CCNA 4 v6.0 Study Material – Chapter 5: Network Security and Monitoring

Chapter 5 – Sections & Objectives

  • 5.1 LAN Security
    • Explain how to mitigate common LAN security.
  • 5.2 SNMP
    • Configure SNMP to monitor network operations in a small to medium-sized business network.
  • 5.3 Cisco Switch Port Analyzer (SPAN)
    • Troubleshoot a network problem using SPAN.

5.1 LAN Security

LAN Security Attacks

Common attacks against the Layer 2 LAN infrastructure include:

  • CDP Reconnaissance Attacks
  • Telnet Attacks
  • MAC Address Table Flooding Attacks
  • VLAN Attacks
  • DHCP Attacks

LAN Security Best Practices

This topic covers several Layer 2 security solutions:

  • Mitigating MAC address table flooding attacks using port security
  • Mitigating VLAN attacks
  • Mitigating DHCP attacks using DHCP snooping
  • Securing administrative access using AAA
  • Securing device access using 802.1X port authentication

LAN Security Best Practices

There are several strategies to help secure Layer 2 of a network:

  • Always use secure variants of these protocols such as SSH, SCP, SSL, SNMPv3, and SFTP.
  • Always use strong passwords and change them often.
  • Enable CDP on select ports only.
  • Secure Telnet access.
  • Use a dedicated management VLAN where nothing but management traffic resides.
  • Use ACLs to filter unwanted access.

5.2 SNMP

SNMP Operation

    • SNMP allows administrators to manage and monitor devices on an IP network.
    • SNMP Elements
      • SNMP Manager
      • SNMP Agent
      • MIB
    • SNMP Operation
      • Trap
      • Get
      • Set

    • SNMP Security Model and Levels

Configuring SNMP

  • Configuration steps
  • Configure community string
  • Document location of device
  • Document system contact
  • Restrict SNMP Access
  • Specify recipient of SNMP Traps
  • Enable traps on SNMP agent

Securing SNMPv3

5.3 Cisco Switch Port Analyzer (SPAN)

SPAN Overview

Port mirroring

  • The port mirroring feature allows a switch to copy and send Ethernet frames from specific ports to the destination port connected to a packet analyzer. The original frame is still forwarded in the usual manner.

SPAN terminology

RSPAN terminology

SPAN Configuration

  • Use monitor session global configuration command

SPAN as a Troubleshooting Tool

    • SPAN allows administrators to troubleshoot network issues
    • Administrator can use SPAN to duplicate and redirect traffic to a packet analyzer
    • Administrator can analyze traffic from all devices to troubleshoot sub-optimal operation of network applications

5.4 Chapter Summary


  • At Layer 2, a number of vulnerabilities exist that require specialized mitigation techniques:
    • MAC address table flooding attacks are addressed with port security.
    • VLAN attacks are controlled by disabling DTP and following basic guidelines for configuring trunk ports.
    • DHCP attacks are addressed with DHCP snooping.
  • The SNMP protocol has three elements: the Manager, the Agent, and the MIB. The SNMP manager resides on the NMS, while the Agent and the MIB are on the client devices.
    • The SNMP Manager can poll the client devices for information, or it can use a TRAP message that tells a client to report immediately if the client reaches a particular threshold. SNMP can also be used to change the configuration of a device.
  • SNMPv3 is the recommended version because it provides security.
  • SNMP is a comprehensive and powerful remote management tool. Nearly every item available in a show command is available through SNMP.
  • Switched Port Analyzer (SPAN) is used to mirror the traffic going to and/or coming from the host. It is commonly implemented to support traffic analyzers or IPS devices.

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