Reason why Dot11Radio is reset in the Cisco AIR1131AG

A problem occurred in the home lab's wireless AP Cisco Aironet AIR1131AG, in which the status of the Dot11Radio interface became reset after recovery from a power outage.

The cause of the blackout was due to excess power supply capacity of the house, sudden power off in all NW equipment. Since config was saved, no change has occurred. Describe what you understood by carving, cause and measures.

Connection configuration of Aironet AIR1131AG

It connects with PoE power via the PoE interface of the Cisco ASA5505 as follows. In addition, Catalyst2960 is used for PC and server connection, and GW of each VLAN is set to ASA.

AIR1131AG
 |(access vlan 1)
ASA5505
 |   |(each VLAN access)
Cat2960
 |   |
(V1) (trunk)
 PC   ESXi

Error investigation

Normally the green lamp at the top of the AP was obviously abnormal red. The interface status is as follows.

AIR1131#sh ip int b
Interface                  IP-Address      OK? Method Status                Protocol
BVI1                       192.168.1.11    YES NVRAM  up                    up      
Dot11Radio0                unassigned      YES NVRAM  reset                 down    
Dot11Radio1                unassigned      YES NVRAM  reset                 down    
FastEthernet0              unassigned      YES NVRAM  up                    up     

AIR1131#sh int Dot11Radio0
Dot11Radio0 is reset, line protocol is down 
  Hardware is 802.11G Radio, address is 001e.136e.1250 (bia 001e.136e.1250)

Even when restarting the equipment, shut / no shut the interface did not change state. Looking at the startup log, it is as follows.

AIR1131#sh log
<snip>
*Mar  1 00:58:26.214: %LINK-5-CHANGED: Interface Dot11Radio1, changed state to reset
*Mar  1 00:58:26.214: %LINK-5-CHANGED: Interface Dot11Radio0, changed state to reset
*Mar  1 00:58:26.215: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0, changed state to up
*Mar  1 00:58:26.906: %LINEPROTO-5-UPDOWN: Line protocol on Interface BVI1, changed state to up
*Mar  1 00:58:27.214: %LINEPROTO-5-UPDOWN: Line protocol on Interface Dot11Radio1, changed state to down
*Mar  1 00:58:27.214: %LINEPROTO-5-UPDOWN: Line protocol on Interface Dot11Radio0, changed state to down
*Mar  1 00:58:39.279: %CDP_PD-2-POWER_LOW: All radios disabled - LOW_POWER_CLASSIC_NO_INJECTOR_CONFIGURED WS-C2960-24-S (0022.bd42.1d01)
*Mar  1 00:58:39.280:  -Verify the required power-injector is installed on this port: WS-C2960-24-S(Fas 0/1).
*Mar  1 00:58:39.280:  -If a power-injector is installed, issue the command:"power inline negotiation injector installed"

%CDP_PD-2-POWER_LOW: All radios disabled - LOW_POWER_CLASSIC_NO_INJECTOR_CONFIGURED WS-C2960-24-S (0022.bd42.1d01)

It exchanges information with Cat 2960 by CDP, and it seems that PoE status check failed. As described above, the PoE power supply source is ASA 5505, not Cat 2960. Therefore, it is natural that an error will occur. Since CDP neighbors are stretched normally, the operation itself is not abnormal.

AIR1131#sh cdp neighbors 

Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID
CAT2960          Fas 0              154          S I      WS-C2960- Fas 0/1

Although it was forming a CDP neighbor before the power failure, it is thought that it continued operation without confirmation at the time of start because PoE power supply started connecting to ASA before Cat 2960 connection.

Countermeasure

Simply, Disable CDP with AIR 1131.

AIR1131(config)#no cdp run 

(Dot11 shut/no shut or reload when not restoring)

*Mar  1 01:11:42.212: %LINEPROTO-5-UPDOWN: Line protocol on Interface Dot11Radio1, changed state to down
*Mar  1 01:11:42.213: %LINEPROTO-5-UPDOWN: Line protocol on Interface Dot11Radio0, changed state to down
*Mar  1 01:12:42.711: %CDP_PD-4-POWER_OK: Full power - NON_CISCO-NO_CDP_RECEIVED inline power source
*Mar  1 01:12:42.742: %DOT11-6-FREQ_SCAN: Interface Dot11Radio1, Scanning frequencies for 14 seconds
*Mar  1 01:12:42.771: %DOT11-6-FREQ_SCAN: Interface Dot11Radio0, Scanning frequencies for 24 seconds
*Mar  1 01:12:56.524: %DOT11-6-DFS_SCAN_START: DFS: Scanning frequency 5260 MHz for 60 seconds.
*Mar  1 01:12:56.524: %DOT11-6-FREQ_USED: Interface Dot11Radio1, frequency 5260 selected
*Mar  1 01:12:56.524: %LINK-3-UPDOWN: Interface Dot11Radio1, changed state to up
*Mar  1 01:12:57.524: %LINEPROTO-5-UPDOWN: Line protocol on Interface Dot11Radio1, changed state to up
*Mar  1 01:13:07.030: %DOT11-6-FREQ_USED: Interface Dot11Radio0, frequency 2467 selected
*Mar  1 01:13:07.030: %LINK-3-UPDOWN: Interface Dot11Radio0, changed state to up
*Mar  1 01:13:08.030: %LINEPROTO-5-UPDOWN: Line protocol on Interface Dot11Radio0, changed state to up
*Mar  1 01:13:30.867: %DOT11-6-ASSOC: Interface Dot11Radio0, Station   0c3e.9f69.656f Associated KEY_MGMT[WPAv2 PSK]
*Mar  1 01:13:57.008: %DOT11-6-DFS_SCAN_COMPLETE: DFS scan complete on frequency 5260 MHz

AIR1131#
AIR1131#sh ip int b
Interface                  IP-Address      OK? Method Status                Protocol
BVI1                       192.168.1.11    YES NVRAM  up                    up      
Dot11Radio0                unassigned      YES NVRAM  up                    up      
Dot11Radio1                unassigned      YES NVRAM  up                    up      
FastEthernet0              unassigned      YES NVRAM  up                    up      

The Dot11 (wireless) interface was able to be used normally.

Conclusion - Reason why Dot11Radio is reset in the Cisco AIR1131AG

When PoE is started, the Cisco Aironet AIR1131AG checks the connection status with the adjacent PoE equipment with CDP when possible. After the power failure restoration, it became Fail by the confirmation, and the Dot11 interface could not be activated due to PoE error.

Disabling CDP of AIR1131, PoE power reception as usual, Dot11 interface started, wireless communication became possible.