Switch configuaration

Switch boot sequence
1.POST 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.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. 4.4. The boot loader initializes the flash file system on the system board.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.
System Crash
tep 1. Connect a PC by console cable to the switch console port. Configure terminal emulation software to connect to the switch.

Step 2. Unplug the switch power cord.

Step 3. Reconnect the power cord to the switch and, within 15 seconds, press and hold down the Mode button while the System LED is still flashing green.

Step 4. Continue pressing the Mode button until the System LED turns briefly amber and then solid green; then release the Mode button.

Step 5. The boot loader switch: prompt appears in the terminal emulation software on the PC.

The boot loader command line supports commands to format the flash file system, reinstall the operating system software, and recover from a lost or forgotten password. For example, the dir command can be used to view a list of files within a specified directory as shown in the figure.

Switch LED Indicators
System LED – Shows whether the system is receiving power and is functioning properly. If the LED is off, it means the system is not powered on. If the LED is green, the system is operating normally. If the LED is amber, the system is receiving power but is not functioning properly.

Redundant Power System (RPS) LED – Shows the RPS status. If the LED is off, the RPS is off or not properly connected. If the LED is green, the RPS is connected and ready to provide back-up power. If the LED is blinking green, the RPS is connected but is unavailable because it is providing power to another device. If the LED is amber, the RPS is in standby mode or in a fault condition. If the LED is blinking amber, the internal power supply in the switch has failed, and the RPS is providing power.

Port Status LED – Indicates that the port status mode is selected when the LED is green. This is the default mode. When selected, the port LEDs will display colors with different meanings. If the LED is off, there is no link, or the port was administratively shut down. If the LED is green, a link is present. If the LED is blinking green, there is activity and the port is sending or receiving data. If the LED is alternating green-amber, there is a link fault. If the LED is amber, the port is blocked to ensure a loop does not exist in the forwarding domain and is not forwarding data (typically, ports will remain in this state for the first 30 seconds after being activated). If the LED is blinking amber, the port is blocked to prevent a possible loop in the forwarding domain.

Port Duplex LED – Indicates the port duplex mode is selected when the LED is green. When selected, port LEDs that are off are in half-duplex mode. If the port LED is green, the port is in full-duplex mode.

Port Speed LED – Indicates the port speed mode is selected. When selected, the port LEDs will display colors with different meanings. If the LED is off, the port is operating at 10 Mb/s. If the LED is green, the port is operating at 100 Mb/s. If the LED is blinking green, the port is operating at 1000 Mb/s.

Power over Ethernet (PoE) Mode LED – If PoE is supported; a PoE mode LED will be present. If the LED is off, it indicates the PoE mode is not selected and that none of the ports have been denied power or placed in a fault condition. If the LED is blinking amber, the PoE mode is not selected but at least one of the ports has been denied power, or has a PoE fault. If the LED is green, it indicates the PoE mode is selected and the port LEDs will display colors with different meanings. If the port LED is off, the PoE is off. If the port LED is green, the PoE is on. If the port LED is alternating green-amber, PoE is denied because providing power to the powered device will exceed the switch power capacity. If the LED is blinking amber, PoE is off due to a fault. If the LED is amber, PoE for the port has been disabled.

Preparing for Basic Switch Management
To prepare a switch for remote management access, the switch must be configured with an IP address and a subnet mask. Keep in mind, that to manage the switch from a remote network, the switch must be configured with a default gateway. This is very similar to configuring the IP address information on host devices. In the figure, the switch virtual interface (SVI) on S1 should be assigned an IP address. The SVI is a virtual interface, not a physical port on the switch.

SVI is a concept related to VLANs. VLANs are numbered logical groups to which physical ports can be assigned. Configurations and settings applied to a VLAN are also applied to all the ports assigned to that VLAN.

By default, the switch is configured to have the management of the switch controlled through VLAN 1. All ports are assigned to VLAN 1 by default. For security purposes, it is considered a best practice to use a VLAN other than VLAN 1 for the management VLAN.

Note that these IP settings are only for remote management access to the switch; the IP settings do not allow the switch to route Layer 3 packets.

Configuring Basic Switch Management Access with IPv4
Configuring Basic Switch Management Access with IPv4

Step 1. Configure Management Interface

An IP address and subnet mask is configured on the management SVI of the switch from VLAN interface configuration mode. As shown in Figure 1, the interface vlan 99 command is used to enter interface configuration mode. The ip address command is used to configure the IP address. The no shutdown command enables the interface. In this example, VLAN 99 is configured with IP address 172.17.99.11.

The SVI for VLAN 99 will not appear as “up/up” until VLAN 99 is created and there is a device connected to a switch port associated with VLAN 99. To create a VLAN with the vlan_id of 99, and associate it to an interface, use the following commands:

S1(config)# vlan vlan_id

S1(config-vlan)# name vlan_name

S1(config-vlan)# exit

S1(config)# interface interface_id

S1(config-if)# switchport access vlan vlan_id

Step 2. Configure Default Gateway

The switch should be configured with a default gateway if it will be managed remotely from networks not directly connected. The default gateway is the router the switch is connected to. The switch will forward its IP packets with destination IP addresses outside the local network to the default gateway. As shown in Figure 2, R1 is the default gateway for S1. The interface on R1 connected to the switch has IP address 172.17.99.1. This address is the default gateway address for S1.

To configure the default gateway for the switch, use the ip default-gateway command. Enter the IP address of the default gateway. The default gateway is the IP address of the router interface to which the switch is connected. Use the copy running-config startup-config command to back up your configuration.

Step 3. Verify Configuration

As shown in Figure 3, the show ip interface brief command is useful when determining the status of both physical and virtual interfaces. The output shown confirms that interface VLAN 99 has been configured with an IP address and subnet mask and that it is operational.

Duplex Communication
Full-duplex communication improves the performance of a switched LAN. Full-duplex communication increases effective bandwidth by allowing both ends of a connection to transmit and receive data simultaneously. This is also known as bidirectional. This method of optimizing network performance requires micro-segmentation. A micro-segmented LAN is created when a switch port has only one device connected and is operating at full-duplex. This results in a micro size collision domain of a single device. However, because there is only one device connected, a micro-segmented LAN is collision free.

Unlike full-duplex communication, half-duplex communication is unidirectional. Sending and receiving data does not occur at the same time. Half-duplex communication creates performance issues because data can flow in only one direction at a time, often resulting in collisions. Half-duplex connections are typically seen in older hardware, such as hubs. Full-duplex communication has replaced half-duplex in most hardware.

Most Ethernet and Fast Ethernet NICs sold today offer full-duplex capability. Gigabit Ethernet and 10Gb NICs require full-duplex connections to operate. In full-duplex mode, the collision detection circuit on the NIC is disabled. Frames that are sent by the two connected devices cannot collide because the devices use two separate circuits in the network cable. Full-duplex connections require a switch that supports full-duplex configuration, or a direct connection using an Ethernet cable between two devices.

Standard, shared hub-based Ethernet configuration efficiency is typically rated at 50 to 60 percent of the stated bandwidth. Full-duplex offers 100 percent efficiency in both directions (transmitting and receiving). This results in a 200 percent potential use of the stated bandwidth.

Switch Ports at the Physical Layer
Switch ports can be manually configured with specific duplex and speed settings. Use the duplex interface configuration mode command to manually specify the duplex mode for a switch port. Use the speed interface configuration mode command to manually specify the speed for a switch port. In Figure 1, port F0/1 on switch S1 and S2 are manually configured with the full keyword for the duplex command, and the 100 keyword for the speed command.

The default setting for both duplex and speed for switch ports on Cisco Catalyst 2960 and 3560 switches is auto. The 10/100/1000 ports operate in either half- or full-duplex mode when they are set to 10 or 100 Mb/s, but when they are set to 1000 Mb/s (1 Gb/s), they operate only in full-duplex mode. Auto-negotiation is useful when the speed and duplex settings of the device connecting to the port are unknown or may change. When connecting to known devices, such as servers, dedicated workstations, or network devices, best practice is to manually set the speed and duplex settings.

When troubleshooting switch port issues, the duplex and speed settings should be checked.

Note: Mismatched settings for the duplex mode and speed of switch ports can cause connectivity issues. Auto-negotiation failure creates mismatched settings.

All fiber optic ports, such as 100BASE-FX ports, operate only at one preset speed and are always full-duplex.

Use the Syntax Checker in Figure 2 to configure port F0/1 of switch S1.

Network Access Layer Issues
The output from the show interfaces command can be used to detect common media issues. One of the most important parts of this output is the display of the line and data link protocol status. Figure 1 indicates the summary line to check the status of an interface.