4 Questions for WIFI....

[CSCO11733516]

Just doing some reading and had some questions that came up, if anyone could answer - I'd appreciate it.

1.  I do understand that once an LWAP joins a WLC, it remembers that WLC IP and always tries to connect to it - even after you clear the AP or the delete the configs.  All of my cisco readings and videos are always saying "there is no way to flush that out", does that stand true even if you were to re-image the AP?

2.  If there are 2 DHCP Servers configured for 1 Guest SSID, would this cause an issue?  E.g., 1 DHCP on a router handing out 192.168.1.10 - .20 and the other DHCP Server on WLC handing out 192.168.1.15-50.

If this would cause an issue, what kind of issues might be expierenced?  Which DHCP Server would be preferred by the APs?

3.  For AP's to go through the registration process, I typically configure the DHCP Server with Option43.  Are there any other options that would be recommended to use?  If so, which and why.

4.  I have always seen the AP's receive there IP Address dynamically via DHCP.  However, I have seen one instance where the 10 WAP's (1 WLC) were all statically assigned.  Someone told me that this is not good.  Why would that be a bad implementation idea? 

[Scott Fella · Accepted solution]

1. I do understand that once an LWAP joins a WLC, it remembers that WLC IP and always tries to connect to it - even after you clear the AP or the delete the configs. All of my cisco readings and videos are always saying "there is no way to flush that out", does that stand true even if you were to re-image the AP?

You erase the nvram

2. If there are 2 DHCP Servers configured for 1 Guest SSID, would this cause an issue? E.g., 1 DHCP on a router handing out 192.168.1.10 - .20 and the other DHCP Server on WLC handing out 192.168.1.15-50.
If this would cause an issue, what kind of issues might be expierenced? Which DHCP Server would be preferred by the APs?

You need to use a split scope meaning that each dhcp server would hand out addresses in different ranges.

Example:
192.168.1.10 - .20
192.168.1.21 - .30

3. For AP's to go through the registration process, I typically configure the DHCP Server with Option43. Are there any other options that would be recommended to use? If so, which and why.

It depends on what works best for you and what you prefer. DNS is a good option and also staging the APs on the same subnet as the WLC is another that I use 99% of the time.

4. I have always seen the AP's receive there IP Address dynamically via DHCP. However, I have seen one instance where the 10 WAP's (1 WLC) were all statically assigned. Someone told me that this is not good. Why would that be a bad implementation idea?

This is preference. I have done and still implement AP's with static addresses. Why not is the question. When there are monitoring the APs you don't want the APs to obtain a different ip. So do you do dhcp with Mac reservations. Sure if you want to manage that. The APs even with a static will fall back to dhcp if it doesn't join a WLC.

Hope this helps

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[Rob Huffman]

Hey Scott,

Great work (as always buddy!) +5

Cheers!

Rob

"Spend your life waiting,
for a moment that just don't come,
Well, don't waste your time waiting" 

-Springsteen

[Scott Fella]

Thanks Rob!

Thanks,

Scott

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[CSCO11733516]

Scott-

  Thanks for the reply, in reference to your responses.

2.  I understand what you are saying, but I am trying to understand if the scenario was I outlined.  Which DHCP would be preferred?  The external DHCP Server (external to the WLC) or the WLC?

3.  You mentioned "Staging the WAP's on the same subnet" - isn't this Cisco Best Practice?

4.  Ah thanks for providing the information.  I didn't know that regardless with the static IP's, the AP's would still fall back to DHCP.

[Scott Fella · Accepted solution]

2. I understand what you are saying, but I am trying to understand if the scenario was I outlined. Which DHCP would be preferred? The external DHCP Server (external to the WLC) or the WLC?

-The internal, but it depends on who hands out the dhcp response first.  You never want to overlap dhcp scopes because you will get duplicate address issues on your network!

3. You mentioned "Staging the WAP's on the same subnet" - isn't this Cisco Best Practice?

-Not really.... its our best practice because its a layer 2 discovery which is one of the discovery process the LAP performs.  Again, once the AP joins the WLC, it knows of the WLC's ip address and any WLC in the same mobility group and thus you can then move that LAP to another subnet and the AP will join as long as it gets an ip address and has connectivity back to the WLC.

4. Ah thanks for providing the information. I didn't know that regardless with the static IP's, the AP's would still fall back to DHCP.

-Yes it does... but this can cause issues to.  If you leave AP's in a production subnet, the AP will request dhcp address and try to join a WLC.  If it fails to discover a WLC, it reboots and goes through the whole discovery process.  Well that means the AP will send out a dhcp request and will take up another dhcp address and that starts to increment.  You will then see multiple ip address for that AP mac address and your MS dhcp server will mark the previous address as bad.  This will go on until you run out of addresses.  So its a good idea to stage the AP's or at least put them on the same subnet as the WLC.

Hope this helps!

Thanks,

Scott

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[CSCO11733516]

Thanks Scott.

[Scott Fella]

No problem... Hopefully I didn't confuse you:)

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