Networking basics

Moving data 5 topics

• Warm-up studio: a first look at the network
  A forty-five minute first look at every idea in the course: devices, packets, addresses, masks and a first fault to find, with no prior knowledge needed.
• What a network is: devices, links and packets
  Devices, links, protocols and topologies; packet switching; the four delays, overhead and goodput; the bandwidth-delay product; and the arithmetic to put numbers on a…
• Layers and encapsulation
  Why networks are built in layers, the TCP/IP and OSI models, how a message is wrapped and unwrapped using real headers, how next-protocol fields connect the layers, and…
• Ethernet, MAC addresses and the switch
  Where Ethernet came from, cables, speed and duplex, the full frame, MAC address bits, how a switch learns, forgets, forwards and floods, its limits, and how to read a…
• Hubs, switches and routers: who decides what
  What each device looks at and decides, one network against many, a router's table and longest match, what a router changes in a packet, the access point and the end of…

Addresses 4 topics

• IPv4 addresses, masks and CIDR
  An address as 32 bits, the mask and prefix, finding the network and broadcast with AND, the local-or-gateway decision, special ranges, and how classes gave way to CIDR.
• Subnetting by hand
  Why to split a network, the block-size method, borrowing bits, VLSM with the largest need first, summarising, and the mistakes that cause overlaps.
• Planning an ISP block
  What a block is and which addresses servers cannot use, the 12, 28, 60 and 124 for servers in /28 to /25, handoff against routed blocks, growth, one address per service…
• Private and public addresses, and NAT
  The private and special ranges, why they exist, static NAT, PAT and port forwarding, a table model, what NAT does and does not do, and the security view.

Finding things 4 topics

• The default gateway and the host's routing table
  A host's connected, static and default routes, longest prefix then metric, the four conditions a gateway must meet and the symptom of each failure, the four-command…
• ARP: from an IP address to a MAC address
  Why ARP is needed, the request and reply exchange and its 28 bytes, the cache and its states, how far ARP reaches, gratuitous and proxy ARP, and ARP's weakness as the…
• DNS: names to addresses
  The DNS tree and who answers, the files on a computer, record types, the query on the wire, the records for the ISP block, TTL planning and split DNS, reading dig, and…
• DHCP: addresses for clients
  What a lease carries, the four messages, scopes, pools, reservations and relay, the renewal timers, sizing and lease length, what happens with no server, and the…

Is it working? 4 topics

• ping and traceroute: reading the answer
  ICMP and its message types, reading ping line by line, how traceroute uses the TTL, stars and the last responding router, path MTU, and the security view: the sweep, the…
• Ports, TCP and UDP
  Ports and the five facts of a conversation, TCP's handshake, numbers and states, UDP, the three answers of a port and what each means, the tools, and the security view…
• Wi-Fi next to the wired network
  Bands, channels and standards, measuring signal in dBm and SNR, SSID and BSSID, why airtime is shared, planning channels, capacity and backhaul, and the security view…
• A layered troubleshooting method
  Define, scope, ask what changed, choose an approach, test one thing at a time, fix and verify, document; the ladder of rungs with the command for each, common patterns…

Infrastructure behind the office network 4 topics

• The network map: components and the path of one request
  The seven components of the office network, the path of one request and what dominates it, a card of seven boxes for each part, the inventory as a check, and the…
• Sizing the office network: ports, addresses, airtime and lines
  The sizing method, ports and the oversubscription ratio, addresses and leases, access points and airtime, table sizes, utilisation and the trend, finding the bottleneck…
• Failure, security and recovery: blast radius, hardening and backups
  Blast radius and critical parts, redundancy and the arithmetic of availability, hardening part by part, backups and restore tests, the recovery runbook, and the…
• Operating it: monitoring, change and handover
  Monitoring state, use and errors, thresholds and alerts including missing data, trends and the days until full, safe change, logs and clocks, the handover folder, and…

Interview ready 2 topics

• Interview ready: networking fundamentals
  The questions people really ask about layers, addresses, subnets, switches and routers, ARP, DHCP, DNS and TCP, with model answers, timed terminal tasks and a mock round.
• Interview ready: troubleshooting and a mock round
  The questions people really ask about layered troubleshooting, with model answers, timed terminal tasks and a mock round.

The office address plan

A written address plan for a small office from a stated ISP block, with the reasoning shown.

Component cards and a failure drill

Seven cards for the parts of the office network, a sizing for a stated load and one failure drill worked through.

Why take this course

• Understand how a network works
• Plan an address block yourself
• Practise on a simulator that checks your work

You will build

• An address plan for an office
• A set of component cards
• A worked failure drill

What you can do afterwards

• Explain a network in plain words
• Find a fault with a method
• Answer networking interview questions