Computer Networks and Security, Lecture notes of Computer Networks

Comprises of 12 modules plus 3 special modules. Learn Router and Routing Basics, and introduction to Ethical Hacking.

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 4: Learning about Devices
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.
Cisco Discovery Protocol (CDP)
Cisco Discovery Protocol (CDP) is a Layer 2 protocol that connects lower physical media
and upper network layer protocols
CDP is used to obtain information about neighboring devices, such as the types of
devices connected
CDP is media and protocol independent, and runs on all Cisco equipment
When a Cisco device boots up, CDP starts up automatically and allows the device to
detect neighboring devices that are also running CDP
It runs over the data link layer and allows two systems to learn about each other
Each device configured for CDP sends periodic messages, known as advertisements, to
multiple routers.
Each device advertises:
at least one address at which it can receive Simple Network Management Protocol (SNMP) messages.
“time-to-live” or holdtime information, indicating the length of time that receiving devices should hold CDP
information before discarding it.
each device also listens to periodic CDP messages sent by others in order to learn about neighboring devices.
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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 4: Learning about Devices

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

ORIGINAL COPY

Cisco Discovery Protocol (CDP)

  • Cisco Discovery Protocol (CDP) is a Layer 2 protocol that connects lower physical media and upper network layer protocols
  • CDP is used to obtain information about neighboring devices, such as the types of devices connected
  • CDP is media and protocol independent, and runs on all Cisco equipment
  • When a Cisco device boots up, CDP starts up automatically and allows the device to detect neighboring devices that are also running CDP
  • It runs over the data link layer and allows two systems to learn about each other
  • Each device configured for CDP sends periodic messages, known as advertisements, to multiple routers. Each device advertises:
    • at least one address at which it can receive Simple Network Management Protocol (SNMP) messages.
    • “time-to-live” or holdtime information, indicating the length of time that receiving devices should hold CDP information before discarding it.
    • each device also listens to periodic CDP messages sent by others in order to learn about neighboring devices.

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

Information obtained with CDP

  • Cdp info can be used to create a network map of the connected devices
  • show cdp neighbors displays

information about

  • Networks directly connected to the router
  • Each CDP neighbor device using type length values (TLVs) - Information embedded in advertisements - Device ID - Local Interface - Holdtime - Capability - Platform - Port ID - VTP Management Domain Name (CDPv2 only) - Native VLAN (CDPv2 only) - Full/Half-Duplex (CDPv2 only)

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

  • Allows connections to be made to remote hosts
  • An IOS EXEC command used to verify the application layer software between

source and destination

  • The most complete test of connectivity
    • Works at the Application layer (7)
  • You can have up to 5 Telnet sessions
    • 0 - 4 Router>connect/Telnet < hostname > Router>connect/Telnet < ip address > Router>exit/logout

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

Ping to Test Connectivity

  • Ping
    • Sends echo packet to destination host
    • Waits for an echo reply packet from that destination
  • Results from echo protocol can help

evaluate

  • Path-to-host reliability
  • Delays over the path
  • Whether destination host can be reached
  • Is destination host functioning