Cisco CCNA in 60 Days

1. Understanding Network Fundamentals: OSI and TCP/IP Models

The ISO created the OSI model to help vendors agree on a set of common standards with which they could all work.

Foundation of networking. The OSI model, with its seven layers, provides a conceptual framework for understanding how network communications occur. Each layer performs specific functions, from the physical transmission of data (Layer 1) to end-user applications (Layer 7). Understanding the OSI model is crucial for troubleshooting and designing networks.

TCP/IP model. The TCP/IP model, also known as the DoD model, is an alternative framework with four or five layers. It is the standard used on the Internet. While Cisco expects you to understand the OSI model, they now prefer the TCP model as a network framework.

Encapsulation and troubleshooting. As data moves down the OSI or TCP/IP model, it's encapsulated in different types of data units (segments, packets, frames, bits). Troubleshooting network issues often involves identifying the layer at which the problem occurs, using a bottom-up approach, starting with physical connections and working your way up the stack.

2. Mastering IP Addressing: IPv4 and IPv6

As a Cisco engineer, you will spend a lot of time installing, configuring, and troubleshooting routers.

IPv4 and IPv6. IP addressing is fundamental to network communication. IPv4 uses 32-bit addresses, while IPv6 uses 128-bit addresses, offering a vastly larger address space. Understanding binary and hexadecimal numbering systems is essential for working with IP addresses.

Subnetting and VLSM. Subnetting divides a network into smaller, more manageable subnets, while Variable Length Subnet Masking (VLSM) allows for more efficient use of IP addresses by using different subnet masks for different subnets. Classless Inter-Domain Routing (CIDR) notation (e.g., /24) is used to represent subnet masks concisely.

Private vs. Public. Private IP addresses (10.x.x.x, 172.16.x.x-172.31.x.x, 192.168.x.x) are used for internal networks and are not routable on the Internet. Network Address Translation (NAT) is used to translate private IP addresses to public IP addresses for Internet access. IPv6 eliminates the need for NAT due to its vast address space.

3. VLANs and Trunking: Segmenting and Extending Networks

Using a switch allows you to divide your network into smaller, more manageable sections (known as segments).

VLANs for segmentation. Virtual Local Area Networks (VLANs) logically segment a network into smaller broadcast domains, improving performance and security. Switches use MAC addresses to forward traffic within a VLAN.

Trunking for VLAN extension. Trunk links carry traffic from multiple VLANs between switches. Frame tagging (using protocols like 802.1Q) is used to identify which VLAN a frame belongs to as it traverses the trunk link.

Configuration and troubleshooting. Configuring VLANs involves creating VLANs, assigning ports to VLANs, and configuring trunk links. Troubleshooting VLAN issues often involves verifying VLAN configurations, port memberships, and trunk settings.

4. Routing Essentials: Static vs. Dynamic Routing

A router is a device used for networking.

Connecting networks. Routing enables communication between different networks. Routers use routing tables to determine the best path for forwarding packets.

Static vs. Dynamic. Static routing involves manually configuring routes, while dynamic routing protocols (like OSPF and EIGRP) automatically learn and adapt to network changes. Dynamic routing protocols offer scalability and resilience.

Key concepts. Understanding administrative distance (AD), routing metrics, and prefix matching is crucial for understanding how routers choose the best path. Topology-based switching, such as Cisco Express Forwarding (CEF), improves packet forwarding performance.

5. Securing Your Network: ACLs and Basic Security Practices

I hear these comments every day from Cisco students on forums and via e-mails to my office.

Controlling traffic flow. Access Control Lists (ACLs) filter network traffic based on various criteria, such as source/destination IP addresses, protocols, and port numbers. ACLs are applied to router interfaces to control inbound and outbound traffic.

Types of ACLs. Standard ACLs filter based on source IP addresses, while extended ACLs offer more granular control. Named ACLs use names instead of numbers for easier identification.

Basic security. Securing network devices involves protecting physical access, securing console and Telnet/SSH access, and implementing strong passwords. Disabling unused services and setting appropriate banner messages are also important security measures.

6. DHCP and DNS: Essential Network Services

The problem is a lack of two things which mean the difference between success and obscurity – a plan and structure.

DHCP for automatic IP configuration. Dynamic Host Configuration Protocol (DHCP) automatically assigns IP addresses and other network configuration parameters to hosts, simplifying network administration. DHCP operations involve a four-step process: Discover, Offer, Request, and Acknowledge.

DNS for name resolution. Domain Name System (DNS) translates domain names (e.g., www.example.com) to IP addresses, allowing users to access resources using easy-to-remember names. DNS operations involve querying DNS servers to resolve domain names.

Configuration and troubleshooting. Configuring DHCP involves creating DHCP pools, excluding addresses, and setting lease times. Troubleshooting DHCP and DNS issues often involves verifying configurations, checking connectivity, and analyzing packet captures.

7. Troubleshooting Common Network Issues: A Layered Approach

Using a layered approach can be very effective when you’re troubleshooting your network.

Layered troubleshooting. A systematic approach to troubleshooting network issues is crucial. The OSI model provides a framework for identifying the layer at which the problem occurs.

Physical and Data Link. Common Layer 1 issues include cable problems, module issues, and incorrect speed/duplex settings. Common Layer 2 issues include VLAN misconfigurations, trunking problems, and STP loops.

Troubleshooting tools. Useful troubleshooting tools include LEDs, CLI commands (e.g., show interfaces, show vlan, ping, traceroute), and packet captures. A combination of physical inspection and command-line analysis is often required to diagnose and resolve network issues.

8. Spanning Tree Protocol (STP): Preventing Loops

My idea for the programme came whilst following a keep fit programme provided by a special forces soldier.

Loop prevention. Spanning Tree Protocol (STP) prevents loops in switched networks by creating a loop-free logical topology. Switches exchange Bridge Protocol Data Units (BPDUs) to determine the network topology.

Key concepts. Understanding the Bridge ID (BID), Root Bridge election, port costs, and port states (Blocking, Listening, Learning, Forwarding) is essential for understanding STP operation.

Cisco enhancements. Cisco has introduced several enhancements to STP, such as PortFast, BPDU Guard, and Loop Guard, to improve network stability and security. Troubleshooting STP often involves identifying incorrect Root Bridges, incorrect Root Ports, and incorrect Designated Ports.

9. EtherChannels: Increasing Bandwidth and Redundancy

I’ve completely rewritten this book.

Combining links. EtherChannels aggregate multiple physical links into a single logical link, increasing bandwidth and providing link redundancy. EtherChannels can be Layer 2 or Layer 3.

Protocols. Port Aggregation Protocol (PAgP) is a Cisco-proprietary protocol for EtherChannel negotiation, while Link Aggregation Control Protocol (LACP) is an open standard.

Configuration and load balancing. Configuring EtherChannels involves assigning ports to a channel group and setting the appropriate mode (e.g., auto, desirable, active, passive). EtherChannel load balancing distributes traffic across the links based on various criteria, such as source/destination IP addresses or MAC addresses.

10. First Hop Redundancy Protocols (FHRP): Ensuring Gateway Availability

Cisco are a pretty clever company, especially when it comes to marketing and positioning their products and certifications.

Gateway redundancy. First Hop Redundancy Protocols (FHRPs) provide gateway redundancy, ensuring that hosts can still access the network even if the primary gateway fails.

Protocols. Hot Standby Router Protocol (HSRP) is a Cisco-proprietary FHRP, while Virtual Router Redundancy Protocol (VRRP) is an open standard. Gateway Load Balancing Protocol (GLBP) is a Cisco-proprietary FHRP that allows for load balancing across multiple gateways.

Configuration and operation. Configuring FHRPs involves assigning a virtual IP address, setting priorities, and enabling preemption. Understanding the election process and the different states is crucial for troubleshooting FHRP issues.

11. Managing and Maintaining Cisco Devices: IOS and Licensing

I’ve used several tools this time, including my personal experience in the exams, dual CCIE Farai Tafa’s CCNP study guides, real-world experience, RFCs, and what I’ve learned since 2000, when I left the police force in the UK and started my career in Cisco networking.

Router memory and files. Understanding router memory components (ROM, NVRAM, Flash, DRAM) and their functions is essential for managing Cisco devices. The configuration register sets instructions for booting.

IOS management. Managing the Cisco IOS involves backing up and restoring configurations, upgrading the IOS image, and understanding the boot process.

Licensing. Modern Cisco IOS images require licensing to enable advanced features. Understanding the licensing process and how to activate licenses is crucial for managing Cisco devices.

Last updated: March 3, 2025