Subject
CCNA 200-301
Sixteen articles following the CCNA blueprint from one cable upward: what a network is made of, the arithmetic of addressing, the switch and the loops it has to avoid, how a router picks a path, the services that make it usable, the controls that keep it honest, and what changes when the command line stops being the interface. Written to be read in order, and to make sense a year later.
Articles
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1 · How a network is built: hosts, switches, routers and the layers between them
The pieces a network is made of, the two layer models everyone argues about, what each box actually reads before forwarding, the cables and speeds behind the ports, and the vocabulary the rest of the series assumes.
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2 · IPv4 addressing and subnetting: the arithmetic you learn to do in your head
What the 32 bits mean, how a mask splits them into network and host, the special ranges, and a method for cutting a block into subnets and reading an address in a few seconds without a calculator.
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3 · IPv6 addressing: longer numbers, simpler rules
Why 128 bits, how to shorten an address without breaking it, the address types that replaced broadcast, how a host configures itself with SLAAC, and what neighbour discovery does that ARP used to.
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4 · Cisco IOS from the console: the commands everything else assumes
How a switch boots, the modes and prompts, the two configuration files and the difference between them, setting up remote access safely, and the handful of show commands and shortcuts that make the rest of the series readable.
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5 · Switching: how a frame crosses a switch
The Ethernet frame a switch reads, how it learns where every device lives, the three things it can do with a frame, why collisions vanished, and how to read the interface counters when a port misbehaves.
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6 · VLANs and trunks: one switch pretending to be many
Why one broadcast domain stops being enough, how an access port assigns a VLAN, what 802.1Q actually adds to a frame, the native VLAN trap, and the three ways to route between VLANs.
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7 · Spanning tree: the protocol that saves the network from itself
Why a single redundant cable can take down a whole switched network in seconds, how switches elect a root and block their way back to a loop-free tree, what RSTP changed, and the edge-port protections every access switch should have.
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8 · EtherChannel, CDP and LLDP: bundling links and finding your neighbours
How several cables become one logical link that spanning tree will not block, why the load balancing is per conversation rather than per packet, LACP against PAgP, and the two protocols that tell you what is plugged into each port.
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9 · Wireless fundamentals: the network with no cable to blame
How radio turns a network back into a shared medium, the bands and the three channels that matter, what an SSID really names, how a client associates, the split-MAC controller model, and what WPA3 fixed.
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10 · Routing: how a router chooses a path
What actually happens to a packet inside a router, how to read a routing table, why the longest prefix always wins, what administrative distance settles, and how to write static, default and floating routes that behave.
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11 · OSPF: routers that agree on the same map
How link-state routing differs from counting hops, what has to match before two routers become neighbours, why a designated router exists, how areas keep the database small, and the configuration and show commands that prove it works.
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12 · First hop redundancy: what happens when the default gateway dies
Why a host cannot fail over on its own, how two routers share one virtual address and MAC, the differences between HSRP, VRRP and GLBP, and why tracking an uplink matters more than tracking the router.
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13 · NAT and PAT: many hosts, one public address
The four address names Cisco insists on, static and dynamic translation, how port overloading squeezes a whole office behind one address, reading the translation table, and the things NAT quietly breaks.
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14 · IP services: DHCP, DNS, NTP, syslog, SNMP and a little QoS
The supporting cast that makes a network usable — how addresses are handed out and relayed across subnets, why clocks matter more than they look, the eight syslog levels, what SNMP still does, and the parts of quality of service worth knowing.
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15 · Securing the network: ports, lists and the traps between them
Hardening the device itself, AAA and why TACACS+ and RADIUS differ, the first-hop protections that stop a laptop impersonating a server, how to write an access list that does what you meant, and the VPN types worth naming.
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16 · Automation and programmability: when the CLI stops being the interface
Why typing into three hundred devices does not scale, what separating the control plane from the data plane actually buys, REST and the data formats around it, NETCONF and YANG, and what changes for the person who used to type.