IP SLA answers "is this path usable," which is not the same question as "is this link up." Captured on CML with IOS XE 17.18.2: ICMP and jitter probes against a deliberately degraded link, then a full tracked failover with the SLA timing out, %TRACK-6-STATE logging the object down, and the...
Four names, one job: tell a collector which conversations crossed the router and how big they were. The differences between NetFlow v5, v9, Flexible NetFlow, and IPFIX are not academic trivia, because picking the wrong one means either losing the
NetFlow answers the question your monitoring dashboard cannot: not "is the link busy" but "who is making it busy, talking to what, on which port, and how much." It is the difference between knowing you have
An MPLS L3VPN route makes a long journey. It starts as an IP prefix in a customer's routing table, gets learned by a PE into a VRF, redistributed into MP-BGP, tagged with a route target, given a
MPLS forwarding runs on labels, not on IP reachability, so a dead LDP session leaves every green light green while the customer blackholes. Captured on CML with IOS XE 17.18.2: the unusable: no label CEF entry, the full LDP LIB, a hop-by-hop walk to find where the binding stops, and No Label...
Ask ten network engineers to explain the difference between a route distinguisher and a route target and you will get four confident wrong answers, three "they're basically the same thing," and maybe three correct ones. The
Once the MPLS core is built and MP-BGP is carrying VPNv4 between your PEs, one question remains: how does a PE router actually learn the customer's routes? That is the PE-CE routing protocol, and it is
MPLS L3VPN is the service that made MPLS a service-provider standard, and it is still what most enterprises are actually buying when their carrier sells them "an MPLS circuit." The concept is simple to state and surprisingly
DMVPN failures cluster hard. After the underlay itself, almost every broken cloud comes down to a spoke that cannot register, a tunnel that is up/up while silently eating packets, or shortcuts that never form. So instead of writing another
Everything DMVPN sends is cleartext. GRE is an envelope with the contents printed on the outside, and a DMVPN cloud over the internet without encryption is a packet capture away from a very bad week. The fix is IPsec applied
NHRP builds the tunnels; the routing protocol decides what flows through them, and DMVPN is unusually opinionated about how you run one. A hub that relays routes between spokes on a single multipoint interface trips over split horizon, next-hop
This is the complete, working DMVPN Phase 3 build: one hub, two spokes, a router simulating the internet underlay, EIGRP over the top, every command shown and every verification step captured from live IOS XE 17.18 devices. Nothing here