Free CCNA | Switch Interfaces | Day 9 | CCNA 200-301 Complete Course
Introduction
In this section, the instructor introduces himself and the course. He also encourages viewers to subscribe to his channel and download Anki flashcards.
- The course is a free, complete CCNA course.
- Viewers are encouraged to subscribe, like, comment, and share the videos.
- Anki flashcards can be downloaded from the link in the description.
Overview of Switch Interfaces
In this section, the instructor discusses switch interfaces and how they differ from router interfaces.
- Switch interfaces are different from router interfaces because they do not have the 'shutdown' command applied by default.
- The instructor will discuss configuring Layer 1 characteristics of switch interfaces such as speed and duplex.
- Autonegotiation allows two devices to negotiate speed and duplex settings without manual configuration.
- Interface status refers to whether an interface is up or down. Cisco devices keep various counters regarding traffic that passes through them.
Multilayer Switching
In this section, the instructor talks about multilayer switching and assigns IP addresses to switches.
- Multilayer switching involves assigning IP addresses to switches.
- This concept will be covered in a future lesson.
Network Topology
In this section, the instructor introduces the network topology used for this video.
- The network topology consists of one LAN with one router (R1), two switches (SW1 and SW2), and four PCs (PC1, PC2, PC3, PC4).
- SW1's network interfaces will be configured in this video.
CLI of SW1
In this section, the instructor enters privileged exec mode on SW1 and uses 'show ip interface brief' to check the status of the interfaces.
- The instructor enters privileged exec mode on SW1.
- 'Show ip interface brief' is used to check the status of the interfaces.
- Four interfaces connected to devices have a status and protocol column of up/up.
- Interfaces not connected to any other devices have a status and protocol column of down/down.
Difference Between Cisco Routers and Switches
In this section, the instructor discusses the difference between Cisco routers and switches.
- Router interfaces are in an administratively disabled state by default, meaning they have the 'shutdown' command applied.
- Switch interfaces do not have the 'shutdown' command applied by default, so if they are connected to another device, they will usually be in the up/up state with no configuration required.
- Down/down means that an interface is not connected to another device.
Show Interfaces Status
In this section, the instructor introduces another useful command for checking switch interfaces: 'show interfaces status'.
- 'Show interfaces status' is a useful command for checking switch interfaces.
Understanding the 'show interfaces status' command
In this section, we learn about the 'show interfaces status' command and its output. We also learn about the different fields displayed in the output.
Status Field
- The status field shows whether an interface is connected or not.
- Connected interfaces show a status of 'connected', while unconnected interfaces show a status of 'notconnect'.
- There are other possible statuses that will be covered later in the course.
VLAN Field
- The VLAN field displays the VLAN number associated with each interface.
- The default VLAN is 1, but some interfaces may have a different VLAN number.
- Interfaces connected to other switches may show as trunks instead of displaying a VLAN number.
Duplex and Speed Fields
- The duplex field indicates whether an interface can send and receive data at the same time (full-duplex) or not (half-duplex).
- By default, duplex is set to auto on Cisco switches, meaning it will negotiate with neighboring devices and use full-duplex if possible.
- The speed field displays the speed at which an interface can operate. Auto-negotiation works well so usually youâll leave it be.
Type Field
- The type field displays information about the type of cable used for each interface.
- RJ45 interfaces for copper UTP cables are common, but small form-factor pluggable (SFP) modules may also be used.
Disabling Unused Interfaces
In this section, we learn how to disable unused switch interfaces using a single command.
Interface Range Command
- Instead of disabling each interface individually, we can use the 'interface range' command to disable multiple interfaces at once.
- From global config mode, type 'interface range', followed by the range of interfaces to be disabled (e.g. f0/5 to 12).
- This will bring us to interface range config mode, where we can enter a description and then shut down the interfaces.
- All interfaces in the specified range will be administratively down.
Non-Consecutive Interfaces
- The 'interface range' command can also be used for non-consecutive interfaces.
- For example, we can disable f0/5,6,9,10,11,and 12 while leaving f0/7 and 8 shutdown using the command: interface range f0/5 to 6, COMMA, f0/9 to 12.
Understanding Full and Half Duplex
In this section, we learn about full-duplex and half-duplex modes of operation.
Half-Duplex Mode
- In half-duplex mode, a device cannot send and receive data at the same time.
- If it is receiving a frame, it must wait before sending a frame.
Full-Duplex Mode
- In full-duplex mode, a device can send and receive data at the same time.
Hubs vs Switches
This section explains the difference between hubs and switches, how they operate, and how they handle collisions.
Hubs
- A hub is a simple repeater that floods any frame it receives to all connected devices.
- All devices connected to a hub are part of whatâs called a collision domain.
- In a half-duplex situation like this, Ethernet devices use a mechanism called âCSMA/CDâ to deal with collisions.
Switches
- Switches operate at layer 2 using MAC addresses to send frames to specific hosts. They also wonât try to send two frames to the same host at once.
- Because of the improved functionality of switches over hubs, these devices can now operate in full duplex, meaning they donât have to worry about whether or not other devices are sending data at the same time.
Speed and Duplex Autonegotiation
This section explains speed and duplex autonegotiation on interfaces for routers and switches.
Autonegotiation Enabled
- Interfaces advertise their capabilities to their neighbors, and they negotiate the best speed and duplex settings they are both capable of.
- Devices attached to a switch can operate in full duplex.
Autonegotiation Disabled
- If autonegotiation is disabled on the device connected to the switch, then the switch will try sensing its speed first before using slowest supported speed if it fails.
- If the speed is 1000 mbps or greater, it will use full duplex.
Interface Speed and Duplex
In this section, the speaker explains how interface speed and duplex work in a network.
Understanding Interface Speed and Duplex
- Ethernet interfaces can operate at different speeds such as 10 Mbps, 100 Mbps, or 1000 Mbps.
- Half-duplex means that data can only be sent or received at one time while full duplex allows for simultaneous sending and receiving of data.
- Autonegotiation is a feature that allows devices to find the appropriate speed and duplex settings without manual configuration.
Duplex Mismatch
- A duplex mismatch occurs when two connected devices have different duplex settings.
- This results in collisions which cause poor network performance.
- The 'show interfaces' command can be used to view statistics on interface errors.
Review of Key Concepts
In this section, the speaker reviews key concepts related to interface speed and duplex.
Key Concepts
- Full duplex is preferred over half-duplex for better network performance.
- Autonegotiation should be enabled on all devices in the network to avoid duplex mismatches.
- A duplex mismatch will result in collisions occurring on the half-duplex side causing poor network performance.
Quiz Questions
In this section, the speaker asks quiz questions related to interface speed and duplex.
Quiz Questions
- What will happen if there is a duplex mismatch between two connected devices with autonegotiation disabled?
- Answer: Collisions will occur.
- What is used on half-duplex interfaces to detect and avoid collisions?
- Answer: CSMA/CD.
- Which command shows various counters of errors detected on an interface?
- Answer: show interfaces.
Viewing Interface Information
In this section, the speaker explains how to view interface information using the "show interfaces" command.
Using "show interfaces"
- Use the command "show interface f0/1" to view information for a specific interface.
- The counters are located at the bottom of the output.
- This command is useful for viewing detailed information about individual interfaces.
Network Interface Errors
In this section, the speaker discusses errors that can occur on a network interface and provides examples.
Types of Errors
- Possible errors include runts, giants, and CRC.
- Broadcasts are not considered errors as they are part of normal network operations.
- Runts are frames that are too small, giants are frames that are too big, and CRC counts frames that failed their CRC check in the frame check sequence in the trailer of the Ethernet frame.
Autonegotiation Settings
In this section, the speaker explains how autonegotiation settings work when one device has it enabled and another has it disabled.
Autonegotiation Settings
- If autonegotiation is disabled on one device but enabled on another device, then the local device will attempt to sense the speed of the remote device.
- The local device will set its interface speed to match that of SW2's (100 Mbps).
- However, it cannot sense SW2's duplex mode so half duplex will be used resulting in a duplex mismatch between devices which may cause poor performance due to collisions.
Conclusion and Resources
In this section, the speaker concludes by reminding viewers about supplemental materials available for further study.
Supplemental Materials
- Flashcards are available to help remember what was learned in the video.
- A packet tracer practice lab is also available for hands-on practice configuring Cisco devices.
- The speaker encourages viewers to subscribe, like, comment, and share the video.