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Cisco ISE MAB Fallback Not Hitting: When the Printer Never Gets a VLAN

  • 3 days ago
  • 2 min read
Cisco ISE network security troubleshooting lab
Cisco ISE · Techclick CLI troubleshooting lab
802.1X times out on a printer. MAB should give it the printer VLAN. Port stays unauthorized.

This is a live-ticket style lesson from Techclick Infosec. You will isolate the fault with CLI first, then prove the fix with one clean packet or log.

What you will be able to do

  • Name the first CLI command to run on Cisco ISE for this ticket

  • Separate the layer that is actually broken from the layer people blame

  • Apply one scoped fix instead of a global disable

  • Prove the ticket closed with a session, log, or counter

Quick answer

The switch must fail to MAB, and ISE must have an endpoint identity group for that MAC. Missing either one leaves the port dark.

Why this ticket shows up

MAB is a second authentication. If the switch never starts it, or ISE has no MAC, there is no fallback.

Symptoms operators actually see

  • Printer unauthorized

  • No MAB request in Live Logs

  • MAC not in endpoint database

  • IBNS 2.0 policy missing mab

CLI first — copy this block

Run these on the Cisco ISE device or console named in the ticket. Do not skip the first show command — it tells you which later command matters.

show authentication sessions interface Gi1/0/12 details
show running-config interface Gi1/0/12
show mac address-table interface Gi1/0/12
test aaa group radius ISE_GROUP mab test test new-code

How to read that output

The session must show Method MAB. If it stays 802.1X running, the switch never fell back. If MAB is there and ISE rejects, the MAC is unknown.

Triage order

  1. Read the switch session method

  2. Confirm MAB is in the interface policy

  3. Look up the MAC in ISE endpoints

  4. Add it to the printer identity group

  5. Bounce the port once

Classic traps

What you see

Real cause

Fix

Create a new policy set

MAC is not in ISE

Add the endpoint

Disable 802.1X on the whole switch

One printer

Fix MAB

Static VLAN on the port

You lose the design

Use MAB as designed

Proof the ticket is closed

  • Session method MAB, status Authorized

  • Printer VLAN correct

  • Live Log Auth Passed

Say this in an interview

MAB fallback is two devices. I prove the switch started MAB and ISE knew the MAC.

Need the full vendor lab, mock interview, and production runbooks? Techclick trains Palo Alto, Zscaler, F5, FortiGate, Check Point, Cisco ISE, Azure and routing with live CLI — start at https://www.techclick.in/

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