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New Member

LWAPP Discovery request - discarded ?

Greetings all,

I'm starting to grow a huge headache over a WLC-implementation (4402-12). From my point of view, the controller seems to be configured correctly and the DHCP-scope has been set up with the correct pointers as well as as the DNS-record, all pointing towards the AP-Manager i/f (tagged vlan20 on port 1, mgmt untagged) - still, no access-points will associate. The AP is pingable from the controller. A debug of lwapp events and details shows the following;

///

Sat Jan 7 19:36:17 2006: Received a message from AP of length 97 on inteface = 1

Sat Jan 7 19:36:17 2006: Entered spamGetLCBFromMac file spam_lrad.c line 433**

Sat Jan 7 19:36:17 2006: Received LWAPP DISCOVERY REQUEST from AP 00:0b:85:5a:bd:50 to ff:ff:ff:ff:ff:ff on port '1'

Sat Jan 7 19:36:17 2006: Discarding L3 Mode LWAPP DISCOVERY REQUEST on intf '1', vlan = '20', Management vlan = '0'.

///

Anyone with a clue regarding what might be causing this? I'm also a little confused regarding the destaddr (bcast) since the AP should've received the ucast address of the controller. We have to handover this system to the cust. fairly soon .. :-)

WLC Version: 3.2.78.0

TIA & Best regards,

/M

1 ACCEPTED SOLUTION

Accepted Solutions
Bronze

Re: LWAPP Discovery request - discarded ?

You need to use the Management Interface for LWAPP controller discovery. That's what the WLC expects. So when it sees an LWAPP Discovery Request coming in on another interface, it discards its.

In L3 LWAPP mode, the AP tries to find a WLC using IP subnet broadcast, over the air provisioning (OTAP), DHCP Option 43, DNS, and WLC IP addresses stored in memory. It will always use ALL of these techniques. That's why you're seeing the broadcast. From the LWAPP Discovery Responses it selects a controller to join.

Now, you would've seen it join in L2 mode because the AP does an Ethernet "broadcast" to find the WLC. Hence, the mgmt interface sees the LWAPP Discovery, and responds with an Ethernet frame. At L2 mode, all LWAPP is Ethernet encapsulated as opposed to IP encapsulated. When you switched back to L3 mode, the AP remembers the management IP address of the WLC from the L2 join and uses that. That's why it worked after switching L3-->L2-->L3.

Hope this helps.

19 REPLIES
New Member

Re: LWAPP Discovery request - discarded ?

A brief update - I've actually got the access-points to associate, by changing from L3 LWAPP to L2-mode, bringing up the AP and then return to L3 again. Voilá, and the AP is alive and kicking in L3-mode. The only thing that can come to my mind with this matter would be some kind of incompatibility in the code - can anyone confirm this?

I also have an issue with modifying AP-parameters from WCS, clicking save results in the following error-message; "SNMP Operation to device failed." - anyone with any input on this?

TIA & Best regards,

/M

New Member

Re: LWAPP Discovery request - discarded ?

Hey,

This is almost getting funny ... The previous described workaround worked like a charm, for the 10xx-AP's. The really interesting part comes when trying to convert 1200-series IOS-based AP's. I've followed procedure and installed the JX-code per instructions - and the same problem occurs, the controller discards the discovery-request. I've actually tried the same workaround this time, but for obvious reasons - it didn't work. (JX-code can't speak L2).

Is there ANYONE that actually can provide some info regarding these issues? I'm almost out of hair to rip off by now :)

TIA & Best regards,

/M

Bronze

Re: LWAPP Discovery request - discarded ?

You need to use the Management Interface for LWAPP controller discovery. That's what the WLC expects. So when it sees an LWAPP Discovery Request coming in on another interface, it discards its.

In L3 LWAPP mode, the AP tries to find a WLC using IP subnet broadcast, over the air provisioning (OTAP), DHCP Option 43, DNS, and WLC IP addresses stored in memory. It will always use ALL of these techniques. That's why you're seeing the broadcast. From the LWAPP Discovery Responses it selects a controller to join.

Now, you would've seen it join in L2 mode because the AP does an Ethernet "broadcast" to find the WLC. Hence, the mgmt interface sees the LWAPP Discovery, and responds with an Ethernet frame. At L2 mode, all LWAPP is Ethernet encapsulated as opposed to IP encapsulated. When you switched back to L3 mode, the AP remembers the management IP address of the WLC from the L2 join and uses that. That's why it worked after switching L3-->L2-->L3.

Hope this helps.

New Member

Re: LWAPP Discovery request - discarded ?

Hi Jake,

Your attention to this matter is greatly appreciated. Yes, that was really valueable in helping me understand why the broadcast-address shows up.

However, there are still some points that I'm a little confused about, isn't the ap-manager supposed to be the interface for the discovery? If not, I've totally missed the concept with regards of using the mgmt-i/f. Clarification in this matter would be really helpful, I've found it very hard to find a documentation that actually describes the various i/f's.

I will give it a shot with modifying the DHCP-option to point to the mgmt-i/f right away.

Best regards,

/M

Bronze

Re: LWAPP Discovery request - discarded ?

You use the mgmt i/f for the WLC IP address for LWAPP Discovery. The AP sends an LWAPP Discovery Request to the mgmt i/f. The LWAPP Discovery Response sent by the WLC to the AP includes the IP addresses of each of its AP Manager interfaces (there can be more than one) and their current AP "load". The AP then selects an AP Manager IP address to use for subsequent LWAPP communications based on the least utilized address. It's designed to provide for dynamic AP/LWAPP load balancing across all of the WLC ports.

I'm publishing a whitepaper on Cisco.com that goes into the details. I've submitted it for publishing, but that means it goes into this dark place called "Corporate Edit". I haven't gotten a date from them yet, but keep an eye out for it!

New Member

Re: LWAPP Discovery request - discarded ?

Jake, I've been researching the same issue to fix a potential problem I'm going to have as I deploy recently LWAPP'ed AP's in L3 mode. Here's a nice briefing that covers the various L2/L3 discovery modes fairly well. Thanks for all the details you put in.

New Member

Re: LWAPP Discovery request - discarded ?

Hi jakew.. i would love to get my hands on that white paper you are writing for about the conversation between an AP and the WLC, as i am currently trying to setup a WLC behind a firewall

New Member

Re: LWAPP Discovery request - discarded ?

Jake,

Changing the DHCP-option made it work like a charm !

I would still really appreciate if you could write the clarifications I asked for in my previous message for future reference.

Best regards,

/M

New Member

Re: LWAPP Discovery request - discarded ?

I had this same problem about a year ago and I do have a copy of the pre-release whitepaper from Cisco on configuring the DHCP options.

Let me know if you want it I can get it to you.

Another option would be to use a seed ap, you put it on the same VLAN as the WLC and let it find the controller by broadcast. Then install that seed ap on the remote subnet where other APs are located. The others will find the WLC via communication over the air with the seed ap.

Feel free to contact me with questions I've been working on the Airespace stuff for 2 years.

New Member

Re: LWAPP Discovery request - discarded ?

Hi,

I am currently having a problem with providing DHCP option 43 to my AP's. I would certainly be interested in this white paper as info is short on ground. Let me know where I can collect it from.

Thx Jon.

New Member

Re: LWAPP Discovery request - discarded ?

I've attached the Win2K doc I just received from a Tech at Cisco. Has more info than just the Option 43 so may get additional info out of it.

This shows how to do the DHCP option for Win2K DNS server. I also have docs to do it for NetID DNS/DHCP servers.

Bronze

Re: LWAPP Discovery request - discarded ?

Has anyone got the [hex string] to handle Option 43 in Lucent VitalQIP?

Bronze

Re: LWAPP Discovery request - discarded ?

FYI - to get the string working in QIP:

Be Sure to include Option 60 Vendor Class Identifier with the appropriate name for your AP:

Cisco AP c1200 - for the 1200 Series

Add Option 43 (Vendor Specific Information, under Application and Servie Parameters) to your Option Template using the string:

[4104hexip1hexip2hexip3hexip4] with

41 - the Tag for the VCI

04 the length - 4 per IP address

hexip1hexip2hexip3hexip4 - hexed IP bytes as written

Bronze

Re: LWAPP Discovery request - discarded ?

Make sure NTP is set accurately on the WLC. Have your time source do the proper Timezone offset and make no adjustments on the WLC.

New Member

Re: LWAPP Discovery request - discarded ?

Let me throw in something here... I just finished wrestling with a problem that looks similar to this one... And the answer to my problem... get one of the APs primed, then use OTAP. As it turns out, I possess a bunch of AP1000s containing pre-3.0 firmware... thus DNS controller discovery cannot be done. If your controller sits on a different VLAN, then the only recourse for the older AP firmware - get it up >= 3.0 or use dhcp option 43. If you get one AP up, then enable OTAP on the controller to allow that AP to get the others up.

Even the poor guys at TAC didn't realize the impact of the older firmware with respect to DNS lookup... It only took a few weeks for me to get going (I've got about 90 APs in-place and another few hundred to go!)

New Member

Re: LWAPP Discovery request - discarded ?

Actually, if you can get the initial AP firmware updated to support DNS discovery, then you shouldn't need option 43 - so two methods exist if your controller management interface sits on different VLAN from the APs...

New Member

Re: LWAPP Discovery request - discarded ?

Yes on the newer Cisco 1010 and 1131 APs the DNS lookup is great you don't have to set the DHCP option on the DHCP scope for the AP's VLAN. It doesn't however seem to work on the Nortel Branded 2230 APs. DHCP 43 or OTAD seem to be the only option for those APs.

Although I am in the middle of an Interesting case where APs wouldn't attach to their Primary controller as specified in their config. They would only attach to their secondary or any other that would answer. Cisco's answer was to enable DHCP Option 43, and that it is required to get the APs to associate to a specific controller each time they boot.

This is bogus and I am trying to get the TAC guy to come forward with correct info.

I use the Option 43 just for initial installation and then remove it once the APs are up. Then they actually do associate to the correct Primary once they are configured.

New Member

Re: LWAPP Discovery request - discarded ?

The Nortel gear lacks the correct firmware level to support DNS lookup... Now whether these APs can interoperate with the Cisco-branded code is another question...The AP support for the full set of discovery options is my point...

New Member

Re: LWAPP Discovery request - discarded ?

We have upgraded about 100 of the Nortel branded 2230 APs and have not had any major problems. I have been told the 1131AG will be the preferred AP to use with the system in the future as it has more memory to handle new features in the code.

We have the 2230 APs associate to both the 4136 and 4404 switches with no problems. They don't seem to support the DNS lookup because of the boot firmware version.

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