Computer Networks and Security, Lecture notes of Computer Networks

A set of slides customized by Engr. Vernon Degala for educational purposes only. It covers the topic of basic router troubleshooting, including static and dynamic routing, advantages and disadvantages of each, and the gateway of last resort. The document also explains how path determination occurs at the network layer and how routers evaluate available paths to a destination.

Typology: Lecture notes

2021/2022

Available from 06/18/2022

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All slides are customized by Engr. Vernon Degala. For educational purposes only.All slides are customized by Engr. Vernon Degala. For educational purposes only.
Module 9: Basic Router Troubleshooting
inspired by Cisco Networking Academy
Computer Networks and Security
CCNA 2: Routers and Routing Basics
ORIGINAL COPY
All slides are customized by Engr. Vernon Degala. For educational purposes only.
Router#show ip route
Displays the content of the IP routing table
Entries for all known networks and subnets
Code that indicates how network was learned
Statically
Administrator manually defines routes
Routes do not change until administrator
manually programs the changes
Static Routing Advantages
Lower processor overheads
Lower memory overheads
No bandwidth utilization
Secure operation
Predictability
Static Routing Disadvantages
High maintenance configuration
No adaptability to change
Dynamically
Routing protocol exchange routing information
Router independently selects the best path
Routes change automatically as neighboring
routers update each other with new information
Dynamic Routing Advantages
High degree of adaptability
Low maintenance configuration
Dynamic Routing Disadvantages
Increased Processor overheads
Increased memory utilization
High bandwidth utilization
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All slides are customized by Engr. Vernon Degala. For educational purposes only.All slides are customized by Engr. Vernon Degala. For educational purposes only.

Module 9: Basic Router Troubleshooting

inspired by Cisco Networking Academy Computer Networks and Security CCNA 2: Routers and Routing Basics

ORIGINAL COPY

Router#show ip route

  • Displays the content of the IP routing table
    • Entries for all known networks and subnets
    • Code that indicates how network was learned Statically Administrator manually defines routes Routes do not change until administrator manually programs the changes Static Routing Advantages
  • Lower processor overheads
  • Lower memory overheads
  • No bandwidth utilization
  • Secure operation
  • Predictability Static Routing Disadvantages
  • High maintenance configuration
  • No adaptability to change Dynamically Routing protocol exchange routing information Router independently selects the best path Routes change automatically as neighboring routers update each other with new information Dynamic Routing Advantages
  • High degree of adaptability
  • Low maintenance configuration Dynamic Routing Disadvantages
  • Increased Processor overheads
  • Increased memory utilization
  • High bandwidth utilization

All slides are customized by Engr. Vernon Degala. For educational purposes only.

Gateway of Last Resort (Default Gateway)

  • Used when the router is unable to match a destination network
  • keep routing tables as lean as possible
    • Router can forward packets destined to any Internet host without having to maintain entry for every Internet network
  • Configured by administrator
    • Router(config)#ip default network
    • Router(config)#ip route 0.0.0.0 0.0.0.0 <next-hop or outgoing port>
  • To find out the default route use show ip route

Route Source and Destination

  • Path determination occurs at network layer
  • The network layer provides best-effort, end-to-end, packet delivery across interconnected networks
  • Path determination enables a router to
    • Evaluate the available paths to a destination
    • Establish the preferred handling of a packet
    • Uses the IP routing table to do this
  • After the router determines which path to use - it takes the packet from one interface and forwards it to another interface (switching)

Troubleshooting L1& L1 using

show interface

• Show interfaces displays the status of

  • physical hardware (layer 1)
  • logical software (layer 2) Part 1 is configuration L2 problems Part 2 is hardware Line status L1 problems