Multicast routing looks backward: a packet is accepted only if it arrives on the interface unicast would use to reach its source. This post explains the RPF check, deliberately breaks it in the lab, and fixes it with a static mroute.
PIM sparse mode in three acts: receivers join a shared tree at the RP, sources register to the same RP, and the edge rebuilds onto shortest-path trees. Walk the whole lifecycle on IOS XE with live captures, including the SPT switchover.
The one real difference between IGMPv2 and IGMPv3 is the source list, and it decides whether SSM works. Real reports, show output and snooping tables from a lab with a Debian receiver.
Maps the entire 224.0.0.0/4 space: which ranges routers forward, which need an RP, how the IP-to-MAC mapping creates a 32:1 overlap at Layer 2, and how scoping keeps multicast inside your organization.
IP multicast delivers one packet to a hundred receivers with exactly one copy per link. Learn why unicast and broadcast fail at that job, and the group and tree concepts every multicast protocol builds on.
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...
A complete dual-stack OSPFv3 configuration on Cisco IOS XE, from ipv6 unicast-routing to verified end-to-end reachability, with every capture taken from a live CML lab.
OSPFv3 is a protocol redesign, not OSPF with longer addresses, and with address families it carries IPv4 too. See what changed from OSPFv2, what stayed identical, and what it looks like on the wire in a live Cisco IOS XE lab.
Default hello timers take tens of seconds to notice a dead neighbor. This post configures BFD on Cisco IOS XE and races it against OSPF defaults: 34 seconds without BFD, 0.58 seconds with it, captured live with a stopwatch.
VRF-Lite gives one IOS XE router multiple isolated routing tables without MPLS or MP-BGP. This guide builds two VRFs, proves the isolation, then punches a deliberate, controlled hole between them with static route leaking.
PBR routes on source address, protocol, port, or size instead of destination alone. This post configures it on Cisco IOS XE, proves it with debug ip policy and route-map counters, and covers the failure modes.
Two border routers redistributing between the same domains give every prefix a feedback path. Build the forwarding loop live on Cisco IOS XE, capture it happening, then fix it with route tags the way production networks do.