Core networking tutorials covering protocols, addressing, infrastructure design, and foundational concepts for network engineers and certification candidates.
The Cisco MQC three-construct model (class-map, policy-map, service-policy) covers every QoS feature on IOS, IOS XE, and IOS XR. The grammar, common actions, hierarchical policies, and verification.
DSCP is the 6-bit Layer 3 marking that drives modern QoS. The byte format, the standardized PHBs (CS, AF, EF), Cisco's DSCP-to-CoS-to-MPLS-EXP mapping, and trust boundary discipline.
A good VLAN design scales cleanly, keeps STP domains small, and makes troubleshooting obvious. Here is how to plan VLANs for a multi-building campus network.
VLANs provide segmentation, not security. Without explicit hardening — disabling DTP, fixing the native VLAN, enabling DHCP snooping and DAI — your Layer 2 network is wide open to attack.
Inter-VLAN routing failures are usually caused by SVIs in down state, missing routes, DHCP misconfiguration, or ARP timeouts. Learn to diagnose and fix them systematically.
Most VLAN outages stem from ports in the wrong VLAN, trunks not allowing required VLAN, or native VLAN mismatches. Here's how to diagnose and fix them systematically.
Private VLANs let you enforce micro-segmentation within a single VLAN—isolating hosts completely or grouping them into communities while keeping them behind a single gateway IP.
Voice VLANs let a single access port carry both data traffic from a PC and voice traffic from an IP phone — each in its own VLAN with its own QoS treatment.
Layer 3 switches route between VLANs in hardware at wire speed — no external router bottleneck. Here is how to configure SVI-based inter-VLAN routing on a Catalyst 9300.
When you don't have a Layer 3 switch, router-on-a-stick provides inter-VLAN routing via a single physical link split into subinterfaces. Learn when this design is appropriate, how to configure subinterfaces, and why it's a bandwidth bottleneck.
VLANs are more than a configuration checkbox — they change how every frame is tagged, forwarded, and filtered inside the switch. Here's the mechanics.
VLANs let you carve one physical switch into multiple isolated broadcast domains — without buying more hardware. Here's how they work and why every network uses them.