Network+ Domain 2 - Network Implementation (20%)¶

Routing, switching, wireless, and the physical layer. This is where the concepts from Domain 1 become configuration.

Routing¶

Static route - manually configured. Predictable, no protocol overhead, does not adapt to failure.
Dynamic route - learned from a routing protocol. Adapts automatically, at the cost of complexity and CPU.
Default route - 0.0.0.0/0, the route of last resort.
Administrative distance (AD) - trustworthiness of a route source when two protocols offer the same destination. Lower wins.
Metric - the cost used to choose between routes within one protocol.
Longest prefix match - the most specific matching route wins, regardless of protocol or metric. This rule is applied before AD.

Protocols

RIP - distance vector, metric is hop count, maximum 15 hops. Simple and slow to converge.
OSPF - link state, metric is cost derived from bandwidth, organized into areas with area 0 as the backbone. The most commonly tested interior protocol.
EIGRP - Cisco's advanced distance vector, metric from bandwidth and delay.
BGP - path vector, the routing protocol of the internet, chooses paths between autonomous systems using policy rather than pure speed.
Interior gateway protocol (IGP) - runs within one autonomous system: RIP, OSPF, EIGRP.
Exterior gateway protocol (EGP) - runs between autonomous systems: BGP.
Convergence - the time for all routers to agree on the topology after a change.

VLAN (Virtual LAN) - a logical broadcast domain. Hosts in different VLANs need a router to communicate.
Access port - carries one VLAN, connects to an end device.
Trunk port - carries multiple VLANs between switches, tagging frames with 802.1Q.
Native VLAN - the untagged VLAN on a trunk. Mismatched native VLANs cause traffic to leak between VLANs.
Voice VLAN - a separate VLAN for IP phones, so voice traffic is isolated and prioritized.
Inter-VLAN routing - performed by a Layer 3 switch or a router-on-a-stick subinterface configuration.

Spanning Tree Protocol

STP (802.1D) - prevents Layer 2 loops by blocking redundant paths. Without it, a loop causes a broadcast storm that collapses the network.
RSTP (802.1w) - rapid STP, converges in seconds rather than tens of seconds.
Root bridge - the reference point of the spanning tree, elected by lowest bridge ID.
PortFast - moves an access port straight to forwarding, for end devices only.
BPDU guard - disables a port that receives a BPDU, protecting against a rogue switch.
Root guard - prevents a downstream switch from becoming root.

Other switch features

Link aggregation (LACP, 802.3ad) - bundles physical links into one logical link for bandwidth and redundancy.
Port security - restricts which MAC addresses may use a port.
Port mirroring (SPAN) - copies traffic to a monitoring port for capture.
Power over Ethernet (PoE) - delivers power over the data cable. 802.3af is roughly 15 W, 802.3at (PoE+) roughly 30 W, 802.3bt (PoE++) higher still. Check the power budget of the switch, not just the port.

Standard	Common name	Band	Notes
802.11a	-	5 GHz	Legacy
802.11b/g	-	2.4 GHz	Legacy, long range, slow
802.11n	Wi-Fi 4	2.4 and 5 GHz	Introduced MIMO
802.11ac	Wi-Fi 5	5 GHz	MU-MIMO downlink
802.11ax	Wi-Fi 6 / 6E	2.4, 5, and 6 GHz	OFDMA, better in dense environments
802.11be	Wi-Fi 7	2.4, 5, 6 GHz	Multi-link operation

Channel planning - in 2.4 GHz only channels 1, 6, and 11 are non-overlapping. Overlapping channels are a leading cause of poor performance.
Co-channel interference - neighboring access points on the same channel contending for airtime.
Service set identifier (SSID) - the wireless network name.
BSSID - the MAC address of the radio, identifying a specific access point.
Antenna types - omnidirectional radiates in all directions; directional (Yagi, parabolic) focuses energy for point-to-point links.
Site survey and heat map - measuring actual coverage and interference before and after deployment.

Wireless security

WPA2 - AES-CCMP encryption. Still widespread.
WPA3 - replaces the pre-shared key handshake with SAE, protecting against offline dictionary attacks.
802.1X - port-based network access control, authenticating users rather than sharing one key. Uses EAP with a RADIUS server.
EAP variants - PEAP and EAP-TTLS tunnel credentials inside TLS; EAP-TLS uses certificates on both sides and is the strongest.
Captive portal - intercepts web traffic to force authentication or acceptance of terms.

Twisted pair categories - Cat 5e up to 1 Gbps, Cat 6 up to 10 Gbps over shorter runs, Cat 6a 10 Gbps to 100 m, Cat 8 for short data-center runs.
100 meter limit - the maximum copper Ethernet run, 90 m of solid cable plus 10 m of patch leads.
Fiber: single-mode versus multimode - single-mode carries one light path over long distances; multimode is cheaper and used for shorter runs.
Straight-through versus crossover - modern equipment auto-negotiates with Auto-MDIX, making crossover cables largely historical.
Rack units (U) - 1.75 inches of vertical rack space each.
Environmental factors - temperature, humidity, and airflow. Hot aisle and cold aisle containment manages data-center heat.
Grounding and bonding - protects equipment and people, and reduces interference.

Longest prefix match is checked before administrative distance. Questions frequently test the order.
A trunk carrying only some VLANs is a classic cause of "these two hosts cannot talk but everything else works."
A broadcast storm with all switch lights flashing is a spanning-tree failure or a physical loop.
If a wireless problem mentions many access points in a small area, look at channel overlap.
If a PoE device will not power up, check the switch's total power budget and the PoE standard supported.

📖 CompTIA Network+ N10-009 objectives - authoritative domain list 📖 IEEE 802.11 standards - wireless specifications 📖 IEEE 802.1Q - VLAN tagging