Network Fundamentals

20% of the CCNA · blueprint 200-301 v1.1 (effective 2024-08-20)

Short answer

Domain 1.0 is 20% of the CCNA 200-301 and is where subnetting lives. It covers the roles of routers, switches, firewalls, access points and controllers; two-tier, three-tier, spine-leaf and WAN topologies; copper and fiber cabling and how to spot duplex, speed and collision problems; TCP versus UDP; IPv4 addressing and subnetting; IPv6 address types; wireless principles; virtualization; and switching concepts such as MAC learning and aging.

Why it matters on this exam

Subnetting appears here and inside IP Connectivity questions. If you cannot find a network address quickly, you lose time on two domains worth 45% together.

Key concepts (objectives 1.1–1.13)

Devices: L2 switch (MAC table), L3 switch/router (routing table, ARP), next-gen firewall, WLC + lightweight APs, endpoints and servers.
Topologies: two-tier (collapsed core) vs three-tier; spine-leaf (every leaf to every spine, predictable latency); SOHO; on-prem vs cloud.
Cabling and interface issues: copper (UTP categories, straight-through vs crossover, auto-MDIX), fiber (SMF vs MMF, SFP); duplex mismatch shows as late collisions/CRC errors on the half-duplex side.
TCP vs UDP: connection-oriented, reliable, ordered, flow-controlled vs connectionless, best-effort; port numbers to know (20/21 FTP, 22 SSH, 23 Telnet, 25 SMTP, 53 DNS, 67/68 DHCP, 69 TFTP, 80/443, 110, 123 NTP, 161/162 SNMP, 514 syslog).
IPv4: classes A/B/C, private ranges (RFC 1918: 10/8, 172.16/12, 192.168/16), APIPA 169.254/16, loopback 127/8; subnetting by block size; /31 (RFC 3021) and /32.
IPv6: global unicast 2000::/3, unique local fc00::/7, link-local fe80::/10, multicast ff00::/8, anycast, modified EUI-64; SLAAC; no broadcast.
Wireless: non-overlapping 2.4 GHz channels 1/6/11, 5 GHz channels, SSID, RF basics; virtualization: hypervisors, VMs, containers, VRFs.
Switching concepts: frame flooding, MAC learning and aging, frame switching.

Common mistakes

Treating the broadcast address as usable, or forgetting /31 has two usable addresses.
Confusing wildcard masks (inverse of subnet masks) in ACL questions.

Worked example

172.16.45.200/20: mask 255.255.240.0, block size 16 in the third octet; multiples of 16 are 32 and 48, and 45 falls in the 32 block, so the network is 172.16.32.0, broadcast 172.16.47.255, hosts 172.16.32.1–172.16.47.254 (4,094). Check it in the subnet calculator.

Original practice questions

Network FundamentalsDifficulty 2/5

What is the network address for host 172.16.45.200 with a /20 mask?

A172.16.32.0
B172.16.40.0
C172.16.48.0
D172.16.45.0

Show answer and rationale

Correct: A. A /20 mask is 255.255.240.0, so the interesting octet is the third with block size 256 − 240 = 16. Multiples of 16 up to 45 are 0, 16, 32, 48; 45 falls in the 32 block, so the network is 172.16.32.0 and the broadcast is 172.16.47.255.

D — That would require a /24 or longer mask.
B — 40 is not a multiple of the block size 16.
C — 48 is the start of the next block; 45 is below it.

Network FundamentalsDifficulty 3/5

How many usable host addresses are in a /31 subnet on a point-to-point link, and why?

A0, because network and broadcast consume both addresses
B2, because RFC 3021 allows both addresses to be assigned on point-to-point links
C1, because one address is reserved for the broadcast
D4, because /31 has four addresses

Show answer and rationale

Correct: B. A /31 has two addresses. RFC 3021 permits using both on point-to-point links, since no broadcast address is needed there. Cisco IOS supports this with the ip address ... 255.255.255.254 form.

A — The classic 2^n − 2 rule does not apply to /31 per RFC 3021.
C — No broadcast address is reserved on a /31 point-to-point link.
D — 2^(32−31) = 2 addresses, not 4.

Network FundamentalsDifficulty 2/5

Which address is in a private range defined by RFC 1918?

A172.33.10.1
B192.169.5.5
C10.255.254.1
D169.254.10.10

Show answer and rationale

Correct: C. RFC 1918 reserves 10.0.0.0/8, 172.16.0.0/12 (172.16–172.31) and 192.168.0.0/16. 10.255.254.1 is inside 10.0.0.0/8.

A — 172.33 is outside 172.16.0.0–172.31.255.255.
B — 192.169.0.0 is outside 192.168.0.0/16.
D — 169.254.0.0/16 is link-local (APIPA), not RFC 1918.

All 5 Network Fundamentals questions →

Tools for this topic

Subnet calculator (IPv4, CIDR, wildcard) — Enter any IPv4 address with a prefix or mask and get the network and broadcast addresses, usable host range, host count, wildcard mask, class and RFC 1918 status, with the binary shown.
VLSM calculator — Give it a base network and the hosts each subnet needs; it allocates largest-first, non-overlapping subnets with network, mask, usable range and broadcast for each, exactly as a CCNA VLSM question expects.

4 flashcards for Network Fundamentals

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Blueprint-mapped questions with full rationales for every choice.

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Related areas: Network Access · IP Connectivity · IP Services · Security Fundamentals

Primary references

CCNA Exam v1.1 (200-301) Exam Topics — Cisco Systems · primary · retrieved 2026-09-21, verified 2026-09-21
RFC 1918 — Address Allocation for Private Internets — IETF · government · retrieved 2026-09-21, verified 2026-09-21
RFC 4632 — Classless Inter-domain Routing (CIDR) — IETF · government · retrieved 2026-09-21, verified 2026-09-21

Last reviewed: 2026-09-21Next review by: 2026-11-20Draft — pending editorial reviewHow we verify facts