APs replace without breaks

[Jaro]

Hello

I need replace old APs (with newer, different type) which are connected to the WLC, without breaks (or with very little time).

There are 2 WLCs, one of them is active.

I need to keep old IP adress plan and same VLANs.

Theoretically I can increase power of APs around AP, which I wanna to change, so It ensures, nobody will lose connection.

Do you think that it is good idea, or could you please give me some another idea how to do it? 

Thank you

[patoberli · Accepted solution]

I assume you use capwap and not standalone.

Make sure to preprovision them, but be aware of IP address conflict if you set it manually.

To make your life a little bit easier, create a small DHCP pool in the AP VLAN, with maybe 5 addresses and a very short lifetime (5 minutes maybe). With this you can just plugin your new AP, let it update and get assigned to the WLC and once that is done, turn of the old AP and change the IP on the new AP.

If you use RRM, it should automatically increase the power if you turn off an AP.

From plugging it in until it's ready to serve clients, it takes around 5 minutes for an AP, if the software is on the same level as the WLC. This is why you need to preprovision them, for a short as possible downtime. If you have 2 LAN cables at the AP place you could run them in parallel for a short time. I suggest to replace them in the lunch break or so, that way you would effect only a little amount of clients.

[Jaro]

Thank you for your answer, but for sure:  I will connect new AP with wlc and different IP adress, then AP will make update and join with wlc. Then I change IP address and connect  it instead of old AP and after that it takes approximetly 5 minutes, is it correct ?

[patoberli]

This is correct. Best is, if you test it once and get used to the procedure.

[Jaro]

Thanks, last question, is there some different option how to do it with less than 5 minutes break? do you have any ides ? I have one cable only.

[patoberli]

With only one cable, probably not. You might be able to power it up with a power supply, but I fear it doesn't switch to PoE without reboot if you just unplug the PSU.

If you have enough coverage from your other AP around (check for example with the app "WiFi Overview" for Android) it should not produce an outage.

[Jaro]

Thank you for your answer, there are more  APs around, so I hope that it will be enough.

I hope that last question: about impact, when APs around increase power, what about boarder of zones, if there will be some breaks or only limited speed?

[patoberli]

Should only cause a bit limited speed, if there is some traffic load.

[Jaro]

okay, and what about TPC set, by default, TPC runs automatically every 10 minutes, but when I unplug device, I need immediately change of power - solution could be set it to "On Demand", will it change power when I will unplug AP ? Thanks

[patoberli]

This is true. When a new AP boots for the first time, it runs on 20 Mhz channels at full power, until TPC has run. I don't think you will actually feel this in a production network, if TPC really runs every 10 minutes (check first to make sure it's still configured to 10 minutes).

You could theoretically preprovision the AP with the current settings of the one it's going to replace with manual settings, and once you have replaced them all, set it back to automatic. But I honestly don't think that this will be needed at all, those few minutes it runs at full power shouldn't cause any issues. As long as TPC is on it's default 10 minutes setting. For example in my environment I've set it to run every 8 hours, I don't want the APs to change the power/channels to often throughout the day. RRM and CleanAir, in case an AP fails or a disturbance is found, is active though.

[Jaro]

thanks, but this is question about APs around, I mean, that when I unplug one AP(or AP fails), whether APs around will immediately increase power or they will wait 10 minutes ?

[patoberli]

I think this is the feature Event driven RRM that comes into play here (requires CleanAir APs and it must be enabled and configured):

https://mrncciew.com/2013/05/02/event-driven-rrm/

http://www.cisco.com/c/en/us/td/docs/wireless/controller/7-0/configuration/guide/c70/c70cleanair.html

The other feature is TPC, running by default all 10 minutes, which would also fix this.

From the document:

The Transmit Power Control (TPC) algorithm both increases and decreases an access point’s power in response to changes in the RF environment. In most instances, TPC seeks to lower an access point's power to reduce interference, but in the case of a sudden change in the RF coverage—for example, if an access point fails or becomes disabled—TPC can also increase power on surrounding access points. This feature is different from coverage hole detection, which is primarily concerned with clients. TPC provides enough RF power to achieve desired coverage levels while avoiding channel interference between access points. 

Source: http://www.cisco.com/c/en/us/td/docs/wireless/controller/7-4/configuration/guides/consolidated/b_cg74_CONSOLIDATED/b_cg74_CONSOLIDATED_chapter_010000011.html

[Jaro]

Thanks, but when CelanAir is not supported on APs (1231), is there any another option to ensure increase power of APs (when AP unplug, fail...) immediately  ?

[patoberli]

You could manually run the TPC every time you replace an AP. But unless you have a very wide separation of the current APs with nearly no signal overlap, you shouldn't have a problem.

If you have specific key areas, where you really need to have coverage, take a mobile phone and a Wireless Overview app and check if you see at least 2 APs at the specific location with a better than -75dB signal. That should be enough for a stable and fast signal if you unplug one of the listed APs.

[Thushara · Accepted solution]

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