Module 9

Question 1

WAN Characteristics

Answer 1

• Connects LANs over large geographical areas • High data throughput, long-distance support • Uses routers, modems, and specialized transmission media • Often leased from telcos (NSPs): AT&T, Verizon, Spectrum, Comcast • Corporations pay based on bandwidth used/reserved • May connect directly to IX (Internet Exchange) to reduce costs • Uses OSI Layers 1 & 2 differently than LANs • Same protocols as LANs for Layer 3 and above • WAN site = individual location • WAN link = connection between WAN sites o Point-to-point: 1-to-1 connection o Multipoint: 1-to-many connection

Question 2

Differences Between LAN, CAN, MAN, WAN

Answer 2

LAN (Local Area Network) • Connects devices within small geographic area • Owned/operated by a single organization • Ethernet-based • Uses switches and routers CAN (Campus Area Network) • Multiple LANs in a campus/school area • Typically owned by a single organization • Confined to single or nearby properties MAN (Metropolitan Area Network) • Collection of LANs across a city/province • Network media is leased, often across public property • May serve one customer or general public • Examples: o Police station networks o Hospital to regional medical centers o Home office to branches WAN (Wide Area Network) • Large geographic scope (e.g., global) • Leased from ISPs or NSPs • Mix of tech and media types • Example uses: o Bank connecting offices and global partners o Sales reps uploading to HQ o Manufacturer working with remote contractors o Global e-commerce

Question 3

Entry Point Equipment & Terms

Answer 3

• Modem: Modulates/demodulates analog ↔ digital • Router: DTE (Data Terminal Equipment), customer-owned • Modem: DCE (Data Circuit-Terminating Equipment), ISP-owned • DTE = customer LAN-side device • DCE = ISP WAN-side device • Sometimes DTE & DCE combined in one unit

Question 4

CPE & Demarcation

Answer 4

CPE (Customer Premises Equipment) • All equipment on customer site • Owned by customer or ISP • Examples: Router, modem, CSU/DSU, line driver • ISP services only their own devices Demarc (Demarcation Point) • Division between ISP responsibility and customer responsibility • Equipment beyond demarc = customer-managed • Equipment before demarc = ISP-managed

Question 5

Devices at/near Demarcation Point

Answer 5

NIU / NID (Network Interface Unit/Device) • Connects ISP’s local loop to customer’s network • Smartjack / INID = intelligent NIU o Diagnostic features (e.g., loopback testing) o Sends signal back to ISP CO (Central Office) Line Driver • Repeater to boost signals over long distances • Copper or fiber versions • Can be located on either side of demarc • May be customer- or ISP-owned CSU/DSU (Channel Service Unit / Data Service Unit) • Endpoint for dedicated WAN connection • Converts digital signals for transmission • Usually located between demarc and router • Can be owned by either ISP or customer

Question 6

Routers – Core Concepts

Answer 6

• Connects 2+ networks, routes packets between them • Makes forwarding decisions using Layer 3 (and often Layer 4) data • Components: o Processor o OS o Memory o Network ports/interfaces o Console interface • All routers can: o Connect dissimilar networks (e.g., LAN ↔ WAN) o Interpret L3/L4 headers o Calculate & select best path (most efficient) o Reroute if path fails

Question 7

Routers – Optional Functions

Answer 7

• Filter broadcasts to reduce congestion • Basic firewalling (block certain traffic) • Support local & remote connections • Redundancy (e.g., power supplies, NICs) • Monitor/report traffic statistics • Diagnose issues and trigger alarms

Question 8

Router Types (by Network Location)

Answer 8

• Core/Interior Router o Operates within a single AS (Autonomous System) o Communicates only inside the same organization/network o Trusted, internal domain • Edge/Border Router o Connects an AS to an external/untrusted network o E.g., ISP connection • Exterior Router o Outside any specific AS o Often on Internet backbone o May also refer to other organizations’ edge routers

Question 9

Router Installation

Answer 9

• Small/Home Networks o Simple setup: plug modem into WAN port, devices into LAN port o Config via web utility • Enterprise Routers o Multiprotocol & high-powered o Complex configuration o Requires networking expertise • L3/L4 switches can also route (similar functionality)

Question 10

Routing Table – Overview

Answer 10

• Database for host location & best path info • Router = member of all connected networks • Each interface → unique network • Table = list of route entries: o Destination network (IP + netmask) o Gateway (next hop IP) o Interface (router port to use) o Metrics (route preference ranking)

Question 11

Routing Table – Decision Process

Answer 11

1. Packet arrives at router 2. Router checks destination IP 3. For each table row: o Compute IP range from IP + netmask o If destination IP fits range:  Read gateway IP (next hop)  Read output interface 4. If multiple matching routes → use lowest metric (better route) 5. If no match → look for 0.0.0.0 entry (default route) o Gateway in default = Gateway of last resort 6. If no default route → drop the packet

Question 12

Routing Table Example: LAN A → LAN D

Answer 12

• Workstation sends job to printer (different LAN) • Steps: 1. IP forwards to default gateway (Router A) 2. Router A searches routing table → finds 2 possible routes  Chooses one with lower metric  Identifies next hop = Router C  Identifies interface to use  Decreases packet TTL 3. Forwards to Router C 4. Router C decreases TTL again  Searches routing table  Sees destination is on its LAN  Forwards to Switch D 5. Switch D:  Looks up printer MAC via ARP (if needed)  Sends to printer

Question 13

Routing Path Types

Answer 13

• Static Routes o Manually configured by network admin o Fixed path between networks (e.g., small biz to ISP) o No adaptation to: congestion, failures, relocation o Requires manual updates • Dynamic Routes o Router calculates best path automatically o Routing table updates in real-time o Can reroute during congestion/failure o Auto-updates when routers are added

Question 14

Route Utility & Routing Table Access

Answer 14

• View Routing Table (OS-specific commands): o Linux/UNIX: route o Windows: route print o Cisco IOS: show ip route (Privileged EXEC Mode) • Routing Tables: o Workstations: Few entries (default gateway, loopback) o ISP Backbone Routers: Hundreds of thousands of entries

Question 15

Routing Metrics (Best Path Criteria)

Answer 15

• Hop Count – Number of network segments crossed • Bandwidth / Throughput – Theoretical vs actual • Delay (Latency) – Time delay along a path • Load – Traffic/processing burden on a router • MTU (Max Transmission Unit) – Largest IP packet size allowed without fragmentation (excludes frame) • Routing Cost – Admin-assigned; lower = more desirable • Reliability – Based on historical path performance • Topology – Network layout/design

Question 16

Routing Protocol Evaluation Factors

Answer 16

• AD (Administrative Distance) o Default number per protocol o Lower AD = higher priority o Can be manually changed by admins • Convergence Time o Time to identify a new best path after change/outage o Faster convergence = more desirable • Overhead o Burden on network (processing + data exchanged) o Higher overhead = more resources used

Question 17

Routing Protocols Overview

Answer 17

• Routing Protocol ≠ Routable Protocol (e.g., IP) • Used by routers to exchange network status data • Typically operate at OSI Layers 3, 4, or 7 • Help populate and update routing tables

Question 18

Common Routing Protocols Summary

Answer 18

Protocol Type Algorithm RIP IGP Distance-vector RIPv2 IGP Distance-vector OSPF IGP Link-state IS-IS IGP Link-state EIGRP IGP Advanced distance-vector BGP EGP Advanced distance-vector / Path vector

Question 19

IGPs vs EGPs

Answer 19

• IGPs (Interior Gateway Protocols): o Used within autonomous systems (AS) o Used by core and edge routers o Types: Distance-vector, Link-state, Hybrid • EGPs (Exterior Gateway Protocols): o Used between autonomous systems o Used by edge and exterior routers o Only protocol used: BGP

Question 20

Distance-Vector Protocols (e.g. RIP, RIPv2)

Answer 20

• Determine best path by number of hops (sometimes latency) • Routing by rumor: routers trust neighbors’ info • Periodically exchange entire routing tables, even without changes • Slow convergence, higher risk of persistent errors • Examples: RIP, RIPv2

Question 21

Link-State Protocols (e.g. OSPF, IS-IS)

Answer 21

• Determine best path using state of links, not just hops • Routers map the entire network themselves • Share info only when changes occur • Faster convergence, more scalable • Require more CPU and memory • Examples: OSPF, IS-IS

Question 22

Hybrid Protocols (e.g. EIGRP)

Answer 22

• Combine features of distance-vector and link-state • Example: EIGRP o Shares updates only on change o Fast convergence o Lower CPU/memory requirements than OSPF o Proprietary to Cisco (partially open since 2013) o Supports multiple protocols o Preferred on Cisco-only LANs

Question 23

RIP, RIPv2, RIPng

Answer 23

• Type: Distance-vector IGP • Hop limit: 15 (if exceeded, destination unreachable) • Simple, quick to configure • Broadcasts table every 30 sec • Limited metrics: only hop count considered • Slow convergence • Not suited for large networks • RIPv1 (1988): original, less secure • RIPv2 (1994/1998): less broadcast traffic, more secure • RIPng (1997): adds IPv6 support • All versions considered outdated

Question 24

OSPF (Open Shortest Path First)

Answer 24

• Type: Link-state IGP • Works on core or edge routers • No hop limit • Uses complex algorithms for best path • Recalculates paths when links fail • Fast convergence, low bandwidth overhead • Prevents routing loops • Supported on multi-vendor routers • Common in mixed environments

Question 25

IS-IS (Intermediate System to Intermediate System)

Answer 25

• Type: Link-state IGP • Works on core routers only • Uses algorithm similar to OSPF • Developed by ISO • Easily supports IPv6 (not tied to IPv4) • More scalable than OSPF • Preferred by service providers

Question 26

EIGRP (Enhanced Interior Gateway Routing Protocol)

Answer 26

• Type: Hybrid IGP • Developed by Cisco (partially open since 2013) • Combines distance-vector base with link-state features • Fast convergence • Low overhead, minimal unnecessary traffic • Supports multiple protocols • Best for large, Cisco-based networks • Easier configuration than OSPF

Question 27

BGP (Border Gateway Protocol)

Answer 27

• Type: EGP, used on the Internet • Only EGP still in use • Used by edge and exterior routers • Path-vector protocol (uses TCP sessions) • Determines best paths using many customizable factors • Allows policy-based routing • Can span multiple autonomous systems • Most complex routing protocol • Required knowledge for ISPs / large-scale networks

Question 28

Routing Redundancy Concepts

Answer 28

• Fault tolerance through redundant: o Hardware o Connections o Services o Data copies • If one router fails, another can take over • Small network example: o 2–3 ISP connections o 1–2 routers per ISP • Large network example: o Multiple ISPs using geographically separate hardware and media o E.g., ISP 1 enters from one side of building; ISP 2 from the opposite o Protects from:  Underground cable damage  Flooding, fire  Power outage  Localized failures

Question 29

Redundancy Types (Active-Active vs. Active-Passive)

Answer 29

• Active-Active Redundancy: o All redundant resources active o Workload is distributed (e.g., load balancing between ISPs) o Either resource can take over if another fails o Increases performance under normal conditions • Active-Passive Redundancy: o One/few resources active; backups standby only o Backup activated only if primary fails o Example: Single ISP in use, second ISP on standby

Question 30

Gateway Redundancy Problem & Solution

Answer 30

• Problem: o Devices can only be configured with one default gateway o Manual gateway failover is impractical • Solution: o Use FHRP (First Hop Redundancy Protocol) o Provides a single VIP (Virtual IP) address as default gateway o VIP can point to multiple routers o Seamless failover and/or load balancing

Question 31

FHRP Protocols

Answer 31

• VRRP (Virtual Router Redundancy Protocol): o Industry standard (multi-vendor support) o VIP points to primary active router o Others standby as backups o Config: vrrp command • HSRP (Hot Standby Routing Protocol): o Cisco proprietary o VIP points to active router o One standby router configured for failover o Other routers listen for failure signals o Config: standby command • GLBP (Gateway Load Balancing Protocol): o Cisco proprietary o Gateways weighted by priority o Traffic load balanced across all o Config: glbp command

Question 32

WAN Connectivity Options

Answer 32

• Broadband o Shared medium (many customers on same cable/bandwidth) o Asymmetrical speeds (faster download than upload) o “Best effort” bandwidth (actual speed varies by usage) o Often used for residential connections o Businesses can pay more for speed/static IPs o No guarantees on uptime or bandwidth • Dedicated Internet Access (DIA) o Dedicated bandwidth or cable for one customer o Symmetrical speeds (equal upload/download) o Service-Level Agreement (SLA) defines uptime + recovery o Common for businesses needing consistent, reliable service o Often includes static IP addresses

Question 33

DSL (Digital Subscriber Line) Overview

Answer 33

• Introduced in mid-1990s by Bell Labs • Operates over PSTN (public switched telephone network) • PSTN uses: o Fiber backbone o Twisted-pair copper for local loop o Digital transmission, computer-controlled switching • Local Loop = “last mile” (residence to central office) • DSL shares line with voice using higher frequencies • Requires DSL modem (handles modulation) • Modulation types affect speed and range • Distance from central office affects speed • Lower cost than leased lines; speed varies • Competes with cable broadband

Question 34

Types of DSL (xDSL)

Answer 34

• ADSL (Asymmetric DSL) o Asymmetrical: faster download, slower upload o Suited for media streaming/web surfing o Requires splitter at both ends to separate voice/data o ADSL2+:  Range: up to 2 km  Max downstream: 24 Mbps  Max upstream: 3.3 Mbps  Bandwidth divided into voice/up/downstream • VDSL (Very High Bitrate DSL) o Asymmetrical: faster download than upload o Max 52 Mbps (down), 16 Mbps (up) o Max range: 1.6 km (VDSL2 = higher speed, shorter range) o Not suited for long-distance customers • SDSL (Symmetric DSL) o Symmetrical speeds: up to 2 Mbps both ways o Ideal for high-volume upload/download users (e.g., banks) o Uses separate wire pair (cannot share with voice)

Question 35

PSTN & DSL Infrastructure

Answer 35

• PSTN (Public Switched Telephone Network) o Backbone: fiber-optic o Local loop: copper (analog or digital) o Termination point: NIU (Network Interface Unit) at customer o CO (Central Office): where lines terminate and switch • Line Sharing o Voice: 300–3300 Hz o DSL uses higher frequencies for data • Modulation Techniques o Physical layer modulates high frequencies o Types: amplitude/phase modulation (varies by DSL type) o Determines throughput + distance • DSL Modem o Connects phone line to network device o Handles signal modulation/demodulation

Question 36

Cable Broadband (Cable Internet)

Answer 36

• Uses coaxial cable (or fiber in HFC networks) • Based on DOCSIS (Data Over Cable Service Interface Specifications) • Asymmetric speeds typical (e.g. 70 Mbps download / 7 Mbps upload) • DOCSIS 4.0 supports up to 10 Gbps down / 6 Gbps up • Requires a cable modem: o Operates at physical and data link layers o Connects via RJ-45, USB, or wireless o Can interface with a router or SOHO gateway • Infrastructure: o HFC (Hybrid Fiber-Coaxial) = fiber from headend to optical node o Cable drop = final coax/fiber link to customer premises • Shared bandwidth among subscribers o Security risk: data may be intercepted (encryption is present but can be bypassed) o Throughput decreases with more users • Cost: ~$30–$60/month when bundled • Less used in business due to coaxial cable infrastructure limitations

Question 37

DOCSIS Versions (Cable Broadband Standards)

Answer 37

• DOCSIS 1.x (1.0, 1.1) o 10 Mbps up / 40 Mbps down o Outdated, single channel • DOCSIS 2.x (2.0, 2.0 IPv6) o 30 Mbps up / 40 Mbps down o Outdated, reduces upstream/downstream disparity • DOCSIS 3.0 o 100 Mbps up / 1000 Mbps down o Minimum 4 channels; no max • DOCSIS 3.1 o 1–2 Gbps up / 10 Gbps down o Full Duplex DOCSIS 3.1 supports symmetrical Gigabit speeds • DOCSIS 4.0 o 6 Gbps up / 10 Gbps down o RF bandwidth support; multigigabit full-duplex

Question 38

Fiber Internet (WAN Option)

Answer 38

• Backbone of the Internet already uses fiber • Last-mile determines speed limitations • Options (based on distance to customer): o FTTN (Node/Neighborhood): serves a few hundred o FTTC (Curb): nearby cabinet or pole, serves few o FTTB/FTTH (Building/Home): directly at customer demarc • Closer fiber = higher speed / higher cost • Home/small biz speeds: 1–2 Gbps symmetric • Monthly cost: up to $100 • Speed unaffected by customer distance • Becoming increasingly available due to demand and ISP investment

Question 39

Metropolitan Optical Networks (MONs)

Answer 39

• Bring fiber closer to customers in urban zones • Focus on access-level infrastructure • Aim to replace copper/coax with dense fiber grids • Goal: make direct fiber available to many customers • Challenge: existing fiber tech (e.g., DWDM) o Designed for long-haul, not metro scale o Struggles with varied protocols/channels in metro settings o Known as the “metro gap” • New/adapted tech for MONs now emerging • Target speeds: up to 100 Gbps (matching long-haul connections)

Question 40

Leased Lines

Answer 40

• Dedicated bandwidth o Exclusive use; not shared with others o Throughput remains constant regardless of external traffic • Symmetrical speeds o Equal upload & download speeds • SLA guarantees o Uptime, repair time, and sometimes backup connection included o SLAs define recourse if bandwidth drops below threshold • Installation o May use existing fiber or require new cabling o Connects business location to nearest ISP PoP (Point of Presence) o Some install costs covered by ISP; some may be charged to customer • Cost o Varies by bandwidth & distance to PoP or between customer sites o Ranges ~$300–$1000/month per line • Scalability o Easy to add more locations via new leased lines • Communication routing o Inter-location communication travels over ISP’s high-speed backbone • Point-to-point option o Dedicated leased line between 2 customer locations o Lacks ISP-managed services like traffic optimization or uptime monitoring

Question 41

MPLS (Multiprotocol Label Switching)

Answer 41

• General description o Supports multiple Layer 3 protocols over any Layer 2 connection o Centrally manages bandwidth across multiple diverse connections • Use case o Suited for multi-site businesses needing scalable, manageable interconnectivity o Ideal when managing multiple leased lines becomes inefficient • Connection diversity o Different connection types per site (e.g., DSL, fiber, leased line) • QoS (Quality of Service) o Prioritize traffic types (e.g., VoIP > email) o Allows fine-grained control over network performance • Traffic handling o Ingress router adds MPLS labels (shim layer between Layer 2 & 3) o Labels contain next-hop & prioritization info o Transit routers (LSRs) update labels but don’t recalculate paths o Enables faster, switch-like routing with lower latency • MPLS Layer o Sometimes referred to as "Layer 2.5" • Benefits o Lower latency (less noticeable today) o Highly scalable and cost-effective compared to leased lines o Reliable and predictable routing o Enables user-defined traffic priorities o Enhanced security when well implemented

Question 42

Cloud Connectivity Options

Answer 42

• Initial setup o VPNs used for secure cloud access o Requires VPN device at each location o VPN traffic travels over existing Internet connections • Cloud migration benefits o Email, websites, customer DBs, HR tools moved to cloud o Removes need for local hosting infrastructure o Scales without hardware purchases • VPN limitations o Sufficient early on but not suitable for high-demand locations (e.g., HQ) • Private-direct connection o Leased line to cloud provider’s PoP or colocation facility o Secure and high-performance alternative to VPN • Costs o Leased line fee + cloud interconnection + data transfer fees (e.g., $0.02/GB outbound) • Multicloud benefit o One leased line to colocation can serve multiple cloud providers o Reduces total cost; improves hybrid cloud flexibility • Use cases o Ideal for hosting virtual desktops o Supports full hybrid cloud deployment

Question 43

SD-WAN Overview

Answer 43

• Stands for Software-Defined Wide Area Network • Centralized control of network functions across global infrastructure • Abstracted management layer, similar to Software-Defined Networking (SDN) • Designed for dynamic, scalable WAN deployments

Question 44

SD-WAN Benefits

Answer 44

• Transport agnostic: o Supports various WAN types: broadband, leased line, MPLS, 5G, DSL, etc. o Manages all types from a single controller • Active-active load balancing: o Uses all WAN links simultaneously o Routes traffic based on current network conditions and traffic type priority o Enables automatic failover if a link goes down • Intent-based management: o Admin sets policies via GUI (e.g. limit bandwidth for app X) o Controller applies changes across all devices • Zero-touch provisioning: o Devices can be shipped with no local configuration o Auto-connects to controller o Fully deployed remotely by central IT • Reduced cost: o Allows use of cheaper Internet options (fiber, cable, 5G) o Minimizes need for expensive leased lines/MPLS o Can still integrate some leased lines if needed

Question 45

SD-WAN Limitations / Challenges

Answer 45

• Internet security still a concern when traffic crosses public networks • MPLS and leased line cost still relevant for some needs • Cloud and mobile flexibility improvements needed • Still undergoing technological refinement, but gaining widespread adoption

Question 46

WIRELESS WAN OVERVIEW

Answer 46

• Wireless WANs enable long-distance digital data exchange (city/state level) • Used in surveillance, remote learning, telemedicine, emergency alerts • Unlike WLANs, designed for high throughput and long-range

Question 47

CELLULAR NETWORK INFRASTRUCTURE

Answer 47

• Area divided into cells served by cell sites (antenna + base station) • Towers often leased; base station equipment assigns frequencies • Handoff: Seamless transition of communication between cells • Cell size: 1000 ft to 12 miles (depends on traffic, terrain, topology) • Coverage gaps due to terrain, EMI, antenna patterns • MSC (Mobile Switching Center): Connects base stations to wired networks o Manages clients, assigns IPs, routes packets o Linked via fiber or microwave to telephone central office

Question 48

CELLULAR GENERATIONS

Answer 48

• 1G: 1970s–80s; analog only • 2G: 1990s; digital; texting/media downloads; max 240 Kbps • 3G: Early 2000s; up to 384 Kbps; fully digital o Two main 3G technologies:  GSM (Global System for Mobile Communications)  Uses TDMA (time slots from multiple devices)  Requires SIM card  Evolved into GPRS, EGPRS/EDGE  CDMA (Code Division Multiple Access)  Spread-spectrum over wider bandwidth  No SIM card (whitelist-based) except for LTE use  Used by some US carriers (e.g., Verizon); less common globally • 4G: All-IP for voice + data; min 100 Mbps, goal 1 Gbps o LTE: Transitional tech; faster than 3G, not true 4G  Typical: ~100 Mbps down / ~75 Mbps up o LTE-A (LTE-Advanced): True 4G; sometimes marketed as “5G E”

Question 49

5G TECHNOLOGY DETAILS

Answer 49

• Min: 1 Gbps down; Max: 20 Gbps down / 10 Gbps up • First deployed in 2019; standards released in 2016 • Unrelated to Wi-Fi’s 5 GHz band 5G Improvements: • Bands: o Low-band: same as 4G (< 2 GHz), wider coverage, lower speed o Mid-band: 2–10 GHz; moderate range + speed o High-band (mmWave): 20–100 GHz; high speed, short range • Cell Density: Requires many small antennas for coverage • Channels: o 4G: up to seven 20-MHz channels o 5G: up to eight 100-MHz channels (high band) o Mid-band: 2 × 100-MHz channels; stackable low-band (20 MHz) • Client Volume: o 5G supports more simultaneous users per cell site o Ideal for IoT and sensor networks

Question 50

Satellite Communication Basics

Answer 50

• Arthur C. Clarke theorized satellite communication in 1945 • First practical use in 1960s: US transmitted phone & TV across Atlantic • Now used for voice, video, music, data transmission • Cost reductions made it accessible for consumer use

Question 51

Satellite Orbits

Answer 51

• Most satellites orbit 22,300 miles above equator • GEO (Geosynchronous Earth Orbit): same rotation rate as Earth • Geostationary Orbit: special GEO case, stays above same equator point • Used for reliable communications (fixed Earth-based dishes)

Question 52

Satellite Signal Flow

Answer 52

• Uplink: Earth → Satellite o Signal scrambled (encoded) to prevent unauthorized access • Transponder: receives uplink → retransmits via downlink • Downlink: Satellite → Earth o Downlink uses unique, FCC-regulated frequencies • Received via dish antenna, which focuses signal for receiver

Question 53

Satellite Internet Services

Answer 53

• Provided via GEO satellites • Requires: o Small dish antenna (≈ 2ft x 3ft) o Receiver → connected to satellite modem o Modem uses Ethernet to link to router/computer • Antenna must have line-of-sight to sky (clear, unobstructed view) • North American dishes point south (toward equatorial GEO satellites)

Question 54

Satellite Service Characteristics

Answer 54

• Common in rural/remote areas or for mobile clients (e.g., yachts) • Connection type: asymmetrical (downlink faster than uplink) • Shared bandwidth across subscribers • Downlink speed: up to 100 Mbps • Uplink speed: much slower • Issues: o Latency and jitter reduce signal quality o Not suitable for latency-sensitive tasks • Chosen when: o No better alternatives o Existing satellite infrastructure available

Question 55

Internet Connectivity Issues

Answer 55

• Interference o Affects both wired and wireless o Causes intermittent or network-wide issues • DNS Issues o Must have correct DNS server info o DNS must be functional o Can use corporate, ISP, or public (Google, Cloudflare) servers • Router Misconfiguration o Incorrect routes → dropped messages (no error feedback) o Other issues: blocked ports, duplex/speed mismatch, wrong IP/subnet/default gateway o Misconfigs can also be exploited for DoS-style attacks • Interface Error o Incorrect default gateway or missing DNS → errors o Test: Switch interface (e.g., use Wi-Fi if Ethernet fails)

Question 56

Cisco CLI Modes

Answer 56

• User EXEC Mode o Prompt: Router> o Command: Login to device o Use: View-only access, no config changes • Privileged EXEC Mode o Prompt: Router# o Command: enable or en o Use: Full access to EXEC commands (testing, status, etc.) o Run EXEC from other modes using do prefix • Global Configuration Mode o Prompt: Router(config)# o Command: configure terminal or conf t o Use: Make global config changes, enter submodes • Interface Configuration Mode o Prompt: Router(config-if)# o Command: interface or int o Use: Configure interfaces, DHCP, routing, etc. o Can enter deeper config submodes • Exiting Modes o exit → one level down o end or Ctrl+Z → return to Privileged EXEC

Question 57

Configuration Files: Running vs Startup

Answer 57

• Show Running Config o Command: show running-config or sh run o Displays config in RAM (temporary) o Navigation:  Enter = line-by-line  Space = page-by-page  Tab/↓ = exit output • Persistent Config o Save config: copy running-config startup-config or copy run start o Running config = RAM (lost on restart) o Startup config = NVRAM (survives reboot) o View startup config: show startup-config or sh start

Question 58

Interface Status & Troubleshooting (show interface)

Answer 58

• Link State o Layer 1: Physical cable check o Layer 2: Line protocol, framing, clocking o “Administratively down” = use no shutdown • MTU (Max Transmission Unit) o Default: 1500 bytes for Ethernet • Bandwidth (BW) o Used by routing protocols to calculate path metrics o Includes delay, reliability, load • Encapsulation o Ethernet = ARPA o “Loopback not set” = not using loopback test mode • Duplex & Speed o Info on full/half-duplex, Mbps, connection type (e.g., RJ-45) • Traffic Statistics o Track since last reset o Includes:  Dropped packets (queue overflow)  Input/output rates  Total packets/bytes sent/received  Broadcasts  Runts = frames < 64 bytes (caused by collisions)  Giants = frames > 1518 bytes (or > jumbo frame limit)  CRC errors = transmission damage (bad cable/NIC)

Question 59

Interface IP Info (Layer 3)

Answer 59

• Command: show ip interface or sh ip int o Displays Layer 3 details: IPs, NAT, accounting, compression, helper addresses • Command: show ip interface brief or sh ip int br o Concise view: interface name, IP address, status

Question 60

Routing Table and Route Types

Answer 60

• show ip route — Displays router’s routing table • Route types: o C (Connected): Networks directly attached to router interfaces o S (Static): Manually configured routes by admin o Protocol codes: R = RIP, B = BGP, D = EIGRP, O = OSPF o Gateway of last resort: Default route used when no other route matches

Question 61

Common Routing Issues

Answer 61

• Missing route: o Causes message drops if no matching route o Use gateway of last resort commands to fix:  ip default-gateway (no routing configured)  ip default-network (routing configured, classful route)  ip route 0.0.0.0 0.0.0.0 (default route, routing configured) o Missing advertisement of connected routes can cause reachability issues • Routing loop: o Messages circulate endlessly, degrading network performance o Caused by too many topology changes too quickly o Distance-vector protocols converge slowly o Mitigations:  Conservative TTL (time-to-live) drops packets after max hops  Split horizon prevents route info looping back to origin  Routing timers synchronize route table updates to prevent outdated info • Asymmetrical routing: o Traffic paths differ in opposite directions of a conversation o Common on Internet (especially with BGP) o Problems for NAT and firewalls needing bidirectional traffic visibility o Can cause firewalls to reject legitimate traffic due to mismatched sessions o Multi-firewall setups require careful traffic and routing design to avoid issues

Question 62

Cisco Router and Switch Common Commands

Answer 62

• show running-config / sh run — View current running config (RAM) • show startup-config / sh start — View saved config (NVRAM) • copy running-config startup-config / copy run start — Save current config permanently • show interface / sh int — Interface status, stats, errors, bandwidth, duplex, MTU • show ip interface / sh ip int — Layer 3 IP details on interfaces • show ip interface brief / sh ip int br — Concise interface list and status • enable / en — Switch to privileged EXEC mode • configure terminal / conf t — Enter global config mode • interface / int — Enter interface config mode • exit — Step down one mode level • end or Ctrl+Z — Return to privileged EXEC mode