ACE-A1-2 Practice Questions

An Arista Multi-Chassis Link Aggregation (MLAG) domain is fundamentally designed as a high-availability pair. It consists of exactly two Arista switches, referred to as MLAG peers. These peers are connected via a dedicated peer-link and synchronize their state information, such as MAC address tables and LACP states, using the MLAG control protocol. This architecture allows the two physical switches to function as a single logical switch from the perspective of a connected device, enabling active-active forwarding, device-level redundancy, and hitless software upgrades. The core design of the MLAG protocol is based on this two-switch pairing.

B. 4: An MLAG domain is strictly limited to two peer switches. Architectures with more than two switches, like a spine-leaf fabric, use different technologies such as EVPN, not a single MLAG domain.

C. 8: This is incorrect. The MLAG protocol is designed for a peer-to-peer relationship between only two switches to ensure state consistency and redundancy.

D. 16: This is incorrect. MLAG is not a stacking technology and does not support more than two switches within a single failure domain.

1. Arista Networks, EOS 4.31.1F Manual (2024), Section: MLAG Introduction, Page 1.

"Multi-chassis link aggregation (MLAG) enables a pair of switches (MLAG peers) to form a high availability system that appears as a single switch on the network."

2. Arista Networks, MLAG - Basic Configuration Guide (2023), Section: Introduction.

"Multi-chassis link aggregation (MLAG) allows a pair of Arista switches to appear as a single, logical switch to a connected device."

3. Arista Networks, MLAG Design and Best Practices (2021), Section: MLAG Overview, Page 4.

"MLAG allows for two switches to be bonded together and act as one. This allows for a connected device to create a port-channel across two separate physical switches."

The VXLAN (Virtual Extensible LAN) specification, defined in IETF RFC 7348, uses a 24-bit field for the VXLAN Network Identifier (VNI). This 24-bit identifier space allows for a theoretical maximum of 2^24 unique virtual networks. Calculating this value gives 16,777,216 possible VNIs. This large address space is a primary advantage of VXLAN over traditional VLANs, enabling massive scalability required in modern multi-tenant data centers and cloud environments.

A. 4096 is the total number of identifiers (2^12) available with the 12-bit VLAN ID field defined in the IEEE 802.1Q standard.

B. 4094 is the number of usable VLAN IDs in the 802.1Q standard, as VLAN IDs 0 and 4095 are reserved.

D. 16,000,000 is an imprecise approximation and not the exact number of unique identifiers provided by a 24-bit field.

1. IETF RFC 7348: Mahalingam, M., et al. "Virtual eXtensible Local Area Network (VXLAN): A Framework for Overlaying Virtualized Layer 2 Networks over Layer 3 Networks." August 2014.

Reference: Section 5, "VXLAN Header Format," page 6. The document states, "VXLAN Network Identifier (VNI): 24 bits. This is an identifier for the virtual network segment."

2. Arista Networks EOS Documentation: "VXLAN Configuration Guide."

Reference: In the "VXLAN Overview" section, the documentation states: "VXLAN extends the layer 2 segment ID field to 24-bits, which overcomes the 4094 segment limitation of VLANs. With 24-bits, VXLAN can create over 16 million segments."

3. Arista Networks White Paper: "Arista VXLAN Unified Forwarding."

Reference: Page 3. "VXLAN defines a 24-bit network identifier (VNI) which allows for up to 16M virtual L2 networks, overcoming the 4K limitation of VLANs."

Arista EOS Event Manager is a powerful on-box automation feature that allows network administrators to create event handlers. These handlers are composed of two main parts: a trigger and an action. A trigger defines the specific system event or condition to monitor, such as an interface state change, a syslog message pattern, or a scheduled time. When the trigger condition is met, the handler executes a predefined action, which can be a sequence of CLI commands, a shell command, or the execution of a custom script. This enables proactive, automated responses to network events directly on the switch.

B. Event Monitor: Event Monitor is a separate EOS feature used for detailed logging and monitoring of specific system events, but it does not natively include the ability to execute automated actions based on those events.

C. Event Trigger: A trigger is a component within an Event Manager configuration that defines the condition for an action. It is not the name of the feature itself.

D. Event History: This is a general term for a log of past occurrences. While EOS maintains event histories (e.g., show event-monitor mac history), it is not a feature for automating future actions.

1. Arista EOS Configuration Guide: In the "Event Manager" section, it states, "Event Manager is a powerful and flexible tool for automating tasks and customizing the behavior of an Arista switch. It allows you to create handlers that are triggered by various events within the system." This section details the configuration of triggers and actions. (Reference: Arista EOS 4.28.0F Configuration Guide, Section 51: Event Manager).

2. Arista White Paper - Automating the Network with Arista EOS: This document describes Event Manager as a key component of on-box automation. It explains, "Event Manager provides the ability to trigger on any state change or syslog message and take an action... This allows for simple event-driven automation to be built directly into the switch." (Reference: Arista Networks, "Automating the Network with Arista EOS," Page 4, "On-box Automation").

Arista's Multi-Switch CLI feature leverages the Extensible Messaging and Presence Protocol (XMPP) to enable a single command-line interface to manage a group of switches. This architecture requires a central XMPP server, also known as a broker, to facilitate communication. The Arista switches act as XMPP clients that connect to this server and join a multi-user chat room. Without the XMPP server, there is no central point for the switches to connect to, and the feature cannot be implemented. EJabberd is a commonly used open-source XMPP server suitable for this purpose.

A. While enabling XMPP on the Arista devices is a necessary configuration step, the external XMPP server is the foundational infrastructure that must be in place first.

C. Management is performed via the native Arista EOS command-line interface on a master switch, not through a separate, third-party instant messaging client application.

D. An SSD is a hardware choice related to performance and logging capacity, not a fundamental software or architectural requirement for the Multi-Switch CLI feature to function.

1. Arista EOS Configuration Guide: In the section on Multi-Switch CLI, the guide explicitly states the prerequisite: "Multi-Switch CLI uses the Extensible Messaging and Presence Protocol (XMPP) to enable communication between switches. To use Multi-Switch CLI, you must first set up an XMPP server..." (Arista EOS Version 4.28.0F Configuration Guide, Section 43.10: Multi-Switch CLI).

2. Arista EOS Configuration Guide: The guide further clarifies the architecture: "The switches act as XMPP clients, connecting to the server and joining a multi-user chat room. One switch is designated as the master, and commands entered on the master are sent to all other switches in the chat room." This explains the client-server relationship and invalidates the need for a separate IM client. (Arista EOS Version 4.28.0F Configuration Guide, Section 43.10.1: Multi-Switch CLI Operation).

Arista's Multi-Chassis Link Aggregation (MLAG) allows two physical switches to appear as a single logical switch to a connected device. This enables the creation of a standard Link Aggregation Group (LAG) with member ports spread across the two MLAG peer switches. The primary benefit of this architecture is that both uplinks in the LAG can be active and forward traffic simultaneously. This active-active forwarding model eliminates the need for Spanning Tree Protocol (STP) to block one of the redundant links to prevent loops, thereby utilizing the available uplink bandwidth much more efficiently and providing superior resiliency.

B. combines up to seven switches in a ring topology

This is incorrect. MLAG creates a domain between a pair of two switches, not seven. Ring topologies are associated with other protocols, not the core function of MLAG.

C. negotiates speed and duplex settings on 10Gb interfaces

This describes autonegotiation, a fundamental Ethernet feature. While MLAG operates over Ethernet, its purpose is not to negotiate physical link parameters.

D. saves all dropped packets to be used at a later time

This describes a function that does not exist in standard networking. Dropped packets are discarded, not stored for later use. This is unrelated to MLAG.

1. Arista Networks, EOS 4.31.1F - MLAG Configuration Guide: In the "MLAG Basics" section, it states, "MLAG allows a client to form a Port-Channel to two upstream switches for physical diversity and increased bandwidth." Under the "MLAG and Spanning Tree Protocol (STP)" section, it clarifies, "MLAG replaces Spanning Tree Protocol (STP) at the aggregation layer of the network, using all links to forward traffic." This directly supports the concept of utilizing bandwidth more efficiently by avoiding STP blocks.

2. Arista Networks, Design and Deployment Guides - L2 MLAG - Recommended Configuration (2023): Section 1.2, "Benefits of MLAG," states: "All links in an MLAG are used for forwarding traffic. Spanning-tree can be eliminated from the access to aggregation layer of the network where MLAG is deployed, allowing for faster convergence times." This confirms that MLAG avoids STP blocking to use all available bandwidth.

VMTracer's Adaptive Segmentation feature is a function that operates on the local Arista switch where it is configured. It integrates with a virtualization manager, such as VMware vCenter, to discover which VLANs are actively being used by virtual machines on a connected ESXi host. The switch then dynamically modifies the allowed VLAN list on its own trunk port(s) that connect to that specific ESXi host. This ensures that only necessary VLANs are trunked to the hypervisor, pruning unused ones to prevent unnecessary broadcast and multicast traffic from being forwarded to the host. The scope of this automation is local to the switch and its direct connection to the hypervisor.

A. VMTracer's scope is the local switch-to-hypervisor link, not trunks between different Arista switches across the network.

C. This feature does not have a network-wide scope; it configures only the local switch's ports connected to the monitored hypervisor.

D. The core purpose of Adaptive Segmentation is specifically to add and prune VLANs from the trunk ports leading to the hypervisor.

1. Arista EOS Configuration Guide: In the "VM Tracer Configuration Guide" section, the "Adaptive VLAN Trunking" subsection states, "Adaptive VLAN trunking prunes VLANs from the trunk that are not in use by any VM on the attached hypervisor. This prevents unnecessary broadcast and multicast traffic from being sent to the hypervisor." This confirms the feature modifies the trunk connecting to the local hypervisor.

2. Arista EOS Configuration Guide: The "VM Tracer Overview" section explains, "...VM Tracer detects the VM and its VLAN, then configures the switch port connected to the hypervisor to allow traffic on that VLAN." This explicitly limits the configuration scope to the switch port connected to the hypervisor, supporting answer B and refuting A and C.

Within the Arista EOS command-line interface, configuration of the SSH server is performed under the management ssh context. To modify the period an SSH session can remain inactive before being automatically disconnected, the idle-timeout command is used. This command accepts a value in minutes (from 0 to 1440), where a value of 0 disables the timeout. This is a security feature to prevent idle, authenticated sessions from remaining open indefinitely, reducing the risk of unauthorized access.

B. timed: This is not a valid command in the management ssh context for configuring session timeouts.

C. timeout: This is too generic and is not the correct command. The specific command required in this context is idle-timeout.

D. ssh-idle: This is a syntactically incorrect and non-existent command in Arista EOS for this purpose.

1. Arista Networks EOS Configuration Guide: In the section describing the configuration of the SSH server, the idle-timeout command is explicitly listed as the method for setting the idle session timeout.

Source: Arista EOS Version 4.31.1F Configuration Guide

Reference: Section: "Management > Securing the Switch > SSH > Configuring the SSH Server". The guide states: "The idle-timeout command configures the idle timeout period for SSH sessions." The command syntax is shown as idle-timeout .

The correct command to copy a file from a USB drive to the internal flash memory on an Arista switch is copy usb1:/ flash:/. In Arista's Extensible Operating System (EOS), physical storage devices are accessed using specific prefixes. The internal flash memory is designated as flash:, and the first USB port is identified as usb1:. The command structure follows the copy format, making option A the syntactically and functionally correct choice for this operation.

B. copy usb:/EOS-4.15.0.swi flash:/EOS-4.15.0.swi

This is incorrect because EOS requires a specific port number (e.g., usb1, usb2) to identify the USB drive; usb: is not a valid identifier.

C. copy drive0:/EOS-4.15.0.swi flash:/EOS-4.15.0.swi

This is incorrect as drive0: is not a recognized device prefix for a USB drive within the Arista EOS file system.

D. copy usb0:/EOS-4.15.0.swi flash:/EOS-4.15.0.swi

This is incorrect because Arista EOS numbers its physical USB ports starting from 1 (e.g., usb1), not 0.

1. Arista Networks EOS Configuration Guide: In the section on "Managing Files on a Switch," the guide specifies the syntax for file operations. It demonstrates that USB drives are referenced as usb1:, usb2:, etc., and the internal flash is flash:. The copy command examples confirm this structure.

Reference: Arista EOS 4.28.0F Configuration Guide, "File Transfers" section, subsection "Copying Files".

2. Arista Networks EOS Central - "EOS Upgrade": This official documentation article outlines the standard procedure for upgrading EOS. Step 1 of the process explicitly shows the command copy usb1:/EOS-x.y.z.swi flash: to transfer the new image from a USB stick to the switch's flash memory.

Reference: Arista EOS Central, "EOS Upgrade" article, section "Upgrading EOS".

3. Arista Networks Command Line Interface Reference Guide: The reference for the copy command details the valid source and destination file systems. It lists flash: and usb: (where n is the port number) as valid filesystem identifiers.

Reference: Arista Networks Command Line Interface Reference, copy command description.

The statement is false. The zerotouch cancel command in Arista EOS provides a persistent method for disabling Zero Touch Provisioning (ZTP) by creating a specific marker file. When this command is executed, it creates a file named zerotouch-cancelled in the /mnt/flash/ directory. The presence of this file is what the boot process checks for. If this file exists, the ZTP process is skipped on all subsequent reboots, even if a startup-config file is not present. Therefore, issuing the write memory command is not required to make the cancellation of ZTP persistent.

The "True" option is incorrect because the persistence of the ZTP cancellation is not tied to the running-config or startup-config. The zerotouch cancel command performs a direct and persistent file system operation on the switch's flash memory, which survives a reboot independently of any configuration-saving commands like write memory. While saving a valid configuration is the ultimate goal after canceling ZTP, it is not the mechanism that makes the cancellation itself persist.

1. Arista EOS Configuration Guide: In the section describing Zero Touch Provisioning, the guide explains the cancellation process. It states, "To permanently disable ZTP, enter the zerotouch cancel command from the CLI. This command creates the file /mnt/flash/zerotouch-cancelled and ZTP will be disabled on all subsequent reboots." This explicitly confirms that the command itself creates a persistent state via a file, not through a configuration change that needs to be saved.

Source: Arista Networks, EOS 4.27.1F Configuration Guide, Section: "Zero Touch Provisioning (ZTP)", Subsection: "Disabling ZTP".

Arista's Event Manager allows automated actions based on specific system events. An event handler script is initiated by a defined trigger. The on-boot trigger executes the handler after the switch boots and the startup configuration is applied. The on-startup-config trigger executes the handler whenever a write memory or copy running-config startup-config command is issued, indicating a change to the startup configuration. These are both explicitly documented and valid trigger conditions within Arista EOS for event handlers.

B. on-schedule: While Event Manager supports time-based execution, it is configured using the schedule command with cron syntax, not with an on-schedule trigger keyword.

D. on-reload: There is no specific on-reload trigger. The on-boot trigger encompasses the scenario of a system reload, executing its action after the device has booted up.

1. Arista EOS 4.28.0F System Configuration Guide, Section: Event Manager > Configuring an Event Handler. This section details the trigger command and lists the valid event types. It explicitly shows on-boot and on-startup-config as valid options and does not list on-reload.

Reference Snippet: "The trigger command specifies the event that initiates the handler... trigger on-boot... trigger on-startup-config"

2. Arista EOS 4.28.0F System Configuration Guide, Section: Event Manager > Scheduling an Event Handler. This section describes the separate schedule command for time-based execution, confirming that on-schedule is not a trigger type.

Reference Snippet: "The schedule command configures the switch to run the event handler script at specified times."

3. Arista EOS CLI Reference, Command: event-handler . The command reference for event-handler configuration mode lists the available sub-commands, showing trigger and schedule as distinct configuration methods, further clarifying the difference between event-based triggers and time-based schedules.