How to Master One of the Hardest Parts of the Cisco CCNA Exam: IP Connectivity

IP Connectivity is the largest domain on the Cisco CCNA exam, and it’s where many candidates feel the pressure. It’s hard for a few specific reasons. You have to read dense show ip route and show ip ospf neighbor output quickly. You need to apply three forwarding rules in the correct order. And small details, such as a mismatched hello timer or a missing exit interface on an IPv6 static route, can change the right answer completely.

The good news is that this domain rewards systematic study. Once you understand how a router thinks, the questions become predictable. In this guide, we’ll break down what the domain covers, the core concepts you need, the traps that catch candidates, and two worked scenarios.

What Does IP Connectivity Cover on the CCNA Exam?

In the CCNA v1.1 (200-301) exam topics, effective August 20, 2024, domain 3.0 IP Connectivity makes up 25% of the exam. It has five objectives:

  • 3.1 Interpret the components of the routing table: routing protocol code, prefix, network mask, next hop, administrative distance, metric, and gateway of last resort.
  • 3.2 Determine how a router makes a forwarding decision by default: longest prefix match, administrative distance, and routing protocol metric.
  • 3.3 Configure and verify IPv4 and IPv6 static routing: default, network, host, and floating static routes.
  • 3.4 Configure and verify single-area OSPFv2: neighbor adjacencies, point-to-point, broadcast (DR/BDR selection), and router ID.
  • 3.5 Describe the purpose, functions, and concepts of first-hop redundancy protocols.

Notice the verbs. Objectives 3.3 and 3.4 say “configure and verify,” so expect command-level and output-reading questions. Objective 3.5 only says “describe,” so you need concepts, not FHRP configuration.

How Do You Read a Routing Table?

Take this sample entry:
O 10.2.0.0/16 [110/3] via 192.168.1.2, 00:05:12, GigabitEthernet0/0

  • O is the routing protocol code (OSPF). Other codes you’ll see include C (connected), L (local), S (static), and S* (static default route).
  • 10.2.0.0/16 is the prefix and mask.
  • [110/3] shows administrative distance (110) and metric (an OSPF cost of 3).
  • via 192.168.1.2 is the next hop, and GigabitEthernet0/0 is the exit interface.

The gateway of last resort line at the top of the table tells you whether a default route (0.0.0.0/0) exists and where it points. If it says “not set,” packets that match no route are dropped.

How Does a Router Make a Forwarding Decision?

This is the concept candidates mix up most. The router uses two separate processes:

  1. Longest prefix match (forwarding): When a packet arrives, the router picks the most specific matching route in the routing table. A /24 beats a /16, and a /32 host route beats everything, regardless of administrative distance or metric.
  2. Administrative distance (building the table): If two different sources offer the same prefix and length, the router installs the one with the lowest AD.
  3. Metric (within one protocol): If one protocol learns several paths to the same prefix, the lowest metric wins. Equal metrics can mean equal-cost load balancing.

Know these default administrative distances:

  • Connected: 0
  • Static: 1
  • eBGP: 20
  • EIGRP (internal): 90
  • OSPF: 110
  • RIP: 120
  • iBGP: 200
  • Unusable (never installed): 255

What Do You Need to Know About Static Routes?

Static routes are configured with ip route for IPv4 and IPv6 route for IPv6. The four types in the blueprint are:

  • Default route: 0.0.0.0/0 for IPv4 (ip route 0.0.0.0 0.0.0.0 203.0.113.1) or ::/0 for IPv6. It sets the gateway of last resort.
  • Network route: a route to a specific subnet, such as 172.16.10.0/24.
  • Host route: a route to a single address, using /32 in IPv4 (mask 255.255.255.255) or /128 in IPv6.
  • Floating static route: a backup static route configured with an AD higher than the primary route’s, such as ip route 10.2.0.0 255.255.0.0 192.168.2.2 115 to back up an OSPF-learned route (AD 110). It stays out of the routing table until the primary route disappears.

For IPv6, remember that if the next hop is a link-local address, you must also specify the exit interface, because link-local addresses are only unique per link. You also need IPv6 unicast-routing enabled for the router to forward IPv6 packets.

What Do You Need to Know About Single-Area OSPFv2?

OSPF is a link-state protocol that uses cost as its metric. By default, Cisco calculates cost as a reference bandwidth of 100 Mbps divided by the interface bandwidth, so FastEthernet and anything faster all get a cost of 1 unless you raise the reference bandwidth.

Neighbor Adjacencies

Two routers become OSPF neighbors only if these match:

  • Area ID
  • Subnet and subnet mask on the connecting interfaces
  • Hello and dead timers (10 and 40 seconds by default on broadcast and point-to-point networks)
  • Authentication settings, if configured
  • Stub area flag

Router IDs must also be unique. An MTU mismatch lets routers see each other but leaves them stuck in the EXSTART/EXCHANGE states instead of reaching FULL. The neighbor states run Down, Init, 2-Way, ExStart, Exchange, Loading, and Full.

Router ID

OSPF selects the router ID in this order: the manually configured router-id, then the highest IPv4 address on an up loopback interface, then the highest IPv4 address on an up physical interface. A new router ID takes effect only after the OSPF process restarts (clear ip ospf process), or the router reloads.

Broadcast vs. Point-to-Point Networks

On broadcast networks such as Ethernet, OSPF elects a designated router (DR) and backup designated router (BDR). The highest interface priority wins (default 1; priority 0 means the router never becomes DR or BDR), and the highest router ID breaks ties. The election is not preemptive, so a better router that joins later doesn’t take over until the DR fails or OSPF resets. Routers that are neither DR nor BDR (DROTHERs) stay in the 2-Way state with each other and go FULL only with the DR and BDR. That’s normal, not a fault.

On point-to-point networks, there is no DR/BDR election. Configuring ip ospf network point-to-point on a link between two routers is a common way to speed up adjacency.

What Do You Need to Know About First Hop Redundancy Protocols?

FHRPs protect hosts from losing their default gateway. Two or more routers share a virtual IP address and virtual MAC address, and hosts use that virtual IP as their gateway. If the active router fails, another takes over without changing any host settings.

  • HSRP (Cisco proprietary): active and standby routers. Default priority is 100, and preemption is disabled by default.
  • VRRP (open standard): master and backup routers. Preemption is enabled by default.
  • GLBP (Cisco proprietary): adds load balancing, with multiple routers forwarding traffic for the same virtual IP.

What Are Common IP Connectivity Traps?

  • Using AD to choose between different prefix lengths. A static /16 (AD 1) does not beat an OSPF /24 (AD 110) for a destination inside the /24. Longest prefix match comes first.
  • Forgetting the floating static AD. A backup static route with no AD specified defaults to 1 and will replace the OSPF route instead of backing it up.
  • Treating 2-Way as a failure. Between two DROTHERs on a broadcast segment, 2-Way is the expected final state.
  • Assuming the DR election is preemptive. Raising a router’s priority doesn’t make it DR right away.
  • Missing the IPv6 link-local exit interface. A static route to a link-local next hop without an interface is incomplete.
  • Mixing up HSRP and VRRP defaults. HSRP preemption is off by default, while VRRP preemption is on.

Worked Sample Scenarios

Scenario 1: Which Route Is Used?

Consider a question where a router’s table contains three routes: S 10.1.0.0/16 via 192.168.1.1, O 10.1.1.0/24 via 192.168.2.1, and D 10.1.1.0/25 via 192.168.3.1. A packet arrives for 10.1.1.200. Which next hop does the router use?

Start with the longest prefix match. The /25 covers 10.1.1.0 through 10.1.1.127, so 10.1.1.200 is outside it. The /24 covers 10.1.1.0 through 10.1.1.255, and the /16 covers all of 10.1.0.0 through 10.1.255.255. Both match, but /24 is more specific. The router forwards to 192.168.2.1. The static route’s lower AD doesn’t matter, because AD only compares routes with identical prefixes. The distractor that tempts most people is the /25, which looks the most specific but doesn’t include the destination.

Scenario 2: Why Won’t OSPF Form an Adjacency?

Now consider two routers connected on GigabitEthernet interfaces in the 10.0.12.0/30 subnet, both configured in area 0. show ip ospf neighbor on R1 shows nothing. The question displays show ip ospf interface output: R1 shows “Hello 10, Dead 40,” and R2 shows “Hello 5, Dead 20.”

Walk through the adjacency checklist. Area matches, and the subnet matches. The timers do not. OSPF neighbors must agree on hello and dead intervals, so the fix is to make the timers match on both routers. If the output had instead shown both routers stuck in EXSTART, you’d look for an MTU mismatch.

How Does IP Connectivity Connect to Other CCNA Domains?

  • Network Fundamentals: You can’t evaluate longest prefix match without fast, accurate subnetting and IPv6 prefix skills.
  • Network Access: Inter-VLAN routing and Layer 3 EtherChannel both depend on routing working correctly on switches and routers.
  • IP Services: NAT, DHCP relay, and NTP all assume routes exist between the devices involved.
  • Security Fundamentals: An ACL can block OSPF hellos or hide a route’s effect, so troubleshooting often spans both domains.

How Should You Study IP Connectivity?

Give this domain three to four focused weeks in your plan.

  1. Week 1: Read routing tables daily and memorize the AD list. Solve longest prefix match problems until they’re automatic.
  2. Week 2: Lab IPv4 and IPv6 static routes in Packet Tracer or Cisco Modeling Labs, including a floating static that takes over when you shut down the primary link.
  3. Week 3: Build single-area OSPFv2 on both a broadcast segment and a point-to-point link. Break it on purpose (timers, area, MTU, passive interfaces) and read the resulting output.
  4. Week 4: Review FHRP concepts, then mix IP Connectivity questions with other domains so you learn to spot routing problems when a question doesn’t announce them.

In Pocket Prep, use Build Your Own Quiz to target IP Connectivity, then review every miss with the Missed Questions quiz. Once your accuracy holds steady, add Timed Quizzes to build speed.

Start Preparing for the Cisco CCNA Exam With Pocket Prep

Pocket Prep’s Cisco CCNA practice questions give you 650 questions with detailed explanations that walk through the reasoning behind every answer, plus a full-length mock exam to test your readiness. Use the Weakest Subject quiz to keep your routing skills sharp alongside the other five domains. With consistent studying, you’ll walk into exam day with confidence!