DHCP DORA Explained with a Real Packet Capture
Discover, Offer, Request, Ack. You can recite DORA in your sleep, and it still will not help you the day a client comes up with a 169.254 address and the server insists the pool is fine. What helps is
IP Services
The services running alongside routing that keep a network usable. Articles tagged IP Services cover NAT, DHCP, NTP, SNMP, syslog, NetFlow and IP SLA on Cisco IOS XE.
Latest posts
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.
Router Service Hardening: Turning Off What You Never Needed
Harden a Cisco router by disabling unused services, proven with a real before-and-after Nmap scan taking Telnet from open to closed, plus syslog design.
NTP Authentication: Trusting the Clock Your Logs Depend On
Configure authenticated NTP on Cisco IOS XE, why IOS flags MD5 as weak, and how ntp authenticate and trusted-key stop a rogue server moving your clock.
Expert Services Troubleshooting: NAT, DHCP, and SLA Ticket Scenarios
NAT, DHCP, and IP SLA faults rarely leave clues in show ip route. Five services ticket scenarios with the exact translation table, binding, or tracking object to check for each, grounded in real lab behavior.
IPv6 Services Closure: NPTv6, DHCPv6-PD, and General Prefix
DHCPv6 prefix delegation, general prefixes, and NPTv6: the IPv6 services engineers often skip, shown with real CML output of a delegated prefix flowing all the way to a downstream interface.
Embedded Packet Capture: Wireshark Inside Your Router
Embedded Packet Capture puts Wireshark-grade capture inside the IOS XE router itself: no SPAN, no capture laptop, no cabling. Includes a real on-router capture from a CML lab and the syntax difference that will bite you.
SNMPv3 in Production: Users, Groups, Views, Traps, and Informs
Build SNMPv3 in production form: users, groups, views, and the three security levels. The payoff is a real encrypted trap arriving and being decrypted on a Linux receiver, with no cleartext community strings on the wire.
The IOS DHCP Server in Depth: Options, Classes, and Manual Bindings
The IOS DHCP server does far more than network, default-router, dns-server. This article covers options for PXE boot and phones, DHCP classes, and manual bindings, with real lease output from a CML lab.
VRF-Aware NAT on Cisco IOS XE
Two customers with identical 10.5.5.0/24 subnets reach one shared exit through a single router. VRF-aware NAT on IOS XE keeps them separate, and this CML lab build shows two translation tables holding identical inside-local addresses.
Conditional Debugging on Cisco IOS XE: Debug Without Melting the Box
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.
PTP vs NTP: When Microseconds Matter
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.