Lecture Notes: Router Functions and Routing Tables

Key Functions of a Router

• Evaluate Incoming Traffic: Determines the destination for traffic.
• Forward Traffic: Sends the traffic through the appropriate interface.
• Routing Table Usage: Central to a router's decision-making process.
  • All devices, including workstations and servers, have routing tables.

Understanding Routing Tables

• Structure:
  • Legend: Information about codes used within the table.
  • Routing Entries: Each entry provides details about routes.

Codes in Routing Tables

• Directly Connected Routes: Marked with 'C'.
• RIP Version 2 Routes: Marked with 'R'.
  • Shows routes received using the RIP dynamic routing protocol.

Routing Table Example

• Route Codes:
  • 'C' for directly connected.
  • 'R' for RIP protocol.
• Destination Subnet: Indicates subnet and prefix length (e.g., S/24).
• Administrative Distance: Numeric value that influences route preference.
• Routing Metric: Specific to protocol used, e.g., hop count for RIP.
• Next Hop: The next destination IP to forward traffic.
• Time Value: Duration a route has been active.
• Outgoing Interface: Sometimes optional, indicates the physical interface.

Specificity in Routes

• IP Address and Prefix Length: Key factors in matching the best route.
• Evaluating Routes:
  • Compare routes based on specificity (e.g., /32 vs /24).
  • The most specific route (longer prefix) is preferred.

Administrative Distance

• Definition: Represents route trustworthiness.
• Comparison:
  • Local connections have a distance of 0.
  • Static routes (configured manually) have a distance of 1.
  • Various routing protocols have assigned distances (e.g., EIGRP is 90).

Routing Metrics

• Purpose: Used to break ties for routes within the same protocol.
• Protocol-Specific: Metrics cannot be compared across protocols.
• Examples:
  • BGP, EIGRP, and RIP each have unique routing metrics.

Redundancy and Virtual IPs

• Default Gateway Limitation: Only one can be defined.
• Virtual IP (VIP): Provides redundancy.
  • Failover protocol (e.g., FHRP) ensures seamless switch to a backup in case of failure.

Subinterfaces

• Definition: Multiple virtual interfaces on a single physical interface.
• Use Case:
  • Trunk connections managing multiple VLANs.
  • Each subinterface configured with separate IPs.

Network Configuration Example

• VLAN Separation: Devices in different VLANs.
• Subinterface Setup:
  • Physical interface (e.g., Ethernet 1/1) has several subinterfaces.

These notes provide an overview of router functions, routing tables, and related concepts. They include detailed explanations of routing table components, administrative distances, routing metrics, redundancy protocols, and subinterfaces.