How to Use iPerf3: Commands and Examples From a Real Lab
Learn iPerf3 from install to JSON automation, with every output block captured live from a routed Cisco lab - including how to actually read Retr, Cwnd, and sender vs receiver lines.
Ping Labz
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CCNA 200-301 Mega Lab: The All-in-One Hands-On Campus
One 10-node CML topology that exercises the entire CCNA 200-301 hands-on blueprint: VLANs, STP, EtherChannel, HSRP, OSPF, NAT, DHCP, NTP and the security baseline, with real Cisco IOS XE captures.
What Is BGP? The Protocol That Runs the Internet
Every time you load a webpage, your traffic crosses networks owned by different organizations. BGP, the Border Gateway Protocol, is what stitches 75,000+ autonomous systems into a single working internet. Here is how, and why.
BGP Next-Hop-Self: When and Why You Need It
One of the most common iBGP problems is routes that show up in the BGP table but never hit the routing table because the next-hop is unreachable. Here is when next-hop-self is the fix, and when it actually makes things worse.
How to Configure eBGP Neighbors on Cisco IOS XE
A single mismatch in neighbor IP, AS number, or filtering keeps a BGP session down without a helpful error. A practical Cisco IOS XE eBGP configuration walkthrough including dual-homed peering and source/TTL considerations.
Topics
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VLANs
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Native VLAN Mismatch: Read the CDP Log, Fix the Trunk
%CDP-4-NATIVE_VLAN_MISMATCH hands you both interfaces and both native VLANs in one line. The real damage is underneath it: untagged frames get re-homed at the trunk boundary and two VLANs quietly become one. Captured live on IOS XE 17.18.2 in CML.
Layer 2
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Errdisable Recovery on Cisco: Every Cause and How to Bring the Port Back
An err-disabled port stays down forever by default, because nothing auto-recovers until you arm it. The full cause list from IOS XE 17.18.2, how to identify which one fired in ten seconds, and the captured proof that auto-recovery is a retry loop rather than a fix.
802.1X
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MAB with FreeRADIUS on Cisco: MAC Authentication Bypass Without ISE
MAB with no ISE node and no licence: FreeRADIUS 3.2.7 against a Catalyst 9000v, with the freeradius -X trail that proves MAB is bare PAP, the MAC format everyone gets wrong, and a real Method: mab / Authc Success on a live switchport.
802.1X
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802.1X with FreeRADIUS on Cisco: The Full Lab, No ISE Required
Every 802.1X guide assumes you have Cisco ISE. You do not need it. Here is the whole chain built on FreeRADIUS and a Catalyst 9000v, with real Access-Accept output, a port flipping to Authorized, and the CML switch image that silently wastes your evening.
NAT
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NAT and PAT Troubleshooting on Cisco IOS XE: An Empty Translation Table
The NAT config looks correct and nothing is translating. One command splits the problem in two: no entry means the traffic never matched, an entry means the failure is downstream. Captured on IOS XE 17.18.2 in CML, where a single missing ip nat inside leaves the table empty at 0 hits.
FHRP
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HSRP Troubleshooting: Both Routers Active and Flapping States
Dual-active HSRP is invisible from one router: each end looks like a healthy Active gateway until you put both outputs side by side and see Standby=unknown on each. Captured live on IOS XE 17.18.2 in CML, plus the preempt behaviour that silently inverts your design.
Routing
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Routing Loop Troubleshooting: Detect, Break, and Prevent Them
A traceroute whose hop addresses repeat until the TTL runs out is a routing loop, and nothing else. Captured on CML with IOS XE 17.18.2: the symptom signature, why TTL keeps a routing loop from behaving like a Layer 2 loop, the four causes ranked by real frequency, and the Null0 discard route...
Routing
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CEF Load Balancing and Polarization: Why One Link Gets All the Traffic
Two equal links, one carrying everything. CEF picks a path per flow, not per packet, and when every router in a tier runs the same hash you get polarization. Proven on real route, CEF and exact-route output from a CML lab on IOS XE 17.18.2.
IPv6
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IPv6 Neighbor Discovery Troubleshooting: Stuck at Link-Local
An IPv6 host with only an FE80:: address is waiting on a Router Advertisement that never came. Captured on CML with IOS XE 17.18.2: the five NDP messages, the neighbor cache states, the A/M/O flags in a real RA, and why filtering ICMPv6 unplugs a segment.
Security
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Detecting Nmap Scans: The View From the Defender's Side
The site already teaches you how to run every nmap scan. This one flips the camera around: what a SYN scan, a UDP scan and a ping sweep actually look like in an IOS XE ACL counter, in syslog and in a packet capture, plus why a slow scan beats most of it.
Security
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Scapy vs Cisco Layer 2 Defenses: Crafting and Spoofing Packets
Craft spoofed ARP and IP packets with Scapy against a Cisco IOS-XE lab, then watch Dynamic ARP Inspection drop every forgery and name the attacker's real MAC.
tcpdump for Network Engineers: A Practical Reference
Interface selection, BPF filters, reading the output line, writing and re-filtering pcap files, and safe long captures - all from a live run of tcpdump 4.99.5 against IOS-XE routers. Includes the privilege drop that kills rotating captures, and a telnet password readable on the wire.