs only on layer 2 (data link layer) on Cisco-manufactured devices (routers). routers, bridges, access servers, and switches).
Point-to-Point Protocol (PPP):
Point-to-Point Protocol (PPP) is basically a set of asymmetric protocols for different connections or links that do not provide frames, i.e., raw bit pipes. PPP also wants other protocols to establish connections, authenticate users, and also transport network layer data. PPP is not a single protocol, but a set of protocols consisting of simple protocols that address various aspects of Layer 2 point-to-point communication.
Troubleshooting PPP:
| Command |
Description |
| # show controllers S0/0/0 |
To Show interface, connected type of cable, clock rate |
| # show interfaces |
To Show encapsulation, logical bandwidth |
| # show ppp all |
To Show session state, auth type, peer ip and name |
| # debug ppp authentication |
To Debug PPP authentication |
RIP:
Routing Information Protocol (RIP) is a dynamic routing protocol that uses hop count as a routing metric to find the best path between source and destination networks. It is a distance vector routing protocol with an AD value of 120 and operates on the network layer of the OSI model. RIP uses port number 520.
Troubleshooting RIP:
| Command |
Description |
| # show ip[v6] protocols |
Show rip timers, interfaces, networks, |
| # show ip rip database |
Routes learned by rip were used to compile the routing table |
| # show ip route |
Show learned routes |
| # clear ip route * |
Get rid of all routes |
EIGRP:
EIGRP (Enhanced Interior Gateway Routing Protocol) is a dynamic routing protocol used to find the best path between any two Layer 3 devices for packet delivery. EIGRP works on top of the network layer protocol of the OSI model and uses protocol number 88. It uses metrics to find the best path between two Layer 3 devices (Layer 3 routers or switches). using EIGRP.
| Command |
Description |
| # show run | section eigrp |
To Show EIGRP settings. |
| # show interfaces g1/1 |
To Show configured/default bandwidth and delay. |
| (config-if)# bandwidth |
To Overwrite bandwidth used for eigrp metric. |
| (config-if)# delay |
To Overwrite display used for eigrp metric. |
| (config)# router eigrp 23 |
To Add and conf EIGRP AS#23 |
| (config-router)# network 10.20.30.0 0.0.0.255 |
To Announce routes to 10.20.30.0/24 |
| (config-router)# no shutdown |
On some iOS versions, 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 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, must match, the number 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 big one. |
| # show ip[v6] eigrp neighbors |
To show Neighbor address, if, hold time, uptime, queued pkgs |
| # show ip[v6] eigrp interfaces [if-name] |
To Show If, Number of peers, pending routes, queued pkgs |
| # show ip[v6] route [eigrp] |
To ShowRoutes starting with D were learned via EIGRP |
| # show ip[v6] eigrp topology [all-links] |
Topology table |
EIGRP with ipv6:
OSPF:
Open Shortest Path First (OSPF) is a link-state routing protocol used to find the best path between source and destination router using its own shortest path first). OSPF was developed by the Internet Engineering Task Force (IETF) as one of the Internal Gateway Protocols (IGP), i.e., a protocol aimed at moving packets within a large autonomous system or routing domain.
Router Types:
| Term |
Definition |
| Internal Router |
List All OSPF interfaces in one area |
| Backbone Router |
It has one or more OSPF interfaces in the backbone |
| Area Boundary Router (ABR) |
It has at least one interface in the backbone area and at least one in another area |
| Autonomous System Boundary Router (ASBR) |
To Injects routes into OSPF via redistribution from other routing protocols |
OSPF with ipv6 (OSPFv3):
| Command |
Description |
| (config)# ipv6 unicast-routing |
To show unicast routing through ipv6 |
| (config)# ipv6 router OSPF |
To show config of ipv6 on the router |
| (config-router)# router-id |
Required if we don’t have any v4 address configured. |
| (config-if)# ipv6 OSPF area |
Required for OSPFv3. |
The network’s command does not exist, and non mentioned commands are the same.
Troubleshooting OSPF:
| Command |
Description |
| # show run | sect ospf |
To run OSPF |
| # show ip(v6) protocols |
To show ipv6 in OSPF |
| # show ipv6 ospf |
To show reference bandwidth, router-id, networks, interface per area |
| # show ip(v6) ospf neighbor |
To show neighbor IDs, IPs, and via the interface. |
| # show ip(v6) ospf neighbor detail |
To show dr, bdr, timers, etc. |
| # show interface brief |
To show admin downlink |
| # show ip(v6) ospf interface brief |
To show OSPF enabled interfaces |
| # show ip(v6) ospf interface g1/1 |
To show OSPF related Infos for g1/1, passive? |
| # show ip(v6) route (ospf) |
To show OSPF routes are marked O, show route ad and cost |
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