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

Comprehensive and Detailed In-Depth Explanation:

To determine the cost value of the route 10.0.35.0/24 in the routing table of R1, let's analyze the possible shortest paths from R1 to R3 (which owns the 10.0.35.0/24 network) based on the given OSPF link costs:

Path 1: R1 → R2 → R3

R1 to R2: Cost = 20

R2 to R3: Cost = 10

Total Cost = 20 + 10 = 30

Path 2: R1 → R4 → R3

R1 to R4: Cost = 10

R4 to R3: Cost = 10

Total Cost = 10 + 10 = 20 ✅ (Lowest cost path)

Path 3: R1 → R5 → R3

R1 to R5: Cost = 10

R5 to R3: Cost = 10

Total Cost = 10 + 10 = 20 ✅ (Equal-cost path)

Final Calculation:

The two best equal-cost paths (R1 → R4 → R3 and R1 → R5 → R3) have a cost of 20.

Since OSPF supports equal-cost multi-path (ECMP) routing and maximum load-balancing 8 is enabled, OSPF will install both routes into the routing table with the same cost of 20.

The path R1 → R2 → R3 has a higher cost (30) and will not be chosen.

Final Answer: ✅ 20 (Option C)

References:

HCIP-Datacom-Advanced Routing & Switching Technology V1.0 – OSPF Route Calculation & Load Balancing

OSPF Equal-Cost Multi-Path (ECMP) and Route Selection

OSPF Fast Reroute (FRR) Mechanism

Comprehensive and Detailed In-Depth Explanation:

1. Understanding Site of Origin (SoO) in MPLS VPNs

SoO (Site of Origin) is used in MPLS VPNs to prevent loops in multi-homed CE scenarios.

Routes with the same SoO value are not advertised back to the same site.

2. Analysis of Each Answer Choice

A. "To enable CE3 to receive the route, run the command peer 10.1.1.1 soo 200:1 on PE1." (❌ False)

SoO is used to prevent loops by tagging routes that belong to the same site.

Applying SoO (200:1) on PE1 for CE1 means that any other PE (such as PE2) receiving the route will not advertise it back to the same site (CE1).

This statement is false because applying SoO here does not directly enable CE3 to receive the route. Instead, CE3 must accept routes with SoO values properly configured.

B. "If the commands peer 10.1.1.1 soo 200:1 and peer 10.1.2.1 soo 200:1 are run on PE1, CE2 accepts the route." (❌ False)

SoO ensures that a route received from one CE is not sent back to another CE in the same site.

If SoO (200:1) is assigned to CE1 and CE2, routes will be blocked because they share the same SoO tag.

Thus, CE2 will not accept the route, making this statement false.

C. "If the command peer 10.1.3.1 substitute-as is run on PE2, CE3 accepts the route." (✅ True)

substitute-as allows a router to replace the received AS number in the AS_PATH with another AS number, ensuring that routes are accepted even when AS_PATH filtering is in place.

This prevents CE3 from rejecting the route due to AS-Path loop prevention.

✅ Thus, this statement is true.

D. "If no additional action is taken, CE3 discards the route." (✅ True)

By default, CE3 will discard the route because of BGP loop prevention (same AS in the AS_PATH).

To allow CE3 to receive the route, the allowas-in or substitute-as command must be configured on PE2.

✅ Thus, this statement is true.

3. Evaluating the Answer Choices

Option

Correct?

Reasoning

A

❌ False

Applying SoO does not directly enable CE3 to receive the route.

B

❌ False

If both CE1 and CE2 have the same SoO value, CE2 will reject the route.

C

✅ True

Substitute-AS allows CE3 to accept the route by modifying the AS-Path.

D

✅ True

Without additional configuration, CE3 will discard the route due to AS-Path loop prevention.

✅ Correct Answer: A and B are false.

Final Conclusion:

SoO prevents routing loops in MPLS VPN multi-homing.

CE2 will reject the route if it has the same SoO as CE1.

CE3 requires the substitute-as or allowas-in command to accept the route.

Thus, statements A and B are false.