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Training series · NetFun II · level 2

Network Fundamentals II: addressing and routing

Layer 3, from the address on an interface to the path a packet takes across the internet: IPv4 subnetting and summarisation, IPv6, how a host gets its address and finds a name with DHCP and DNS, and how routers choose, from the routing table and the longest match to OSPF, IS-IS, BGP and MPLS.

At the end: you will be able to design an address plan, read a routing table, and explain why a packet went where it went.

Before this series: NetFun I.

4 modules · 54 articles

Begin: part 1, Cómo funcionan las direcciones IPv4 →

How the series works

  1. Read the parts in order. Each one builds on the ones before it, and every part's page shows where you are in the series and what comes next.
  2. Each module ends with a stated outcome: what you will be able to do once you have read it.
  3. Practise on the tools each module names. They run in your browser, with nothing to install.
  4. Parts still being written are named in their places, so the series shows its whole shape from the start.

The series, module by module

  1. Module 1 IPv4 addressing 10 parts

    Subnet any block by hand, size subnets with VLSM, summarise routes, and tell private address space from public.

    1. 1 Cómo funcionan las direcciones IPv4
    2. 2 Fundamentos de subredes
    3. 3 La notación CIDR explicada
    4. 4 VLSM: dividir un bloque en subredes desiguales
    5. 5 Una asignación VLSM, resuelta de principio a fin
    6. 6 Supernetting y agregación de rutas
    7. 7 Sumarización de rutas
    8. 8 Solapamientos y huecos de subredes
    9. 9 Espacio de direcciones IPv4 privadas y la RFC 1918
    10. 10 Private, Reserved, and Public IP Ranges

    Practice with: Calculadora CIDR / de subredes

  2. Module 2 IPv6 5 parts

    Read and shorten an IPv6 address, plan IPv6 subnets, and explain how a host configures itself and finds its neighbours.

    1. 1 Entendiendo el direccionamiento IPv6
    2. 2 Cómo los hosts IPv6 obtienen direcciones: SLAAC y DHCPv6
    3. 3 Subredes IPv6 y la frontera /64
    4. 4 Descubrimiento de Vecinos: cómo IPv6 reemplaza a ARP
    5. 5 Ejecutar IPv6 e IPv4 juntos: dual-stack y traducción

    Practice with: Kit de herramientas IPv6

  3. Module 3 Getting an address and a name 18 parts

    Follow a DHCP lease from discovery to renewal, read a DNS answer field by field, and say which server is authoritative for a name.

    1. 1 DHCP: the Lease Lifecycle Behind Automatic Addressing
    2. 2 BOOTP and DHCP options: what a client asks for, and what it is told
    3. 3 How an Access Point Finds Its Controller
    4. 4 The DHCP relay agent: one server for many subnets
    5. 5 PXE and network boot: how a machine with no disk finds what to run
    6. 6 TFTP: the simplest file transfer, and where it still runs
    7. 7 DNS: A File Maintained During Business Hours
    8. 8 Reading a DNS answer: the line you skipped is the diagnosis
    9. 9 The DNS Header: Opcode, Status, and Flags
    10. 10 Reading the Records in a dig Answer
    11. 11 Authoritative vs Non-Authoritative Answers
    12. 12 Public DNS resolvers: what you are actually choosing
    13. 13 Reading dig Output From Top to Bottom
    14. 14 Anatomy of a dig command line: how dig reads what you type
    15. 15 Zone transfers and NOTIFY: how secondary name servers stay in step
    16. 16 DNSSEC end to end: from the root's key to a validated answer
    17. 17 DoT, DoH and DoQ compared: encrypting the question
    18. 18 Anycast: one address in many places

    Practice with: DHCP option 43 generator · dig command builder · dig output explainer · nslookup output explainer

  4. Module 4 Routing 21 parts

    Read a routing table, predict which route wins and why, and explain what OSPF, IS-IS and BGP each decide.

    1. 1 Routing Tables and the Default Gateway: How a Packet Picks Its Next Hop
    2. 2 Static routes, longest prefix match and administrative distance: how a router chooses between answers
    3. 3 Reading ip route, netstat and route print, field by field
    4. 4 The Router: From Gateway to Commodity, and the Names Left Out
    5. 5 ICMP, ping, and traceroute: the Control Messages That Explain Your Network
    6. 6 NAT Explained: Source, Destination, and Why the Internet Still Works
    7. 7 CGNAT: what breaks when a thousand subscribers share one address
    8. 8 Port blocks and port sets: the arithmetic of sharing one IPv4 address
    9. 9 First-hop redundancy: VRRP, HSRP, and the gateway that is a fiction
    10. 10 BFD: when a link is up and dead at the same time
    11. 11 Sizing BFD timers: the arithmetic of detection
    12. 12 Dynamic routing compared: distance vector, link state and path vector
    13. 13 Dijkstra: the twenty-minute algorithm your routers run every day
    14. 14 OSPF: the map, the math, and area 0
    15. 15 IS-IS: the routing protocol hiding under the internet
    16. 16 BGP: how the internet decides where traffic goes
    17. 17 Route redistribution and the loops it invites
    18. 18 BGP: the trust fall the whole internet is standing on
    19. 19 Route origin validation, worked by hand: Valid, Invalid, NotFound
    20. 20 MPLS: labels, stacks, and the BGP-free core
    21. 21 Multicast: what it costs to not flood

    Practice with: Routing table explainer · Flow Path Reasoner · CGN port blocks and MAP port sets · BFD timer calculator · Route origin validation calculator