CCNA2 - Module 1&2.1 Flashcards
SWITCH BOOT SEQUENCE
When a Cisco switch powers on, it follows these five steps:
- POST: The switch runs a self-test (POST) to check the CPU, DRAM, and part of the flash storage.
- Boot Loader: A small program in ROM is loaded after POST, starting the boot process.
- CPU Initialization: The boot loader sets up CPU registers, memory mapping, and speed.
- Flash Initialization: The boot loader prepares the flash file system.
- Load IOS: The boot loader finds and loads the default IOS operating system into memory, taking control of the switch.
Differentiate boot system, flash:, c2960-lanbasek9-mz.150-2.SE/ and c2960-lanbasek9-mz.150-2.SE.bin
- Boot system - the main command
- flash: - the storage device
- c2960-lanbasek9-mz.150-2.SE/ - the path to the file system
- c2960-lanbasek9-mz.150-2.SE.bin - the IOS file name
Shows whether the system is receiving power and functioning properly.
System LED (SYST)
Shows the RPS status.
Redundant Power Supply LED (RPS)
When green, indicates port status mode is selected, which is the default. Port status can then be understood by the light associated with each port.
Port Status LED (STAT)
When green, indicates port duplex mode is selected. Port duplex can then be understood by the light associated with each port.
Port Duplex LED (DUPLX)
When green, indicates port speed mode is selected. Port speed can then be understood by the light associated with each port.
Port Speed LED (SPEED)
Present if the switch supports PoE. Indicates the PoE status of ports on the switch.
Power over Ethernet LED (PoE)
Recovering from a System Crash
If the switch’s operating system is missing or damaged, the boot loader allows access to the switch through a console connection. Here’s how to access it:
- Connect a PC to the switch via console cable and open terminal software.
- Unplug the switch power cord.
- Reconnect the power and, within 15 seconds, press and hold the Mode button while the System LED flashes green.
- Keep holding until the LED turns amber and then solid green, then release the Mode button.
- The boot loader prompt will appear in the terminal software.
The boot loader lets you format the flash, reinstall the OS, or recover a lost password using commands like dir
to view files.
To manage a switch remotely, assign it an IP address, subnet mask, and a default gateway. This setup is similar to configuring a host device.
The switch’s virtual interface (SVI) on S1 should be given an IP address. The SVI is a virtual, not physical, interface. Use a console cable to connect to a PC for initial configuration.
Switch Management Access
Switch SVI Configuration Example
By default, the switch uses VLAN 1 for management. For security, it’s best to use a different VLAN for management.
- Configure the Management Interface: Assign an IP address and subnet mask to the switch’s management SVI (e.g., VLAN 99). The SVI won’t be “up/up” until VLAN 99 is created and a device is connected to a port in that VLAN. If using IPv6, configure the switch for dual IP modes first.
- Configure the Default Gateway: If managing the switch remotely from another network, set a default gateway. No IPv6 gateway is needed since the switch receives this info from a router advertisement.
-
Verify Configuration: Use
show ip interface brief
andshow ipv6 interface brief
to check the status of interfaces and confirm the IP setup. The IP on the SVI allows remote management, but not routing of Layer 3 packets.
Duplex Communication
- Full-Duplex: Allows data to be sent and received simultaneously, improving efficiency. It requires microsegmentation (one device per switch port) and eliminates collisions. Gigabit Ethernet and 10 Gb NICs need full-duplex to function properly.
- Half-Duplex: Only allows data to flow in one direction at a time, causing potential collisions and performance issues.
Full-duplex provides 100% efficiency in both directions, doubling the bandwidth usage.
Configure Switch Ports at the Physical Layer
- Switch ports can be configured with specific duplex and speed settings using the
duplex
andspeed
commands. - By default, Cisco Catalyst 2960 and 3560 switch ports are set to auto for both duplex and speed. At
10/100 Mbps
, they can be ihalf- or full-duplex, but at1000 Mbps
, they are always full-duplex. -
Autonegotiation
is useful when device settings are unknown or may change, but it’s best to manually set speed and duplex for known devices like servers or workstations. - When troubleshooting, check duplex and speed settings, as mismatched configurations can cause
connectivity issues
. Fiber-optic ports like1000BASE-SX
always operate at a fixed speed and full-duplex.
Auto-MDIX
- Auto-MDIX allows the switch to automatically detect and adjust for the correct cable type (straight-through or crossover) needed for the connection.
- Without auto-MDIX, use straight-through cables for devices like servers and routers, and crossover cables for connecting switches or repeaters.
- With auto-MDIX, either cable type works, and the interface adjusts automatically for proper communication.
- On newer Cisco switches, enable auto-MDIX with the
mdix auto
command, and set speed and duplex to auto for proper function. - Auto-MDIX is enabled by default on Catalyst 2960 and 3560 switches but not on older models like the Catalyst 2950 and 3550. Use the
show controllers ethernet-controller
command to check the setting.
The ___________ command can be used to verify that the switch has been correctly configured. From the sample abbreviated output on S1, some important information is shown in the figure:
show running-config
The _____________ command is another commonly used command, which displays status and statistics information on the network interfaces of the switch. The show interfaces command is frequently used when configuring and monitoring network devices.
show interfaces
The first line of the output for the ___________________________ command indicates that the FastEthernet 0/18 interface is up/up, meaning that it is operational. Further down, the output shows that the duplex is full and the speed is 100 Mbps.
show interfaces fastEthernet 0/18
Network Access Layer Issues
The show interfaces
command helps identify common media problems by displaying line and data link protocol statuses.
-
Up/Down Status:
- Interface up, line protocol down: This suggests issues like an encapsulation mismatch, an error-disabled interface, or a hardware problem.
- Both down: Likely indicates no cable attached or an interface issue, such as the other end being administratively down.
-
Interface administratively down: This means the interface was manually disabled using the
shutdown
command.
The output also shows interface counters and statistics, which can reveal errors that impact network performance, even if they don’t cause complete failures.
Give the 7 Error Type and differentiate them
- Input Errors Total number of errors. It includes runts, giants, no buffer, CRC, frame, overrun, and ignored counts.
- Runts Packets that are discarded because they are smaller than the minimum packet size for the medium. For instance, any Ethernet packet that is less than 64 bytes is considered a runt.
- Giants Packets that are discarded because they exceed the maximum packet size for the medium. For example, any Ethernet packet that is greater than 1,518 bytes is considered a giant.
- CRC CRC errors are generated when the calculated checksum is not the same as the checksum received.
- Output Errors Sum of all errors that prevented the final transmission of datagrams out of the interface that is being examined.
- Collisions Number of messages retransmitted because of an Ethernet collision.
- Late Collisions A collision that occurs after 512 bits of the frame have been transmitted
is the sum of all errors in datagrams
that were received
on the interface being examined. This includes runts, giants, CRC, no buffer, frame, overrun, and ignored counts. The reported input errors from the show interfaces command include the following:
* run frames
* giants
* CRC errors
“Input errors”
- Ethernet frames that are shorter than the 64-byte minimum allowed length are called _________. Malfunctioning NICs are the usual cause of excessive _______ frames, but they can also be caused by collisions.
Runt Frames
- Ethernet frames that are larger than the maximum allowed size are called ___________.
Giants
- On Ethernet and serial interfaces, ___________ usually indicate a
media
orcable error
. Common causes includeelectrical interference
, loose ordamaged connections
, orincorrect cabling
. If you see many __________, there is too much noise on the link and you should inspect the cable. You should also search for and eliminate noise sources.
CRC errors
is the sum of all errors
that prevented the final transmission
of datagrams out the interface that is being examined. The reported __________ from the show interfaces command include the following:
* collision
* late collision
“Output errors”