Who logged in, what they could run, and who typed the command that broke the network. This article configures real AAA on Cisco IOS XE, authenticates a live login against RADIUS, shows the exchange on the wire, and compares TACACS+ vs RADIUS.
Conditional debug lets you ask a Cisco IOS XE router a narrow question instead of melting it with unfiltered output. Proven in the lab: two pings run, and only the matching one appears in the debug.
NTP keeps most networks within a second; trading floors, 5G fronthaul, and substations need microseconds. This article explains the structural limit that makes NTP incapable of that job and how PTP (IEEE 1588) solves it.
SLAAC, stateless DHCPv6, and stateful DHCPv6 can all run at once, arbitrated by the M and O flags. This article untangles all three, then builds a stateful server with a relay on Cisco IOS XE and a real Linux client taking a lease.
SPAN, RSPAN, and ERSPAN configured on real Cisco gear, with the ERSPAN packets captured arriving at a real Linux host. Three ways to mirror traffic to Wireshark, separated by how far the analyzer sits from the traffic.
A static route stays in the table as long as the interface is up, even when the path is dead. This post pairs object tracking with an IP SLA probe to build a static route that tests the path, then kills the path to prove it works.
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...
NetFlow v5, v9, Flexible NetFlow, and IPFIX do the same job differently. This comparison shows which fields, templates, and transport each supports so you pick the one your collector and your data actually need.
Flexible NetFlow tells you who is making the link busy, talking to what, on which port. Build the record, monitor, and exporter on Cisco IOS XE, export flows to a real Linux collector, and decode them so you see the data arrive.
An L3VPN route can quietly disappear at six points between customer VRF and remote CE, none of them logging an error. This article gives you a repeatable path to walk the route, with captures from a live five-router IOS XE lab with induced failures.
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...
Route distinguishers make prefixes unique; route targets control which VRFs import them. They look identical and do unrelated jobs, and this article proves it with one BGP table holding the same prefix twice.