Testing MTU With Ping and the DF Bit
Find the path MTU with nothing but ping, from Linux and IOS XE, against a real 1400-byte link. The 28-byte math and the PMTUD black holes that hang TCP.
Jaime
Latest posts — page 27
Cisco Extended Ping and Response Characters Explained
Source interfaces, the DF bit, repeat counts, and the response characters (! . U M) that tell you exactly what failed. Extended ping on Cisco IOS XE, captured live.
Ping Timeout vs Destination Unreachable: Decoding Every Failure
Silent 100% loss and Destination Unreachable are different failures pointing at different problems. Every ping failure message decoded with live lab captures.
How Ping Works: The ICMP Echo Exchange Explained
What actually happens between typing ping and the reply line, decoded field by field on a live 3-hop Cisco lab: ICMP echo, TTL, RTT, and jitter.
SD-WAN Routing Explained: Underlay, Overlay, and OMP
SD-WAN has two routing problems at once: how sites learn prefixes across the overlay with OMP, and how the physical transports route underneath. This post keeps the two layers separate using the Cisco Catalyst SD-WAN model.
What Is a Wireless LAN Controller (WLC)?
A wireless LAN controller turns a pile of access points into a managed network: the APs become radios and the WLC becomes the brain. Covers the problem it solves, the controller-and-AP split, and WLC form factors.
Nmap Output Formats: -oN, -oX, -oG, -oA and Parsing Results
Nmap's -oN, -oX, -oG, and -oA output formats, when each one earns its place, and the shell one-liners that turn a saved scan into an answer. Save scans you can diff week over week and hand to the audit team as evidence.
Nmap Timing and Performance: -T0 to -T5 and Rate Controls
Nmap's timing templates -T0 through -T5 and its rate control flags decide whether a scan finishes fast or slips under an IDS. This guide shows when to push packets on a /16 sweep and when to trickle probes past a rate-based SIEM alert.
Nmap Firewall and IDS Evasion: Fragmentation, Decoys, and Timing
Nmap's evasion flags are your test harness: fragmentation, decoys, source-port tricks, and timing, run against your own firewall and IDS to prove your controls actually catch them. Real captures from a Cisco lab and the internet.
Nmap NSE Scripts: The Scripting Engine, Categories, and Real Examples
NSE turns Nmap from a port scanner into an inventory and audit tool: enumerate HTTP methods, list SSH algorithms, flag open directory listings. This post covers the script categories with real captured output.
Nmap UDP Scanning (-sU): Why It Is Slow and How to Read It
Half your infrastructure runs on UDP: DNS, SNMP, NTP, DHCP. This guide covers how nmap -sU decides port states, how to read the ambiguous open|filtered results, which UDP services are worth scanning, and how to keep a scan from taking all night.
Nmap OS Detection (-O): How TCP/IP Fingerprinting Works
Nmap -O fingerprints a host's TCP/IP stack to guess its operating system, no login and no banner required. Learn what it measures, how to read every field it prints, and why it fails in predictable ways on lab gear and appliances.