H12-831_V1.0 Exam Dumps : HCIP-Datacom-Advanced Routing & Switching Technology V1.0

Comprehensive and Detailed In-Depth Explanation:

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 Answer:

Answer: B (There is no label).

HCIP-Datacom-Advanced Routing & Switching Technology References:

MPLS Label Forwarding Mechanism

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

MPLS Label Swapping and Label Forwarding Table (LFIB)

Comprehensive and Detailed In-Depth Explanation:

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 References:

OSPF Inter-Router Communication and Route Advertisement

Default Gateway and Routing in Multi-Router Networks

Troubleshooting End-to-End Connectivity in Routed Networks