View Full Huawei H12-821 Exam Dumps and Practice Test Dumps.

Question 141. What is the PRIMARY purpose of configuring a non-backbone OSPF area as a stub area?

1. To allow unlimited external LSAs into the area
2. To reduce routing information by preventing AS-external routes from being flooded into the area
3. To allow the area to function as Area 0
4. To require an ASBR inside the area

Correct Answer: 2. To reduce routing information by preventing AS-external routes from being flooded into the area

Explanation:

An OSPF stub area is designed to reduce the amount of routing information maintained by routers in a non-backbone area. The ABR does not flood AS-external Type 5 LSAs into the stub area. Instead, the ABR can advertise a default route that routers inside the area use to reach destinations outside the OSPF domain. This reduces LSDB size, routing-table entries, memory usage, and processing requirements. Area 0 cannot be configured as a stub area, and an ASBR cannot normally reside inside a stub area because stub areas do not support locally imported AS-external routes.

Question 142. What is the key difference between an OSPF NSSA and a regular stub area?

1. An NSSA cannot contain an ABR
2. An NSSA supports only Type 1 LSAs
3. An NSSA must be Area 0
4. An NSSA can import external routes into OSPF, whereas a regular stub area cannot**

Correct Answer: 4. An NSSA can import external routes into OSPF, whereas a regular stub area cannot

Explanation:

A Not-So-Stubby Area combines characteristics of a stub area with the ability to import external routes. Like a stub area, an NSSA prevents ordinary Type 5 external LSAs received from other OSPF areas from entering. Unlike a regular stub area, however, an NSSA may contain an ASBR that redistributes external routes. Those imported routes are represented by Type 7 LSAs inside the NSSA. This design is useful when a branch area should remain relatively small but still needs to redistribute routes from another protocol or routing domain into OSPF.

Question 143. Which OSPF router generates a Type 7 LSA for an external route imported inside an NSSA?

1. The ASBR inside the NSSA
2. The DR in Area 0
3. Every internal router
4. The BDR only

Correct Answer: 1. The ASBR inside the NSSA

Explanation:

When an Autonomous System Boundary Router inside an NSSA redistributes a route from another routing source into OSPF, it generates a Type 7 NSSA LSA. The Type 7 LSA is flooded only within the NSSA rather than throughout the complete OSPF autonomous system. When the external information needs to reach other OSPF areas, an NSSA ABR can translate the Type 7 LSA into a Type 5 AS-external LSA. This mechanism allows an NSSA to support locally imported external routes while still limiting ordinary external LSAs from other areas.

Question 144. What normally happens to an NSSA Type 7 LSA when the external route must be advertised to other OSPF areas?

1. It is converted to a Type 2 LSA by the DR
2. It is discarded at every ABR
3. An NSSA ABR translates it into a Type 5 AS-external LSA
4. It becomes a Type 1 Router LSA

Correct Answer: 3. An NSSA ABR translates it into a Type 5 AS-external LSA

Explanation:

Type 7 LSAs have NSSA-local significance and are not directly flooded throughout the complete OSPF autonomous system. When a route imported in the NSSA needs to be advertised beyond that area, an NSSA Area Border Router performs Type 7-to-Type 5 translation. The resulting Type 5 LSA can then be flooded through normal OSPF areas according to standard external-route rules. This translation mechanism is one of the defining features of an NSSA and distinguishes it from a regular stub area, which does not permit an ASBR to import external routing information.

Question 145. Which routing information is normally suppressed inside an OSPF totally stubby area?

1. Both ordinary external routes and inter-area routes, with a default route supplied by the ABR
2. Only intra-area routes
3. Router-LSAs and Network-LSAs
4. All routing information, including the default route

Correct Answer: 1. Both ordinary external routes and inter-area routes, with a default route supplied by the ABR

Explanation:

A totally stubby area reduces OSPF information more aggressively than a regular stub area. A standard stub area blocks Type 5 external LSAs but can still receive inter-area Type 3 routes. A totally stubby area suppresses most inter-area route advertisements as well. The ABR instead advertises a Type 3 default route that internal routers can use for destinations outside the area. Intra-area LSAs remain necessary because routers still need to understand their local area topology. This design can substantially reduce routing-table and LSDB size on routers in simple branch areas.

Question 146. Which statement about OSPF virtual links and special areas is correct?

1. A virtual link must always cross an NSSA
2. A virtual link converts a stub area into Area 0
3. Virtual links are mandatory inside every stub area
4. An OSPF virtual link cannot pass through a stub area or NSSA

Correct Answer: 4. An OSPF virtual link cannot pass through a stub area or NSSA

Explanation:

OSPF virtual links are used in specific backbone-connectivity situations, such as connecting a disconnected backbone component through a transit area. However, Huawei documentation specifies that a virtual link cannot pass through a stub area or an NSSA. A transit area for a virtual link must support the routing information required for proper backbone operation. Special areas intentionally restrict certain LSA types, so they are unsuitable as virtual-link transit areas. Administrators designing multi-area OSPF should therefore maintain proper physical or logical Area 0 connectivity rather than expecting a stub or NSSA to provide transit for a virtual link.

Question 147. What problem does a BGP Route Reflector primarily solve?

1. Lack of external BGP connectivity
2. The scalability problem created by requiring a full mesh of IBGP sessions
3. OSPF LSA flooding
4. MPLS label allocation

Correct Answer: 2. The scalability problem created by requiring a full mesh of IBGP sessions

Explanation:

Traditional IBGP requires a logical full mesh because an IBGP speaker normally does not advertise a route learned from one IBGP peer to another IBGP peer. As the number of BGP routers increases, the number of required sessions grows rapidly according to n(n−1)/2. A Route Reflector changes this behavior by reflecting routes between selected IBGP peers called clients. Clients therefore need to establish IBGP sessions mainly with the RR instead of maintaining sessions with every other client. This dramatically improves BGP scalability and reduces configuration and control-plane resource usage in large autonomous systems.

Question 148. How does a BGP Route Reflector normally advertise a route learned from one of its clients?

1. Only back to the same client
2. Only to EBGP peers
3. To other clients and to non-client IBGP peers according to route-reflection rules
4. It never advertises client routes

Correct Answer: 3. To other clients and to non-client IBGP peers according to route-reflection rules

Explanation:

A Route Reflector modifies normal IBGP advertisement behavior. Huawei documents that an RR can advertise a route learned from one client to the RR’s other clients and to its non-client peers. A route learned from a non-client is reflected to clients, while routes learned through EBGP can generally be advertised to both clients and non-clients. These reflection rules remove the requirement for clients to maintain a full IBGP mesh with one another. Loop-prevention attributes such as Originator_ID and Cluster_List are added where necessary to keep route reflection safe.

Question 149. What is the PRIMARY purpose of the BGP Originator_ID attribute in a route-reflector environment?

1. To configure the BGP TCP port
2. To identify the OSPF DR
3. To control MPLS labels
4. To identify the original IBGP router that originated a reflected route and help prevent loops

Correct Answer: 4. To identify the original IBGP router that originated a reflected route and help prevent loops

Explanation:

When an RR reflects a route for the first time, it can add an Originator_ID attribute representing the router ID of the route’s original IBGP originator. If a device later receives a reflected route whose Originator_ID matches its own router ID, it recognizes that the route has returned to its origin and discards it. This helps prevent routing loops within a route-reflector cluster. Originator_ID is therefore a BGP route-reflection control attribute, not an MPLS label, transport parameter, or OSPF identifier.

Question 150. How does the BGP Cluster_List attribute help prevent route-reflection loops?

1. It records the clusters a reflected route has traversed so an RR can reject a route containing its own cluster ID
2. It lists every AS in the Internet
3. It replaces the AS_Path attribute
4. It specifies the BGP peer TCP port

Correct Answer: 1. It records the clusters a reflected route has traversed so an RR can reject a route containing its own cluster ID

Explanation:

A Route Reflector and its clients form a cluster identified by a cluster ID. Each RR adds its local cluster ID to the Cluster_List when reflecting a route. If an RR later receives a route whose Cluster_List already contains its own cluster ID, it detects that the route has passed through its cluster previously and discards it. This prevents loops between route-reflector clusters. Cluster_List complements Originator_ID: Originator_ID helps prevent a reflected route from returning to its original router, while Cluster_List helps prevent repeated circulation between RR clusters.

Question 151. Why should redundant Route Reflectors belonging to the same BGP cluster normally use the same cluster ID?

1. To force all clients to use EBGP
2. To allow Cluster_List loop detection to work correctly between the redundant RRs
3. To disable route reflection
4. To make their router IDs identical

Correct Answer: 2. To allow Cluster_List loop detection to work correctly between the redundant RRs

Explanation:

Deploying redundant Route Reflectors improves availability by preventing a single RR from becoming a single point of failure. Huawei recommends that RRs belonging to the same cluster use the same cluster ID. When one RR reflects a route to the other, the receiving RR examines the Cluster_List. Because the same cluster ID is already present, the route can be recognized as having passed through the cluster and discarded, preventing a reflection loop. The RRs do not need identical BGP router IDs; the shared cluster ID specifically supports route-reflection loop prevention.

Question 152. What is the PRIMARY benefit of BGP Add-Path in a Route Reflector deployment?

1. It prevents BGP from selecting any best path
2. It changes IBGP into OSPF
3. It allows the RR to advertise multiple paths for the same prefix to clients, improving backup or load-balancing possibilities
4. It disables route reflection

Correct Answer: 3. It allows the RR to advertise multiple paths for the same prefix to clients, improving backup or load-balancing possibilities

Explanation:

A conventional Route Reflector typically selects one optimal route for a destination and reflects that route to clients. If the selected path fails, clients may have to wait for BGP reconvergence before receiving an alternative. BGP Add-Path allows an RR to advertise two or more routes for the same prefix to its clients. Those routes can potentially act as backups or participate in load balancing when other conditions permit. Huawei describes Add-Path as particularly useful in RR environments requiring higher forwarding reliability and faster response to failures.

Question 153. Which statement correctly describes Huawei’s BGP PrefVal attribute?

1. It is locally significant on the device, and a larger PrefVal is preferred during BGP route selection
2. It is advertised unchanged throughout the Internet
3. A smaller PrefVal is always preferred
4. It is an OSPF-specific metric

Correct Answer: 1. It is locally significant on the device, and a larger PrefVal is preferred during BGP route selection

Explanation:

Huawei’s PrefVal is a proprietary BGP route-selection attribute that is valid only on the local device where it is configured. It is not propagated to BGP neighbors. During Huawei BGP best-path selection, the route with the largest PrefVal is preferred before Local Preference and several other common BGP attributes are considered. This makes PrefVal useful for influencing routing decisions on one specific router without changing how other routers evaluate the route. Because it is locally significant, it should not be confused with Local Preference, which is distributed within an AS.

Question 154. What does the well-known BGP community No_Export indicate?

1. The route must be advertised to every external peer
2. The route must be redistributed into OSPF
3. The route should be removed from the local BGP table
4. The route should not be advertised outside the local autonomous system**

Correct Answer: 4. The route should not be advertised outside the local autonomous system

Explanation:

The BGP No_Export community is a well-known community value used to control route propagation. When a BGP route carries No_Export, a router should not advertise that route to peers outside the local autonomous system. This provides a convenient policy mechanism for keeping selected routes internal while still allowing them to circulate among appropriate IBGP peers. Huawei also supports other well-known communities, such as No_Advertise, which prevents advertisement to any peer, and No_Export_Subconfed, which limits propagation beyond the local AS or confederation sub-AS as applicable.

Question 155. When BGP compares the Origin attribute and other earlier selection criteria are equal, which order is preferred?

1. Incomplete, EGP, IGP
2. IGP, EGP, Incomplete
3. EGP, Incomplete, IGP
4. All three have equal preference

Correct Answer: 2. IGP, EGP, Incomplete

Explanation:

The BGP Origin attribute identifies how a route was originally introduced into BGP. Huawei’s BGP route-selection rules prefer an Origin value of IGP over EGP, and EGP over Incomplete, assuming earlier selection criteria are equal. Routes injected using the BGP network mechanism typically receive an IGP origin, while routes introduced through redistribution can receive an Incomplete origin. Origin is only one step in the overall BGP best-path process; attributes such as PrefVal, Local Preference, and AS_Path length are evaluated before Origin in Huawei’s normal route-selection sequence.

Question 156. Why would an administrator set the IS-IS overload bit on a router undergoing maintenance?

1. To make every other router prefer it as a transit device
2. To delete its IS-IS process permanently
3. To discourage other routers from using it as a transit path while allowing controlled isolation
4. To convert Level-1 routes to BGP

Correct Answer: 3. To discourage other routers from using it as a transit path while allowing controlled isolation

Explanation:

The IS-IS overload bit can be set when a router should not be used as a transit node, such as during maintenance or partial initialization. Other IS-IS routers see the overload indication and avoid calculating normal transit paths through that device, helping prevent traffic from being forwarded through a router that is not ready to handle it correctly. Huawei specifically describes overload as a mechanism for temporarily isolating an IS-IS device and avoiding black-hole routes. This provides a controlled way to keep the protocol running while discouraging transit traffic.

Question 157. Why can the IS-IS overload bit be configured during startup while waiting for BGP to converge?

1. To make BGP converge more slowly
2. To disable IS-IS neighbor formation
3. To force every route through the restarting router
4. To prevent traffic from transiting the router before its BGP routing information is fully ready, reducing black-hole risk**

Correct Answer: 4. To prevent traffic from transiting the router before its BGP routing information is fully ready, reducing black-hole risk

Explanation:

IS-IS often converges faster than BGP after a router starts or restarts. Without protection, other routers might begin using the restarted device as an IS-IS transit node before its BGP table has fully converged. The router could then receive traffic for destinations it cannot yet forward correctly, creating a temporary black hole. Huawei supports setting the IS-IS overload bit at startup and keeping it active while waiting for BGP convergence. Once BGP is ready, the overload condition can be removed and the router can resume normal transit operation.

Question 158. What is the PRIMARY purpose of IS-IS route leaking from Level-2 into Level-1?

1. To eliminate Level-2 routing completely
2. To give Level-1 routers more specific information so they can choose a more optimal path instead of relying only on the nearest Level-1-2 router
3. To convert IS-IS into BGP
4. To disable the ATT bit

Correct Answer: 2. To give Level-1 routers more specific information so they can choose a more optimal path instead of relying only on the nearest Level-1-2 router

Explanation:

A pure Level-1 IS-IS router normally has detailed information only about its own area. For destinations elsewhere, it commonly sends traffic toward a nearby Level-1-2 router based on the ATT indication. If several Level-1-2 routers provide exits, the geographically or metrically nearest one may not produce the optimal end-to-end path. Route leaking can inject selected Level-2 routing information into the Level-1 area so Level-1 routers can make better path decisions. Huawei specifically describes route leaking as a method for optimizing route selection in two-level IS-IS networks.

Question 159. In which environment is PIM-DM generally most appropriate?

1. A relatively small multicast network where receivers are densely distributed
2. A very large network where receivers are extremely sparse
3. A network in which only unicast traffic exists
4. A network that requires no multicast routing protocol

Correct Answer: 1. A relatively small multicast network where receivers are densely distributed

Explanation:

PIM Dense Mode is designed around the assumption that multicast receivers are relatively densely distributed across the network. It initially floods multicast traffic and then prunes branches that do not need the traffic. This approach can work effectively in smaller environments where many network segments contain interested receivers, but it can create unnecessary traffic in large sparse networks. Huawei identifies PIM-DM as suitable for small-scale multicast networks with densely distributed group members. In contrast, PIM-SM builds multicast forwarding state more selectively and is better suited to sparse receiver distribution.

Question 160. Which scenario is BEST suited to PIM-SM?

1. A network with no multicast receivers
2. A small network in which almost every subnet has a multicast receiver
3. A large multicast network in which group members are distributed sparsely across the topology
4. A Layer 2 network requiring only STP

Correct Answer: 3. A large multicast network in which group members are distributed sparsely across the topology

Explanation:

PIM Sparse Mode is intended for networks where multicast receivers are sparsely distributed. Instead of flooding traffic everywhere and pruning unwanted branches, PIM-SM creates multicast forwarding entries and distribution trees as receivers explicitly join groups. In the ASM model, an RP can act as a meeting point for sources and receivers during tree establishment. Huawei identifies PIM-SM as suitable for large-scale networks with sparsely distributed multicast group members, making it more bandwidth-efficient than PIM-DM in such environments. Source-Specific Multicast can provide an additional alternative when receivers know the exact source in advance.