Huawei H12-821 Exam Questions
HCIP-Datacom-Core Technology V1.0 (Page 6 )

Updated On: 12-Jun-2026

Which command is used to enable association between BFD and VRRP?

  1. vrrp vrid 1 track bfd-session session-name 1 reduced 100
  2. vrrp vrid 1 track bfd-session-name 1 reduced 100
  3. bfd-session vrrp vrid 1 track session-name 1 reduced 100
  4. track vrrp vrid 1 bfd-session session-name 1 reduced 100

Answer(s): A

Explanation:

The command vrrp vrid 1 track bfd-session session-name 1 reduced 100 is used to enable the association between BFD (Bidirectional Forwarding Detection) and VRRP (Virtual Router Redundancy Protocol). Here's what each part of the command does:
1. vrrp vrid 1:
Specifies the VRRP group ID (1 in this case).

2. track bfd-session:
Configures VRRP to track the status of a BFD session.

3. session-name 1:
Refers to the specific BFD session name being tracked.

4. reduced 100:
Specifies the priority reduction value. If the BFD session goes down, the priority of the VRRP group will be reduced by 100.
By tracking the BFD session, VRRP can dynamically adjust its behavior (e.g., reducing priority) based on the status of the link monitored by BFD, which helps maintain redundancy and reliability.



BFD control packets are encapsulated in UDP packets for transmission.
What is the destination port number of multi-hop BFD control packets?

  1. 4784
  2. 2784
  3. 5784
  4. 3784

Answer(s): A

Explanation:

In BFD (Bidirectional Forwarding Detection), control packets are encapsulated in UDP packets for transmission. The destination port numbers differ based on the type of BFD:
Single-hop BFD: Uses UDP port 3784.

Multi-hop BFD: Uses UDP port 4784.

For multi-hop BFD, the higher destination port (4784) is used because it involves additional processing to validate multi-hop sessions.



One VRRP virtual router can only have the virtual IP address.

  1. TRUE
  2. FALSE

Answer(s): B

Explanation:

A VRRP (Virtual Router Redundancy Protocol) virtual router can have multiple virtual IP addresses.
While a single virtual IP address is commonly configured for simplicity, VRRP supports multiple virtual IPs to provide redundancy and load balancing for multiple subnets or networks.
Each virtual IP address is associated with the same VRRP group, and traffic destined for any of these addresses will be managed by the active router in the VRRP group.
This capability allows VRRP to handle multiple subnets more efficiently.
Thus, the statement that a VRRP virtual router can only have one virtual IP address is false.



The interface IP address and VRRP virtual IP address can be the same

  1. TRUE
  2. FALSE

Answer(s): A

Explanation:

In VRRP (Virtual Router Redundancy Protocol), the interface IP address of a router can be configured as the VRRP virtual IP address. This is a common practice and is fully supported by VRRP.
When the interface IP address and the VRRP virtual IP address are the same, the router owning that IP address is typically the Master router by default, as it has the highest priority (255).
This configuration simplifies the setup because the router with the interface IP address acts as the default gateway for the network when it is in the Master role.
Thus, the statement is true.



What is the default sending interval of BFD packets?

  1. 100ms
  2. 1000ms
  3. 10s
  4. 5s

Answer(s): A

Explanation:

The default sending interval for BFD (Bidirectional Forwarding Detection) packets is 100 milliseconds (ms). This interval is used to rapidly detect faults in the communication path between two systems.
BFD operates with high speed and precision, enabling the detection of link failures within milliseconds.
The 100ms default interval can be adjusted depending on the requirements for failure detection speed and network stability.



Which of the following statements about a DHCP server on a large-scale Layer 3 WLAN are false? (Choose all that apply.)

  1. APs can obtain the AC's IP address from a DHCP server using Option 43.
  2. APs can obtain the AC's IP address from a DHCP server using Option 60.
  3. An independent DHCP server is recommended.
  4. The AC is recommended as a DHCP server.

Answer(s): B,D

Explanation:

APs can obtain the AC's IP address from a DHCP server using Option 43.
True: Option 43 is specifically used in DHCP to provide the IP address of the Access Controller (AC) to Access Points (APs). This is a standard and widely used practice.
APs can obtain the AC's IP address from a DHCP server using Option 60.
False: Option 60 is used to convey the Vendor Class Identifier (VCI) from the AP to the DHCP server, identifying the type of device. It does not provide the AC's IP address.
An independent DHCP server is recommended.
True: For large-scale Layer 3 WLAN deployments, an independent and centralized DHCP server is recommended to handle the large number of clients and ensure scalability and reliability.
The AC is recommended as a DHCP server.
False: Using the AC as a DHCP server is not recommended in large-scale Layer 3 WLAN deployments. The AC has limited resources, and adding DHCP functionality can affect its performance. A standalone or external DHCP server is more suitable in such scenarios.



As shown in the figure, data traffic from a STA is forwarded by the HAP to the upper-layer network in direct forwarding mode before roaming, and the HAP is configured as the home agent.
What is the flow direction of data traffic after Layer 3 roaming?

  1. STA -> FAP -> FAC -> HAC -> HAP -> Upper-layer network
  2. STA -> FAP -> FAC -> HAC -> HAP -> HAC -> Upper-layer network
  3. STA -> FAP -> FAC -> HAC -> Upper-layer network
  4. STA -> FAP -> FAC -> Upper-layer network

Answer(s): A

Explanation:

In this scenario:
The STA (station) is initially connected to the HAP (Home Access Point) and its data is forwarded to the upper-layer network in direct forwarding mode.
After Layer 3 roaming, the STA connects to the FAP (Foreign Access Point), which is in a different VLAN

and subnet.
Since the HAP is configured as the home agent, traffic from the STA must first traverse back to the HAP for processing before being sent to the upper-layer network.
Flow Direction After Layer 3 Roaming:
1. STA -> FAP: The STA connects to the Foreign Access Point after roaming.
2. FAP -> FAC (Foreign AC): The FAP sends the data to its associated controller, the FAC.
3. FAC -> HAC (Home AC): The FAC tunnels the traffic to the Home Access Controller (HAC), where the HAP resides.
4. HAC -> HAP: The HAC forwards the traffic to the HAP (home agent).
5. HAP -> Upper-layer network: The HAP processes the traffic and forwards it to the upper-layer network.



MAC address-prioritized Portal authentication allows disconnected users who have completed Portal authentication to directly access the network again within a certain period of time after the disconnection without having to perform Portal authentication again.

  1. TRUE
  2. FALSE

Answer(s): A

Explanation:

MAC address-prioritized Portal authentication allows a user who has already completed Portal authentication to bypass the authentication process if they reconnect to the network within a configured time period. This is achieved by associating the user's MAC address with their authenticated session. The mechanism works as follows:
6. Authentication Tracking by MAC Address: After a user authenticates via Portal, their MAC address is recorded along with the authentication information.
7. Reconnection within a Certain Period: If the user disconnects and reconnects to the network within the specified timeout period, the MAC address is recognized, and the user is allowed network access without repeating the Portal authentication process.
8. Enhanced User Experience: This avoids unnecessary authentication prompts for frequent reconnects, improving the overall user experience.
Thus, the statement is true.



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