H12-891_V1.0試験無料問題集「Huawei HCIE-Datacom V1.0 認定」
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As shown in the figure, a sham link is established between PE1 and PE2 through the loopback interfaces. CE2 can learn the 192.168.1.0/24 route (directed route on CE1) through the sham link and backdoor link. If other parameters use their default settings, the cost of the 192.168.1.0/24 route on CE2 should be ______. (Enter an Arabic numeral without symbols.)
As shown in the figure, a sham link is established between PE1 and PE2 through the loopback interfaces. CE2 can learn the 192.168.1.0/24 route (directed route on CE1) through the sham link and backdoor link. If other parameters use their default settings, the cost of the 192.168.1.0/24 route on CE2 should be ______. (Enter an Arabic numeral without symbols.)
正解：
20
Explanation:
This is a classic MPLS L3VPN with OSPF + Sham Link scenario.Key Components:CE1 to PE1 (GE0/0/0): OSPF cost = 10CE2 to PE2 (GE0/0/0): OSPF cost = 10PE1 to PE2 via Sham Link (over loopback interfaces)What happens:CE1 advertises 192.168.1.0/24 to PE1.PE1 redistributes it into the VPNv4 BGP routing table.PE2 learns this route and redistributes it back into OSPF for CE2.Route Options Seen by CE2:Backdoor link (intra-area):CE1 ↔ CE2 directly, via GE0/0/1 on each CE → OSPF cost = 10 + 10 = 20Sham Link (inter-area route): By default, if no sham link is used, the BGP-learned route is treated as an inter-area route by CE2, with a default OSPF cost of 1 (which would make CE2 prefer this over the real CE-CE backdoor link).Purpose of Sham Link:Sham link is configured to equalize or override the cost of the BGP route so that CE2 prefers the backdoor link or sees both paths equally.In this case, Huawei defaults will cause CE2 to compute the total cost as:PE1-CE1 = 10Sham link route via PE1-PE2-CE2 = also 10 (CE1 to PE1) + 10 (PE2 to CE2) = 20Final OSPF Cost Calculation at CE2:Route learned via sham link path: 10 (CE1 to PE1) + 10 (PE2 to CE2) = 20Correct answer: 20In Huawei MPLS L3VPN OSPF deployment:A sham link ensures that the cost via the MPLS VPN path is comparable to the real CE-to-CE OSPF backdoor path, preventing suboptimal routing.Without sham link: BGP redistributed routes appear as inter-area Type 3 LSAs with low cost (usually 1).With sham link: Route appears as intra-area and OSPF calculates true cost based on interface metrics.
Reference:
Huawei HCIE-Datacom V1.0 Study GuideChapter: MPLS L3VPN Integration with OSPFSection: Sham Link Design and Cost Calculation
Explanation:
This is a classic MPLS L3VPN with OSPF + Sham Link scenario.Key Components:CE1 to PE1 (GE0/0/0): OSPF cost = 10CE2 to PE2 (GE0/0/0): OSPF cost = 10PE1 to PE2 via Sham Link (over loopback interfaces)What happens:CE1 advertises 192.168.1.0/24 to PE1.PE1 redistributes it into the VPNv4 BGP routing table.PE2 learns this route and redistributes it back into OSPF for CE2.Route Options Seen by CE2:Backdoor link (intra-area):CE1 ↔ CE2 directly, via GE0/0/1 on each CE → OSPF cost = 10 + 10 = 20Sham Link (inter-area route): By default, if no sham link is used, the BGP-learned route is treated as an inter-area route by CE2, with a default OSPF cost of 1 (which would make CE2 prefer this over the real CE-CE backdoor link).Purpose of Sham Link:Sham link is configured to equalize or override the cost of the BGP route so that CE2 prefers the backdoor link or sees both paths equally.In this case, Huawei defaults will cause CE2 to compute the total cost as:PE1-CE1 = 10Sham link route via PE1-PE2-CE2 = also 10 (CE1 to PE1) + 10 (PE2 to CE2) = 20Final OSPF Cost Calculation at CE2:Route learned via sham link path: 10 (CE1 to PE1) + 10 (PE2 to CE2) = 20Correct answer: 20In Huawei MPLS L3VPN OSPF deployment:A sham link ensures that the cost via the MPLS VPN path is comparable to the real CE-to-CE OSPF backdoor path, preventing suboptimal routing.Without sham link: BGP redistributed routes appear as inter-area Type 3 LSAs with low cost (usually 1).With sham link: Route appears as intra-area and OSPF calculates true cost based on interface metrics.
Reference:
Huawei HCIE-Datacom V1.0 Study GuideChapter: MPLS L3VPN Integration with OSPFSection: Sham Link Design and Cost Calculation
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The ingress VTEP performs both Layer 2 and Layer 3 table lookup for packet forwarding. The forwarding mode is _____ IRB forwarding. (Capitalize the first letter.)
The ingress VTEP performs both Layer 2 and Layer 3 table lookup for packet forwarding. The forwarding mode is _____ IRB forwarding. (Capitalize the first letter.)
正解：
Symmetric
Explanation:
Understanding IRB (Integrated Routing and Bridging) Forwarding in VXLAN VXLAN (Virtual Extensible LAN) supports Layer 2 and Layer 3 forwarding between Virtual Network Identifiers (VNIs).
IRB (Integrated Routing and Bridging) enables inter-subnet communication within a VXLAN fabric.
There are two modes of IRB forwarding:
Symmetric IRB
Asymmetric IRB
Why the Answer is "Symmetric" IRB Forwarding?
✔ Ingress VTEP performs both Layer 2 and Layer 3 lookups:
Symmetric IRB requires both ingress and egress VTEPs to perform Layer 3 lookups.
The ingress VTEP (source gateway) performs a Layer 2 MAC lookup, then a Layer 3 lookup to find the destination VTEP.
The egress VTEP (destination gateway) performs another Layer 3 lookup before forwarding the packet to the destination.
✔ Asymmetric IRB does not perform two lookups at the ingress VTEP:
In Asymmetric IRB, the ingress VTEP performs both Layer 2 and Layer 3 forwarding and sends a Layer 2 packet to the egress VTEP.
The egress VTEP only does a Layer 2 lookup, not a Layer 3 lookup.
Since the question states that both L2 and L3 lookups occur at the ingress VTEP, asymmetric IRB is incorrect.
✔ Why Symmetric IRB is More Common?
Scalability: Supports any-to-any communication across VXLAN networks.
More Efficient Routing: Uses Layer 3 VXLAN encapsulation, ensuring efficient routing between VNIs.
📖 Reference: Huawei HCIE Datacom - VXLAN Symmetric and Asymmetric IRB Forwarding
Explanation:
Understanding IRB (Integrated Routing and Bridging) Forwarding in VXLAN VXLAN (Virtual Extensible LAN) supports Layer 2 and Layer 3 forwarding between Virtual Network Identifiers (VNIs).
IRB (Integrated Routing and Bridging) enables inter-subnet communication within a VXLAN fabric.
There are two modes of IRB forwarding:
Symmetric IRB
Asymmetric IRB
Why the Answer is "Symmetric" IRB Forwarding?
✔ Ingress VTEP performs both Layer 2 and Layer 3 lookups:
Symmetric IRB requires both ingress and egress VTEPs to perform Layer 3 lookups.
The ingress VTEP (source gateway) performs a Layer 2 MAC lookup, then a Layer 3 lookup to find the destination VTEP.
The egress VTEP (destination gateway) performs another Layer 3 lookup before forwarding the packet to the destination.
✔ Asymmetric IRB does not perform two lookups at the ingress VTEP:
In Asymmetric IRB, the ingress VTEP performs both Layer 2 and Layer 3 forwarding and sends a Layer 2 packet to the egress VTEP.
The egress VTEP only does a Layer 2 lookup, not a Layer 3 lookup.
Since the question states that both L2 and L3 lookups occur at the ingress VTEP, asymmetric IRB is incorrect.
✔ Why Symmetric IRB is More Common?
Scalability: Supports any-to-any communication across VXLAN networks.
More Efficient Routing: Uses Layer 3 VXLAN encapsulation, ensuring efficient routing between VNIs.
📖 Reference: Huawei HCIE Datacom - VXLAN Symmetric and Asymmetric IRB Forwarding
