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

Comprehensive and Detailed Step-by-Step Explanation:

BGP Route Filtering:

BGP provides flexible policies for route filtering to optimize routing table size and reduce network resource usage.

By configuring route filters, a device can advertise only required routes to peers, thereby improving efficiency.

Purpose of Filtering:

Reduces the routing table size.

Decreases CPU and memory usage on routers.

Limits unnecessary route propagation.

References:

HCIA-Datacom Study Guide, Chapter: BGP Policy Control

Huawei BGP Route Filtering Configuration

 Link fault alarm

 The BFD session goes down.

 Interrupted OSPF neighbor relationship

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 ​.

In the PIM protocol, Register Stop and Graft messages are sent with unicast destination addresses, typically to specific neighbors or RP (Rendezvous Point) routers. Other messages like Bootstrap and Assert use multicast addresses for broader dissemination across the network ​.

Understanding DIS Election in IS-IS:

On an IS-IS broadcast network, a Designated Intermediate System (DIS) is elected to create and update pseudonodes for efficient communication.

The election is based on the following criteria:

DIS Priority: The router with the highest priority is elected as the DIS.

Router ID (tie-breaker): If priorities are equal, the router with the highest Router ID is elected.

Analyzing the DIS Priorities and Router IDs:

R1: Priority = 64, Router ID = 1.1.1.1

R2: Priority = 1, Router ID = 2.2.2.2

R3: Priority = 127, Router ID = 3.3.3.3

R4: Priority = 10, Router ID = 4.4.4.4

Among the routers, R3 has the highest DIS priority (127), making it the DIS.

Correct Option:

Option B (R3): Correct, as R3 has the highest priority.

Option A (R1): Incorrect, as its priority is lower (64).

Option C (R4): Incorrect, as its priority is lower (10).

Option D (R2): Incorrect, as its priority is the lowest (1).

References:

HCIA-Datacom Study Guide, Chapter: IS-IS DIS Election

Huawei IS-IS Configuration and DIS Role Details

Comprehensive and Detailed Step-by-Step Explanation:

1. What is First-Time Authentication in SSH?

When an SSH client connects to an SSH server for the first time, the server's public key is not yet known to the client.

Enabling first-time authentication allows the SSH client to accept the server's public key and save it for future connections. This feature eliminates the need for manual configuration of the server's public key on the client.

2. Process Explanation:

The SSH client connects to the server and receives the server's public key.

The client accepts the key and saves it in its local key database (e.g., known_hosts file).

For subsequent connections, the client uses the saved public key to authenticate the server.

3. Why the Statement is TRUE:

First-time authentication simplifies SSH setup and is a commonly used method when connecting to new servers. It ensures that future connections are authenticated using the saved public key.

 MQC and PBR

MQC (Modular QoS Command-Line Interface): Applied to interfaces for classifying and controlling traffic.

PBR (Policy-Based Routing): Used to influence packet forwarding based on policies rather than traditional routing tables.

Both MQC and PBR can be configured on device interfaces to filter incoming/outgoing packets or control their forwarding paths.

 HCIP-Datacom-Core Reference

The use of MQC and PBR on device interfaces is elaborated in the QoS and routing control chapters​​.

1. Understanding Prefix List Configuration:

The command ip ip-prefix huawei index 10 permit 10.1.1.0 24 greater-equal 26 defines a prefix filter:

The base prefix is 10.1.1.0/24.

The greater-equal 26 condition specifies that the mask length of matching prefixes must be at least 26 bits.

If the less-equal parameter is not explicitly defined, the default value is 32, meaning the longest possible mask length for IPv4.

2. Explanation of Values:

greater-equal-value: Specifies the minimum mask length. In this case, the value is 26.

less-equal-value: Specifies the maximum mask length. Since it is not explicitly configured, the default value is 32.

3. Summary:

greater-equal-value = 26

less-equal-value = 32

The command output indicates that the OSPF neighbor state is Full and that the neighbor relationship has been established. The statement confirms that the negotiation process during the exchange of DD (Database Description) packets has determined the role of the router, with the local device becoming the slave in the Master-Slave relationship, which is critical for LSA synchronization. The other options do not align with the output or OSPF principles ​

The correct command for configuring the VRRP (Virtual Router Redundancy Protocol) preemption delay is vrrp vrid 1 preempt-delay 20. This command sets the delay before a higher-priority VRRP router preempts the master role, ensuring stable operation during network transitions ​.

Understanding DHCPv6:

DHCPv6 (Dynamic Host Configuration Protocol for IPv6) is used to assign configuration parameters to IPv6 clients.

It supports both stateful and stateless modes:

Stateful: Assigns IPv6 addresses and other configuration parameters.

Stateless: Assigns only configuration parameters (e.g., DNS server) without providing IPv6 addresses.

 During WLAN roaming, the STA sends a Reassociation Request frame to the foreign AP to maintain connectivity. Association frames are used during initial connections, not roaming.

 APs with which a STA is associated before and after roaming can work on different channels, as roaming often occurs across channels in environments like multi-SSID or multi-channel setups.Options C and D are false, as they contradict standard WLAN roaming procedures ​.

RSTP improves convergence by introducing changes to the BPDU handling mechanism and port roles. However, RSTP does not rely on a fixed timeout of four Hello intervals for negotiation failure. Instead, RSTP uses a more dynamic mechanism to detect topology changes. The other options describe valid RSTP improvements ​.

Comprehensive and Detailed Step-by-Step Explanation:

1. What is NETCONF?

NETCONF (Network Configuration Protocol) is an XML-based protocol used for network device configuration and management.

It enables reading, modifying, deleting, and restoring configurations programmatically.

2. Supported Operations:

Option A: Modifying configurations

Correct.

NETCONF allows you to modify existing configurations on network devices.

Option B: Deleting configurations

Correct.

Configurations can be deleted using NETCONF operations.

Option C: Restoring configurations

Correct.

NETCONF can restore configurations by applying previously saved configuration data.

Option D: Backing up configurations

Correct.

NETCONF can retrieve and save the current configuration as a backup.

3. Summary:

NETCONF supports all listed operations: modifying, deleting, restoring, and backing up configurations.

Comprehensive and Detailed Step-by-Step Explanation:

Default Next Hop Behavior in BGP:

Locally Originated Routes (A): The next hop is set to the advertising router's interface IP address.

Routes Received from EBGP (B): The next hop is not changed when these routes are advertised to IBGP peers. (This makes Option B false.)

Routes Advertised to EBGP (C): The next hop is set to the interface IP address of the advertising router.

Routes Advertised Between IBGP Peers (D): The next hop is not modified by default.

Incorrect Statement:

Option B is incorrect because the next hop of a non-labeled route received from an EBGP peer is not changed when it is advertised to IBGP peers.

References:

HCIA-Datacom Study Guide, Chapter: BGP Next Hop Behavior

Huawei BGP Routing Principles

OSPF (Open Shortest Path First) mandates that the backbone area (Area 0) serves as the central area for routing information exchange. To avoid inter-area routing loops, routing information is only exchanged between the backbone area and non-backbone areas, not directly between two non-backbone areas. Consequently, each Area Border Router (ABR) must connect to the backbone area to facilitate this routing exchange ​.

Comprehensive and Detailed Step-by-Step Explanation:

1. What is GRE (Generic Routing Encapsulation)?

GRE is a tunneling protocol that allows the encapsulation of various types of packets (e.g., IPv4, IPv6, multicast, etc.) to be transmitted over another protocol (e.g., IP).

GRE is used to create point-to-point connections over heterogeneous networks.

2. Analysis of Each Option:

Option A: GRE is a Layer 2 VPN encapsulation technology.

Incorrect.

GRE operates at Layer 3 (Network Layer) and encapsulates Layer 3 packets. It is not a Layer 2 VPN encapsulation technology like MPLS or Ethernet-over-IP.

Option B: GRE enables encapsulated data packets to be transmitted over another network layer protocol, but cannot encapsulate multicast data.

Incorrect.

GRE supports the encapsulation and transmission of multicast data packets. This is one of its key features, making it suitable for protocols like OSPF and multicast applications.

Option C: GRE tunnels can work with IPsec to ensure the security of multicast services such as voice and video.

Correct.

GRE by itself does not provide encryption or security. However, GRE can work with IPsec to secure the encapsulated traffic, including multicast data, for services like voice and video.

Option D: GRE tunnels can extend the working range of network protocols with hop limits.

Correct.

GRE encapsulates packets, effectively resetting their hop limits and allowing protocols with limited hop counts (e.g., RIP) to work over larger networks.

3. Summary:

The correct options are C and D.

 R1 is a Level-1 router in Area 49.0001, while R4 is in Area 49.0004. Level-1 routers only maintain LSDBs for their own area and do not contain LSPs from other areas, such as R4’s LSP.

 R2 is a Level-1-2 router, so it maintains LSDBs for both Area 49.0001 (Level-1) and Level-2 domains, which include LSPs from R4.

 R3 and R4, as Level-2 routers, exchange LSPs with each other within the Level-2 domain.

 Thus, the LSDB of R1 does not include R4’s LSP ​.

Application Specific Packet Filtering (ASPF) is a feature that allows the firewall to understand and handle multi-channel protocols such as FTP, H.323, and SIP. ASPF inspects the control channel to dynamically create temporary rules for the data channels, enabling the firewall to secure and manage complex application protocols. This feature ensures that appropriate security policies are applied to these multi-channel applications ​.

 BGP Next_Hop Attribute

Unlike IGP, the Next_Hop attribute in BGP does not necessarily have to be the IP address of a peer interface. For example, in multi-hop BGP configurations, the Next_Hop can point to a different router or interface within the network.

 HCIP-Datacom-Core Reference

Details of the Next_Hop attribute and its behavior are outlined in BGP path selection principles​​.

 ACL Number Ranges

Basic ACLs: Numbered from 2000 to 2999.

Advanced ACLs: Numbered from 3000 to 3999.

Layer 2 ACLs: Numbered from 5000 to 5999.

User-defined ACLs: Numbered from 4000 to 4999.

 HCIP-Datacom-Core Reference

ACL classifications and their number ranges are covered in the ACL principles and configuration chapters​​.

Comprehensive and Detailed Step-by-Step Explanation:

1. Understanding Hybrid Interfaces on a Layer 2 Switch:

Layer 2 switches support different interface types, such as access, trunk, and hybrid interfaces.

A trunk interface allows traffic from multiple VLANs to pass through, but frames belonging to the native VLAN are sent untagged, while all other VLAN frames are tagged.

A hybrid interface is more flexible:

It allows traffic from multiple VLANs to pass through, just like a trunk interface.

However, you can configure whether frames for specific VLANs are tagged or untagged as they leave the interface. This feature is useful in certain networking scenarios, such as connecting devices that do not support VLAN tagging.

2. Key Differences Between Trunk and Hybrid Interfaces:

A screenshot of a computer Description automatically generated

3. Why the Statement is TRUE:

The statement accurately describes the functionality of a hybrid interface:

It supports traffic from multiple VLANs.

It allows administrators to configure whether outgoing frames are tagged or untagged for specific VLANs.

4. Summary:

The statement is TRUE because hybrid interfaces on a Layer 2 switch support traffic from multiple VLANs and allow flexible tagging configurations.

The DHCPNAK message is sent by the DHCP server to the client to indicate that the requested configuration is not valid. Messages like DHCPDiscover, DHCPRequest, and DHCPRelease are initiated by the client in the DHCP process ​.

Comprehensive and Detailed In-Depth Explanation:

Router LSAs (Type 1 LSAs) are generated by every OSPF router to describe its directly connected links and their states.

The E (External) bit in the Options field of a Type 1 LSA indicates whether the router is acting as an Autonomous System Boundary Router (ASBR).

If E = 1, it means that the router is an ASBR, which means it is redistributing external routes (e.g., BGP, static routes) into OSPF.

IR (Internal Router), ABR (Area Border Router), and DR (Designated Router) do not set the E-bit in their Router LSA unless they are also ASBRs.

???? Reference: Huawei HCIA-Datacom Study Guide, OSPF Router Types and LSA Options.

 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).

 HCIP-Datacom-Core Reference

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

Comprehensive and Detailed In-Depth Explanation:

Internal Router (IR): A router that exists entirely within a single OSPF area (e.g., Area 0). It does not have to be a Border Router (BR).

Area Border Router (ABR): A router that connects two or more OSPF areas. It maintains separate LSDBs for each area and forwards summary LSAs between them.

Autonomous System Boundary Router (ASBR): A router that connects the OSPF domain to an external network (e.g., BGP, another OSPF AS).

The statement is false because:

An IR in Area 0 does not have to be a BR (Border Router). It can just be a normal internal router.

An ASBR does not have to be an ABR. An ASBR can exist inside any OSPF area, even a single area, without needing to connect multiple areas.

???? Reference: Huawei HCIA-Datacom Study Guide, OSPF Router Types and Area Concepts.

When configuring VRRP, the virtual router priority and virtual IP address are mandatory because they define the VRRP instance and its role within the group. Preemption mode and preemption delay are optional configurations that influence how routers take over the master role when priorities change. These are not mandatory for the VRRP protocol to function ​.

The Forwarding Information Base (FIB) is derived from the router's routing table and contains the exact forwarding entries used to route packets. It directly guides packet forwarding decisions by matching incoming packets with the correct output interface or next-hop address ​.

Comprehensive and Detailed Step-by-Step Explanation:

1. Port Priority in RSTP:

RSTP (Rapid Spanning Tree Protocol) elects root and designated ports based on port priority and port ID.

Port priority is a configurable value that helps determine which port becomes the root or designated port when multiple ports are eligible.

The port ID consists of the port priority and port number. When priorities are equal, the port number is used as a tiebreaker.

2. Default Port Priority on Huawei Switches:

On Huawei switches, the default port priority is 128.

This value can be adjusted in increments of 16 using the command stp port priority.

3. Analysis of Options:

Option A: 1

Incorrect. This is not the default port priority value.

Option B: 128

Correct. This is the default port priority value on Huawei switches.

Option C: 4096

Incorrect. This is not a valid default port priority value.

Option D: 32768

Incorrect. This is the default bridge priority, not the port priority.

4. Summary:

The default port priority on Huawei switches is 128.

Comprehensive and Detailed Step-by-Step Explanation:

Packet Filtering Firewall:

A packet filtering firewall inspects packets at the network and transport layers based on predefined rules (e.g., ACLs).

Correct Statements:

Option B: Packet filtering is performed on a per-packet basis.

Option D: ACLs define the filtering rules for traffic.

Incorrect Statements:

Option A: Packet filtering firewalls do not analyze associated packets. For this, a stateful firewall is required.

Option C: Application-layer inspection is not supported. This functionality is provided by application-layer firewalls.

References:

HCIA-Datacom Study Guide, Chapter: Firewalls

Huawei Firewall Packet Filtering Configuration

The route-policy configuration specifies that node 10 matches the IP prefix 11.1.0.0/16 and applies a cost of 300 to this route. Once a route matches a node, it is no longer processed by subsequent nodes, making option D incorrect. Option B is also incorrect because only specific matching routes have their costs changed ​.

 VRRP and BFD Association:

VRRP (Virtual Router Redundancy Protocol) is used to provide gateway redundancy by electing a master and backup router.

Associating VRRP with BFD (Bidirectional Forwarding Detection) allows faster detection of faults on the master device or the link between the master and the backup.

Access Control Lists (ACLs) can be classified into several types, including Basic ACL (filters based on source IP), Advanced ACL (filters based on multiple parameters like source and destination IP, protocol, and ports), and Layer 2 ACL (filters based on MAC addresses). User-defined ACLs are not a standard classification ​.

The scenario describes a mismatch in OSPF network types between two connected routers: one set to Point-to-Point (P2P) and the other set to Point-to-Multipoint (P2MP). While aligning Hello intervals may seem sufficient for establishing an OSPF neighbor relationship, the fundamental mismatch in network types introduces issues.

OSPF Network Types

P2P: Assumes a direct connection with a single neighbor, uses faster convergence and simpler LSDB synchronization.

P2MP: Supports multiple neighbors on a single interface, requiring different handling for DR/BDR roles and LSDB updates.

Impact of Network Type Mismatch

If Hello intervals are aligned, adjacency establishment might occur. However, mismatched network types affect neighbor role assignment and LSDB synchronization.

P2P expects a direct link and would handle updates differently than P2MP, which assumes multiple neighbors. This leads to inconsistencies in route calculation and forwarding.

HCIP-Datacom-Core Reference

OSPF Basics and Configuration​clearly outlines the criticality of consistent network type configuration for stable OSPF operation.

Lab examples in the HCIP Datacom Lab Guide​further demonstrate the consequences of such mismatches, including unstable neighbor states and incomplete LSDB synchronization.

Hence, the statement that neighbor relationships and LSDB synchronization remain unaffected is incorrect. Proper OSPF operation requires matching network types in addition to aligned Hello intervals.

Root protection ensures that a designated port does not become a root port by discarding superior BPDUs. However, if superior BPDUs are no longer received, the port can return to its original forwarding state, meaning its role can change. This makes option B incorrect, while the other options correctly describe RSTP behavior ​.

Comprehensive and Detailed in-depth Step-by-Step Explanation:To answer this question, we need to understand the roles of OSPF routers:

Area Border Router (ABR):

An ABR is a router that connects multiple OSPF areas. It has at least one interface in the backbone area (Area 0) and one or more interfaces in other OSPF areas.

The ABR performs summarization between areas and propagates routing information between them.

Backup Router (BR):

The term "BR" does not exist in OSPF terminology. Instead, OSPF uses the term "Backup Designated Router (BDR)." The BDR is a backup to the Designated Router (DR) in a specific OSPF broadcast or NBMA (Non-Broadcast Multi-Access) network. The BDR takes over the DR's responsibilities if the DR fails.

Key Clarification:

An ABR is related to the hierarchical structure of OSPF areas and is not tied to the DR/BDR election process.

A router can function as an ABR without ever being a DR or BDR, as these are separate roles.

Therefore, the statement that an ABR must also be a BR is FALSE.

References:

Huawei HCIA-Datacom Study Guide, Chapter on "OSPF Fundamentals".

RFC 2328 – OSPF Version 2.

Huawei OSPF Configuration Guide.

Comprehensive and Detailed Step-by-Step Explanation:

1. Understanding the AS-Path Filter:

The as-path-filter command is used in BGP to filter routes based on the AS_PATH attribute.

In this configuration:

The filter si is defined with the regular expression _65500$.

The _65500$ expression specifies that the AS_PATH must end with 65500, meaning that the route's last hop must have passed through AS 65500.

2. Option Analysis:

Option A: It accepts only the routes whose AS_Path contains AS 65500.

Incorrect.

The _65500$ filter specifically matches routes where AS 65500 is the last AS in the AS_PATH. A route may contain AS 65500 somewhere in the middle of the AS_PATH but will not match this filter unless it is the last AS.

Option B: It accepts only the routes originated from AS 65500.

Incorrect.

Routes that originate from AS 65500 have an AS_PATH that starts with 65500. However, the filter _65500$ only matches routes where AS 65500 is the last AS, not the first AS.

Option C: It accepts only the routes that last pass through AS 65500.

Correct.

The _65500$ filter ensures that the AS_PATH ends with 65500. This means that the route must have last passed through AS 65500 before being received by the local BGP router.

Option D: It accepts only the routes forwarded by AS 65500.

Incorrect.

While AS 65500 may forward the route, this is not what the filter _65500$ specifically checks for. It only ensures that AS 65500 is the last AS in the AS_PATH.

3. Summary:

The as-path-filter with _65500$ accepts only the routes where AS 65500 is the last AS in the AS_PATH.

 DIS and DR Election

The IS-IS Designated Intermediate System (DIS) is responsible for generating and updating pseudonode LSPs on a broadcast network.

Unlike OSPF DR, the IS-IS DIS does not preempt by default. This behavior avoids unnecessary flapping in the network due to frequent DIS re-elections.

 HCIP-Datacom-Core Reference

The characteristics of DIS and DR behavior are explained in IS-IS network operation chapters​​.

Understanding the LSDB and Level-2 DIS Election in IS-IS:

In IS-IS, the Designated Intermediate System (DIS) is elected for both Level-1 and Level-2 on broadcast networks to manage the link-state database (LSDB) and reduce the number of LSAs exchanged.

The election of the DIS is based on the highest priority. If the priority is the same, the router with the highest System ID becomes the DIS.

 Neighbor Discovery Protocol (NDP):

NDP is a key protocol in the IPv6 protocol suite, replacing ARP (Address Resolution Protocol) in IPv4.

It operates using ICMPv6 (Internet Control Message Protocol for IPv6) and is critical for managing interactions between IPv6 nodes on the same link.

Comprehensive and Detailed Step-by-Step Explanation:

1. Overview of BFD Optimization:

BFD (Bidirectional Forwarding Detection) is a protocol that provides rapid detection of link failures.

Optimizing BFD involves adjusting parameters to balance between detection speed and network stability.

2. Analysis of Each Statement:

Option A: After a high priority is configured for BFD packets, BFD packets are preferentially forwarded.

Correct (True Statement).

High priority ensures that BFD packets are not delayed or dropped under congestion, improving detection accuracy.

Option B: To quickly learn about the network status and performance requirements, you can set the interval for sending BFD packets to the minimum value.

Incorrect (False Statement).

Setting the interval to the minimum value can lead to excessive BFD session flapping, which may overload the network or cause instability. The interval should be configured based on network requirements and conditions, rather than set to the minimum.

Option C: On a live network, some devices switch traffic only when a BFD session changes to the Up state... configure a delay to compensate for the time difference.

Correct (True Statement).

This is a valid optimization to avoid issues caused by timing mismatches between BFD and routing protocols.

Option D: If a BFD session flaps, master/backup switchovers are frequently performed... set the WTR time.

Correct (True Statement).

The WTR (Wait to Restore) timer helps stabilize BFD by delaying session recovery after a flap, reducing the risk of frequent switchovers.

3. Summary:

The false statement is B, as setting the BFD packet interval to the minimum can destabilize the network.

According to BGP route selection rules, a higher Local_Pref value indicates a more preferred route. This rule is used to influence traffic flow within an autonomous system (AS), giving preference to routes with a higher Local_Pref for outgoing traffic ​.

 ACL in Routing Policies

ACLs are frequently used in routing policies to match specific routes based on criteria such as source IP, destination IP, and more. This allows ACLs to influence route redistribution, filtering, and forwarding decisions.

 HCIP-Datacom-Core Reference

ACL applications in routing policies are discussed in the routing policy chapters​​.

When OSPF routers exchange LSDBs using Database Description (DD) packets, they first establish a master-slave relationship. The router with the larger Router ID becomes the master, setting the MS (Master/Slave) bit in the DD packets. This hierarchical relationship ensures an orderly exchange of routing information ​.

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 OverviewThe 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 OperationWhen 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

Comprehensive and Detailed In-Depth Explanation:

STP (Spanning Tree Protocol) BPDUs do not contain an explicit port role field. Instead, roles are determined indirectly.

RSTP (Rapid Spanning Tree Protocol) modifies BPDU structure by using the Flags field to indicate:

Port roles (Root, Designated, Alternate, Backup)

Proposal/Agreement (P/A) handshake mechanism

The correct field that specifies the port role in RSTP BPDUs is Flags.

???? Reference: Huawei HCIA-Datacom Study Guide, RSTP BPDU Structure and Flags Field.

 Export Routing Policy Changes

When an export routing policy is modified, BGP does not automatically resend affected routes. Manual intervention, such as a clear ip bgp command, is required to resend Update messages reflecting the new policy.

 Incorrect Options

B. IGP routes can also be advertised into BGP using redistribution, not just the network command.

C. A router can be configured with multiple BGP processes using different AS numbers (multi-instance BGP).

D. Open messages carry additional parameters such as AS number, Hold Time, and Router ID, not just the header.

 HCIP-Datacom-Core Reference

BGP policy and update behavior are detailed in the route control and redistribution chapters​​.

Comprehensive and Detailed Step-by-Step Explanation:

IS-IS Three-Way Handshake:

IS-IS uses a three-way handshake to establish neighbor relationships.

This process is applied on both point-to-point (P2P) and broadcast network types to confirm bidirectional communication.

P2P Networks:

Routers directly exchange IS-IS Hello (IIH) packets to establish adjacency.

Broadcast Networks:

IS-IS also uses the three-way handshake on broadcast networks to ensure that the Designated Intermediate System (DIS) election and adjacency formation are correct.

References:

HCIA-Datacom Study Guide, Chapter: IS-IS Adjacency Establishment

Huawei IS-IS Network Configuration

Comprehensive and Detailed In-Depth Explanation:

A. TRUE → EBGP-learned routes can be advertised to both IBGP and EBGP peers.

B. FALSE → BGP uses incremental updates, meaning it only advertises changed routes, not all routes.

C. TRUE → BGP advertises only the best path to prevent unnecessary routing information.

D. TRUE → IBGP split-horizon rule: Routes learned from IBGP peers are not re-advertised to other IBGP peers (to prevent loops).

???? Reference: Huawei HCIA-Datacom Study Guide, BGP Route Advertisement and Split-Horizon Rule.

The preference of routing protocols determines the selection order of routes when a router receives multiple routes to the same destination from different routing protocols. For instance, OSPF has a higher preference over RIP, so OSPF routes will be selected first. Huawei routing preferences confirm this behavior ​.

Comprehensive and Detailed In-Depth Explanation:

IP Multicast vs. Broadcast:

A. TRUE → Unlike broadcast, which sends data to all hosts in a subnet, multicast only sends data to interested receivers, preventing flooding.

B. TRUE → Multicast optimizes bandwidth usage by sending a single copy of data, which is then replicated at network routers only when necessary.

IP Multicast vs. Unicast:

C. FALSE → Multicast does not improve security; it may expose data to unintended receivers if not properly controlled.

D. FALSE → Multicast reduces the load on the source because a single data stream serves multiple receivers instead of sending individual unicast streams.

???? Reference: Huawei HCIA-Datacom Study Guide, IP Multicast Principles and Benefits.

BFD control packets are encapsulated in UDP packets, and the destination port number for multi-hop BFD control packets is 4784. This is a standardized port for multi-hop BFD operation ​.

A stateful inspection firewall tracks the state of active connections. If a packet matches an existing session in the firewall's state table, it is allowed to pass. The diagram indicates that the TCP packet matches the session state, so the firewall forwards it ​.

IGMP Version Mismatch

If the IGMP snooping version on the device is earlier than the IGMP version on user hosts, the device may fail to parse IGMP Report messages correctly. As a result, the device forwards these messages only to router ports without generating group member ports or forwarding entries.

Consequently, users cannot receive multicast data.

HCIP-Datacom-Core Reference

Multicast and IGMP snooping behaviors under mismatched conditions are described in the multicast configuration chapters​​.

In the given topology, the route from R4 to 10.0.2.2/32 traverses R3, which performs route leaking from Level-2 to Level-1. The cost is calculated as follows: R4 to R3 (40) + R3 to R2 (10) + R2 to the destination (30), resulting in a total cost of 80 ​.

Comprehensive and Detailed Step-by-Step Explanation:

Distance-Vector Protocols:

Distance-vector protocols determine the best path based on the distance to a destination and periodically share the entire routing table with neighbors.

Example: RIP is a distance-vector protocol.

Link-State Protocols:

Link-state protocols share information about directly connected links, enabling routers to build a complete map of the network.

OSPF (Open Shortest Path First) and IS-IS (Intermediate System to Intermediate System) are link-state protocols that use Dijkstra’s algorithm to calculate the shortest path.

Border Gateway Protocol (BGP):

BGP is neither a distance-vector nor a link-state protocol. Instead, it is classified as a path-vector protocol that selects the best path based on attributes such as AS-path, next-hop, and local preference.

References:

HCIA-Datacom Study Guide, Chapter: Routing Protocol Basics

Huawei Networking Fundamentals, Section: Classification of Routing Protocols

Comprehensive and Detailed Step-by-Step Explanation:

Default OSPF Hello Timer:

The OSPF Hello timer is used to send periodic Hello packets and maintain neighbor relationships.

Default Hello timers:

Broadcast and P2P: 10 seconds

NBMA and P2MP: 30 seconds

Network Types Using 30s Hello Time:

P2MP (C): OSPF sends Hello packets every 30 seconds by default.

NBMA (D): OSPF also uses 30 seconds for NBMA networks.

References:

HCIA-Datacom Study Guide, Chapter: OSPF Network Types

Huawei OSPF Timer Configuration

Comprehensive and Detailed Step-by-Step Explanation:

BGP Router ID Selection Rules:

If a router ID is not manually configured:

The largest loopback address is selected as the router ID.

If no loopback interfaces exist, the largest active physical interface address is selected.

Default Behavior:

This ensures that a stable and unique router ID is chosen automatically, even without manual configuration.

References:

HCIA-Datacom Study Guide, Chapter: BGP Router ID

Huawei Routing Device Configuration

Comprehensive and Detailed Step-by-Step Explanation:

1. How Firewalls Match Security Policies:

Firewalls use security policies to define rules for filtering traffic.

Each policy contains matching conditions (e.g., source IP, destination IP, protocol, etc.) and an action (e.g., permit or deny).

Traffic is evaluated against these policies in sequential order, and the first matching policy is applied.

2. Analysis of Each Statement:

Option A: Multiple values can be configured for a single matching condition, and the values are logically ANDed.

Incorrect.

Multiple values for a single matching condition (e.g., multiple source IPs) are logically ORed, not ANDed. For example, traffic from any of the specified source IPs matches the policy.

Option B: If a security policy contains multiple matching conditions, the relationship between them is AND.

Correct.

When a policy has multiple matching conditions (e.g., source IP AND destination IP AND protocol), all conditions must be met for the policy to match.

Option C: The system has a default security policy named default, where all matching conditions are any and the default action is permit.

Incorrect.

The default security policy typically denies all traffic unless explicitly permitted by user-defined policies.

Option D: When multiple security policy rules are configured, they are sorted in a list by configuration sequence by default. A security policy rule configured earlier is placed higher in the list and has a higher priority.

Correct.

Security policies are processed in sequential order based on their configuration sequence. Policies configured earlier have higher priority and are evaluated first.

3. Summary:

The correct statements are B and D.

Comprehensive and Detailed In-Depth Explanation:

IP Prefix lists are used to filter routes based on prefix and mask length.

The optional parameters include:

Index of the prefix list → Specifies priority/order (Optional).

Shortest mask length to be matched → Defines the minimum subnet mask (Optional).

Longest mask length to be matched → Defines the maximum subnet mask (Optional).

Mask length (D) is mandatory because it specifies the exact prefix length being matched.

???? Reference: Huawei HCIA-Datacom Study Guide, Configuring Prefix Lists for Route Filtering.

The traffic limiting policy feature supports not only limiting the number of connections initiated by or received by an IP address but can also apply other traffic metrics such as bandwidth or packet rates. This expanded capability makes the statement false ​.

The prefix list permits the prefix 1.1.1.1/24 with a mask length greater than or equal to /26 and less than or equal to /32. This means only prefixes with the base 1.1.1.1 and mask lengths between /26 and /32 will be permitted. Routes like 1.1.1.2/16 and 1.1.1.1/24 do not meet the mask length criteria, so they will be denied. Conversely, routes like 1.1.1.1/26 and 1.1.1.1/32 satisfy the condition and will be permitted ​.

When a stack splits, the MAC addresses of the newly formed stacks do not change immediately. Instead, they retain their original MAC addresses until new ones are reassigned during topology updates. This delayed update prevents immediate conflicts and allows MAD (Multiple Active Detection) to handle any resulting issues ​.

Comprehensive and Detailed In-Depth Explanation:

In IS-IS, routes are distributed differently based on router levels:

Level-1 (L1) routers → Maintain specific routes only within their own area.

Level-2 (L2) routers → Maintain specific routes for the entire network (inter-area routing).

Level-1-2 (L1/L2) routers → Store both L1 and L2 routes and act as area border routers.

In the diagram, R2 and R3 are L1/L2 routers, meaning they store specific routes for both their area and other areas.

R1 is only an L1 router, meaning it only has intra-area routes, and R7 is an L2-only router, meaning it does not store all specific routes.

Therefore, R2 and R3 have specific routes for the entire network.

???? Reference: Huawei HCIA-Datacom Study Guide, IS-IS Routing Levels and Route Distribution.

Comprehensive and Detailed In-Depth Explanation:

Type 1 LSAs (Router LSAs) are generated by every OSPF router to describe its directly connected links and their states.

The Router ID (RID) must be unique in an OSPF domain; otherwise, OSPF calculations will fail due to ambiguous paths.

If two routers in the same area have the same Router ID, OSPF will fail to calculate Shortest Path First (SPF) correctly, leading to routing inconsistencies.

To prevent this, Huawei routers automatically detect duplicate Router IDs and prevent OSPF from functioning properly until the issue is resolved.

???? Reference: Huawei HCIA-Datacom Study Guide, Chapter on OSPF LSAs and Router ID Uniqueness.

Goal Analysis:

Requirement:

The route to 192.168.3.0/24 must exist in R1's and R3's routing tables.

The route must not exist in R2's routing table.

This requires filtering to ensure the route is either:

Blocked on R2's routing table (via filtering on R2), or

Blocked before it is advertised to R2.

Analysis of Each Option:

Option A (Filter-policy on R2 for filtering received routes):

Applying a filter-policy on R2 to filter received routes will block the route from entering R2's routing table but still allow it to propagate to R3.

This meets the requirement.

Option B (Filter-policy on R2 for filtering the routes to be advertised):

Blocking the advertisement of routes from R2 to other routers does not affect the routes received by R2 itself.

This does not meet the requirement but does not affect the propagation to R3.

This is valid if the received route is blocked.

Option C (Filter-policy on R1 for filtering the routes to be imported):

If the route is filtered on R1 during the import phase, the route will not exist in R1’s routing table and thus cannot be advertised to either R2 or R3.

This fails to meet the requirement because the route must exist in R1's and R3's routing tables.

Option D (Filter-policy on R1 for filtering the imported routes to be advertised):

Filtering routes on R1 before advertising to R2 will prevent R2 from receiving the route but allow R1 to advertise the route to R3.

This meets the requirement.

Correct Option:

C (Filter-policy on R1 for filtering the routes to be imported): This will prevent the route from existing in both R1 and R3, violating the stated requirement.

References:

HCIA-Datacom Study Guide, Chapter: OSPF Route Filtering

Huawei OSPF Configuration and Filtering Methods

In asynchronous mode, two devices exchange BFD Control packets to monitor connectivity. However, this mode does support the echo function, which tests bidirectional paths by sending packets that loop back to the origin. This statement is incorrect. Demand mode, on the other hand, minimizes the control packet exchange, relying on periodic echo packets if configured. Huawei's BFD configuration guides emphasize these distinctions ​.

The CAPWAP heartbeat detection interval is typically multiplied by a predefined factor to determine the switchover time. For instance, in Huawei devices, a common default is three missed heartbeats before a switchover is triggered. With a detection interval of 20 seconds, the switchover occurs after 60 seconds (20 x 3). This ensures that transient network issues do not cause unnecessary switchovers ​.

 ACL Matching in Huawei Routers:

Access Control Lists (ACLs) are used to filter packets based on specific criteria, such as source/destination IP, ports, or protocols.

When a packet arrives, the Huawei router processes it against the configured ACL rules to decide whether to permit or deny the packet.

In a stateful inspection firewall, if the status detection mechanism is enabled, it tracks and validates the state of connections using the session table. If there is no session table and a SYN+ACK packet reaches the firewall, it checks the security policy. If the policy explicitly permits the packet, it will pass through the firewall, but no session table will be created without the initial SYN packet. The other options are either incorrect or misrepresent the behavior of stateful inspection ​.

Configuration Analysis:

On R2, the following configuration has been applied:acl 200rule deny source 10.1.0.0 0.0.3.0rule permit#ospf 1filter-policy 2000 import

On R2, the following configuration has been applied:acl 200rule deny source 10.1.0.0 0.0.3.0rule permit#ospf 1filter-policy 2000 import

On R2, the following configuration has been applied:acl 200rule deny source 10.1.0.0 0.0.3.0rule permit#ospf 1filter-policy 2000 import

On R2, the following configuration has been applied:acl 200rule deny source 10.1.0.0 0.0.3.0rule permit#ospf 1filter-policy 2000 import

On R2, the following configuration has been applied:acl 200rule deny source 10.1.0.0 0.0.3.0rule permit#ospf 1filter-policy 2000 import

On R2, the following configuration has been applied:acl 200rule deny source 10.1.0.0 0.0.3.0rule permit#ospf 1filter-policy 2000 import

On R2, the following configuration has been applied:acl 200rule deny source 10.1.0.0 0.0.3.0rule permit#ospf 1filter-policy 2000 import

On R2, the following configuration has been applied:acl 200rule deny source 10.1.0.0 0.0.3.0rule permit#ospf 1filter-policy 2000 import

This configuration uses ACL 200 to filter routes during import into the OSPF routing table on R2.

Rule deny source 10.1.0.0 0.0.3.0: Blocks routes in the range 10.1.0.0/24 to 10.1.3.0/24 (inclusive).

Rule permit: Allows all other routes to be imported.

Impact of ACL 200 on Route Import:

10.1.0.0/24 to 10.1.3.0/24: These subnets are explicitly denied by ACL 200 and will not appear in R2's routing table.

10.1.4.0/24 and beyond: These subnets are permitted by the rule permit statement and will be imported into R2's routing table.

Routing Table Entries on R2:

Option A (10.1.4.0/24): Exists in R2's routing table because it is permitted.

Option B (10.1.3.0/24): Does not exist because it is denied by ACL 200.

Option C (10.1.2.0/24): Does not exist because it is denied by ACL 200.

Option D (10.1.1.0/24): Does not exist because it is denied by ACL 200.

A (10.1.4.0/24)

Correct Options:References:

HCIA-Datacom Study Guide, Chapter: OSPF Route Filtering

Huawei ACL Configuration for Route Policies

Comprehensive and Detailed Step-by-Step Explanation:

1. Understanding LSA Filtering in OSPF and IS-IS:

The filter-policy command is used in OSPF and IS-IS to control which routing information is imported into the local routing table or advertised to other neighbors.

However, it cannot filter LSAs forwarded by neighbors. In OSPF and IS-IS, LSAs are always forwarded unchanged within the area to ensure all routers have a consistent link-state database.

Filtering only affects the routes that are installed into the local routing table or advertised to other areas or neighbors.

2. Why the Statement is False:

LSAs are forwarded without being filtered. This ensures link-state protocols maintain the same network topology view across the network.

The filter-policy import command only controls routes that are installed into the local routing table, not the forwarding of LSAs.

3. Summary:

The statement is FALSE because LSAs cannot be filtered by filter-policy import.

Comprehensive and Detailed in-depth Step-by-Step Explanation:To understand this question, let's first review the functional planes in network devices, particularly Huawei switches:

Control Plane:

The control plane is responsible for generating and maintaining routing tables and forwarding entries.

It uses protocols like OSPF, BGP, and RIP to exchange routing information with other network devices. Once the routing information is processed, it installs forwarding entries into the forwarding plane for actual packet forwarding.

On Huawei switches, the control plane is mandatory for building and updating the forwarding table. Without it, the data plane cannot forward traffic correctly.

Forwarding Plane (or Data Plane):

This plane handles the actual forwarding of packets based on the forwarding table created by the control plane.

The forwarding plane operates at high speed to ensure that traffic flows efficiently.

Monitoring Plane:

This plane is responsible for network management and monitoring. It gathers statistics and provides tools for troubleshooting and visibility.

In this case, the control plane provides the routing information and forwarding entries required for the data plane to perform packet forwarding. Therefore, the correct answer is B. Control plane.

References:

Huawei HCIA-Datacom Study Guide, Chapter on "Switch Architecture and Planes".

Huawei Official Documentation on Switching and Routing Basics.

Comprehensive and Detailed In-Depth Explanation:

A. TRUE → Firewalls maintain session tables with a default session timeout; adjusting it depends on network conditions.

B. FALSE → Fast session aging does not affect persistent connection sessions. Persistent connections (e.g., TCP keepalives) maintain sessions even if aging settings change.

C. TRUE → Sessions must be constantly matched with ongoing traffic to remain active.

D. TRUE → Even without stateful inspection, the firewall creates session entries for non-first packets to maintain continuity of services.

???? Reference: Huawei HCIA-Datacom Study Guide, Firewall Session Table Mechanism.

When STP and RSTP coexist in a network, RSTP switches will downgrade their operation to STP to ensure compatibility. However, this disables RSTP's rapid convergence features, as the protocol behaves like STP to maintain interoperability ​.

Comprehensive and Detailed In-Depth Explanation:

BGP uses TCP (not UDP) on port 179 to establish peer relationships.

Peer IP must be routable in both IBGP and EBGP, but BGP does not use UDP connections.

The statement is false because of the incorrect mention of UDP.

???? Reference: Huawei HCIA-Datacom Study Guide, BGP Session Establishment and TCP Usage.

 IS-IS Interface Types

IS-IS interfaces are categorized based on physical link characteristics:

Point-to-Point (P2P): Direct connections between two routers.

Broadcast: Shared medium networks where multiple routers communicate.

 Incorrect Options

C. P2MP and D. NBMA are not standard interface classifications in IS-IS.

 HCIP-Datacom-Core Reference

IS-IS physical link classifications are elaborated in IS-IS link configuration sections​​.

Comprehensive and Detailed In-Depth Explanation:

Type 7 LSAs (NSSA External LSAs) are used in Not-So-Stubby Areas (NSSAs) to carry external routing information.

These LSAs are generated only by ASBRs within an NSSA, and later converted to Type 5 LSAs by the ABR.

Stub areas do not allow ASBRs, meaning Type 7 LSAs cannot exist in a stub area.

The question incorrectly states that Type 7 LSAs can be generated in stub areas, which is false.

???? Reference: Huawei HCIA-Datacom Study Guide, OSPF LSA Types and Area Configurations.

Comprehensive and Detailed Step-by-Step Explanation:

1. Single-Hop BFD Session:

A single-hop BFD session is used to detect link failures between directly connected devices.

It is bound to the local IP address and the peer IP address, and the session relies on these parameters to establish connectivity.

2. Why Modifications Require Deletion:

BFD sessions are tightly bound to their configuration parameters (e.g., local and peer IP addresses).

Modifying these parameters is not supported for an existing session. Instead, you must delete the session and recreate it with the updated parameters.

3. Why the Statement is TRUE:

The statement correctly describes the behavior of BFD sessions, where modifying an existing session is not possible without deleting it first.

Comprehensive and Detailed Step-by-Step Explanation:

1. Features of Wi-Fi 6:

Wi-Fi 6 (802.11ax) introduces several new technologies to improve network efficiency, reduce latency, and optimize power usage:

OFDMA (Orthogonal Frequency Division Multiple Access): Allows multiple devices to transmit simultaneously, improving concurrency.

TWT (Target Wake Time): Reduces power consumption by scheduling communication times for devices.

High Bandwidth: Supports up to 9.6 Gbps, significantly faster than Wi-Fi 5.

2. Why Zero Latency is Incorrect:

While Wi-Fi 6 reduces latency compared to earlier standards, zero latency is not achievable due to inherent delays in network communication.

The statement "Realizes zero latency" is misleading and technically inaccurate.

3. Analysis of Each Option:

Option A: Uses OFDMA technology to achieve high concurrency.

Correct (True Statement).

OFDMA is a core feature of Wi-Fi 6 that improves concurrent communication.

Option B: Realizes zero latency, ensuring efficient service running.

Incorrect (False Statement).

Wi-Fi 6 reduces latency but cannot eliminate it entirely.

Option C: Provides high bandwidth, up to 9.6 Gbps.

Correct (True Statement).

Wi-Fi 6 supports a theoretical maximum bandwidth of 9.6 Gbps.

Option D: Uses TWT technology to reduce terminal power consumption.

Correct (True Statement).

TWT schedules communication times, allowing devices to enter low-power states and conserve battery life.

4. Summary:

The false statement is B, as Wi-Fi 6 does not achieve zero latency.

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 ​.

Comprehensive and Detailed in-depth Step-by-Step Explanation:In IS-IS, the interface cost is a metric used to determine the best path to a destination. Lower-cost paths are preferred over higher-cost paths. By default, IS-IS interface costs can range from 1 to 63.

Default Cost Range:

IS-IS allows the configuration of interface costs within the range of 1–63 by default. This range is sufficient for most networks.

Maximum Configurable Cost:

The maximum value that can be configured by default is 63. If there is a requirement for a higher cost range, the metric-style can be changed to wide, which allows the cost range to extend beyond 63.

Option A (67): Incorrect. 67 is not the maximum default value.

Option B (63): Correct. This is the maximum default cost value.

Option C (64): Incorrect. This is beyond the default range.

Option D (68): Incorrect. This is beyond the default range.

References:

Huawei HCIA-Datacom Study Guide, Chapter on "IS-IS Cost and Route Selection".

RFC 5308 – Routing IPv6 with IS-IS.

The operator between if-match clauses under a node is AND, meaning all conditions must be satisfied. However, the operator between nodes is OR, meaning a route matching any node will pass the route-policy ​.

To compress the IPv6 address 2001:0DB8:0000:C030:0000:0000:09A0, the following rules are applied:

Remove leading zeros in each hextet (e.g., 0DB8 becomes DB8).

Replace contiguous blocks of zeros with :: (only once in the address).Thus, the compressed form is 2001:DB8:0:C030::9A0 ​.

Routing Entries in PIM

(S, G) entries: Represent the shortest path tree (SPT) from a specific source (S) to a specific multicast group (G). These entries are created after data packets are transmitted directly from the source to the receivers.

(S, G) entries are used in both PIM-DM and PIM-SM modes.

PIM-DM and PIM-SM Modes

In PIM-DM, multicast traffic is initially flooded throughout the network and pruned where no receivers exist. (S, G) entries represent source-specific paths created after the flooding stage.

In PIM-SM, multicast traffic initially flows through a shared tree, but (S, G) entries are created when the network switches to the SPT for more efficient forwarding.

HCIP-Datacom-Core Reference

The functionality and application of (S, G) routing entries are detailed in multicast and PIM configuration chapters​​.

Comprehensive and Detailed Step-by-Step Explanation:

1. Understanding the Prefix List Configuration:

The command ip ip-prefix test index 10 permit 10.0.0.0 8 less-equal 32 defines the following:

The prefix base is 10.0.0.0 with a mask length of 8 bits.

The less-equal 32 condition allows routes with mask lengths ranging from 8 to 32 bits to match.

2. Analysis of Each Route:

Option A: 10.1.1.1/32

Correct.

The prefix 10.1.1.1/32 falls within the 10.0.0.0/8 network range and has a mask length of 32 bits, which satisfies the less-equal 32 condition.

Option B: 10.1.1.0/6

Incorrect.

The prefix 10.1.1.0/6 has a mask length of 6 bits, which is shorter than the base prefix length of 8. It does not satisfy the condition.

Option C: 10.1.1.0/24

Correct.

The prefix 10.1.1.0/24 falls within the 10.0.0.0/8 network range and has a mask length of 24 bits, which satisfies the less-equal 32 condition.

Option D: 10.0.0.0/16

Correct.

The prefix 10.0.0.0/16 falls within the 10.0.0.0/8 network range and has a mask length of 16 bits, which satisfies the less-equal 32 condition.

3. Summary:

The prefixes that match the configuration are 10.1.1.1/32, 10.1.1.0/24, and 10.0.0.0/16.

 Understanding Router ID and Its Role in OSPF:In OSPF, the Router ID uniquely identifies a router within the OSPF domain. If two routers are configured with the same Router ID, it can lead to issues such as LSA conflicts and flapping. This is because the Router ID is used as a key in OSPF operations, including LSA generation and database synchronization.

The LS age field in OSPF LSAs (Link State Advertisements) is measured in seconds and increments over time in the Link State Database (LSDB). If the LS age reaches the LSRefreshTime (30 minutes), the router that originated the LSA must regenerate it to keep the LSA valid in the network. Options C and B are incorrect since LS age does not decrease, and only the originator regenerates LSAs ​.