QoS on a Router: A Practical Cisco IOS XE Walkthrough
How to build a working QoS policy on a Cisco router: MQC class maps, policy maps, the LLQ + CBWFQ model, and the shaper rule that makes it actually engage.
Fundamentals
Networking fundamentals and CCNA-level reference content. The TCP/IP and OSI models, ethernet basics, encapsulation, IPv4 addressing, layer 2 fundamentals, and the Cisco IOS commands every network engineer reaches for. The foundations beneath the pillar guides.
Latest posts — page 5
BGP Weight: The Cisco-Only Path Attribute (and When to Use It)
BGP weight is the first tiebreaker in the path-selection algorithm, set locally and never propagated. The three ways to set it, how it compares to LOCAL_PREF, and worked examples.
QoS for VoIP Across an MPLS WAN
End-to-end QoS for VoIP across an MPLS L3VPN: DSCP marking, the LLQ + CBWFQ policy at the CE edge, and the DSCP-to-MPLS-EXP mapping the carrier needs.
OSPF Cost: Reference Bandwidth, Manual Overrides, and Gotchas
OSPF cost explained: the formula, the default reference bandwidth that breaks at 1 Gbps and above, manual overrides per interface, ECMP, and the misconfigurations to avoid.
STP and EtherChannel: When They Collide and Who Wins
How EtherChannel hides bundled links from STP, the bundling protocols (LACP, PAgP, on), the dangerous failure modes, and why LACP active on both sides is the only safe configuration.
RSTP: Rapid Spanning Tree Protocol Explained (802.1w)
RSTP (802.1w) explained: the new port roles, three-state model, proposal/agreement handshake, Rapid-PVST+ vs MST, and the real show spanning-tree output.
Inter-VLAN Routing: SVI vs Router-on-a-Stick (with Real IOS XE Config)
The two ways to route between VLANs on Cisco: SVIs on an L3 switch and router-on-a-stick. Real IOS XE config for both, the performance gap, and the gotchas.
MPLS L3VPN vs SD-WAN: When to Migrate
A decision framework for migrating from MPLS L3VPN to SD-WAN: what's different, when to migrate, the 7-step transition that works, and when the right answer is to stay.
BGP Looking Glass: What It Is, Public Servers, and Hosting Your Own
BGP looking glasses explained: what they show, the public servers worth bookmarking, a four-step troubleshooting recipe, and how to host your own with hyperglass.
OSPF Adjacency States: The 8-State FSM, Explained
All 8 OSPF neighbor states (Down, Attempt, Init, 2-Way, ExStart, Exchange, Loading, Full), what triggers each transition, and what to check when a neighbor is stuck.
VLAN, Subnet, and Broadcast Domain: What's the Difference?
VLAN, subnet, and broadcast domain are not the same thing. The layer each lives at, the relationships between them, and the misalignment that breaks hosts silently.
SD-WAN: What Is It? The 5-Minute Primer
SD-WAN in five minutes: what it is, what it replaces, the four-plane architecture, transport-independent overlays, and how it stacks against traditional MPLS WANs.