Chapter 5 – Configure Network Addressing & Internet Connections (Comprehensive Notes)

Internet Connection Types and Modems

• The Internet = global “network of networks” built on high-bandwidth fiber trunks inter-connecting Internet Exchange Points (IXPs).
  • IXPs are usually operated by telecom carriers or academic institutions.
  • ISPs interconnect at IXPs via transit and peering agreements.
  • Hierarchical ISP tiers reflect how much an ISP relies on other providers for transit.
• Customer connectivity workflow
  • Local network → ISP’s nearest Point of Presence (PoP) (e.g., telephone exchange) via a WAN interface.
  • WAN links are point-to-point (only two devices share the medium) unlike shared Ethernet.
  • Hardware requirement: digital modem to establish the physical link + router to implement the Internet Protocol for inter-network forwarding.

Digital Subscriber Line (DSL)

• Uses higher-frequency bands of legacy two-pair copper cabling (the last-mile $\text{POTS}$ loop) on the Public Switched Telephone Network (PSTN).
• Employs advanced modulation + echo-cancellation for full-duplex operation.
• Main DSL families
  • ADSL (Asymmetric DSL) – downlink faster than uplink.
  • Latest ADSL2+ ≈ $24\ \text{Mbps}$ down / $1.25$–$2.5\ \text{Mbps}$ up.
  • SDSL / VDSL (Symmetric / Very-high-speed DSL) – equal up & down rates; attractive for business or branch offices.
• Installation specifics
  • Customer Premises Equipment (CPE) → RJ-11 to phone outlet.
  • RJ-45 from modem → router.
  • Splitter/filter separates voice and data; built-in on modern sockets.

Cable Internet (DOCSIS)

• Provided over CATV Hybrid Fiber-Coax (HFC) infrastructure.
• DOCSIS 3.x supports channel bonding for higher throughput.
  • Initial DOCSIS: $38\ \text{Mbps}$ down / $27\ \text{Mbps}$ up (NA); $50\ \text{Mbps}$ down (EU).
• CPE
  • Coax with F-type connector → cable modem → RJ-45 to router.
  • Neighborhood coax segments terminate at a CMTS that backhauls over fiber to the ISP PoP.

Fiber To The X (FTTx)

• Goal: overcome copper last-mile bottleneck; approach “LAN-like” bandwidth.

FTTC / FTTN (Fiber-to-the-Curb/Node) + VDSL

• Fiber extended to cabinet; last few hundred meters over copper.
• VDSL provides very high bit rates (symmetric or asymmetric) at short range.

FTTP / FTTH (Fiber-to-the-Premises/Home)

• Pure fiber run to building; implemented as a Passive Optical Network (PON).
  • Fiber PoP → Optical Line Terminal (OLT) in street → passive splitters → Optical Network Terminal (ONT) at customer.
  • ONT converts optical to electrical; RJ-45 patch to router.

Fixed Wireless & Satellite Internet

• Useful for rural / difficult cabling scenarios.

GEO Satellite (VSAT)

• Microwave link Earth ↔ satellite at geostationary orbit.
• Typical rates: $2$–$6\ \text{Mbps}$ up / $30\ \text{Mbps}$ down.
• High latency due to $\sim 35{,}786\ \text{km}$ signal path.
• CPE: small dish (VSAT) → coax → DVB-S modem.

LEO Satellite (emerging)

• Lower orbit ⇒ lower latency; still under evaluation (class activity).

Wireless ISPs (WISPs)

• Point-to-multipoint microwave; requires line-of-sight antennas.

Cellular Radio Internet

• Extends coverage beyond Wi-Fi ranges.
• Used by mobile devices & IoT (e.g., smart meters).
• Generational standards (class discussion)
  • 3G – $\approx 384\ \text{kbps}$–$2\ \text{Mbps}$.
  • 4G/LTE – $\approx 100\ \text{Mbps}$ peak mobile / $1\ \text{Gbps}$ stationary.
  • 5G – targets $\ge 10\ \text{Gbps}$, ultra-low latency.

Routers

• Switch ⇒ forwards frames via MAC addresses inside one broadcast domain.
• Router ⇒ forwards packets between networks using IP addresses.
  • Encodes both network ID and host ID within address.
• Types
  • SOHO router – LAN ↔ single WAN link.
  • LAN (internal) router – segments one physical LAN into multiple subnets; benefits: broadcast containment & security filtering.
  • WAN / Border router – connects enterprise LAN(s) to Internet or private WAN; has Ethernet LAN interface + modem/serial WAN interface.

Firewalls

• Enforce security policy via Access Control Lists (ACLs) of allowed/denied sources, destinations, protocols, ports.
• Deployment models
  • Basic filtering in routers.
  • Dedicated appliance / Unified Threat Management (UTM) with deep packet inspection.
• Can also segment internal zones (defense-in-depth).

TCP/IP Protocol Suite Overview

• 4-layer model
  • Link / Network Interface: Ethernet, Wi-Fi.
  • Internet: IP, ARP.
  • Transport: TCP, UDP.
  • Application: HTTP/S, FTP, DNS, DHCP, SMTP, IMAP, POP3, SSH, RDP, Telnet, LDAP, SNMP, Syslog, SMB.
• Encapsulation: each lower layer wraps the payload with its header/trailer.

IPv4 Addressing Essentials

• 32-bit address, shown as four 8-bit octets.
  • Binary example: $11000000\ 10101000\ 00000000\ 00000001$.
  • Dotted-decimal: $192.168.0.1$.
• Value range $0.0.0.0$ – $255.255.255.255$ (some values reserved).

Network Prefix & Subnet Mask

• Prefix of contiguous 1-bits separates network vs host portion.
  • Example mask $/24$ ⇒ binary $11111111\ 11111111\ 11111111\ 00000000$ ⇒ dotted $255.255.255.0$.
• Hosts compare destination address with own mask; if network differs → send to default gateway.

Public vs Private IPv4 Addressing

• Public addresses unique on Internet; scarcity drives private addressing + NAT.
• Private ranges (RFC 1918)
  • $10.0.0.0$ – $10.255.255.255$
  • $172.16.0.0$ – $172.31.255.255$
  • $192.168.0.0$ – $192.168.255.255$
• NAT or proxy server enables Internet access from private hosts.

IPv4 Host Configuration

• Minimum: IP + subnet mask.
• Practical: add default gateway + one or more DNS server addresses.
• Configuration methods
  • Static – manual; error-prone; reserved for servers/router interfaces.
  • Dynamic – DHCP, Automatic Private IP Addressing (APIPA), or SOHO auto-config (class activity).

Dynamic Host Configuration Protocol (DHCP)

• Server allocates addresses within a scope (e.g., $192.168.0.100$–$192.168.0.199$) and states lease duration.
• 4-step DORA handshake over UDP 67/68
  1. DHCPDISCOVER (broadcast)
  2. OFFER
  3. REQUEST (broadcast)
  4. ACK
• Client ARPs to detect conflicts, renews lease before expiry.
• Reservations: bind MAC → consistent IP without static config.

IPv6 Addressing Highlights

• 128-bit addresses ⇒ $\approx 3.4\times10^{38}$ possibilities.
• Written in 8 colon-delimited 16-bit hex blocks; leading zeros truncated, one series of zeros can be “::”.
  • Example: $2001:db8::abc:0:def0:1234$.
• Default split: first 64 bits = network prefix; last 64 bits = interface ID.
• Address categories
  • Global unicast – public; begin with 2 or 3.
  • Link-local – begin with fe80::; automatically generated; mandatory for local comms.
• SLAAC + Neighbor Discovery (ND)
  • Hosts self-assign using router advertisements – no need for explicit default gateway config.

Transport-Layer Protocols & Port Numbers

Transmission Control Protocol (TCP)

• Connection-oriented; reliability via 3-way handshake (SYN, SYN/ACK, ACK), sequencing, ACK/NACK, FIN termination.
• Adds $\ge 20$ bytes of header; used where loss intolerable (HTTP/S port $80/443$, SSH $22$, SMTP $25$, etc.).

User Datagram Protocol (UDP)

• Connectionless, minimal 8-byte header; no reliability or ordering.
• Chosen for latency-sensitive or simple request/response apps (VoIP RTP $5004$, streaming, DNS $53$, DHCP $67/68$, TFTP $69$).

Port Taxonomy

• Well-known (0–1023) – assigned by IANA to common services.
• Registered (1024–49151) – vendor/user processes.
• Dynamic/Private (49152–65535) – ephemeral client ports.

Domain Name System (DNS)

• Maps hostnames/FQDNs ⇄ IPs; hierarchical distributed DB.
• Structure
  • Root (.) → Top-Level Domains (gTLD, ccTLD) → domains / sub-domains → host labels.
• Query process
  • Stub resolver checks cache → queries recursive resolver (port $53$) → follows referrals to authoritative servers → returns Resource Record (RR).
• Key RR types: A/AAAA, CNAME, MX, NS, PTR, SRV, TXT.
• DNS vital for usability & security; mis-config leads to outages/phishing.

Virtual LANs (VLAN)

• Logical segmentation within switch; ports tagged with VLAN ID $2$–$4094$.
• Benefits
  • Limits broadcast domains → performance.
  • Security zoning; inter-VLAN traffic routed & filtered.
  • QoS grouping (e.g., dedicated VoIP VLAN).
• Each VLAN uses distinct IP subnet, DHCP scope, DNS suffix, etc.

Virtual Private Networks (VPN)

• Remote host tunnels into LAN over Internet; appears as local node.
• Security requirements
  • Confidentiality & integrity via encryption (IPsec, SSL/TLS).
  • Authentication of user & device.
• Practical considerations: bandwidth limited by Internet uplink; crucial for tele-work, BYOD, site-to-site links.

Ethical / Practical Implications & Real-World Relevance

• Last-mile technology choice affects digital divide between urban (fiber) and rural (satellite) populations.
• NAT & private addressing conserve scarce IPv4 space but complicate end-to-end connectivity (e.g., P2P, VoIP) ⇒ push toward IPv6.
• Firewalls & VLANs embody defense-in-depth—critical amid rising cyber-threats.
• VPN adoption surged with remote work, raising privacy expectations and corporate security challenges.

Numerical & Formula References (Quick Sheet)

• ADSL2+ down/up: $(24\ \text{Mbps} \downarrow,\ 1.25\text{–}2.5\ \text{Mbps} \uparrow)$
• DOCSIS initial: $38\ \text{Mbps} \downarrow / 27\ \text{Mbps} \uparrow$ (NA); $50\ \text{Mbps} \downarrow$ (EU).
• GEO latency path: $2\times 35{,}786\ \text{km}$ ≈ $\text{~500–600 ms RTT}$.
• IPv4 mask examples: $/8 \Rightarrow 255.0.0.0$, $/16 \Rightarrow 255.255.0.0$, $/24 \Rightarrow 255.255.255.0$.
• DHCP default ports: $67$ (server) / $68$ (client) – UDP.

Study & Discussion Prompts

• Evaluate TCP vs UDP trade-offs—how might QUIC or SCTP bridge the gap?
• Analyze 5G’s promises vs infrastructure challenges & spectrum ethics.
• Design a small office network: pick connection type, plan VLANs, assign DHCP scopes, and outline firewall ACLs.
• Hands-on: use Wireshark to capture DORA sequence and observe port numbers.