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

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 isFALSE.

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 controlchannel 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 ​.

Comprehensive and Detailed Step-by-Step Explanation:

Bidirectional Forwarding Detection (BFD):

BFD is a lightweight protocol that provides rapid fault detection on links independent of the underlying routing protocol or media.

Requirements for BFD:

Both devices at the endpoints of the link must support and configure BFD for it to operate.

If one device does not support BFD, the feature cannot be used for link detection.

ï‚· OSPF LSA Flooding Mechanism

If a router receives an LSA identical to one already in its LSDB, it does not flood the LSA again unless the LSA has changed (i.e., the sequence number or content has been updated).

OSPF ensures efficient use of bandwidth by avoiding redundant flooding of unchanged LSAs.

ï‚· HCIP-Datacom-Core Reference

The OSPF LSDB synchronization process explains that unchanged LSAs are not reflooded, ensuring stability and resource optimization​​.

Comprehensive and Detailed Step-by-Step Explanation:

1. Overview of AS_Path Attribute Modification:

The apply as-path command in a route-policy is used to modify the AS_Path attribute of routes. This is often required to influence the selection of routes or to adjust routing policies for incoming or outgoing BGP updates.

2. Parameters of the apply as-path Command:

Option A: Delete

Correct.

The delete parameter removes specific AS numbers from the AS_Path attribute. This is used to simplify or manipulate the AS_Path for specific routing policies.

Option B: Additive

Correct.

The additive parameter appends an AS number to the existing AS_Path attribute, instead of overwriting it. This is useful when you want to prepend AS numbers to influence route selection without removing the original AS_Path.

Option C: Copy

Incorrect.

The copy parameter is not supported in the apply as-path command for modifying AS_Path attributes.

Option D: Overwrite

Correct.

The overwrite parameter replaces the existing AS_Path with a new one. This provides complete control over the AS_Path attribute but removes the original AS_Path entirely.

3. Summary:

The valid parameters for the apply as-path command are delete, additive, and overwrite.

Huawei HCIA-Datacom Study Guide, Chapter "BGP Route Policies."

BGP Attribute Modification in Huawei Documentation.

Comprehensive and Detailed Step-by-Step Explanation:

1. Overview of PBR (Policy-Based Routing):

Policy-Based Routing (PBR) allows you to override traditional routing decisions by defining user-specific policies.

Interface-Based PBR: Applied to packets arriving at a specific interface and affects traffic being forwarded through the device.

Local PBR: Applied to traffic generated by the local router itself (e.g., locally originated packets such as management traffic).

2. Analysis of Each Statement:

Option A: Interface-based PBR takes effect only for forwarded packets.

Correct (True Statement).

Interface-based PBR applies only to packets arriving at a specific interface and being forwarded through the router. It does not affect locally originated traffic.

Option B: Local PBR takes effect only for locally originated packets.

Correct (True Statement).

Local PBR specifically applies to traffic generated by the router itself, such as pings, SNMP requests, or routing protocol updates.

Option C: Interface-based PBR is configured on an interface and takes effect only for incoming packets on the interface.

Correct (True Statement).

Interface-based PBR is applied directly on the interface using commands like policy-based-route. It only affects traffic entering the specified interface.

Option D: Local PBR is configured in the protocol view.

Incorrect (False Statement).

Local PBR is not configured in the protocol view. It is typically configured using the command local-policy in the system view to handle traffic generated by the router.

3. Summary:

Correct Answer:D (Local PBR is NOT configured in the protocol view).

Huawei HCIA-Datacom Study Guide, Chapter "Policy-Based Routing."

ï‚· LSA Lifetime and Deletion

The LS Age field in the LSA header tracks the age of an LSA. When the LS Age reaches its maximum value (3600 seconds), the LSA is marked for deletion. This ensures old or stale LSAs are removed from the network to maintain accurate routing information.

ï‚· HCIP-Datacom-Core Reference

Detailed explanation of LS Age behavior and LSA deletion processes can be found in the OSPF LSDB and LSA sections​​.

ï‚· LSP Generation in IS-IS

IS-IS routers generate new Link State Packets (LSPs) under the following conditions:

Interface Status Changes: When IS-IS interfaces go up or down, the link state changes, triggering LSP updates.

Periodic Updates: IS-IS periodically regenerates LSPs to ensure link-state information remains synchronized across the network.

Interface Metric Changes: Any modification to interface costs results in a new LSP to reflect the updated cost in the network.

ï‚· Incorrect Option

C. Inter-area IP routes change is incorrect because IS-IS does not inherently differentiate between areas for LSP generation.

ï‚· HCIP-Datacom-Core Reference

IS-IS LSP generation rules are detailed in the IS-IS configuration and implementation chapters​​.

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:

BGP ConnectRetry Timer:

The ConnectRetry timer is used when establishing a TCP connection between BGP peers.

If the connection is successful, the timer is disabled.

If the connection fails, the timer restarts, and the router attempts to reconnect after the timer expires.

Behavior:

This timer prevents excessive connection attempts and ensures efficient resource utilization.