Objective 2.2 Flashcards
Given a scenario, configure switching technologies and features. (20 cards)
What is a VLAN (Virtual Local Area Network)?
A VLAN logically segments a physical switch into multiple, isolated broadcast domains.
Devices on one VLAN cannot communicate directly with devices on another VLAN without a Layer 3 device (like a router or Layer 3 switch).
What is the primary purpose of using VLANs?
- Security: Isolates groups of users (e.g., HR, Finance) from each other.
- Performance: Reduces the size of broadcast domains, minimizing unnecessary broadcast traffic and improving network efficiency.
- Management: Simplifies network administration by grouping devices logically rather than by physical location.
What is a VLAN database?
On many switches (like Cisco), it’s a file (e.g., vlan.dat) stored in flash memory that holds the VLAN configurations for that switch, including VLAN numbers and names.
What is an SVI (Switch Virtual Interface)?
A logical Layer 3 interface created on a switch that represents a specific VLAN.
By assigning an IP address to an SVI, you enable inter-VLAN routing (on a Layer 3 switch) or remote management of the switch (on Layer 2 or Layer 3 switches).
Scenario:
You are trying to ping a Layer 2 switch to check its connectivity, but the pings fail. You have confirmed your computer has a valid IP address.
What must be configured on the switch for it to be managed remotely via its IP address?
An SVI (Switch Virtual Interface) must be created for a specific VLAN and assigned a valid IP address and subnet mask within that VLAN’s subnet.
Your computer must also be on a network that can route to the switch’s SVI address.
What is 802.1Q tagging?
An IEEE standard protocol used by switches to identify which VLAN a frame belongs to as it crosses a trunk link. It works by inserting a 4-byte “tag” into the original Ethernet frame header.
What is the difference between a Trunk Port and an Access Port?
- Access Port: Belongs to a single VLAN and carries untagged frames for that VLAN. Typically connects to an end device like a PC or printer.
- Trunk Port: Carries traffic for multiple VLANs simultaneously. It uses 802.1Q tagging to differentiate between the VLANs. Typically connects switches to other switches or to routers.
What is the Native VLAN?
A special VLAN configured on an 802.1Q trunk port.
Any traffic belonging to the Native VLAN is sent untagged across the trunk link.
For security, it’s best practice to change this from the default (VLAN 1) and not use it for user data.
What is a Voice VLAN?
A separate VLAN configured on a switch port to carry voice traffic from an IP phone. This allows a phone and a PC to share a single physical port, while the switch prioritizes the voice traffic into its own dedicated VLAN for better quality.
What is Link Aggregation?
The process of combining multiple physical network links into a single logical link. This provides two main benefits:
- Increased Bandwidth: The bandwidth is the sum of the aggregated links.
- Redundancy: If one physical link fails, traffic automatically fails over to the remaining links.
Also known as EtherChannel (Cisco), port bonding, or teaming.
What is the difference between Full-duplex and Half-duplex?
- Full-duplex: Allows data to be sent and received simultaneously. Collision detection is turned off. This is the standard for modern switched networks.
- Half-duplex: Data can only be sent or received at one time, not both. Requires collision detection (CSMA/CD). Used in older hub-based networks.
What is the most common problem caused by a speed or duplex mismatch between two connected devices?
Extremely poor performance, often characterized by high error rates, dropped packets, and late collisions being reported on the half-duplex side.
Modern devices should use auto-negotiation to prevent this.
What problem does STP (Spanning Tree Protocol) solve?
STP prevents Layer 2 switching loops.
These loops can cause broadcast storms and constant MAC address table instability, which can bring down an entire network.
How does STP prevent loops?
By creating a loop-free logical topology.
It does this by electing a Root Bridge and then having other switches intelligently block redundant paths to ensure there is only one active path to any destination.
What is a Broadcast Storm?
A network condition where broadcast frames are endlessly forwarded and amplified by switches in a looping topology.
This consumes all available bandwidth and swamps device CPUs, effectively causing a denial of service.
What are the primary STP port states a port transitions through to become active?
- Blocking: Not forwarding frames, but listening to BPDUs.
- Listening: Processing BPDUs to determine the root bridge and its role in the topology. Not forwarding frames.
- Learning: Building the MAC address table. Not forwarding frames.
- Forwarding: The port is fully active and can send and receive user data.
Note: There is also a Disabled state.
What is MTU (Maximum Transmission Unit)?
The largest size of a data payload that a protocol can carry in a single packet or frame.
For standard Ethernet, the MTU is 1500 bytes.
What are Jumbo Frames?
Ethernet frames with an MTU larger than the standard 1500 bytes, typically up to 9000 bytes.
What is the main benefit of using Jumbo Frames and where are they most commonly used?
Benefit: They increase throughput and reduce CPU overhead because fewer frames need to be processed for the same amount of data.
Common Use Case: High-performance networks like Storage Area Networks (SANs) or iSCSI networks where large files are transferred.
What is a critical requirement for successfully implementing Jumbo Frames on a network?
Every device in the data path—including the sender’s NIC, the receiver’s NIC, and all switches in between—must be configured to support the same jumbo frame size.
A mismatch will cause packets to be dropped.
