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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 explained: the formula, the default reference bandwidth that breaks at 1 Gbps and above, manual overrides per interface, ECMP, and the misconfigurations to avoid.

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 (802.1w) explained: the new port roles, three-state model, proposal/agreement handshake, Rapid-PVST+ vs MST, and the real show spanning-tree output.

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.

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.