Wired and Wireless Network Fundamentals (Routing and Switching)
What you must understand
At the core you need Layer 2 forwarding and Layer 3 forwarding, and where they meet. Know how a switch builds a MAC address table by learning source MACs, floods unknown unicast and broadcasts within a VLAN, and how VLANs segment broadcast domains. Understand 802.1Q trunking: the tag is inserted after the source MAC, native VLAN traffic is typically untagged, and both ends must agree on allowed VLANs. For routing, know longest-prefix match, administrative distance versus metric (AD chooses between protocols, metric chooses within one), and how a router resolves the next hop to a MAC via ARP.
Link aggregation matters: LACP negotiates, static trunks do not, and all member links must match in speed, duplex, and VLAN configuration. Spanning tree prevents loops; remember root bridge election is by lowest bridge ID (priority then MAC), and port roles follow cost to root.
Traps to expect
- Confusing a broadcast domain with a collision domain; a VLAN is a broadcast domain.
- Assuming a trunk forwards all VLANs by default when a native VLAN mismatch causes untagged traffic to land in the wrong VLAN.
- Mixing up AD and metric ordering.
- Forgetting that a switch floods a frame when the destination MAC is unknown, not when it is known.
- Believing LACP is required for a static aggregate to pass traffic.
Rule of thumb
Read any forwarding question as: what table is consulted, what is the match key, and what happens on a miss? On a miss, switches flood within the VLAN; routers drop (or use a default route if one exists).
Worked example
Two hosts on different VLANs on the same switch cannot ping. The switch is Layer 2 only, so traffic must go to a router. Check that the router has an interface (or subinterface) in each VLAN, that the switch port facing the router is a trunk carrying both VLANs, and that each host's default gateway is the router address in its own subnet.