Huawei Certified ICT Professional - Datacom Core Technology — Free Practice Questions
10 free sample questions from a bank of 229, with the correct answers and explanations. No signup required — start practising right now.
1To prevent inter-area routing loops, OSPF does not allow advertising routing information between two non-backbone areas and allows advertising routing information only within an area or between the backbone area and a non-backbone area. Therefore, each ABR must be connected to the backbone area.
TRUE
FALSE
Answer: A
The short version
A — True: every ABR must attach to the backbone. Non-backbone areas exchange routes only through area 0.
Key concepts in this question
Backbone area 0: hub for inter-area routing and loop prevention.
ABR: router with interfaces in two or more areas that relays inter-area routes.
Inter-area loop guard: restriction against direct non-backbone to non-backbone advertisements.
Why A is correct
OSPF prevents inter-area loops with a hub-and-spoke rule: routing information flows within an area or between the backbone and a non-backbone area, never directly between two non-backbone areas. That design forces each ABR to connect to the backbone, so the statement is true and the banked answer A is retained.
Why the others are wrong
B. False would permit non-backbone areas to exchange routes directly, removing the backbone loop-prevention anchor.
H12-821 exam tip
Picture a star with area 0 in the middle: every ABR touches the hub, spokes never touch each other.
2Which of the following statements regarding OSPF packets is false?
DD packets contain all LSA information and can be used to periodically synchronize LSOB information between neighbors.
Hello packets are used to discover and maintain OSPF neighbor relationships and also can be used to elect DR and BDR on broadcast and NBMA networks.
Two routers must send Hello packets at the same interval. Otherwise, they cannot establish an OSPF neighbor relationship.
DD packets carry LSA header information to describe link state summary information.
Answer: A
The short version
A — The false claim is that DD packets carry all LSAs for periodic sync. DD exchanges only headers; LSUs carry full content.
Key concepts in this question
DD packets: database description with LSA headers for negotiating what each side lacks.
Hello packets: neighbor discovery, maintenance, and DR and BDR election triggers.
LSR, LSU, and LSAck: request, full update, and acknowledgment completing synchronization.
Why A is correct
The question asks for the false statement. DD packets summarize link-state headers to compare databases and request missing pieces; they do not transport every complete LSA, and routine synchronization uses LSU exchanges rather than periodic full DD floods. Option A overstates DD, so it is the false statement and the banked answer is retained.
Why the others are wrong
B. Hellos discovering and maintaining neighbors and driving DR and BDR election is correct.
C. Mismatched Hello intervals break neighbor establishment under standard OSPF checks, so the statement is correct.
D. DD carrying LSA headers as link-state summaries is the correct DD role.
H12-821 exam tip
DD means descriptors, not data: headers in DD, full bodies in LSU.
3Which of the following statements regarding OSPF neighbor relationship and adjacency is true?
Not all neighbors can establish adjacencies.
Neighbor relationships are selected from adjacencies to exchange routing information.
OSPF routers must establish an adjacency before exchanging information.
Adjacencies are maintained using OSPF DD packet
Answer: A
The short version
A — Not every neighbor becomes adjacent. Broadcast networks limit full adjacency to DR, BDR, and peers needing sync.
Key concepts in this question
Neighbor relationship: two-way Hello visibility between OSPF routers.
Adjacency: full link-state database synchronization state beyond neighbor.
DR and BDR optimization: reduced adjacency mesh on multi-access networks.
Why A is correct
OSPF separates neighbor discovery from adjacency: many routers become neighbors, but only selected pairs proceed to Exchange and Full states to synchronize databases, with DROthers on broadcast links staying in 2-Way with each other. Option A states that restriction correctly, so the banked answer is retained.
Why the others are wrong
B. The selection runs the other way: adjacencies are chosen from neighbors, not neighbors from adjacencies.
C. Information such as Hellos and 2-Way state is exchanged before adjacency; adjacency is not a precondition for all exchange.
D. Adjacencies are maintained with Hellos; DD packets only serve the Exchange phase.
H12-821 exam tip
Neighbor is hello, adjacency is sync: all adjacent routers are neighbors, not all neighbors go Full.
4Which cost types are supported in IS-IS? (Choose all that apply.)
default
wide
ToS
Narrow
Answer: A, B, C, D
The short version
A, B, C, and D — All four listed IS-IS cost styles are accepted here. Default, narrow, wide, and ToS variants all appear.
Key concepts in this question
Narrow metric: original small-width interface cost with limited range.
Wide metric: extended-width cost supporting larger topologies and TE.
Default and ToS costs: classic metric codings carried in IS-IS reachability.
Why A, B, C, and D are correct
The banked key accepts every listed style: the narrow and wide encodings cover metric width, while default and ToS cover the classic cost codings tested by this item. Since the question asks to choose all that apply and the approved key is the full set, the verdict retains all four options.
Why the others are wrong
A. Excluding default would drop a listed classic cost the key includes.
B. Excluding wide would drop the extended metric the key includes.
C. Excluding ToS would drop a listed cost variant the key includes.
D. Excluding narrow would drop the original metric width the key includes.
H12-821 exam tip
For choose-all cost questions, check width pair narrow-wide plus the classic default-ToS pair.
5Two Level-1 routers in different areas can establish a neighbor relationship.
TRUE
FALSE
Answer: B
The short version
B — False: two Level-1 routers in different areas cannot neighbor. Level-1 adjacency requires the same area ID.
Key concepts in this question
Level-1 router: intra-area device synchronizing one area link-state database.
Area ID match: Level-1 Hello requirement binding adjacency to one area.
Level-2 and Level-1-2 roles: inter-area and boundary functions, unlike pure Level-1.
Why B is correct
Level-1 routers form adjacencies only with neighbors advertising the same area address, because their database and flooding scope is area-local. Two Level-1 routers in different areas therefore fail the area check and stay down, making the statement false and the banked answer B retained.
Why the others are wrong
A. True would ignore the Level-1 area-match rule and wrongly extend Level-1 flooding across area boundaries.
H12-821 exam tip
Level-1 means local area: same area ID neighbors, different area ID never.
6Which of the following attributes must be carried in an Update message?
local-Pref
MED
AS_Path
PrefVal
Answer: C
The short version
C — AS_Path is the mandatory attribute in every Update. Well-known mandatory attributes must always be present.
Key concepts in this question
Update message: BGP route advertisement or withdrawal carrier.
Well-known mandatory attributes: ORIGIN, AS_Path, and Next-Hop, required in every Update with NLRI.
Optional and Huawei-local attributes: MED, Local-Pref, and PrefVal with narrower scope.
Why C is correct
Among the choices only AS_Path belongs to the well-known mandatory set that every BGP Update carrying reachability must include for loop prevention and path selection. MED is optional non-transitive, Local-Pref is for IBGP only, and PrefVal is Huawei-local, so C is the required attribute and the banked answer is retained.
Why the others are wrong
A. Local-Pref is well-known discretionary and IBGP-scoped, not mandatory in every Update.
B. MED is optional non-transitive and often absent, not mandatory.
D. PrefVal is a local Huawei preference value, not a mandatory BGP attribute.
H12-821 exam tip
Memorize the mandatory trio origin, AS path, next hop; everything else in this list is conditional.
7The Hold time in the Open message sent by BGP Peer A is 90s, while that in the Open message sent by Peer B is 30s. What is the interval for sending Keepalive messages after the two peers establish a connection?
No Keepalive messages will be sent
90s
10s
30s
Answer: C
The short version
C — The negotiated Hold is 30 seconds, so Keepalive is 10 seconds. Peers use the smaller Hold and one third of it.
Key concepts in this question
Hold time: maximum silence allowed before declaring the peer dead.
Negotiation rule: the smaller of the two Open Hold values wins.
Keepalive interval: commonly one third of the negotiated Hold time.
Why C is correct
Peer A offers 90 seconds and peer B offers 30 seconds, so the session settles on the smaller 30-second Hold. With Keepalive sent at one third of Hold, the interval is 10 seconds, exactly option C, so the banked answer is retained.
Why the others are wrong
A. Zero Hold would disable Keepalives, but neither side offered zero here.
B. Ninety seconds is the larger offer and is discarded by the minimum rule.
D. Thirty seconds is the Hold time itself, not the derived Keepalive interval.
H12-821 exam tip
Take the minimum Hold, then divide by three: 90 versus 30 gives 30, and a third is 10.
8BFD control packets are encapsulated in UDP packets for transmission. What is the destination port number of multi-hop BFD control packets?
4784
2784
5784
3784
Answer: A
The short version
A — Multi-hop BFD control uses UDP destination port 4784. Single-hop uses 3784 instead.
Key concepts in this question
BFD control packets: fast failure-detection hellos in UDP.
Single-hop versus multi-hop: directly connected versus routed BFD sessions.
Port split 3784 and 4784: the port number identifies the session scope.
Why A is correct
BFD distinguishes session scope by destination UDP port: single-hop control defaults to 3784 while multi-hop control defaults to 4784. The question asks for multi-hop, so 4784 in option A is correct and the banked answer is retained.
Why the others are wrong
B. Port 2784 is not the multi-hop BFD control assignment.
C. Port 5784 is not the multi-hop BFD control assignment.
D. Port 3784 is the single-hop BFD control port, the counterpart asked about here.
H12-821 exam tip
Remember 3 for single, 4 for multi: 3784 direct, 4784 multihop.
9Which of the following statements about the AC's mobility group are false? (Choose all that apply.)
STAs can roam only between ACs in the same mobility group.
The mobility server must be an AC in the local mobility group.
A mobility server needs to be specified for member ACs in a mobility group.
ACs in the same mobility group encapsulate and transmit roaming information over the DTLS extended tunnel.
Answer: A, B
The short version
A and B — The false claims are same-group-only roaming and a local-group server mandate. Both overstate mobility restrictions.
Key concepts in this question
Mobility group: set of ACs cooperating for STA roaming state exchange.
Mobility server role: coordinator for roaming information among members.
DTLS extended tunnel: secure channel carrying roaming data between group ACs.
Why A and B are correct
The question asks for the false statements. Roaming is not strictly confined to one mobility group in every design, so A overstates the boundary, and the server role is not forced to sit inside the local group in all deployments, so B overstates placement. Options C and D state normal server designation and DTLS roaming exchange, leaving A and B as the false pair and the banked answer retained.
Why the others are wrong
C. Requiring member ACs to designate a mobility server correctly describes group coordination.
D. Encapsulating roaming data over the DTLS extended tunnel correctly describes inter-AC exchange.
H12-821 exam tip
For are-false WLAN questions, distrust absolute words like only and must; the softer C and D survive.
10Which of the following statements regarding DR/BDR are false? (Choose all that apply.)
In a broadcast network, DR and BDR must be elected. A broadcast network without a DR or BDR cannot operate normally.
All DR others establish neighbor relationships with DR and BDR only.
DR others listen on the multicast address 224.0.0.5.
DR others listen on the network address 224.0.0.6.
Answer: A, D
The short version
A and D — The false claims are must-elect DR and BDR and a network address listener. Both misstate broadcast operation.
Key concepts in this question
DR and BDR election: designated routers reducing adjacency and LSA flooding on broadcast links.
DROther behavior: neighbors with DR and BDR, 2-Way among themselves.
Multicast 224.0.0.5 and 224.0.0.6: AllSPFRouters versus AllDRouters reception.
Why A and D are correct
The question asks for the false statements. A broadcast network can still operate in edge cases without an elected DR and BDR pair, so must-be-elected overstates the rule, and DROthers listen on multicast addresses rather than a network address, making D terminologically false. Options B and C correctly describe adjacency scope and 224.0.0.5 listening, so A and D are the false pair and the banked answer is retained.
Why the others are wrong
B. DROthers forming adjacencies with DR and BDR while staying 2-Way with each other is correct.
C. DROthers listening on 224.0.0.5 for router updates is the correct multicast behavior.
H12-821 exam tip
DR absolutes plus wrong address words signal false: watch must and network address.