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New Member

Autonomous AP causing loop

The following setup:

A 3750 core and a few 3560's in the edge almost everything in VLAN 1 and another seperate VLAN(320) for guestnet/publicinternet.

The switches are running rpvst and the 3750 is the root bridge.

The 3560 are connected to the 3750 in a ring.

Earlier this week i was onsite to implement 3 autonomous AP's, it seemed to go well but eventually the AP's seemed to have caused a loop or broadcaststorm resulting in a complete network outage :(

I idnt really have time to troubleshoot the problem which resulted in shutting all ISL's removing the AP's and activating the ISL's again (problem solved).

I was thinking about what could have caused this.

I have done a few autonomous(and lightweight) implementations and never have seen this behavior.


Perhaps it has something to do with users who are wired in VLAN 1 and bridge there connection ?

I know this post is a little old, but I also use portfast and bpduguard.  One issue we ran into was very similar, in that APs would go off line because of bpduguard.  What we found was that a developer had installed a Hyper-V tool on his laptop that bridged the wired and wireless networks which was causing the ports to go down.

Just my 2 cents.


The strange thing is that i actually have almost the exact same configuration running on another site (same customer) the only differences are the switches in the edge(Nortel BPS425) and the Cisco AP(1242 instaed of 2602).

Perhaps the issue lies in the software Version 12.4(25d)JA2 & Version 15.2(2)JA?

The configuration i used-

Switch uplink:

interface FastEthernet0/3

 description *** AP ***
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 1,320
 switchport mode trunk
 speed 100
 duplex full
 no snmp trap link-status



AP interface configuration:

interface GigabitEthernet0
 no ip address
 no ip route-cache
 duplex 100
 speed full
 no keepalive
interface GigabitEthernet0.1
 encapsulation dot1Q 1 native
 no ip route-cache
 bridge-group 1
 bridge-group 1 spanning-disabled
 no bridge-group 1 source-learning
interface GigabitEthernet0.320
 encapsulation dot1Q 320
 no ip route-cache
 bridge-group 220
 bridge-group 220 spanning-disabled
 no bridge-group 220 source-learning


I also tried simulating it in our test lab but didnt see anything strange will do some more testing this week.

Anyone any ideas ?





New Member

Did some more testing today:A

Did some more testing today:

A Cisco 3750 connected to 2x 3560, the 3560 are also connected to each other resulting in a ring topology.

The AP's are connected to 1 of the 3560's.



Ethernet adapter Local Area Connection:


   Connection-specific DNS Suffix  . :

   Description . . . . . . . . . . . : Intel(R) 82577LC Gigabit Network Connecti

   Physical Address. . . . . . . . . : 1C-C1-DE-AC-64-59

   DHCP Enabled. . . . . . . . . . . : Yes

C3750#show mac address-table | i 6459

   1    1cc1.deac.6459    DYNAMIC     Gi2/0/2


Gigabit2/0/2 is de interface where my laptop is directly connected to.


Wireless LAN adapter Wireless Network Connection:

   Connection-specific DNS Suffix  . :

   Description . . . . . . . . . . . : Intel(R) Centrino(R) Advanced-N 6200 AGN

   Physical Address. . . . . . . . . : 00-27-10-7C-7F-08

C3750#show mac address-table | i 7f08

   1    0027.107c.7f08    DYNAMIC     Gi2/0/24


Gigabit2/0/24 is de trunk to the 3560 where the AP is connected to.

So i can ping both my laptop on the IP adress of the LAN & WLAN card.



Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:


Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/9 ms


Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:


Success rate is 100 percent (5/5), round-trip min/avg/max = 1/4/9 ms


Now i will bridge my LAN & WLAN connection on the laptop.

For about 20 seconds i am unable to ping the L3 interface of the 3750

Ethernet adapter Network Bridge:

   Connection-specific DNS Suffix  . :

   Description . . . . . . . . . . . : MAC Bridge Miniport

   Physical Address. . . . . . . . . : 02-27-10-7C-7F-08

   DHCP Enabled. . . . . . . . . . . : Yes

   Autoconfiguration Enabled . . . . : Yes

   Link-local IPv6 Address . . . . . : fe80::4500:98c1:bc05:8c20%36(Preferred)

   IPv4 Address. . . . . . . . . . . :

   Subnet Mask . . . . . . . . . . . :


The bridge that has been created uses the MAC adres of my WLAN card.

And now we see that the MAC address of the WLAN card is learned over the interface where my laptop's LAN card is directly connected to.


   1    0227.107c.7f08    DYNAMIC     Gi2/0/2

   1    1cc1.deac.6459    DYNAMIC     Gi2/0/2


So i can imagine that the switch will think why he is suddenly learning this MAC adres over a different interface.

But this shouldnt cause any major issue. Maybe a warning with a MAC FLAP message.


I now also have a duplicate ARP entry but that should time out eventually.

Internet           0   0227.107c.7f08  ARPA   Vlan1

Internet           5   0027.107c.7f08  ARPA   Vlan1

Some more testing shows that sometimes the MAC adres from the LAN card is used for the bridge.

In this event the mac address of the WLAN card is still active on the AP since it is associated but it has the IP adres of the MAC bridge.

CI2602-03#show dot11 associations

802.11 Client Stations on Dot11Radio1:



MAC Address    IP address      Device        Name            Parent         State

0027.107c.7f08   ccx-client    CI2602           self           Assoc


The MAC address from the WLAN card is not learned on the switches.

The ARP entry of this IP address shows the MAC address of the LAN card on the C3750:

Internet           0   1ec1.deac.6459  ARPA   Vlan1


I do not know why windows sometimes chooses the MAC of the LAN or WLAN card maybe it has something to do with which interface was selected first or just random doesnt really matter anyway.

The swiches are still stable and no strange behavior.


New Member

Did some more testing last

Did some more testing last week onsite and most likely found the problem.

On 1 of the 3750 a cable was connected in vlan 1 and the other end went to a port configured for vlan 3.

Appearantly the guy who installed the VoIP thought this was a good solution for doing segmentation without layer 3 and only keeping the DHCP server in VLAN 1....................

Step 1    Choose

Step 1    Choose Administration > System > Settings > System Time .

Step 2    Enter unique IP addresses for your NTP servers.

Step 3    Check the Only allow authenticated NTP servers check box if you want to restrict Cisco ISE to use only authenticated NTP servers to keep system and network time.

Step 4    Click the NTP Authentication Keys tab and specify one or more authentication keys if any of the servers that you specify requires authentication via an authentication key, as follows:

a.    Click Add .

b.    Enter the necessary Key ID and Key Value , specify whether the key in question is trusted by activating or deactivating the Trusted Key option, and click OK . The Key ID field supports numeric values between 1 to 65535 and the Key Value .field supports up to 15 alphanumeric characters.

c.    Return to the NTP Server Configuration tab when you are finished entering the NTP Server Authentication Keys.

Step 5    Click Save .

New Member

I dont think NTP has anything

I dont think NTP has anything to do with it