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

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.

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)

Comprehensive and Detailed In-Depth Explanation:

Understanding the IS-IS Network and IPv6 Route Summary Behavior

IS-IS Areas and Router Roles:

Area 49.0001 (Level-1-2): R1, R2, R4

Area 49.0002 (Level-1-2 & Level-1): R3 (Level-1-2), R5 (Level-1 only)

Effect of ipv6 summary 2000::/64 level-1-2 Command on R4

Route summarization in IS-IS allows an L1-L2 router (R4) to aggregate IPv6 prefixes and advertise a summary route (2000::/64) into both Level-1 and Level-2 areas.

This means R4 will advertise only 2000::/64 instead of specific /128 routes (like 2000::4/128).

All Level-1 and Level-2 routers connected to R4 will receive the summary route 2000::/64 instead of the detailed /128 routes.

Route Distribution Analysis for Each Statement

A. The routing table of R1 contains the route 2000::4/128. ✅ (True)

R1 is a Level-1-2 router in the same area (49.0001) as R4, so it receives both the summarized 2000::/64 route and the more specific 2000::4/128 route.

Since R1 is directly connected to R4, it can still learn the 2000::4/128 route.

✅ Statement A is true.

B. The routing table of R3 contains the route 2000::/64. ✅ (True)

R3 is a Level-1-2 router, meaning it can receive both Level-1 and Level-2 routes.

Since R4 (a Level-1-2 router) advertises the summarized 2000::/64 route into both levels, R3 will receive 2000::/64 in its routing table.

✅ Statement B is true.

C. The routing table of R2 contains the route 2000::/64. ✅ (True)

R2 is a Level-1-2 router in the same area as R4, meaning it receives the summarized 2000::/64 route.

This is expected behavior since R4 advertises the summary route into both Level-1 and Level-2 areas.

✅ Statement C is true.

D. The routing table of R5 does not contain the route 2000::/64. ❌ (False - Correct Answer)

R5 is a Level-1 router, meaning it can only receive Level-1 routes unless a default route is provided.

Since R3 (a Level-1-2 router) learns 2000::/64, it can propagate it into the Level-1 area (49.0002).

This means R5 will receive the summary route 2000::/64 from R3.

Thus, R5 does contain 2000::/64, making this statement false.

❌ Statement D is false (correct answer).

Final Conclusion:

✅ A. The routing table of R1 contains the route 2000::4/128. (True)

✅ B. The routing table of R3 contains the route 2000::/64. (True)

✅ C. The routing table of R2 contains the route 2000::/64. (True)

❌ D. The routing table of R5 does not contain the route 2000::/64. (False - Correct Answer)

Thus, the correct answer is: D. The routing table of R5 does not contain the route 2000::/64 (False Statement).