NHRP registration, resolution, and redirects are everything interesting DMVPN does. Walk all three message flows with real debugs and cache states from an IOS XE 17.18 lab with one hub and two spokes.
DMVPN is three well-understood pieces: mGRE, NHRP, and a routing protocol, each covering a gap the others leave. This walkthrough uses real output from an IOS XE 17.18 lab with a hub, two spokes, and an underlay router.
Multicast fails silently, and nearly every ticket collapses into three signatures: a silent receiver, an RPF failure, or a missing RP. Captured on CML with IOS XE 17.18.2: healthy PIM sparse mode state before and after the source goes active, how to read every field of show ip mroute, and each...
Bidirectional PIM collapses per-source state inside a domain; MSDP carries source knowledge between domains and redundant RPs. Includes a live MSDP peering between two lab RPs and a real SA cache capture.
SSM drops the RP, register tunnel, and shared tree entirely: the receiver names the source and the network builds the (S,G) tree directly. Covers the model, configuration, live IOS XE captures, and an IGMPv3 gotcha that cost the lab twenty minutes.
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.