RADIUS systems are integral to networking, facilitating authentication between devices and servers through protocols such as dot1x and MAB. But what happens when trust within this system is broken? A recent incident highlighted just how critical certificate trust is to RADIUS functionality.
Our organization undertook a routine migration of certificates from Entrust to Sectigo, updating nearly 30,000 corporate devices to ensure seamless connectivity. The transition appeared to be a success, with no user complaints. However, a security camera in Taiwan failed to connect after a switch reboot, signaling an underlying issue.
Initially viewed as a typical authentication failure within a mixed environment of ArubaOS and ArubaOS-CX switches, the diagnosis leaned towards checking the RADIUS key matching. However, the error logs revealed a deeper problem: an "Invalid certificate" error. After thorough investigation and multiple support cases, it became clear that the root of the issue lay not in the shared secrets but in the trust established through certificates, which had been compromised.
The key difference arose between the two switch models: ArubaOS (AOS) and ArubaOS-CX (AOS-CX). AOS utilizes Local User Roles (LURs), meaning it configures security and VLAN assignments locally, allowing it to recover automatically during a reboot by redownloading the required certificate from ClearPass. Meanwhile, AOS-CX uses Downloadable User Roles (DURs), necessitating manual configuration of a trusted anchor profile. The reliance on a certificate-based trust model complicated recovery after a reboot, leading to situation where switches rejected ClearPass’s new certificate because their stored root certificate had already expired, preventing new role downloads.
As the situation unfolded, it became evident that once the Sectigo root certificate was manually imported into the affected AOS-CX switches, normal operations could resume. This incident not only illustrates the intricate dance of networking protocols but also serves as a cautionary tale about the critical nature of certificate trust and the sometimes unexpected complications that arise during migration processes.
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