802.1X

Port-based network access control, the standard for authenticating users and devices onto wired and wireless networks. Articles tagged 802.1X cover supplicant and authenticator behavior, RADIUS, EAP methods, Cisco ISE, dynamic VLANs, dACLs, host modes, and phased deployment.

33 posts

802.1X

Guest VLAN, Auth-Fail VLAN, and Critical VLAN in 802.1X: When and How to Use Them

Guest VLAN, Auth-Fail VLAN, and Critical VLAN cover the three 802.1X failure paths: no supplicant, wrong credentials, and RADIUS down. Here is when and how to use each.

Mar 24, 2026 11 min read

802.1X

Dynamic VLAN Assignment with 802.1X and Cisco ISE

Dynamic VLAN assignment returns the target VLAN in RADIUS Tunnel attributes, so identity (not cabling) decides the network segment. Here is the ISE and IOS XE config.

Mar 24, 2026 9 min read

802.1X

802.1X Authentication Host Modes: Single-Host, Multi-Host, Multi-Domain, Multi-Auth

Single-host, multi-host, multi-domain, and multi-auth control how many MACs can use an 802.1X port. Pick the wrong mode and you get silent failures or open ports.

Mar 24, 2026 9 min read

802.1X

Troubleshooting 802.1X with show authentication sessions and debug Commands

show authentication sessions is your first 802.1X diagnostic. Here is how to read the output, when to escalate to debug dot1x and debug radius, and how to stay sane.

Mar 24, 2026 10 min read

802.1X

dACL Not Applying Correctly in 802.1X: Troubleshooting Downloadable ACLs

dACL not applying usually means ISE sent the wrong AVPair name, the switch cannot download it, or the ACL content parsed badly. Here is the full troubleshooting path.

Mar 24, 2026 10 min read

802.1X

Dynamic VLAN Assignment Not Working in 802.1X: Troubleshooting Guide

Dynamic VLAN not working breaks down to four causes: ISE not sending Tunnel attributes, wrong values, switch not processing them, or VLAN not in the database. Here is how to isolate.

Mar 24, 2026 10 min read