CCNA Routing – Clear & Exam-Focused Guide 🚀

🌐 What is Routing?

Routing is the process of selecting the best path for data packets to travel from one network to another using a router.

🧠 Router Basics

• Works at OSI Layer 3 (Network)
• Uses IP addresses
• Maintains a routing table

Check routing table:

show ip route

🗺️ Types of Routing (CCNA)

1️⃣ Static Routing

Manually configured routes.

ip route 0.0.0.0 0.0.0.0 192.168.1.1

✔ Simple

❌ Not scalable

2️⃣ Default Routing

Used when no specific route exists.

Example:

ip route 0.0.0.0 0.0.0.0 192.168.1.1

3️⃣ Dynamic Routing

Routers learn routes automatically.

Protocols in CCNA:

• RIP
• OSPF
• EIGRP (Cisco)

🔁 Routing Protocols (CCNA Level)

🔹 RIP

• Distance Vector
• Metric: Hop count
• Max hops: 15

🔹 OSPF

• Link State
• Metric: Cost
• Fast & scalable
• Uses areas

🔹 EIGRP

• Advanced distance vector
• Metric: Bandwidth + Delay
• Cisco proprietary

📊 Administrative Distance (Very Important)

Route TypeADConnected0Static1EIGRP90OSPF110RIP120

Lower AD = more trusted

🧩 Longest Prefix Match

Router selects the route with:

👉 Most specific subnet mask

Example:

• /24 preferred over /16

🔐 Routing & Security

• Use ACLs
• Disable unused interfaces
• Use authentication for routing protocols