Troubleshooting

JDK 1.8.0u242 and later introduced Kerberos referral handling per RFC 6806, which can break Active Directory name canonicalization and produce a KRB_AP_ERR_MODIFIED error. This post walks through the two configuration fixes that resolve the issue.

Traceroute is one of the most misunderstood tools in a network engineer’s toolkit. This guide walks through how traceroute actually works, how to read the output correctly, and how to avoid the common pitfalls that lead to wrong conclusions.

A quick awk pipeline to pull wp-login.php access attempts from web server logs and flag IPs that exceed a threshold. Useful for spotting brute-force or scanning activity against WordPress sites.

A quick way to verify whether a specific IP address is blocked by iptables rules on a Linux host. Covers the exact command and how to read the output.

A quick bash function to identify which search engine crawlers are hitting your Apache logs and how often, so you can spot unusual traffic patterns at a glance.

Two quick one-liners that count how many unique remote IPs are connected to port 80, using either netstat or ss. Handy for spotting unexpected traffic or verifying that only expected clients are hitting your web server.