H12-831_V1.0 Exam Dumps - Huawei HCIP-Datacom Questions and Answers

Comprehensive and Detailed In-Depth Explanation:

Understanding the LSA Table in the Figure

The LSDB (Link-State Database) of R4 displays an Intra-Area-Prefix-LSA for Area 0.0.0.1. The table contains:

Three LSAs originating from R4 (10.0.4.4)

Prefixes referencing both Router-LSAs and Network-LSAs

Different Sequence Numbers and Checksums, indicating multiple link-state changes

OSPFv3 LSA Types Relevant to the Question

Router-LSA (Type 1)

Generated by every router to describe its links within an area.

Network-LSA (Type 2)

Generated only by the Designated Router (DR) for multi-access networks (such as Ethernet).

Advertises all routers connected to the same segment.

Intra-Area-Prefix-LSA (Type 9)

Advertises IPv6 prefixes associated with a Router-LSA (Type 1) or Network-LSA (Type 2).

Analysis of Each Statement

A. The three LSAs belong to area 1. ✅ (True)

The table explicitly shows "Intra-Area-Prefix-LSA (Area 0.0.0.1)", meaning all LSAs are for Area 1.

The Link State IDs also indicate intra-area advertisements.

✅ Statement A is correct.

B. Area 1 is a stub area. ❌ (False)

There is no indication that Area 1 is a stub area.

Stub areas do not receive Type 5 (External) LSAs, and the LSDB does not show Type 3 (Inter-Area) LSAs either.

Network-LSAs (Type 2) are not typically seen in stub areas unless explicitly configured.

❌ Statement B is incorrect.

C. No OSPFv3 neighbor relationship is established on at least one link of R4. ✅ (True)

One LSA references a Router-LSA, while two reference Network-LSAs.

A Router-LSA alone suggests that R4 has at least one point-to-point or unnumbered link with no OSPFv3 adjacency.

This means R4 has an interface with no neighbor (e.g., a passive interface or down link).

✅ Statement C is correct.

D. R4 is the DR on a link. ✅ (True)

The presence of Network-LSAs (Type 2) indicates that a multi-access link exists.

Since R4 is the origin of the Network-LSA, it must be the DR (Designated Router) for that link.

✅ Statement D is correct.

Final Conclusion:

✅ A. The three LSAs belong to area 1. (True)❌ B. Area 1 is a stub area. (False)✅ C. No OSPFv3 neighbor relationship is established on at least one link of R4. (True)✅ D. R4 is the DR on a link. (True)

Thus, the correct answers are: A, C, D.

Comprehensive and Detailed In-Depth Explanation:

1. Understanding the Hub-Spoke Network Model in MPLS VPN

Hub-Spoke (or Route Reflector) topology is used in MPLS Layer 3 VPNs where multiple spoke sites communicate through a central hub.

The Hub-PE acts as an intermediate BGP speaker and redistributes routes between spokes.

The challenge is preventing routing loops when exchanging routes between spokes.

2. Understanding the Role of Site of Origin (SoO) in BGP/MPLS VPNs

BGP Site of Origin (SoO) is a route attribute used to prevent routing loops in scenarios where a hub redistributes routes between spokes.

If a route originating from a spoke is advertised back to the same site, SoO prevents it from being re-learned.

The SoO value (e.g., 200:1) ensures that a site does not accept its own previously advertised prefixes.

3. Analyzing the Answer Choices

❌ A. [Hub-PE-bgp-VPN_out] peer x.x.x.x allow-as-loop (Incorrect)

The allow-as-loop command allows BGP to accept routes with its own AS number in the AS path.

This is NOT needed in a Hub-Spoke VPN because BGP routes are not being looped through the same AS.

❌ This is unnecessary for preventing loops in a Hub-Spoke VPN.

❌ B. [Hub-PE-bgp-VPN_in] peer x.x.x.x allow-as-loop (Incorrect)

Again, allow-as-loop is used when a router needs to accept its own AS number in the BGP AS path.

This is NOT the mechanism used for preventing loops in Hub-Spoke VPNs; SoO is used instead.

❌ This is not required in this scenario.

✅ C. [Hub-PE-bgp-VPN_in] peer x.x.x.x soo 200:1 (Correct Answer)

The correct way to prevent spoke routes from looping through the hub is to apply the Site of Origin (SoO) attribute.

This command ensures that if a route with SoO 200:1 is received, it is not advertised back to the same spoke.

✅ This is the correct answer.

❌ D. [Hub-PE-bgp-VPN_out] peer x.x.x.x soo 200:1 (Incorrect)

Applying SoO on outgoing routes is NOT effective because the hub should mark received routes and prevent loops when re-advertising them.

SoO should be applied on the inbound (received) routes at the Hub-PE, not outbound.

❌ This is not the correct implementation of SoO.

Final Conclusion:

✅ Correct Answer: C. [Hub-PE-bgp-VPN_in] peer x.x.x.x soo 200:1❌ A. allow-as-loop is unnecessary in a Hub-Spoke MPLS VPN.❌ B. allow-as-loop is not relevant here.❌ D. SoO should be applied inbound, not outbound.

Thus, the correct answer is: C. [Hub-PE-bgp-VPN_in] peer x.x.x.x soo 200:1.

Comprehensive and Detailed In-Depth Explanation:

Step 1: Analyzing the Primary Path

The given network uses IS-IS Auto FRR, which ensures a backup route in case of failure.

The shortest path from R1 to 10.0.3.3/32 is calculated based on the OSPF link costs:

Path 1 (Primary Path): R1 → R2 → R3

Cost: 10 (R1→R2) + 5 (R2→R3) = 15 ✅

Step 2: Checking the Backup Path

The statement claims that the backup path is R1 → R4 → R2 → R3. Let's calculate the cost:

Path 2 (Backup Path via R4): R1 → R4 → R2 → R3

Cost: 10 (R1→R4) + 50 (R4→R2) + 5 (R2→R3) = 65 ❌ (Too high)

The backup path should be an alternative shortest path that is as close as possible to the primary path in cost.

R1 → R4 → R2 → R3 is not a feasible backup path because the cost (65) is significantly higher than the primary path (15).

Step 3: Correct Backup Path Selection

If IS-IS Auto FRR is enabled, a feasible backup path should have a cost close to the primary path.

In this scenario, no viable alternative path meets the Auto FRR requirements efficiently.

The given backup path is incorrect.

Final Answer: ✅ FALSE (Option B)

References:

HCIP-Datacom-Advanced Routing & Switching Technology V1.0 – IS-IS Auto FRR Mechanism

OSPF Route Selection and Fast Reroute Principles

OSPF and IS-IS Path Cost Calculation

Comprehensive and Detailed In-Depth Explanation:

1. Understanding Route Targets (RT) and Route Distribution in MPLS VPN

MPLS Layer 3 VPNs (L3VPNs) use BGP to distribute VPN routes across multiple Provider Edge (PE) routers.

Each VPN instance (VRF) is configured with Route Targets (RTs) to control which VPN routes are imported/exported.

Route Distinguishers (RDs) are unique per VRF but do not affect route selection.

2. Analyzing VPN1 Configuration

VPN1 is exporting routes with the following Route Targets (vpn-target values):

100:1

200:1

300:1

Remote VPNs will import these routes only if their import RT list matches one of the exported RTs.

3. Matching Exported RTs with Import RTs in Remote VPNs

Remote VPN

Import RTs

Matches VPN1 Exported RTs (100:1, 200:1, 300:1)?

Accepts the Route?

VPN1

100:1

✅ Matches 100:1

✅ Yes

VPN2

200:1, 400:1

✅ Matches 200:1

✅ Yes

VPN3

100:1, 300:1

✅ Matches 100:1, 300:1

✅ Yes

VPN4

500:1

❌ No match

❌ No

✅ VPN1, VPN2, and VPN3 accept the route.❌ VPN4 does not accept the route because 500:1 is not in the export list of VPN1.

Final Conclusion:

✅ Correct Answer: VPN1, VPN2, and VPN3 will accept the route.❌ VPN4 does not accept the route because there is no matching RT.

Thus, the correct answer is:✅ A. VPN1: Import RT=100:1✅ B. VPN2: Import RT=200:1, 400:1✅ C. VPN3: Import RT=100:1, 300:1❌ D. VPN4: Import RT=500:1 (No match, does not accept the route).