VLAN Fundamentals and Topology Setup
📌 The video introduces VLAN (Virtual Local Area Network) as a software-based extension of a LAN, configured on switches or routers.
📌 The specific topology involves three switches (A, B, C) connecting clients assigned to VLANs 10, 20, 30, 40 (Voice), 99 (Management), and 100 (Native).
📌 VLAN configuration requires setting a VLAN number and an optional descriptive VLAN name (e.g., VLAN 10 Admin, VLAN 40 Voice).

Port Assignment and VLAN Modes
📌 Ports must be associated with a VLAN; unassigned ports behave like a standard switch.
📌 Access Mode connects a port to exactly one VLAN; the port only forwards tagged traffic matching that specific VLAN ID.
📌 Trunk Mode allows a port to carry traffic for multiple VLANs, essential for inter-switch links, whereas Dynamic Mode (Auto/Desirable) allows ports to negotiate the link type.

Advanced VLAN Configurations (Trunking and Management)
📌 Voice VLAN (VLAN 40) requires specific QoS configuration using the command `mls qos trust cos` and `switchport voice vlan 40` to prioritize voice traffic.
📌 The VLAN Management Interface (VMI), specifically VLAN 99, needs an IP address to allow remote management (Telnet/SSH) of the switch.
📌 Trunking configuration requires setting the port mode to `trunk`, disabling DTP negotiation using `switchport nonegotiate`, and explicitly defining the Native VLAN (set to VLAN 100 in the example) for untagged traffic.

Key Points & Insights
➡️ VLANs provide regrouping capabilities, offering more flexible management of network policies (like access control or bandwidth limits) compared to relying solely on subnetting.
➡️ When configuring static trunks, use `switchport mode trunk`, `switchport nonegotiate`, and ensure the `switchport trunk native vlan XXX` setting matches on both connected trunk ports to avoid connectivity errors.
➡️ Dynamic trunking negotiation (Auto/Desirable) results in an Access port if both sides are set to `dynamic auto`, whereas setting both to `dynamic desirable` establishes a Trunk link.
➡️ PCs in the same subnet but different VLANs cannot communicate because VLANs logically segment the broadcast domains, overriding Layer 3 addressing compatibility within the switch fabric.

📸 Video summarized with SummaryTube.com on Jan 11, 2026, 11:31 UTC