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Question 321. What is the PRIMARY purpose of Huawei Cluster Switch System (CSS) technology?

1. To convert Ethernet traffic into MPLS packets
2. To replace all routing protocols in a campus network
3. To virtualize two supported physical switches into one logical switch for simplified management and improved redundancy
4. To provide wireless roaming between APs

Correct Answer: 3. To virtualize two supported physical switches into one logical switch for simplified management and improved redundancy

Explanation:

Huawei CSS combines two supported physical modular campus switches so they operate logically as a single switch. This simplifies network design because administrators can manage the members through one logical system rather than treating each chassis independently. CSS can also support inter-chassis link aggregation, improve bandwidth utilization, and provide device-level redundancy. Huawei notes that this design can reduce reliance on mechanisms such as MSTP and VRRP in some traditional redundant campus topologies because the two physical switches appear as one logical device to connected equipment.

Question 322. In a Huawei CSS, what is the role of the master switch?

1. It manages the entire logical CSS system
2. It forwards traffic only and performs no control functions
3. It remains powered off until the standby fails
4. It functions only as an external router

Correct Answer: 1. It manages the entire logical CSS system

Explanation:

A Huawei CSS contains one master switch and one standby switch. The master acts as the primary management and control point for the complete CSS. Administrators can log in through the logical system and manage both physical members as one device. The standby backs up the master and can take over if the master becomes unavailable. Importantly, both master and standby switches can forward service traffic during normal operation; the distinction primarily concerns control and management roles. This redundancy allows CSS to improve availability while presenting a simplified single-device view to administrators and connected networks.

Question 323. Before two Huawei modular switches can form a CSS, what requirement applies to their CSS IDs?

1. Both switches must use CSS ID 1
2. Both switches must use CSS ID 2
3. CSS IDs are ignored during CSS formation
4. The two member switches must use different CSS IDs

Correct Answer: 4. The two member switches must use different CSS IDs

Explanation:

Huawei uses the CSS ID to uniquely identify each member switch in a CSS. The supported member IDs are typically 1 and 2, and both switches default to ID 1 before configuration. Because two members with the same ID cannot establish the CSS successfully, administrators must change one member to CSS ID 2 before completing the setup. Huawei documentation specifically warns against changing a member’s CSS ID after the CSS is established because doing so can cause the system to split. Correct identity planning is therefore an important prerequisite for successful clustering.

Question 324. How does CSS priority influence master election when two Huawei CSS members start under otherwise comparable conditions?

1. The lower priority always wins
2. A higher CSS priority increases the likelihood that the switch becomes master
3. Priority affects only data forwarding and never election
4. Priority changes the switch MAC address

Correct Answer: 2. A higher CSS priority increases the likelihood that the switch becomes master

Explanation:

CSS priority is one of the factors Huawei uses during master election. When the two candidate switches start at approximately the same time, the device with the higher CSS priority is preferred as master. If priority is also equal, additional criteria such as MAC address and CSS ID can be evaluated. The default CSS priority is typically 1, so administrators can intentionally raise the value on the chassis they prefer as master. However, the final election follows Huawei’s defined sequence of criteria, and administrators should avoid unnecessary forced role changes in an operating production CSS.

Question 325. What is a major operational benefit of CSS configuration synchronization?

1. It allows the standby to use a completely unrelated configuration
2. It disables configuration changes on the master
3. It requires administrators to configure both members separately
4. It helps both members maintain a consistent logical system configuration for failover and unified management

Correct Answer: 4. It helps both members maintain a consistent logical system configuration for failover and unified management

Explanation:

Huawei CSS uses configuration synchronization so the two physical chassis behave as one logical switch. Configuration changes made through the CSS are stored on the master and synchronized to the standby. This means the standby already has the required configuration if it must assume the master role after a failure. The mechanism also prevents administrators from needing to reproduce every command manually on two separate devices. Huawei additionally provides software synchronization capabilities so compatible member software can be aligned automatically. Together, these mechanisms simplify operation and improve failover consistency across the clustered system.

Question 326. What is the PRIMARY purpose of stacking on Huawei fixed campus switches?

1. To combine multiple physical switches into one logical switch to improve scalability, reliability, and management simplicity
2. To create IPsec tunnels between switches
3. To replace Ethernet with wireless links
4. To convert every switch into a BGP route reflector

Correct Answer: 1. To combine multiple physical switches into one logical switch to improve scalability, reliability, and management simplicity

Explanation:

Stacking virtualizes multiple supported physical switches into one logical switching system. Huawei identifies several benefits, including increased port density, expanded forwarding capacity, simplified management, and improved reliability through member redundancy. Instead of operating multiple independent fixed switches and managing separate control planes, administrators can configure the stack as one logical device. If the master member fails, the standby can assume the master role. Huawei distinguishes this fixed-switch stacking technology from CSS, which is used by supported modular campus switches, although both technologies provide similar horizontal virtualization benefits.

Question 327. Which stack member role acts as the direct backup to the master switch?

1. Slave
2. Standby
3. Root
4. Designated

Correct Answer: 2. Standby

Explanation:

A Huawei stack can include master, standby, and slave member roles. The master manages the complete stack. The standby is specifically elected as the backup to the master and is prepared to assume the master role if the current master fails. Additional members operate as slaves and primarily participate in forwarding. If the standby itself becomes unavailable, a slave can be selected to assume the standby role. This hierarchy provides control-plane redundancy while allowing all members to contribute forwarding resources and physical ports to the logical stack.

Question 328. What is a PRIMARY advantage of adding additional slave switches to a Huawei stack?

1. They eliminate the need for any master switch
2. They prevent software synchronization
3. They can increase port capacity and forwarding resources while remaining part of one logical device
4. They must remain unused until a failure occurs

Correct Answer: 3. They can increase port capacity and forwarding resources while remaining part of one logical device

Explanation:

Slave switches in a Huawei stack are active members rather than cold standby devices. They contribute interfaces and forwarding capacity to the logical switching system, increasing total port density and potentially total bandwidth. Meanwhile, the master provides centralized management and the standby supplies control redundancy. Huawei explains that additional slave members can improve the stack’s forwarding capability while simplifying administration because the entire group remains one logical device. This makes stacking useful when a campus access or aggregation layer needs to expand without introducing the operational complexity of independently managed switches.

Question 329. What happens when a stack member is running a compatible but different software version from the master?

1. The member can automatically obtain the appropriate software from the master, restart, and rejoin the stack
2. The entire stack must be permanently dismantled
3. The member is converted into an M-LAG peer
4. The master automatically downgrades itself

Correct Answer: 1. The member can automatically obtain the appropriate software from the master, restart, and rejoin the stack

Explanation:

Huawei stacks support automatic software-version synchronization among compatible members. If a joining standby or slave member runs a different but compatible system software version, it can download the software used by the master, restart with that version, and then rejoin the stack. This reduces deployment complexity because administrators do not always have to manually preinstall an identical image on every member before connecting the stack. Compatibility requirements still apply, and upgrades should follow the product’s documented procedures, but automatic synchronization helps keep the logical stack operating consistently.

Question 330. Why is Dual-Active Detection (DAD) important in a switch stack?

1. It increases the VLAN ID range
2. It assigns IP addresses to stack members
3. It selects BGP best paths
4. It helps detect and contain a split-stack condition in which more than one member could believe it is master

Correct Answer: 4. It helps detect and contain a split-stack condition in which more than one member could believe it is master

Explanation:

If stack links fail and the logical stack splits into separate components, each component may elect or retain its own master. This dual-active condition is dangerous because both systems can use the same logical configuration, addresses, and forwarding identities on the production network, potentially creating loops and traffic disruption. Huawei DAD mechanisms detect the condition and trigger protective behavior so only an appropriate part of the split system continues normal service forwarding. Huawei supports DAD through mechanisms such as management interfaces on applicable devices, reducing the impact of stack-split failures.

Question 331. What is the PRIMARY purpose of M-LAG?

1. To combine two independent network devices into one software process
2. To allow a downstream device to form one logical link aggregation across two separate upstream devices
3. To create an OSPF virtual link
4. To distribute DHCP addresses

Correct Answer: 2. To allow a downstream device to form one logical link aggregation across two separate upstream devices

Explanation:

Multi-Chassis Link Aggregation allows a server, switch, or other downstream system to build one logical link aggregation using physical links connected to two independent upstream devices. This provides device redundancy as well as link redundancy while allowing active use of multiple links. Unlike stacking or CSS, the two M-LAG peer devices remain independently managed systems rather than becoming one complete logical switch. Huawei M-LAG uses mechanisms including a DFS group, peer-link, and dual-active detection to synchronize state and coordinate forwarding between the peer devices.

Question 332. What is the role of the peer-link in a Huawei M-LAG deployment?

1. It carries only NTP traffic
2. It is used solely for Internet routing
3. It allows the two M-LAG peer devices to synchronize information and can carry traffic when required
4. It replaces all M-LAG member links

Correct Answer: 3. It allows the two M-LAG peer devices to synchronize information and can carry traffic when required

Explanation:

The peer-link is a critical connection between the two devices forming an M-LAG system. Huawei explains that the peers use it to synchronize information such as MAC and forwarding state. It can also carry service traffic in specific failure conditions—for example, if traffic arrives on one peer but the downstream M-LAG member link on that peer has failed, the traffic may cross the peer-link to reach the other peer’s functioning member link. Because of its importance, the peer-link should be designed with appropriate redundancy and capacity.

Question 333. What is the PRIMARY purpose of the DAD link in a Huawei M-LAG?

1. To detect whether both M-LAG devices are still active when peer communication is disrupted
2. To carry all normal server traffic
3. To advertise customer VPN routes
4. To provide the only connection between the peers

Correct Answer: 4. To detect whether both M-LAG devices are still active when peer communication is disrupted

Explanation:

Huawei M-LAG uses a Dual-Active Detection link so the two peer devices can exchange heartbeat information independently of the peer-link. If the peer-link fails, each device uses DAD to determine whether the other peer itself is still alive or whether the remote chassis has actually failed. This distinction is essential because two active M-LAG devices forwarding independently without synchronization can cause broadcast storms, duplicate forwarding, or MAC flapping. DAD therefore enables the system to take controlled protective action after peer-link failure rather than allowing both sides to operate unsafely.

Question 334. What happens on the backup M-LAG device when the peer-link fails but DAD confirms that both peers are still operating?

1. Both devices continue forwarding normally with no restrictions
2. Protective interfaces on the backup are placed into Error-Down so only the master continues forwarding
3. The backup automatically becomes an OSPF DR
4. All peer-link traffic is redirected to DHCP

Correct Answer: 2. Protective interfaces on the backup are placed into Error-Down so only the master continues forwarding

Explanation:

When the M-LAG peer-link fails while DAD still confirms that both devices are alive, the system has detected a potential dual-active conflict. Allowing both peers to continue normal forwarding could create Layer 2 loops, MAC-address flapping, and broadcast storms. Huawei therefore places relevant physical interfaces on the backup M-LAG device into an Error-Down state, leaving the master as the active forwarding device. When the peer-link recovers, the peers renegotiate and restore normal operation. This controlled isolation is a key M-LAG reliability mechanism.

Question 335. If an M-LAG member interface fails on one peer while the other peer’s member interface remains healthy, how can user traffic continue?

1. The M-LAG becomes permanently unavailable
2. The server must manually change its IP address
3. The system can use the remaining active member path, and traffic received by the affected peer can cross the peer-link when required
4. The peers must reboot immediately

Correct Answer: 1. The system can use the remaining active member path, and traffic received by the affected peer can cross the peer-link when required

Explanation:

An M-LAG provides both link and device redundancy. If one M-LAG member interface fails, the downstream connection effectively changes from dual-homed to single-homed through the surviving member. Traffic can continue using the healthy link. Huawei also describes a case in which the peer with the failed member interface receives traffic from the network side; it can send that traffic across the peer-link to the healthy peer, which then forwards it toward the downstream device. Once the member interface recovers, synchronization occurs and normal load-balanced dual-homing operation resumes.

Question 336. Which statement BEST distinguishes M-LAG from stacking or CSS?

1. M-LAG cannot provide device redundancy
2. CSS uses no physical links
3. M-LAG peers remain independently managed devices, whereas stacking/CSS virtualizes members into one logical switch
4. Stacking cannot support link aggregation

Correct Answer: 3. M-LAG peers remain independently managed devices, whereas stacking/CSS virtualizes members into one logical switch

Explanation:

Both M-LAG and stack/CSS designs can provide multi-device redundancy, but their architectures differ significantly. Stacking and CSS merge members into one logical device, including a unified management and control structure. M-LAG keeps the two peer switches as independent devices while coordinating selected forwarding state and presenting an inter-device aggregated connection to downstream equipment. This independence can simplify some upgrade and failure-isolation scenarios, while stacking or CSS often provides simpler management. The appropriate choice depends on topology, hardware capabilities, operational preferences, and availability requirements.

Question 337. What is the PRIMARY purpose of Non-Stop Routing (NSR)?

1. To preserve routing and forwarding state during an active/standby control-board switchover without depending on neighboring devices for state recovery
2. To replace all routing protocols with static routes
3. To detect Layer 2 loops
4. To encrypt management sessions

Correct Answer: 2. To preserve routing and forwarding state during an active/standby control-board switchover without depending on neighboring devices for state recovery

Explanation:

Huawei NSR improves control-plane reliability by synchronizing routing and forwarding information from the active main board to the standby main board. If the active board fails or an administrator triggers a switchover, the standby already has the necessary neighbor and topology information and can take over without relying on neighboring devices to reconstruct that state. Huawei contrasts this with NSF based on Graceful Restart, which depends on cooperation from neighboring devices. NSR can therefore preserve routing relationships through certain local control-plane switchovers and reduce service interruption.

Question 338. What is a key difference between NSR and NSF based on Graceful Restart?

1. NSR requires every neighboring router to restart simultaneously
2. NSF never preserves forwarding
3. NSR operates only at Layer 2
4. NSR can restore synchronized routing state locally, whereas NSF/GR relies on cooperation from neighboring devices

Correct Answer: 4. NSR can restore synchronized routing state locally, whereas NSF/GR relies on cooperation from neighboring devices

Explanation:

NSR and NSF both aim to minimize service interruption during control-plane failures or switchovers, but their recovery models differ. Huawei states that NSR synchronizes routing state internally between active and standby control boards, so the standby can take over without depending on peripheral devices. NSF is implemented using Graceful Restart and relies on neighbors acting as GR helpers to preserve forwarding and routing information while the restarting device’s control plane recovers. NSR can therefore provide stronger local independence, although it requires continuous state synchronization and can consume additional device resources.

Question 339. What is the PRIMARY purpose of In-Service Software Upgrade (ISSU)?

1. To configure a new VLAN automatically
2. To replace the standby main board permanently
3. To minimize service traffic interruption during a system software upgrade or rollback
4. To detect M-LAG split-brain conditions

Correct Answer: 3. To minimize service traffic interruption during a system software upgrade or rollback

Explanation:

Traditional software upgrades often require a device restart, which can interrupt forwarding and network services. Huawei ISSU is designed to reduce this impact by upgrading active and standby processing components in coordinated phases. A standby processing unit can start with the new software, state can be synchronized, and an active/standby switchover can then occur before the original active unit is upgraded. Huawei also provides rollback mechanisms for supported ISSU operations. ISSU therefore improves maintenance availability, although administrators must confirm version compatibility and platform-specific ISSU requirements before performing an upgrade.

Question 340. A campus core requires simplified logical management, redundant chassis forwarding, active use of links from downstream switches, protection against split-brain conditions, and minimal disruption during software maintenance. Which design BEST addresses these requirements?

1. Use CSS or stacking with cross-device link aggregation and DAD, together with supported ISSU/NSR reliability features
2. Use one standalone switch with no redundancy
3. Use only STP and static default routes
4. Use DHCP snooping as the core availability technology

Correct Answer: 1. Use CSS or stacking with cross-device link aggregation and DAD, together with supported ISSU/NSR reliability features

Explanation:

The requirements span device virtualization, link redundancy, split protection, and control-plane maintenance. CSS or stacking can combine multiple physical switches into one logical system, simplifying management and supporting inter-device link aggregation so downstream links can be actively used. Dual-Active Detection protects against dangerous split conditions in which more than one partition might act as master. NSR can preserve routing state through supported control-board switchovers, while ISSU reduces service interruption during compatible software upgrades. Together, these mechanisms provide a much stronger high-availability campus-core design than relying on a single standalone chassis.