The RPF Check: How Multicast Prevents Loops
Unicast routing looks forward: where is this packet going? Multicast routing looks backward: did this packet arrive from the right
Labs
Hands-on Cisco IOS XE lab walkthroughs. Each lab ships with a real CML topology, configs you can paste, and verified show output. Articles tagged Labs cover the full CCNA 200-301 blueprint across Network Fundamentals, Network Access, IP Connectivity, IP Services, and Security Fundamentals.
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PIM Sparse Mode: RPs, Shared Trees, and the SPT Switchover
PIM sparse mode is where multicast stops being theory and becomes state machines. It is the protocol that turns "
IGMP Explained: v2 vs v3, Joins, Leaves, and the Querier
IGMP is the only part of multicast a host ever speaks. Before PIM builds a single tree, before an RP
Multicast Addressing: 224.0.0.0/4, MAC Mapping, and Scoping
Every multicast design decision starts with an address. Which range you pick determines whether routers forward the traffic at all,
What Is IP Multicast? Groups, Trees, and Why Unicast Doesn't Scale
Send one packet, deliver it to a hundred receivers, and put exactly one copy on each link along the way.
Troubleshooting Route Redistribution: Missing, Looping, and Suboptimal Routes
Redistribution fails three ways: routes that never arrive, routes that echo back and loop, and routes that arrive but take the long way. All three captured on CML with IOS XE 17.18.2, including the EIGRP external at AD 170 that loses to OSPF's 110 while the shorter direct path sits unused in the...
OSPFv3 Configuration on Cisco IOS XE
This is the hands-on half of our OSPFv3 coverage: a complete dual-stack configuration on Cisco IOS XE, from
OSPFv3 Explained: OSPF for IPv6 (and Address Families for IPv4)
OSPFv3 is not "OSPF with longer addresses". It is a redesign of the protocol machinery that happens to
BFD: Sub-Second Failure Detection for OSPF, EIGRP, and BGP
Routing protocols detect dead neighbors with hello timers measured in tens of seconds. Modern applications notice outages measured in hundreds
VRF-Lite on Cisco IOS XE: Configuration and Verification
One router, multiple routing tables. That is the entire idea behind VRF (Virtual Routing and Forwarding), and it is the
Policy-Based Routing (PBR): Configuration and Verification
Routing protocols answer one question: what is the best path to this destination? Policy-based routing (PBR) exists for every
Redistribution Loop Prevention: Route Tags, AD, and Filtering
Two-point redistribution is where redistribution stops being a config exercise and starts being a design problem. The moment two