Cisco 1852E Mobility Express APs auto switch from static IP to DHCP

[Hai Dao Tuan]

Hi All

My office have bought 3 AP AIR-AP1852E-S-K9.

I did configure AP1 to mode: AP & Controller with ME controller IP 10.155.241.5 - AP1 10.155.241.6

AP2 and AP3 to mode : AP only with AP2: 10.155.241.7, AP3: 10.51.241.8

In LAN, we only use static IP without any DHCP server.

After I finish, all are OK.

But whenever if any users accidentally plug new wireless router/modem (as TP-Link) or any equipment has DHCP-server  function to LAN, AP2 and AP3 immediately change to DHCP (192.168.1.x/24), and so lost connection ME.

I have to found and unplug the DHCP-server quipment out of LAN, and reboot AP2 and AP3, after rebooting AP2 and AP3 back to static IPs (10.155.241.7-8).

But if any one connect DHCP-server again to LAN, the issue occurs again.

I did try Mobility Express OS 8.2.130 and 8.3.102 on all 3 APs but cannot resolve issue.

Please advise us if this is bug of ME OS or the configuration? Thank you very much.

Information of APs are

AP Running Image     : 8.2.130.0
Primary Boot Image   : 8.2.130.0
Backup Boot Image    : 8.3.102.0
AP Image type    : MOBILITY EXPRESS IMAGE
AP Configuration : MOBILITY EXPRESS CAPABLE
2 Gigabit Ethernet interfaces
2 802.11 Radios
Radio FW version : 5e60ea8b3f29048be1ff55e798dbabf5
NSS FW version : NSS.AK.1.0.c10-00017-E_custC-1.67978.1
....
Product/Model Number                 : AIR-AP1852E-S-K9 

In normal, AP2 show ip int brief

AP-PQA-02#show ip int brief
Interface  IP-Address      Method   Status                 Protocol   Speed     
wired0     10.155.241.7   static   up                     up         100       
wired1     unassigned      unset    down                   up         n/a       
wifi0      unassigned      unset    administatively down   down       n/a       
wifi1      unassigned      unset    administatively down   down       n/a       

But if a DHCP-server modem connect to LAN

AP-PQA-02#show ip int brief
Interface  IP-Address      Method   Status                 Protocol   Speed     
wired0     192.168.1.138   DHCP     up                     up         100       
wired1     unassigned      unset    down                   up         n/a       
wifi0      unassigned      unset    administatively down   down       n/a       
wifi1      unassigned      unset    administatively down   down       n/a   

and log

[*02/08/2017 16:41:45.3992] CAPWAP detected next hop MAC chanaged from0000.5E00.0101 to 001E.F738.D4C0
[*02/08/2017 16:41:45.3992]
[*02/08/2017 16:41:48.8882] CAPWAP State: DTLS Teardown
[*02/08/2017 16:41:53.0069] CAPWAP detected next hop MAC chanaged from001E.F738.D4C0 to 0000.5E00.0101
[*02/08/2017 16:41:53.0069]
[*02/08/2017 16:41:53.5767] DOT11_DRV[0]: Stop Radio0
[*02/08/2017 16:41:53.6067] CAPWAP State: Discovery
[*02/08/2017 16:41:53.6067] Discovery Request sent to 10.155.241.5 with discovery type set to CAPWAP_DISCOVERY_TYPE_STATIC_CONFIG)
[*02/08/2017 16:41:53.9366] Discovery Request sent to 10.155.241.5 with discovery type set to CAPWAP_DISCOVERY_TYPE_STATIC_CONFIG)
[*02/08/2017 16:41:53.9366] Discovery Request sent to 10.155.241.5 with discovery type set to CAPWAP_DISCOVERY_TYPE_STATIC_CONFIG)
[*02/08/2017 16:41:53.9366] Discovery Request sent to 255.255.255.255 with discovery type set to CAPWAP_DISCOVERY_TYPE_UNKNOWN(0)
[*02/08/2017 16:41:53.9566] Discovery Response from 10.155.241.5
[*02/08/2017 16:41:54.0000] CAPWAP State: DTLS Setup

[Yashas Bhadoria]

1.Use  DHCP option 43 || 15 during initial deployment only.

2.Make DHCP option 43 || 15 visible only to their interested APs.

• (Say, some APs are in building A and should join only to the WLC for building A)
• (Say, some APs are in building B and should join only to the WLC for building B)

So, we can make

• (a) separate DHCP scopes for APs in building A and for APs in building B.
• (b) give ip address of different WLCs to the DHCP Option-43 of each scope.

3.Use SSC/MIC of specific APs only to be authorized by specific WLCs.

All APs manufactured after June 2006 have a MIC.

4. Configure ip address of Intended WLCs in the NVRAM of the APs

(this step may make sense for some, but not for others, depending on the situation)

For troubleshooting or for unstable networks, one may prefer to use static ip address

For stable networks, one may prefer to use dynamic ip address

Here is the process of how ap finds :

https://supportforums.cisco.com/document/11936146/joining-process-cisco-access-point#Discovery_Algorithm_in_Layer_2

Please contact TAC if the issue persists