Get Huawei H12-831_V1.0 Exam Practice Questions - Real and Updated

Answer : B

Answer : B

Comprehensive and Detailed In-Depth

1. Understanding MPLS Label Switching

MPLS (Multiprotocol Label Switching) operates by adding labels to packets to enable fast switching across an MPLS domain.

Labels are swapped at each router (LSR - Label Switch Router) based on the LFIB (Label Forwarding Information Base).

When an MPLS packet reaches a router, it checks the incoming label and swaps it with an outgoing label as per its label forwarding table.

The label value '3' is the implicit null label, which is used for PHP (Penultimate Hop Popping).

2. Analyzing the MPLS Label Flow in the Figure

At PE1: The packet enters the MPLS domain and is labeled with 1033.

At P1: P1 forwards the packet based on label 1033.

At P2:

P2 receives label 1033 and swaps it with label 3 (as per the figure).

Label 3 (implicit null) means that the label is removed before reaching PE2 (PHP - Penultimate Hop Popping).

This ensures that PE2 receives a pure IP packet without an MPLS label.

3. Evaluating Each Answer Option

Option A: 'The label value is 3.' Incorrect.

Label 3 (implicit null) is not actually sent to PE2.

Instead, P2 removes the label before sending the packet to PE2.

Option B: 'There is no label.' Correct.

Since P2 performs PHP (Penultimate Hop Popping), the label is removed, and PE2 receives only an IP packet.

Option C: 'The label value is 1033.' Incorrect.

Label 1033 was used earlier in the MPLS path but was swapped out before reaching PE2.

Option D: 'The label values are 3 and 1033.' Incorrect.

Only one label is present at a time.

Label 1033 was swapped for label 3, but label 3 was removed before reaching PE2.

Final Answe r :

Answe r: B (There is no label).

HCIP-Datacom-Advanced Routing & Switching Technology Reference:

MPLS Label Forwarding Mechanism

Penultimate Hop Popping (PHP) and Implicit Null Label (3)

MPLS Label Swapping and Label Forwarding Table (LFIB)

Answer : B, C

Comprehensive and Detailed In-Depth

1. Understanding MPLS LDP (Label Distribution Protocol)

LDP (Label Distribution Protocol) runs over TCP port 646.

LDP uses the transport address (Loopback0 in this case) to establish TCP sessions between neighbors.

For an LDP session to be established, both routers must:

Enable LDP on the interface (GE0/0/1).

Allow TCP traffic on port 646 (used for LDP adjacency formation).

2. Analyzing the Issue and Possible Causes

The figure shows a successful ping from R2 to R1's Loopback0 (10.0.1.1/32).

This means basic IP connectivity between R1 and R2 is working.

OSPF is properly advertising Loopback0 addresses between the routers.

The problem must be related to LDP itself, not general IP reachability.

3. Evaluating Each Answer Option

Option A: 'R1's GE0/0/1 rejects packets with the destination IP address 10.0.2.2.'

Incorrect.

The ping test in the figure shows successful replies from 10.0.1.1 to 10.0.2.2, meaning packets to 10.0.2.2 are not being rejected.

This is NOT the cause of the LDP failure.

Option B: 'MPLS LDP is not enabled on R2's GE0/0/1.'

Correct.

If LDP is not enabled on R2's GE0/0/1, then R1 and R2 cannot form an LDP session.

MPLS LDP must be enabled on both interfaces for label exchange.

This is a valid cause of the issue.

Option C: 'R2's GE0/0/1 rejects packets with TCP destination port 646.'

Correct.

LDP operates over TCP port 646, so if R2's GE0/0/1 has a firewall or ACL blocking TCP port 646, then LDP will fail.

Blocking TCP 646 on R2's interface would prevent the session from establishing.

This is another valid cause of the issue.

Option D: 'R1's GE0/0/1 rejects packets with UDP destination port 646.'

Incorrect.

LDP does not use UDP; it uses TCP port 646.

This is not a valid cause of the issue.

Final Answer:

B and C are correct.

HCIP-Datacom-Advanced Routing & Switching Technology Reference:

MPLS LDP Session Establishment and TCP 646 Dependency

How OSPF Advertises Loopback0 for LDP Transport

Common LDP Debugging Techniques and ACL Issues

Answer : D

Comprehensive and Detailed In-Depth

MPLS packet forwarding is based on label information stored in the LFIB (Label Forwarding Information Base).

The role of different tables in MPLS:

RIB (Routing Information Base): Stores routing information, but does not handle MPLS label forwarding.

LIB (Label Information Base): Stores label bindings but is used for control-plane operations.

FIB (Forwarding Information Base): Used for IP forwarding, not MPLS forwarding.

LFIB (Label Forwarding Information Base): The correct table, which maps incoming labels to outgoing labels (or actions like swap, push, pop) and is used for actual MPLS packet forwarding.

Reference: HCIP-Datacom Advanced Routing & Switching Technology -- MPLS LFIB and Label Forwarding

Answer : A, B, C

Comprehensive and Detailed In-Depth

1. Understanding the Network Topology

R1 and R2 are OSPF-enabled routers connected via the 10.0.12.0/24 subnet (Area 0).

PC1 (192.168.1.2/30) is connected to R1 via GE0/0/1.

PC2 (192.168.1.22/30) is connected to R2 via GE0/0/1.

OSPF ensures that R1 and R2 know about each other's directly connected networks.

2. Analyzing Connectivity

Can R1 ping 192.168.1.22 (PC2)?

Yes, if routing is properly configured.

OSPF ensures that R1 learns about 192.168.1.22 from R2.

Since R1 has a route to 192.168.1.22 via R2, it can ping PC2 successfully.

Option A is correct.

Can R1 ping 192.168.1.21 (R2's interface)?

Yes, since R1 and R2 are OSPF neighbors.

R1 learns 192.168.1.21 via OSPF and can reach it directly.

Option B is correct.

Can R2 ping 192.168.1.2 (PC1)?

Yes, since OSPF ensures that R2 learns about 192.168.1.2 from R1.

Since R2 has a route to 192.168.1.2 via R1, it can ping PC1 successfully.

Option C is correct.

Can PC1 and PC2 ping each other?

Yes, if default gateways and routing are configured correctly.

If R1 and R2 can ping each other and forward packets, PC1 and PC2 should be able to communicate.

Option D is incorrect because PC1 and PC2 should be able to ping each other.

Final Answer:

A, B, and C are correct.

HCIP-Datacom-Advanced Routing & Switching Technology Reference:

OSPF Inter-Router Communication and Route Advertisement

Default Gateway and Routing in Multi-Router Networks

Troubleshooting End-to-End Connectivity in Routed Networks