H12-891 Sample Questions & Answers

Huawei's SD-WAN solution uses a proprietary protocol, OMP (Overlay Management Protocol), not BGP, for the controller to distribute overlay routing, policies, and security information to the CPEs. While CPEs may use BGP to learn routes from the local site, the control plane communication with iMaster NCE-WAN is OMP-based.

Idempotency is a fundamental concept in automation and IaC. It means that applying an operation multiple times produces the same result as applying it once. In Ansible, an idempotent task will check the current state of the system and only make a change if the desired state is not already met. This prevents errors and ensures predictable outcomes.

Route Targets control the distribution of VPNv4 routes between VRFs. For PE2 to import routes from PE1, the export-rt value configured on PE1's VRF must match an import-rt value on PE2's VRF. A mismatch is a very common cause for VPN routes not being installed in the remote PE's VRF routing table, even when the MP-BGP session is up.

The ORIGINATOR_ID is a non-transitive BGP attribute created by a Route Reflector. It carries the Router ID of the BGP speaker that originally advertised the route into the AS. When another router receives this update, if it sees its own Router ID in the ORIGINATOR_ID attribute, it discards the update, thus preventing a routing loop.

Flexible Ethernet (FlexE) is a technology that decouples the MAC layer from the PHY layer, allowing for the creation of hard, isolated slices of a physical Ethernet interface. This provides deterministic bandwidth and latency guarantees, which is essential for the hard slicing required by some 5G services. It is a key component of Huawei's CloudWAN solution for network slicing.

Streaming Telemetry is designed to overcome the limitations of SNMP. It uses a push model where the network device subscribes to specific data models (using YANG) and streams the data to a collector in near real-time. gRPC is a high-performance transport protocol commonly used for telemetry, providing the sub-second granularity required for modern network analytics and anomaly detection.

In PIM-Sparse Mode (PIM-SM), the Rendezvous Point (RP) acts as an initial meeting point. Multicast sources register with the RP, and receivers send their IGMP joins towards the RP. This allows the shared distribution tree (*,G) to be built, enabling receivers to learn about active sources without the network being flooded with traffic.

In tunnel forwarding mode, all client data traffic is encapsulated within a CAPWAP tunnel and sent from the Access Point (AP) to the Access Controller (AC). The AC then de-encapsulates the traffic and forwards it to the wired network. This centralizes the client's network entry point at the AC, allowing the client to maintain the same IP address and session state as it roams between APs, which is essential for seamless Layer 3 roaming.

Single-hop BFD control packets are sent using UDP with a destination port of 3784. If a firewall or an access control list between the peers blocks this port, the BFD session cannot be established.

During BFD session negotiation, both peers exchange their configured detect-multiplier values. The higher of the two values is used for the session. However, some implementations or configurations may require these to match for the session to be successfully established.

SLAAC is the method where clients can automatically configure an IPv6 address without a stateful server. The router sends Router Advertisement (RA) messages containing the network prefix. Clients then combine this prefix with an interface identifier (often generated from their MAC address using the EUI-64 format) to create a unique global IPv6 address.