AP IP Assignment | Static vs Dynamic

[ZK916]

Hello,

I understand that the DHCP feature needs to be enabled on the WAPs during the initial deployment process, however, once the WAP has been fully deployed and operational, what is the best practice with respect to the IP assignment on the WAP. Is it to leave the WAP with the DHCP configuration or staticly assign an ip address to the WAP??

My question stems from actual deployment incidents that occurred with our field techs. The customer didn't have the proper DHCP scope for the new WAPs (decommissioning the old WAP and replacing it with a new one; that's using two IP addresses from the scope). 

Thanks in advance.

\
Best, ~zK

[Leo Laohoo]

Static or DHCP is up to the system or network administrator. 

DHCP is the best because it removes a layer of complexity.  

[MHM Cisco World]

Static can config' but what about op. must AP learn from dhcp.

Op. That make AP learn wlc IP' or dns server.

So you must sure that when you config static IP you also config wlc primary IP and DNS server IP.

MHM

[eglinsky2012 · Accepted solution]

Nearly 12,000 APs here, most are using DHCP without reservations. We have both DNS and DCHP option 43 configured to point the APs to the controllers, so it's as simple as plugging in the AP out of the box and it joins the WLC.

We do have about a dozen wireless bridges that I configured a DHCP reservation for so we could monitor them via ping alongside the switches they're connected to in our NMS. That way, we have more information for troubleshooting should the switches in the buildings the bridges feed go down.

If you customer is concerned about depleting their available IPs when replacing the APs, I have 3 suggestions, easiest to hardest:

1. Shorten the DHCP scope's lease time ahead of the cutover. If it's 24 hours now, set it to 30 minutes, for example. That way, within 30 minutes of an old AP being disconnected, its lease will become available for a new AP to use. Then set it back to 24 hours after the cutover, to reduce load on the DHCP server.
2. Use multinetting/superscopes/shared networks (whatever their routers/DHCP servers call it) to add another subnet in parallel with the existing one. Once the cutover is complete, either keep the two subnets or remove the new subnet from the DHCP server, wait for all APs to move to the old subnet, then remove the new subnet from the router. (Note there will be a momentary loss of service as the leases expire and the APs obtain a new lease and re-join the WLC.)
3. Make a new VLAN with new subnet and reconfigure the switch ports to that VLAN as the APs get replaced.

[Rasika Nayanajith]

Leave it to DHCP is the recommended approach unless you really want to manually touch configs to lock it down via static.

HTH
Rasika
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[absuizo14]

Hi

im trying to convince our client to use DHCP instead of static for APs since they are having ip conflict issues and i have read before that the recommended is indeed DHCP but for the life of me i could not find that cisco official document stating it so i may present it to them. can you point me to that cisco document?

[Rich R]

It's such a basic, fundamental principle that there isn't really any Cisco document telling you to use DHCP. It is the default, it's the way they are designed to work!  You can refer to:
https://www.cisco.com/c/en/us/support/docs/wireless/4400-series-wireless-lan-controllers/69719-wlc-lwap-config.html
"1. Have a DHCP server present so that the APs can acquire a network address."
https://www.cisco.com/c/en/us/support/docs/wireless/5500-series-wireless-controllers/119286-lap-notjoin-wlc-tshoot.html#toc-hId-653266329
https://www.cisco.com/c/en/us/support/docs/wireless-mobility/wireless-lan-wlan/97066-dhcp-option-43-00.html

I think the strongest argument for using DHCP is to be able use Option 43 to direct APs to the correct WLC.  Of course you can use DNS or static config even if you use static IPs but Option 43 allows you to define multiple WLCs (not just a single one like DNS) and it's dynamic so you can re-point the APs simply and easily without having to make changes to every AP.  As mentioned in other replies if the client is desperate to have each AP using a known IP then it is better to do that with DHCP address reservations than with static IP config on the AP.  And remember that by default APs will fall back to using DHCP even if they have a static IP, if they have trouble reaching a WLC.

There are a whole bunch of faults in the past (and still today) which have been/are resolved by doing full factory default reset of the AP.  Using static IP makes that more difficult because you have to get back onto the AP to reconfigure it afterwards.  If you're using DHCP then it's just not something you have to worry about.  Same applies to replacing an AP.

So static IP is the exception - it's more a case of having to justify why you don't use DHCP.  And when you run a large network like we do with 20,000+ APs static addressing would be an administrative nightmare.  We just use the same AP DHCP pool on every site for the APs, simple templates, no worries about addressing.  Option 43 directs the APs to the correct primary and secondary WLCs for the site.  Replacing APs is easy because it's plug and play - nobody needs to do static config on the AP.

[Rich R]

As others have said DHCP is the recommended and preferred method and should be the default.

There will be exceptions when, for one reason or another, you want/need to use static IPs but as @eglinsky2012 mentions still better to do that by IP reservation than static, where possible.

Also remember that even if you assign static IPs, the APs will fall back to using DHCP as a recovery method if they cannot reach a WLC, to prevent them getting stranded due to misconfig.

If your DHCP pool is running out of IPs then simply increase the pool size or use the other options already mentioned!  Don't make it more complicated than it needs to be.

[Scott Fella]

DHCP like what the others have mentioned.  The reason is, if you set a static ip address and the ap can't join a controller, the ap will revert back to DHCP as a measure if the ap is connected to the wrong vlan.  I helped managed a network in the past with over 100K access points and used DHCP.