Jeremy’s IT Lab: CCNA Routing Fundamentals

Introduction

• This session covers routing fundamentals important for the CCNA exam.
• Distinction between how switches and routers forward data.
• Focus on the routing table of a Cisco router.

Key Topics

1. What is Routing?

   • Routers forward packets to their correct destination based on routing.
   • Routing determines the path IP packets should take to reach their destination.
   • Routing table stores routes to known destinations.

2. Routing Table on a Cisco Router

   • Compared to MAC address tables in switches.
   • Important to understand how to read it.
   • Two main types of routes:
     • Connected Routes: Automatically added when an interface is configured.
     • Local Routes: Specific to the router’s own IP addresses.

3. Routing Fundamentals: Route Selection

   • Routers often have multiple routes; they must select the appropriate one.
   • Emphasis on understanding route selection for networking and CCNA.

Routing Methods

• Dynamic Routing: Uses protocols like OSPF to share routing info automatically.
• Static Routing: Routes are manually configured by network engineers.
• Special focus on routes automatically added (Connected & Local routes).

Example Network

• Four routers connected in a WAN scenario.
• IP address configuration on interfaces:
  • Example: 192.168.1.0/24, R1’s G0/2 IP is .1.
  • WAN connections use different address blocks like 12.0/24.

Configuring IP Addresses

• Example configuration steps on R1:
  • Interface configurations with specific IP addresses.
  • Command SHOW IP INTERFACE BRIEF to confirm IP configurations.

Understanding Routing Table Output

• SHOW IP ROUTE Command
  • Displays the routing table.
  • Contains codes for protocols used to learn routes.
  • Important codes:
    • L: Local routes, with /32 mask.
    • C: Connected routes, with interface netmask.
• Explanation of how two routes per interface (Connected and Local) are added automatically.

Detailed Route Explanation

• Connected Routes: Routes to networks directly connected to the router.
• Local Routes: Routes to router’s own interface IPs, using /32 mask.
• Route selection prioritizes the most specific matching route (longest prefix length).

Route Selection Examples

• Practice scenarios to identify route selection based on destination IPs.
• Concept of ‘most specific match’ crucial for correct routing.

Summary of Key Points

• Routers use routing tables to store known destinations.
• Connected and Local routes are automatically added when configuring IPs on interfaces.
• If no route matches a packet's destination, the router drops the packet.
• Most specific matching route is used when multiple routes match.

Quiz Recap

• Understanding local and connected routes and their codes in the routing table.
• Differences in behavior between routers and switches.
• Confirming knowledge through practical quiz questions.