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This chapter is from the book

Summary (2.3)

Now that you are getting the sense of what network administrators do to configure basic features and security features on a switch, you are ready to look back and review all you have learned. Then perform the activity and skills integration challenge to prove to yourself you are ready to move to the next chapter.

When a Cisco LAN switch is first powered on, it goes through the following boot sequence:

Step 1. First, the switch loads a power-on self-test (POST) program stored in ROM. POST checks the CPU subsystem. It tests the CPU, DRAM, and the portion of the flash device that makes up the flash file system.

Step 2. Next, the switch loads the boot loader software. The boot loader is a small program stored in ROM and is run immediately after POST successfully completes.

Step 3. The boot loader performs low-level CPU initialization. It initializes the CPU registers, which control where physical memory is mapped, the quantity of memory, and its speed.

Step 4. The boot loader initializes the flash file system on the system board.

Step 5. Finally, the boot loader locates and loads a default IOS operating system software image into memory and hands control of the switch over to the IOS.

The specific Cisco IOS file that is loaded is specified by the BOOT environmental variable. After the Cisco IOS is loaded it uses the commands found in the startup-config file to initialize and configure the interfaces. If the Cisco IOS files are missing or damaged, the boot loader program can be used to reload or recover from the problem.

The operational status of the switch is displayed by a series of LEDs on the front panel. These LEDs display such things as port status, duplex, and speed.

An IP address is configured on the SVI of the management VLAN to allow for remote configuration of the device. A default gateway belonging to the management VLAN must be configured on the switch using the ip default-gateway command. If the default gateway is not properly configured, remote management is not possible. It is recommended that Secure Shell (SSH) be used to provide a secure (encrypted) management connection to a remote device to prevent the sniffing of unencrypted user names and passwords which is possible when using protocols such as Telnet.

One of the advantages of a switch is that it allows full-duplex communication between devices effectively doubling the communication rate. Although it is possible to specify the speed and duplex settings of a switch interface, it is recommended that the switch be allowed to set these parameters automatically to avoid errors.

Switch port security is a requirement to prevent such attacks as MAC Address Flooding and DHCP Spoofing. Switch ports should be configured to allow only frames with specific source MAC addresses to enter. Frames from unknown source MAC addresses should be denied and cause the port to shut down to prevent further attacks.

Port security is only one defense against network compromise. There are 10 best practices that represent the best insurance for a network:

  • Develop a written security policy for the organization.
  • Shut down unused services and ports.
  • Use strong passwords and change them often.
  • Control physical access to devices.
  • Avoid using standard insecure HTTP websites, especially for login screens. Instead use the more secure HTTPS.
  • Perform backups and test the backed up files on a regular basis.
  • Educate employees about social engineering attacks, and develop policies to validate identities over the phone, via email, and in person.
  • Encrypt sensitive data and protect it with a strong password.
  • Implement security hardware and software, such as firewalls.
  • Keep IOS software up-to-date by installing security patches weekly or daily, if possible.

These methods are only a starting point for security management. Organizations must remain vigilant at all times to defend against continually evolving threats.

NTP is used to synchronize the date and time among network devices. NTP clients can synchronize their time settings with an NTP server. Clock synchronization is important when using system log messages for verification and troubleshooting.

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