Cisco ACL Packet Drop: Trace It with Linux Packet Captures
Follow four echo requests from Linux into Cisco IOL, find an outbound ACL deny with captures and counters, then remove it and verify recovery.
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Latest posts — page 9
TCP Retransmission, Reordering, or a Capture Artifact?
Compare controlled loss, reordering, and one filtered capture frame. Use both endpoint traces and queue evidence before diagnosing TCP loss.
iPerf3 Latency Under Load: Measure Bufferbloat with ping
A 10 Mbit/s path delivered 9.56 Mbit/s while loaded ping RTT rose to a 325 ms median. Follow the queue and verify the delay clears after load.
tc netem: Reproduce Delay, Loss, Jitter, and Reordering
Add one impairment at a time to an isolated Linux path. Compare ping results, queue counters, and packet arrival order, then verify recovery.
Build a Linux Network Lab with Namespaces, veth, and Bridges
Build a bridged LAN and routed server path on one Linux VM. Follow ARP, inspect the routes, and break and repair one missing route.
Cisco Trunk Up, Linux Ping Fails: Find the VLAN Mismatch
Build a working Linux-to-Cisco VLAN link, move the host to the wrong VLAN, and use ARP captures and the MAC table to find and fix the failed ping.
TCP Three-Way Handshake and Teardown, Captured
The three-way handshake is the first thing anyone learns about TCP and the last thing most people actually look at. SYN, SYN-ACK, ACK is easy to draw. What is harder, and far more useful, is reading a real
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
OSPF Hello Packets Explained with a Real Capture
Every OSPF adjacency you have ever built started with a Hello packet, and almost every adjacency that refuses to build is a Hello packet being quietly thrown away. The trouble is that show ip ospf neighbor only tells you the
Install Zabbix 7.0 LTS in Docker Alongside Grafana
Two monitoring platforms, one Ubuntu box, zero port collisions. Plus the built-in host that cannot reach its own agent, and why apt was not an option.
How to Install Grafana Enterprise on Ubuntu Server
From an empty Ubuntu box to a Grafana login screen: APT repo, systemd, and the 20-second gotcha that makes people think the install failed.
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Linux Networking Field Reference (10-Page Printable Cheat-Sheet)
Ten printable pages of Linux networking commands, flags and real lab output, including a ten-symptom troubleshooting decision tree. Free for members.