24 Questions
What is the default dynamic mode for departmental-level or wiring closet-level switches?
auto
What happens when a switch port in auto mode negotiates with a neighboring interface?
It forms a trunk link only if negotiations are initiated by the neighboring interface.
What is the purpose of VLAN 0?
To indicate to an upstream switch that it is sending frames that have a configured 802.1p priority.
What is the native VLAN on a Cisco switch by default?
VLAN 1
What is the range of VLAN IDs available on extended IOS images?
1 through 4094
What happens when a switch port in desirable mode negotiates with a neighboring interface?
It actively negotiates to operate in trunk mode.
What is the purpose of the command 'switchport trunk native vlan vlan-id'?
To change the native VLAN.
What is VLAN 4094 used for?
It is not used for DTP frames unless it has been configured as the native VLAN.
What is the primary function of the CAM table in a switch?
To discover the relationship between Layer 2 addresses and physical ports
What is the purpose of the FIB table?
To contain all the prefixes from the IP routing table
Which table is used by a switch to make forwarding decisions based on destination MAC addresses?
CAM table
What is the relationship between the FIB and the IP routing table?
The FIB is synchronized with the IP routing table
What is the purpose of the adjacency table?
To store information about adjacent devices on a network
What is Cisco Express Forwarding (CEF)?
A hardware-based switching method
What are the two main components of Cisco Express Forwarding (CEF)?
The FIB and the adjacency table
Which command is used to configure DAI on VLANs 2 through 4?
ip arp inspection vlan 2,3,4
What is the purpose of the ARP table?
To resolve IP addresses to MAC addresses
What happens by default to a port when DAI is enabled on that port?
It becomes an untrusted port
What is the purpose of the ip arp inspection trust command?
To override the default configuration for a given port
Which VLAN is used by DTP to negotiate a trunk link when 802.1Q encapsulation is configured on the interface?
The native VLAN
What happens if the native VLAN is not configured identically on both ends of a link?
A trunk is not dynamically formed
What is the default behavior of interfaces on a Cisco switch?
They use DTP to automatically negotiate whether an interface should be an IEEE 802.1Q trunk port or an access port
What is the effect of changing the native VLAN on a trunk link?
It can cause unexpected consequences
What is the purpose of DAI?
To inspect traffic sent from each host
Study Notes
Dynamic Modes of Operation for a Switch Port
- There are two dynamic modes of operation for a switch port: auto and desirable.
- In auto mode, the switch port operates in access mode unless the neighboring interface actively negotiates to operate as a trunk.
- In desirable mode, the switch port actively negotiates to operate in trunk mode and will form a trunk link with a neighboring port that is configured to operate in trunk, desirable, or auto mode.
VLAN Configuration
- VLAN 1 is the default native VLAN on a Cisco switch, but it can be changed using the switchport trunk native vlan vlan-id command.
- VLAN 0 is a special VLAN used by IP phones to indicate to an upstream switch that it is sending frames that have a configured 802.1p priority.
- VLAN IDs can be a value from 1 through 1005 or from 1006 through 4094, depending on the IOS image.
Dynamic Trunking Protocol (DTP)
- DTP uses the native VLAN to negotiate a trunk link when IEEE 802.1Q encapsulation is configured on the interface.
- Changing the native VLAN can have unexpected consequences, such as preventing a trunk from dynamically forming.
Switch Forwarding Decisions
- A switch uses the Content Addressable Memory (CAM) table to discover the relationship between the Layer 2 address of a device and the physical port used to reach the device.
- The CAM table is used to make forwarding decisions based on the destination MAC address contained in a frame's header.
This quiz covers the two dynamic modes of operation for a switch port: auto and desirable. It explains how these modes operate and how they differ.
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