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27 multiple-choice questions and 16 flashcards on Network Implementation — Routing and Switching, about 10% of the CompTIA Network+ bank. Every one carries a written rationale.
Network Implementation — Routing and Switching is one of 7 chapters in CoStudy's CompTIA Network+ bank, and it holds 27 of the bank's 270 multiple-choice questions — roughly 10% of the total. That proportion is not arbitrary: chapters follow the certifying body's published exam outline, and the number of questions in each is set by that domain's published weight, so the share of your practice time this chapter takes matches the share of the real exam it accounts for.
Studying by chapter is worth doing once you have a diagnostic score. A single overall percentage tells you whether you are close; it does not tell you which domain is dragging. Working a weak chapter in isolation, and re-testing it in isolation, is the fastest way to move a score that has stalled — and it is why the mock exams in CoStudy report by domain rather than as one number.
10 questions drawn from this chapter, with the full rationale shown — the controlling principle behind the right answer, and why each wrong option tempts and fails.
A campus with roughly 40 routers needs fast convergence, a loop-free view of the topology, and hierarchical design within a single organization. Which protocol BEST fits?
Answer: D — OSPF, using areas organized around a single backbone area
D) Correct — OSPF is a link-state interior gateway protocol whose area hierarchy scales a campus and whose shortest-path computation converges quickly and loop-free. A) BGP is designed for policy-driven routing between autonomous systems, not for fast interior convergence. B) A periodic distance-vector protocol converges slowly and does not give routers a topology view. C) Static routes at 40 routers becomes unmaintainable and provides no automatic reconvergence.
Which administrative distance does Cisco IOS assign to an internal EIGRP route by default?
Answer: D — 90
Internal EIGRP AD = 90. OSPF = 110. RIP = 120. External EIGRP = 170. Confusing administrative distance with metric (route cost) is the classic direction-reversal trap.
Which STP port state is reached after Listening but before Forwarding?
Answer: C — Learning
Classic 802.1D STP states: Blocking → Listening → Learning → Forwarding (Disabled is administrative). Order reversal is a frequent STP trick. RSTP collapses these into Discarding/Learning/Forwarding.
An engineer needs to bond two switch uplinks for higher throughput and redundancy. Which standard should they configure?
Answer: C — 802.3ad (LACP) — link aggregation of multiple physical ports
802.3ad / LACP provides link aggregation. 802.1Q is VLAN tagging. 802.1X is NAC/port-based authentication. 802.1D is STP. Adjacent-standard confusion is a frequent trap.
After adding a second switch, VLAN 10 works between the switches but VLAN 20 traffic never crosses the uplink, and the uplink shows no errors. Which cause is MOST likely?
Answer: A — VLAN 20 is not allowed on the trunk between the switches
A) Correct — trunk allowed-VLAN lists are the usual culprit when one VLAN passes and another does not on the same physical link. B) A blocked port would stop VLAN 10 as well, since blocking applies to the link, not to a single VLAN in this scenario. C) A duplex mismatch produces errors and affects all VLANs, but the uplink is clean. D) A trunk exists precisely to carry many VLANs over one link, so this reverses the concept.
A VLAN allows network administrators to:
Answer: B — Segment one physical switch into separate broadcast domains without rewiring
B is right: VLANs use 802.1Q tagging to divide one physical infrastructure into separate broadcast domains, improving security and performance without recabling. A reverses the effect, since VLANs split rather than merge broadcast domains. C confuses a Layer 2 feature with radio behavior. D is unrelated to Layer 4 transport choice. Inter-VLAN traffic needs a router or Layer 3 switch.
A small stub site connects to headquarters through a single WAN circuit with no alternate path. Which routing choice is MOST appropriate?
Answer: B — Configure a static default route toward headquarters
B) Correct — with only one exit there is no path decision to make, so a static default is simplest, uses no CPU or bandwidth for adjacency, and cannot flap on protocol state. A) Dynamic routing adds overhead and complexity with nothing to choose between. C) BGP toward the provider is for multihomed or policy-driven sites, not a single-circuit stub. D) Redistribution assumes two routing domains exist, which is not the case here and risks loops.
What is the role of Spanning Tree Protocol (STP, 802.1D)?
Answer: C — Block redundant ports to leave one loop-free Layer 2 path
C is right: STP elects a root bridge, computes least-cost paths, and blocks the remaining redundant ports so no Layer 2 loop or broadcast storm forms. A describes link aggregation, which is a different feature. B is unrelated to loop prevention. D confuses a Layer 2 mechanism with Layer 3 routing. E describes something STP does not do. RSTP and MSTP are the modern variants.
What does VLAN tagging (802.1Q) do?
Answer: A — Inserts a 4-byte tag naming the VLAN a frame belongs to
A is right: 802.1Q inserts a 4-byte tag carrying a 12-bit VLAN ID (1-4094) plus priority bits, so a trunk can carry many VLANs between switches. B is wrong because tagging provides no confidentiality. C describes tunneling such as GRE or 6in4. D is not part of the standard. E is tempting because the tag does include priority bits, but VLAN identification is its main job.
A company obtains transit from two different providers and wants to influence which provider is preferred for inbound traffic to its own address block. Which protocol characteristic makes this possible?
Answer: A — BGP is a path-vector protocol whose attributes support routing policy
A) Correct — BGP carries AS-path and other attributes with each advertised prefix, and manipulating them is the standard way to influence how the internet reaches a multihomed block. B) OSPF is interior and is not exchanged with providers, so its costs cannot influence external senders. C) EIGRP is likewise interior and would not be run toward transit providers. D) Administrative distance on static defaults affects outbound choice on the local router only, not inbound path selection.
2 cards from the 16 in this chapter.
What are the differences between routing protocols RIP, OSPF, EIGRP, BGP?
RIP: distance-vector, hop count, slow. OSPF: link-state, fast, area-based. EIGRP: hybrid (Cisco), DUAL algorithm. BGP: path-vector, the Internet's exterior protocol.
What is STP and what does it prevent?
Spanning Tree Protocol (802.1D, RSTP 802.1w, MSTP 802.1s) — prevents L2 loops by blocking redundant paths and electing a root bridge.
These are a sample. The full Network Implementation — Routing and Switching chapter runs 43 items with per-chapter progress tracking, on the web and in the iOS app.
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