Networking fundamentals and CCNA-level reference content. The TCP/IP and OSI models, ethernet basics, encapsulation, IPv4 addressing, layer 2 fundamentals, and the Cisco IOS commands every network engineer reaches for. The foundations beneath the pillar guides.
The three RFC 1918 blocks, the rules that come with them, and why private addresses need NAT. Includes a live packet's journey from a private host through PAT to a real machine, captured in the Network Fundamentals lab.
Two-tier and three-tier campus models, spine-leaf in the data center, and where SOHO, WAN, and cloud designs fit. CCNA exam objective 1.2 and the vocabulary every design conversation assumes you already know.
A duplex mismatch leaves the link up and pings working while throughput dies. This post shows the exact syslog message CDP prints when it spots one and how to read every error counter in show interfaces.
Learn, forward, flood: the three rules a switch applies to every frame. Watch MAC addresses enter the CAM table, age, and trigger flooding, with real Cisco IOS XE output from two Linux hosts and a router in VLAN 10.
Subnetting has exactly one right answer and the exam gives you under a minute to find it. Learn the block-size method, walk a VLSM plan the way you would on a real network, and verify it all with real Cisco IOS XE output.
EIGRP has three administrative distances, not one: 90 internal, 170 external, 5 for summaries. Each value encodes a deliberate trust decision. This post explains why they differ and how to read and change them.
SD-WAN has two routing problems at once: how sites learn prefixes across the overlay with OMP, and how the physical transports route underneath. This post keeps the two layers separate using the Cisco Catalyst SD-WAN model.
A wireless LAN controller turns a pile of access points into a managed network: the APs become radios and the WLC becomes the brain. Covers the problem it solves, the controller-and-AP split, and WLC form factors.
PortFast skips the 30-second spanning tree wait so a host gets an IP the moment it plugs in. This post covers where it belongs, where it can take down a network, and the two guard features that keep it safe.
The native VLAN is the one untagged VLAN on an 802.1Q trunk, and it can break a link through a mismatch or get hopped through double tagging. This post explains why it exists, both failure modes, and how to configure it safely.
Before LSA types make sense, you need what an LSA actually is: one record in the link-state database describing one piece of the network. This post covers the LSA as a building block and how it gets everywhere it needs to be.
Basic BGP peering takes half a dozen lines; what trips people up is eBGP vs iBGP behavior, getting routes into BGP, and the iBGP next-hop quirk that silently breaks reachability. A full IOS XE walkthrough.