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31 multiple-choice questions and 20 flashcards on Addressing, IPv4/IPv6 and Subnetting, about 11% of the CompTIA Network+ bank. Every one carries a written rationale.
Addressing, IPv4/IPv6 and Subnetting is one of 7 chapters in CoStudy's CompTIA Network+ bank, and it holds 31 of the bank's 270 multiple-choice questions — roughly 11% 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.
After a conference week, guest users report failures to obtain addresses even though many devices have left the building. The scope shows nearly all addresses leased. Which change BEST addresses the recurrence?
Answer: C — Reduce the guest scope lease duration to a few hours
C) Correct — transient populations exhaust a scope when leases outlive the visit; a short lease returns addresses to the pool quickly after devices leave. A) A relay only matters when the server is on another subnet; leases are being issued, so relay is not the fault. B) Gateway options do not affect pool capacity in any way. D) Static addressing for unmanaged guest devices is unworkable and does not scale to a conference.
Which DNS record type is used to direct mail for a domain to the correct server?
Answer: C — MX
MX (mail exchange) lists mail servers and priorities. NS lists authoritative name servers. SRV publishes service endpoints (SIP, Kerberos, etc.). TXT carries text (SPF/DKIM). Adjacent-record-type trap.
Which address is a valid IPv6 link-local address?
Answer: C — fe80::1
Link-local is fe80::/10. 2001:db8::/32 is documentation/global. fc00::/7 is Unique Local (ULA). ::1 is loopback. Confusing fe80 with fc00 or 2001:db8 is a frequent IPv6 trap.
Which CIDR block correctly summarizes 192.168.4.0/24, 192.168.5.0/24, 192.168.6.0/24, and 192.168.7.0/24?
Answer: C — 192.168.4.0/22
Four contiguous /24s starting at a /22-aligned boundary summarize to /22. /23 only covers two /24s. /21 covers eight /24s but starts at .0. Supernetting/summarization boundaries are a Network+ favorite trick.
Two IPv6-enabled sites must exchange IPv6 traffic, but the provider WAN between them forwards only IPv4. Which method allows the sites to communicate?
Answer: C — Encapsulate IPv6 packets inside IPv4 through a tunnel between site routers
C) Correct — tunnelling encapsulates IPv6 in IPv4 so an IPv4-only transit can carry it, which is the standard answer when the middle of the path lags the edges. A) Unique local addresses are private in scope and providers do not carry them; addressing is not the obstacle here. B) SLAAC assigns host addresses on a link and does nothing about an IPv4-only transit path. D) Host-level translation is not how dual-stack transition works and would require rewriting every application's addressing.
Which is true about a /31 subnet in modern point-to-point links?
Answer: A — Two usable host addresses; no network or broadcast reserved
RFC 3021 allows /31 on point-to-point links with both addresses usable. Older subnetting formula would yield 0 — the off-by-one trap. /30 has 2 usable. /29 has 6.
An office of 300 workstations reaches the internet through a single public IPv4 address on the edge router. Which mechanism makes this possible?
Answer: B — Port address translation multiplexing sessions by source port
B) Correct — PAT (NAT overload) maps many inside addresses to one public address by rewriting source ports, so the translation table distinguishes sessions. A) Static NAT is one public address per inside host and cannot compress 300 hosts onto one address. C) Proxy ARP answers layer 2 address requests on a segment and performs no address translation. D) Dynamic NAT requires a pool of public addresses at least as large as the number of concurrent hosts, which is not available here.
An auditor asks how the organization can prove that DNS responses for its zone were not altered in transit by an intermediate resolver. Which control MOST directly satisfies the request?
Answer: D — DNSSEC signing so resolvers validate response authenticity
D) Correct — DNSSEC adds cryptographic signatures to zone data, letting a validating resolver detect any modification or forgery of the records. A) Lower TTLs shorten how long a bad answer persists but do not detect tampering. B) DoH encrypts the client-to-resolver hop for privacy but proves nothing about the integrity of the zone data itself upstream. C) Split-horizon controls which answers each audience sees; it does not authenticate them.
IPv6 clients on a segment form addresses automatically from the router's prefix but receive no DNS server information. Which explanation is MOST likely?
Answer: B — SLAAC is supplying the prefix while no DHCPv6 or RDNSS option provides resolvers
B) Correct — SLAAC builds an address from the advertised prefix, but resolver information must come from a DHCPv6 server or an RDNSS option in the router advertisement; without either, addressing works and name resolution does not. A) A prefix longer than /64 breaks SLAAC address formation entirely, which is not the observed symptom. C) If router advertisements were suppressed, clients would not obtain a prefix at all. D) IPv6 option delivery is independent of whether an IPv4 gateway exists.
Security staff notice that browser DNS lookups now bypass the corporate resolver and its category filtering, and the queries are indistinguishable from normal web sessions on port 443. Which behaviour explains this?
Answer: B — The clients are using DNS over HTTPS to an external resolver
B) Correct — DoH carries queries inside ordinary HTTPS on 443, which is why it blends with web traffic and evades resolver-based filtering. A) DoT also encrypts queries but uses a separate well-known port, so it is easy to identify and block rather than indistinguishable. C) Local broadcast name resolution stays on the segment and never appears as outbound 443 traffic. D) DNSSEC validation authenticates answers on the existing resolver path and does not redirect clients elsewhere.
4 cards from the 20 in this chapter.
Why are tunnelling techniques used during an IPv6 rollout, and what do they do to the packet?
Tunnelling carries IPv6 traffic across network segments that only forward IPv4, by encapsulating the IPv6 packet inside an IPv4 packet (or the reverse) at a tunnel endpoint and stripping it at the far end. It buys time when the transit path cannot be upgraded, at the cost of extra header overhead that reduces the usable MTU and of tunnel endpoints that become troubleshooting and security choke points.
What is the IPv6 link-local address range?
fe80::/10 — automatically assigned to every IPv6 interface; only valid on the local segment. Required for IPv6 operation.
What is the difference between IPv4 and IPv6 address formats?
IPv4: 32-bit, dotted decimal (e.g., 192.168.1.1). IPv6: 128-bit, eight 16-bit hex groups (e.g., 2001:db8::1) — zeros can be compressed with ::.
What is APIPA and when does it appear?
Automatic Private IP Addressing — Windows assigns 169.254.x.x/16 when DHCP fails. Indicates a DHCP problem (bad server, network, or no scope).
These are a sample. The full Addressing, IPv4/IPv6 and Subnetting chapter runs 51 items with per-chapter progress tracking, on the web and in the iOS app.
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