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10 Step Wireless AP Controler Solution?


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#1 DC4Networks

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Posted 22 May 2009 - 07:13 AM

Hi,

Below is an CCNP BCMSN exam simulation question with a partial answer.
I suspect that this partial answer isn't correct and needs completing with an explanation.

I will look forward to any feed back with the solution and the source of an explanation.


You work as a network administrator.
Your boss, is asking you about lightweight access points WLAN controller associations.
What is the proper sequence a lightweight access point associates with a WLAN controller?

• The lightweight AP searches for a WLAN in layer 3 mode.
• The lightweight AP searches for a wireless LAN controller using CDP.
• The lightweight AP searches for a wireless LAN controller using LWAPP in layer 2 mode.
• The lightweight AP chooses the AP manager with the most number of associated access points and sends the join request.
• The lightweight AP sends a LWAPP Discovery Request to the management IP address of the wireless LAN controller via broadcast.
• The lightweight AP chooses the AP Manager with the least number of associated access points and sends the join request.
• The wireless LAN controller responds with a Discovery Response from the Manager IP address.
• The IP address is statically configured on the lightweight AP.
• The lightweight AP requests an IP address via DHCP.
• The lightweight AP sends a LWAPP Discovery Requests to the management IP address of the wireless LAN controller via unicast.

Partial Answer Given:

1st Step: The lightweight AP searches for a wireless LAN controller using CDP.
2nd Step: The lightweight AP chooses the AP manager with the most number of associated access points and sends the join request.
3rd Step: The wireless LAN controller responds with a Discovery Response from the Manager IP address.
4th Step: The lightweight AP sends a LWAPP Discovery Requests to the management IP address of the wireless LAN controller via unicast.
5th Step: The lightweight AP requests an IP address via DHCP.
6th Step: The lightweight AP searches for a WLAN in layer 3 mode.
7th Step: ?
8th Step: ?
9th Step: ?
10th Step: ?

Cheers,

DC4Networks


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#2 kdavison007

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Posted 04 June 2009 - 06:38 AM

QUOTE (DC4Networks @ May 21 2009, 04:13 PM) <{POST_SNAPBACK}>
Hi,

Below is an CCNP BCMSN exam simulation question with a partial answer.
I suspect that this partial answer isn't correct and needs completing with an explanation.

I will look forward to any feed back with the solution and the source of an explanation.


You work as a network administrator.
Your boss, is asking you about lightweight access points WLAN controller associations.
What is the proper sequence a lightweight access point associates with a WLAN controller?

• The lightweight AP searches for a WLAN in layer 3 mode.
• The lightweight AP searches for a wireless LAN controller using CDP.
• The lightweight AP searches for a wireless LAN controller using LWAPP in layer 2 mode.
• The lightweight AP chooses the AP manager with the most number of associated access points and sends the join request.
• The lightweight AP sends a LWAPP Discovery Request to the management IP address of the wireless LAN controller via broadcast.
• The lightweight AP chooses the AP Manager with the least number of associated access points and sends the join request.
• The wireless LAN controller responds with a Discovery Response from the Manager IP address.
• The IP address is statically configured on the lightweight AP.
• The lightweight AP requests an IP address via DHCP.
• The lightweight AP sends a LWAPP Discovery Requests to the management IP address of the wireless LAN controller via unicast.

Partial Answer Given:

1st Step: The lightweight AP searches for a wireless LAN controller using CDP.
2nd Step: The lightweight AP chooses the AP manager with the most number of associated access points and sends the join request.
3rd Step: The wireless LAN controller responds with a Discovery Response from the Manager IP address.
4th Step: The lightweight AP sends a LWAPP Discovery Requests to the management IP address of the wireless LAN controller via unicast.
5th Step: The lightweight AP requests an IP address via DHCP.
6th Step: The lightweight AP searches for a WLAN in layer 3 mode.
7th Step: ?
8th Step: ?
9th Step: ?
10th Step: ?

Cheers,

DC4Networks


This is wrong. From my CCNP study guide I believe it is:

1. The AP searches for a wireless controller using LWAPP in Layer 2 mode
2. The AP requests an IP address via DHCP
3. The AP searches for a wireless controller in layer 3 mode
4. The AP sends a LWAPP discovery request to the management IP address via directed broadcast
5. The wireless LAN controller responds with a Discovery Response from the Manager IP address.
6. The lightweight AP chooses the AP Manager with the least number of associated access points and sends the join request.



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#3 DC4Networks

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Posted 04 June 2009 - 10:28 PM

Hi,

Thanks for your feedback regarding this question.

I have been advised from another source that this question isn't likely to appear in the exam.

Not that I likely to see it now because I've now passed the CCNP Composite exam;-)

Cheers,

DC4Networks
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#4 kdavison007

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Posted 04 June 2009 - 11:05 PM

Congrats on passing the composite. You're braver than I am. I actually just barely failed the BCMSN, but this question was on my test. I don't think it has quite as many options, but it was basically asking the order of how a LWAPP connects to a controller.
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#5 sirkozz

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Posted 11 June 2009 - 10:02 PM

Check out this link for the exact sequence: hxxp://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note09186a00806c9e51.shtml
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#6 kdavison007

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Posted 12 June 2009 - 03:55 AM

According to that document the AP tries to get an IP address first. I always thought that was the second step according to what I see on the console of my lightweight access point at my desk which indicates it goes to LWAPP discovery BEFORE getting an IP address:

*Mar 1 00:00:07.231: %LINK-3-UPDOWN: Interface FastEthernet0, changed state to up
*Mar 1 00:00:08.230: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0, changed state to up
*Mar 1 00:00:20.226: %CDP_PD-4-POWER_OK: Full power - NEGOTIATED inline power source
*Mar 1 00:00:25.601: %LWAPP-5-CHANGED: LWAPP changed state to DISCOVERY
*Mar 1 00:00:34.114: %DHCP-6-ADDRESS_ASSIGN: Interface FastEthernet0 assigned DHCP address 10.30.202.225, mask 255.255.255.0, hostname AP001d.7097.d2c6

Translating "CISCO-LWAPP-CONTROLLER.hosp.wisc.edu"...domain server (10.1.20.100) [OK]
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#7 sirkozz

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Posted 12 June 2009 - 04:54 AM

If the AP is operating in layer3 mode and did not have statically assigned IP than how could it go into discovery mode? It has to have an IP to get the LWAPP traffic to the WLC. Your console session is only showing you what IOS is told to tell you and in the order it is programmed to do. Put a sniffer on the network and you’ll see exactly what Cisco says you’ll see. Contact Cisco and maybe they will change this, believe me you’re not the first person to be confused by this console output, or complain to Cisco about this issue. If you interested in seeing the LWAPP draft check this out:

hxxp://tools.ietf.org/html/draft-ohara-capwap-lwapp-04

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#8 SaramiR

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Posted 01 September 2009 - 11:20 PM

This is wrong. From my CCNP study guide I believe it is:

1. The AP searches for a wireless controller using LWAPP in Layer 2 mode
2. The AP requests an IP address via DHCP
3. The AP searches for a wireless controller in layer 3 mode
4. The AP sends a LWAPP discovery request to the management IP address via directed broadcast
5. The wireless LAN controller responds with a Discovery Response from the Manager IP address.
6. The lightweight AP chooses the AP Manager with the least number of associated access points and sends the join request.



Why directed broadcast in step 4?
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#9 sirkozz

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Posted 05 September 2009 - 06:20 AM

Saramir if you read the Cisco doc I referenced earlier its spells out exactly how a layer2 or layer3 adoption occurs. If you have a sniffer check out the traffic when you plug in a lwap on the net and you’ll see its right.

Copied from the doc:
“This sequence of events must occur in order for an LAP to register to a WLC:
1. The LAPs issue a DHCP discovery request to get an IP address, unless it has previously had a static IP address configured.
2. The LAP sends LWAPP discovery request messages to the WLCs.
3. Any WLC that receives the LWAPP discovery request responds with an LWAPP discovery response message.
4. From the LWAPP discovery responses that the LAP receives, the LAP selects a WLC to join.
5. The LAP then sends an LWAPP join request to the WLC and expects an LWAPP join response.
6. The WLC validates the LAP and then sends an LWAPP join response to the LAP.
7. The LAP validates the WLC, which completes the discovery and join process. The LWAPP join process includes mutual authentication and encryption key derivation, which is used to secure the join process and future LWAPP control messages.
8. The LAP registers with the controller”

Forget about layer2 adoption, only 1000 series AP’s support it, it’s not current and Cisco no longer supports layer2 adoption or 1000 series AP with up to date IOS on 2100 or 4400 controllers.

Been working with WLAN’s for over 10 years, and the 1 thing that always manages to amaze me is the lacking of knowledge of said. With the exception of some big fortune 500’s most companies do not have anyone working with any real WLAN skills. That said most “Cisco” books written from a non-WLAN perspective are also lacking in both precision and utter failure to adhere to the most basic Cisco WLAN docs. Best example I can give you is in the latest Todd Lammle CCNA book when showing a 1200 AP config he gives an IP to the radio, this is a major departure from any 1200 doc. Not saying it won’t work just that it’s a security issue unless it’s a mesh WLAN and then you need it.
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