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OSPF, EIGRP, and BGP Basics at Network+ Depth

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CompTIA Network+ N10-009

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1 Introduction & Exam Overview

Current Exam Facts and Applied Networking Judgment Official Domain Weights and an 8-12 Week Study Plan How to Use Labs, Practice, and PBQ Workflow Missed-Question Notebook and Final Readiness Metrics

2 Domain 1: Networking Concepts (23%)

OSI and TCP/IP Models with Device and Protocol Mapping Networking Appliances and Where They Operate Ports and Protocol Decision Table Traffic Types and Encapsulation Flow

3 Domain 1: Media, Connectors, Transceivers, and Network Architectures

Copper, Fiber, Coax, and DAC Media Connector and Transceiver Selection Network Topologies and Design Patterns Cloud and Virtual Networking Concepts

4 Domain 1: IP Addressing and Subnetting Mastery

IPv4 Classes, Private/Public, APIPA, and Loopback CIDR, VLSM, and Subnet Math IPv6 Address Types and Notation Routing Basics and Longest Prefix Match

5 Domain 2: Network Implementation - Routing

Static vs Dynamic Routing and Route Selection OSPF, EIGRP, and BGP Basics at Network+ Depth NAT/PAT, VIP/FHRP, and Subinterfaces Routing PBQs and Troubleshooting Route Table Clues

6 Domain 2: Network Implementation - Switching

VLANs, Access Ports, Trunks, and Native VLAN STP/RSTP Loop Prevention and Bridge Roles Port Aggregation/LACP, MTU, Jumbo Frames, and Interface Settings Switch Implementation PBQs and Common Misconfigurations

7 Domain 2: Network Implementation - Wireless and Physical Implementation

Wi-Fi Standards, Bands, and Channels SSID Security, Guest Networks, and Authentication Antennas, Coverage, Roaming, Interference, and Site Surveys Physical Installation Implications

8 Domain 2: Network Implementation - Services Implementation

DNS Record Types and Troubleshooting Cues DHCP, DHCPv6, SLAAC, Scopes, Leases, and Relay NTP, PTP, NTS, and Time-Sensitive Networking Service Implementation PBQs: DNS, DHCP, VLANs, and Firewall Direction

9 Domain 3 Part A: Network Operations Documentation and Governance

Physical, Logical, Rack, Cable, Wireless Diagrams, and IPAM Asset Inventory, Baselines, SLAs, SOPs, and Runbooks Change Management and Request Tracking Lifecycle, EOL, EOS, Decommissioning, and Configuration Management

10 Domain 3 Part B: Monitoring, Remote Access, and Resilience

SNMP, Flow, Syslog, Packet Capture, Log Aggregation, APIs, and Port Mirroring Baselines and Performance Metrics Remote Access, Management Paths, and Secure Admin Habits DR and HA Concepts: RPO, RTO, MTTR, MTBF, Sites, Failover, and Testing

11 Domain 4: Logical Security and Secure Access (14%)

Encryption in Transit, Encryption at Rest, PKI, and Certificates IAM, MFA, SSO, Directory Services, and AAA Authorization, Least Privilege, RBAC, Geofencing, and Time-Based Access VPNs and Secure Management Design

12 Domain 4: Segmentation, Risk, and Network Attacks (14%)

Segmentation for Guest, BYOD, IoT, IIoT, SCADA, ICS, and OT Risk, Compliance, Audit, Data Locality, PCI, and GDPR Network Attacks and Scenario Cues Attack-to-Mitigation PBQ Tables

13 Domain 4: Security Controls and Hardening (14%)

Firewalls, IDS, IPS, Security Zones, and Screened Subnets ACLs, Filtering, NAC, Hardening, and Key Management Deception Technologies and Physical Security Zero Trust, SASE, and Trusted or Untrusted Zone Decisions

14 Domain 5: Troubleshooting Methodology and Tools (24%)

Official Troubleshooting Methodology and Evidence Handling Command-Line Tools: ping, traceroute, nslookup, dig, ipconfig, ifconfig, ip, arp, netstat, ss, and route Packet, Protocol, and Wi-Fi Analyzers Choosing the Right Tool by Symptom PBQs

15 Domain 5: Physical, Interface, and Wireless Troubleshooting (24%)

Cable Issues: Type, Attenuation, Crosstalk, Termination, and TX/RX Interface Issues: Errors, Discards, Duplex, Speed, Port Status, and PoE Transceiver, Fiber, and Signal Strength Troubleshooting Wireless Troubleshooting: Interference, Channels, Roaming, RSSI/SNR, Security, and Captive Portals

16 Domain 5: Network Services, Switching, Routing, and Performance Troubleshooting (24%)

DHCP, DNS, NTP, and IP Addressing Issues VLAN, STP, Trunk, Native VLAN, and ACL Issues Routing, Default Gateway, Route Table, and NAT Issues Congestion, Latency, Jitter, Packet Loss, and Application Performance Clues

17 Performance-Based Question Labs

Subnetting and VLSM Design Lab VLAN, Trunk, Router-on-a-Stick, and Firewall Rule Lab Wireless Deployment and Troubleshooting Lab Monitoring, Log Triage, and Route or Service Troubleshooting Lab

18 High-Yield Reference and Final Study Plan

High-Yield Ports and Protocols Table Wi-Fi, Cabling, Connectors, and Transceivers Quick Table Acronyms and Command-Line Tool Quick Table Final 7-Day Review Plan and Readiness Checklist

19 Final Synthesis: Strategy, Remediation, and Readiness

Mixed-Set Decision Strategy for Qualifiers and Close Answers Missed-Question Remediation Notebook by Error Type Exam-Day Time Management and PBQ Order 100-Question Readiness Simulation Blueprint Mapped to N10-009 Weights

OSPF, EIGRP, and BGP Basics at Network+ Depth

Key Takeaways Explain This Topic AI

OSPF is a link-state interior gateway protocol that uses areas, neighbor adjacencies, and bandwidth-based cost.

EIGRP is an advanced distance-vector IGP known for fast convergence via feasible successors and a composite metric.

BGP is the path-vector exterior gateway protocol used between autonomous systems and at internet edges over TCP 179.

Network+ tests purpose, relationship formation, and the clues that explain missing routes - not full configuration.

Area mismatches, timer mismatches, authentication mismatches, passive interfaces, and route filters all suppress expected routes.

Last updated: June 2026

Why Dynamic Routing Protocols Exist

Routing protocols automate route exchange so administrators do not hand-configure every path. Network+ N10-009 expects you to recognize each protocol's purpose, how it forms relationships, and how to read a symptom - not to write vendor configuration. The three you must distinguish are OSPF, EIGRP, and BGP.

  • Protocol Type Scope Default AD Selection idea Common use
  • OSPF Link-state IGP Inside one organization 110 Cost (bandwidth-based) Enterprise LAN/WAN

EIGRP Advanced distance-vector IGP Inside one organization 90 (internal) Composite metric Cisco-heavy enterprises

BGP Path-vector EGP Between autonomous systems 20 eBGP / 200 iBGP Path attributes + policy Internet and provider edge

An interior gateway protocol (IGP) runs within a single administrative domain. An exterior gateway protocol (EGP) runs between separate domains. BGP is the dominant EGP, exchanging routes between autonomous systems (AS) - independently administered networks each identified by an AS number.

OSPF Essentials

OSPF routers form neighbor adjacencies , flood link-state advertisements (LSAs) , build an identical topology database, then independently run the Dijkstra shortest-path algorithm to pick best paths.

  • OSPF concept Meaning
  • Area Logical grouping of routers and links
  • Area 0 (backbone) Central area all other areas must touch
  • Neighbor adjacency Relationship between compatible OSPF routers
  • Cost Metric, commonly reference-bandwidth / interface-bandwidth
  • DR/BDR Designated and backup designated routers on multiaccess links
  • Router ID 32-bit ID identifying the OSPF router

For two OSPF routers on the same link to become neighbors, several values must match. The exam loves these failure causes:

Area number mismatch - interfaces must share the same area.

Subnet mask / network mismatch - the link addresses must agree.

Hello/Dead timer mismatch - default 10s hello, 40s dead on broadcast links.

Authentication mismatch - key or type differs.

Passive interface - advertises the subnet but refuses to form an adjacency.

MTU mismatch - blocks adjacency at the exchange state.

EIGRP Essentials

EIGRP exchanges routing information with neighbors and uses the DUAL algorithm to converge fast when a route fails.

  • EIGRP concept Meaning
  • Autonomous system number Must match between neighbors
  • Neighbor table Tracks adjacent EIGRP routers
  • Topology table All learned routes and alternatives
  • Successor Current best (lowest-metric) route
  • Feasible successor Pre-qualified backup, installed instantly on failure
  • Composite metric Derived from bandwidth and delay by default

At Network+ depth, know EIGRP is an IGP whose neighbors require a matching AS number and compatible settings. A feasible successor is why EIGRP can fail over almost instantly - the backup is already verified loop-free, so no recalculation is needed. If an expected EIGRP route is missing while the interface is up, check the AS number, the advertised networks, whether the interface is passive, and any route filters or distribute lists.

BGP Essentials

BGP is policy-based routing between autonomous systems, common at internet edges and in multihomed organizations.

  • BGP concept Meaning
  • Autonomous system Network under one routing policy
  • eBGP BGP between different ASes
  • iBGP BGP within the same AS
  • AS path List of ASes a route traversed (loop prevention)
  • Prefix advertisement A network announced to a peer
  • TCP 179 The port BGP peers use to establish a session

BGP is not chosen for fast LAN convergence - it is chosen for internet-scale routing and granular policy control.

Symptom-to-Cause Map and PBQ Guidance

  • Symptom First place to look
  • OSPF neighbors stuck or absent Area, timers, authentication, subnet, network type, MTU
  • EIGRP route missing but interface up AS number, passive interface, network statement, filter
  • BGP peer down (Idle/Active) Remote AS number, neighbor IP reachability, TCP 179, auth
  • Route learned but path is unexpected Metric, route policy, prefix length, administrative distance
  • Route on one router but not another Redistribution, filtering, summarization, area design
  • Match protocol to requirement (PBQ-style)
  • Requirement Best match
  • Dynamic routing across a multi-router enterprise LAN OSPF
  • A Cisco-heavy enterprise already running EIGRP EIGRP
  • Exchange routes with an ISP using an AS number BGP
  • A small branch with a single path to HQ Static or default route

If a PBQ shows a neighbor table, solve from compatibility and reachability first. Do not start adjusting metrics when the neighbor has not even formed.

Common traps: using BGP for every dynamic need (it is for interdomain/policy routing); treating OSPF cost as hop count (cost is bandwidth-derived, RIP uses hops); ignoring a passive interface (it advertises but will not peer); and changing VLANs to fix a BGP peer before confirming IP reachability and TCP 179.