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

Comprehensive and Detailed In-Depth Explanation:

To verify the correct answers, let's analyze how BGP/MPLS IP VPN is used for secure communication and isolation in an enterprise network.

1. Understanding BGP/MPLS IP VPN Concepts

MPLS VPN (Multiprotocol Label Switching Virtual Private Network) is used to:

Allow communication between specific sites by using Route Targets (RTs).

Ensure isolation of specific areas (e.g., R&D vs. non-R&D) by controlling RT import/export policies.

Utilize Route Distinguisher (RD) to make overlapping IP addresses unique within the VPN.

2. Analyzing the Answer Choices

✅ A. "To enable communication between the headquarters and branch R&D areas, both the ERT and IRT of VPN1 and VPN2 can be set to 100:100." → TRUE

Explanation:

ERT (Export Route Target) and IRT (Import Route Target) define which VPNs share routing information.

If VPN1 (HQ R&D) and VPN2 (Branch R&D) use the same RT (100:100), they will exchange routes, enabling communication.

Correct configuration:

VPN1: ERT 100:100, IRT 100:100

VPN2: ERT 100:100, IRT 100:100

✅ This is correct and enables communication between HQ and branch R&D areas.

❌ B. "To implement communication between the headquarters and branch R&D areas, the RDs of VPN1 and VPN2 need to be set to the same value." → FALSE

Explanation:

RD (Route Distinguisher) is only used to make overlapping IP addresses unique within the MPLS VPN.

RD does NOT control route exchange between VPNs (RTs control route exchange).

VPN1 and VPN2 can have different RDs but still communicate if they share the same RT (100:100).

✅ RDs do NOT need to be the same for VPNs to communicate.

❌ This statement is false.

❌ C. "R&D areas and non-R&D areas have overlapping address spaces. Therefore, services in the two areas cannot be isolated." → FALSE

Explanation:

Overlapping address spaces are common in MPLS VPNs and can be isolated using unique Route Targets (RTs).

As long as VPNs have different RTs, their traffic remains isolated.

For example:

VPN1 (R&D): RT 100:100

VPN3 (non-R&D): RT 200:200

Even with overlapping IPs, R&D and non-R&D areas are completely isolated.

❌ This statement is false.

✅ D. "To isolate R&D areas from non-R&D areas at the headquarters, the RTs of VPN1 can all be set to 100:100 and the RTs of VPN3 can all be set to 200:200." → TRUE

Explanation:

Setting different RTs for R&D (100:100) and non-R&D (200:200) ensures complete isolation.

Correct configuration:

VPN1 (R&D): RT 100:100

VPN3 (non-R&D): RT 200:200

Since VPN1 and VPN3 do NOT share the same RTs, their routes remain separate.

✅ This ensures isolation between R&D and non-R&D areas.

Comprehensive and Detailed In-Depth Explanation:

Step 1: Understanding OSPF Areas and Summarization

Loopback0 on R5 has IP 10.0.5.5/32 and is advertised into OSPF.

The abr-summary 10.0.5.0 255.255.255.0 command is applied in area 2 on R1, which means:

Instead of advertising individual host routes (like 10.0.5.5/32), R1 advertises the summarized route 10.0.5.0/24 into Area 0 (Backbone).

This summarized route is then propagated into other areas via Area 0 (Backbone).

Step 2: Analyzing the Routing Table of Each Router

R5 (Originating Router in Area 2)

R5 only knows 10.0.5.5/32 because it's the originating router.

The abr-summary command does not affect R5 itself.

❌ R5 does not have 10.0.5.0/24.

R1 (ABR for Area 2, Summarizing the Route)

R1 creates and advertises 10.0.5.0/24 into Area 0.

This summary route is sent to other areas via Area 0.

R2 (Connected to Area 0 & Area 1)

Since R2 is part of Area 0 (Backbone), it receives 10.0.5.0/24 from R1.

✅ R2 has 10.0.5.0/24 in its routing table.

R3 (Connected to Area 0 & Area 2)

Since R3 is also connected to Area 0, it receives the summary route 10.0.5.0/24 from R1.

✅ R3 has 10.0.5.0/24 in its routing table.

R4 (In Area 1, which is not directly connected to Area 2)

R4 belongs to Area 1, and unless explicitly advertised through inter-area summarization, it will not have 10.0.5.0/24.

Since no specific mention of summary advertisement into Area 1 is made, R4 does not get 10.0.5.0/24.

❌ R4 does not have 10.0.5.0/24.

Final Answer: ✅ R2, R3 (Option B, C)

References:

HCIP-Datacom-Advanced Routing & Switching Technology V1.0 – OSPF Route Summarization

OSPF Inter-Area Route Advertisement via ABRs

OSPF Backbone (Area 0) Behavior and Route Distribution

Comprehensive and Detailed In-Depth Explanation:

Step 1: Identify the Primary Path

The shortest OSPF cost to 10.0.3.3/32 from R1 is through R5:

R1 → R5 (Cost 10) → R3 (Cost 10) = Total Cost 20

The primary outbound interface from R1 to R5 is GE0/0/1.

Step 2: Identify the Backup Path (OSPF IP FRR & ECMP)

OSPF IP Fast Reroute (FRR) provides a backup next-hop in case the primary link (R1 → R5) fails.

A feasible backup path must have a cost equal to or close to the primary path, but it must avoid the same failure point.

Alternative Path Calculation:

Path 1 (R1 → R2 → R3)

R1 → R2 (Cost 10), R2 → R3 (Cost 10) → Total Cost = 20 ✅

Uses interface GE0/0/2 on R1.

Path 2 (R1 → R4 → R3)

R1 → R4 (Cost 10), R4 → R3 (Cost 10) → Total Cost = 20 ✅

Uses interface GE0/0/3 on R1.

Final Decision on the Backup Interface

Since both paths R1 → R2 → R3 and R1 → R4 → R3 have equal costs, either can be used for backup.

However, R1 → R2 → R3 shares a direct cost path with R5, meaning it may not be preferred as a full FRR backup.

The best backup outbound interface in this scenario is GE0/0/3 (R1 → R4 → R3).

Final Answer: ✅ C (GE0/0/3)

References:

HCIP-Datacom-Advanced Routing & Switching Technology V1.0 – OSPF IP FRR (Fast Reroute) Mechanism

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

OSPF Route Calculation and Best-Path Selection