Huawei H12-821_V1.0 - HCIP-Datacom-Core Technology V1.0

Option A is false . When advertising a route to an IBGP peer, the BGP speaker does not modify the AS_Path. It simply advertises the route as-is , preserving the AS_Path learned from EBGP.

Clarification of the options:

B is correct: When a route is sent to an EBGP peer, the local AS is prepended to the AS_Path.

C is correct: The AS_Path begins with the local AS when a new route is advertised to an EBGP neighbor.

D is correct: IBGP does not modify AS_Path when passing routes within the same AS.

Reference from Huawei HCIP-Datacom-Core Technology Study Guide:

“BGP speakers prepend their AS number to the AS_Path only when advertising to EBGP peers. IBGP peers do not alter the AS_Path.”

(Chapter: BGP Path Attributes – Section: AS_Path)

Explanation of Root Port Election in STP:

In a Spanning Tree Protocol (STP) network, the Root Port is selected on each switch (except the Root Bridge). The Root Port is the port with the lowest path cost to the Root Bridge. If there is a tie in path cost, the following criteria are used in sequence to break the tie:

Steps for Root Port Election in Sequence:

RPC Comparison (Root Path Cost):

The port with the lowest Root Path Cost is preferred.

Root Path Cost is the cumulative cost of the path to the Root Bridge.

Peer BID (Bridge ID) Comparison:

If the Root Path Costs are equal, the Bridge ID of the connected switch (peer) is compared.

The port connecting to the switch with the lower Bridge ID is preferred.

Peer PID (Port ID) Comparison:

If the Bridge IDs are equal, the Port ID of the peer ' s sending port is compared.

The port connecting to the lower Port ID is preferred.

Local PID (Port ID) Comparison:

If all else is equal, the Local Port ID of the switch is used.

The port with the lower Local Port ID is selected.

In VRRP HSB (Hot Standby Backup) mode for WLAN deployments (typically between ACs or access controllers), backup of critical data ensures fast failover and minimal service disruption.

A. Real-time backup – Supported. Configuration and session information are synchronized in real-time between the active and standby ACs.

B. Scheduled synchronization – Not supported . HSB requires instant synchronization, not based on a scheduled time.

C. Batch backup – Supported. Some types of less time-sensitive data (e.g., logs or counters) may be backed up in batches.

D. Cloud backup – Not part of HSB functionality . Cloud backup is a separate mechanism, typically used for archival purposes, not real-time failover.

Reference from Huawei HCIP-Datacom-Core Technology Study Guide:

“VRRP HSB mode supports real-time and batch backup between ACs to protect WLAN services. Scheduled and cloud backups are not part of HSB functionality.”

(Chapter: WLAN Reliability – Section: AC Redundancy and HSB Mechanism)

A is false – The correct formula is: Skew_Time = (256 - Priority)/256 × Advertisement_Interval.

B is false – By default, the preemption delay is typically 0s , not 1s, meaning a higher-priority backup router can preempt immediately unless configured otherwise.

C is true – The default Advertisement interval in VRRP is 2 seconds .

D is true – The formula Master_Down_Interval = 3 × Advertisement_Interval + Skew_Time is correct.

Reference from Huawei HCIP-Datacom-Core Technology Study Guide:

“The VRRP Skew_Time is calculated as (256 - Priority)/256 × Adver_Interval. The Master_Down interval includes this Skew_Time to stagger failover.”

(Chapter: High Availability – Section: VRRP Timer Mechanism)

In Layer 3 roaming scenarios, STAs (stations) remain on different subnets before and after roaming. To ensure that user traffic reaches the original subnet, it must be tunneled back over a CAPWAP tunnel. This technique prevents disruptions in communication and enables seamless roaming. Huawei’s Layer 3 roaming design guidelines emphasize the use of CAPWAP tunnels for user traffic forwarding ​.

The question indicates that a router performs a lookup in its FIB table for a packet and determines that the tunnel ID in the matching entry is 0, suggesting that the packet needs to be forwarded through a tunnel such as an MPLS tunnel. However, this is a misunderstanding of the FIB functionality.

FIB Table Overview The Forwarding Information Base (FIB) is used to make packet-forwarding decisions. Entries in the FIB include next-hop information, which can be directly linked to an interface or a tunnel.

If the Tunnel ID is 0 , it indicates that the packet is forwarded via a normal routing path and not through a tunnel.

For MPLS or other tunnels, the Tunnel ID would have a non-zero value pointing to the associated tunnel.

MPLS Tunnel Operation When a router forwards packets through an MPLS tunnel, a label-switched path (LSP) is set up. The FIB would reflect specific tunnel identifiers for packets that need such encapsulation.

HCIP-Datacom-Core Reference

Routing Principles and MPLS ​explain the forwarding mechanisms clearly, stating that if a packet is routed normally, the tunnel ID remains 0 .

The section on MPLS​clarifies the encapsulation process and the role of tunnel identifiers.

Hence, the claim in the question is incorrect. A Tunnel ID of 0 implies no tunneling is required, and normal IP forwarding occurs

In a route-policy, attributes such as MED (Multi-Exit Discriminator) and Local-Preference can be used in apply clauses to influence BGP route selection. Attributes like AS_Path and Tag are typically matched or filtered but not directly applied in the apply clause ​.

ï‚· Permanent Group Addresses for Routing Protocols

The range 224.0.0.0 to 224.0.0.255 is reserved for local network protocols, including routing protocols. Examples include OSPF (224.0.0.5/6) and RIP (224.0.0.9).

ï‚· HCIP-Datacom-Core Reference

Reserved multicast address ranges are detailed in the multicast configuration sections​​.

The summary automatic command in BGP is used to enable automatic summarization of routes, particularly for classful networks. However, manual summarization takes precedence over automatic summarization when both are configured. This makes the statement claiming automatic summarization takes precedence false ​.