// TOPICS — 4 topics

Tools and articles for what you want to do

Choose a topic and read in order, starting with its introduction. Links to background reading and further exploration are listed separately. You can also find articles from our series here, so you can read just what you need or continue through the whole book.

topics — index

$ topic open --rule

require: tools >= 2 AND articles >= 3

$ topic status

out 4 topics available

Topics

// TOPICS

IP addresses// TOPIC · three branches

How packets find their destination

Branch 1 2 articlesIdentify the destination and size the address block

Compare your address and the destination address using the same criteria, then calculate a subnet size that fits the number of devices you need.

Branch 2 2 articlesAssign addresses to devices and connect them to the internet

Separate the steps: a device uses DHCP to receive an address and its gateway settings, then communicates with the internet through NAT.

Branch 3 2 articlesManage internal and public addresses without overlap

Plan the enterprise's private address space, then see why public address allocation and registration are separate responsibilities from advertising internet routes.

Enterprise network design// TOPIC · four branches

Layers and redundancy for growth and resilience

Branch 1 3 articlesStart with business needs, then define roles and layers

First, see why you would separate the functions combined in a router. Identify who uses each service and how much downtime they can tolerate. Then compare those needs with Cisco's reference designs and the roles of Access, Distribution, and Core.

Branch 2 3 articlesChoose equipment and plan addresses for a small site

Compare when one router is enough with when you need separate switches and APs. Check ports, PoE, wireless requirements, and the gateway, and plan addresses that will not overlap when you connect to branches or the cloud.

Branch 3 3 articlesSet link capacity, failure domains, and L2/L3 boundaries

Calculate the capacity needed both during normal operation and on the paths left after a failure. Distinguish the effects of shared power and cable pathways from equipment failures. Then decide how far to extend each VLAN and where to separate networks with routing.

Branch 4 3 articlesConnect wiring closets and buildings with redundancy

Start with a two-tier design that aggregates access switches. Then examine failure detection and path switching for switches, gateways, and routers. Finally, decide when you need a separate Core to connect multiple distribution blocks.

Routing// TOPIC · four branches

How paths between networks are chosen

Branch 1 2 articlesChoose routes and prepare static routes for failures

Distinguish the routing table from the information used for forwarding, and learn how to detect failures beyond a directly connected link.

Branch 2 1 articleCalculate routes from connectivity within an organization

Follow OSPF neighbor formation, link-state exchange, route calculation, and updates to forwarding information, in that order.

Branch 3 2 articlesApply policy to routes learned from other networks

Examine BGP route attributes and policies. Track the source of redistributed routes and control which ones are allowed, so they do not cause problems by reentering their original network.

Branch 4 1 articleUse routing controls to limit the impact of attacks

Decide where to act before the link becomes saturated. Distinguish how blocking, observation, and traffic scrubbing affect normal service.

Switching// TOPIC · four branches

How frames travel across a local network

Branch 1 1 articleFind the other device's MAC address and forward the frame

Distinguish a destination on the same network from the gateway used to reach another network. See what the ARP table tells you and what a switch's MAC address table tells you.

Branch 2 1 articleSeparate communication domains on the same switch

Use VLANs to separate local communication domains, and see how a trunk carries multiple VLANs to another switch.

Branch 3 2 articlesUse redundant links safely

STP prevents loops by limiting active paths; EtherChannel distributes separate traffic flows across links. Learn why these are different functions.

Branch 4 1 articleConnect different VLANs

Follow the round trip: a device sends data to its gateway, which forwards the packet to another network after a route lookup and creation of a new frame. See how it reaches the other VLAN and how traffic returns.

How a topic takes shape

// HOW A TOPIC FORMS

Topics take shape in two ways. Sometimes we start with an outline and fill it in. Other times, separate tools and articles come together under one name. Either way, we do not force a topic into existence.

↓ Top-down · Start with the topic

Start with a topic people need

Some broad topics come up again and again in IT work, such as dividing address space or concealing and verifying values. We start with those topics and build them out with articles explaining the principles and tools you can use.

This approach works when it is clear what you need to learn. The knowledge provides the framework; the tools make it practical.

↑ Bottom-up · Let the topic emerge

Find the topic connecting separate pieces

As you use different tools and read articles across several subjects, you start to see connections. Bringing those tools and articles together under one topic helps you understand how they fit together—something you might miss when viewing each one on its own.

In this approach, we do not choose a topic in advance. We give it a name once enough material has come together.

Both approaches lead to the same result: a topic opens when it has 2 tools and 3 articles. We do not set up empty sections in advance, so you never click into a topic only to find nothing there.