Question about CAPWAP tunnel

[athan1234]

Hi,

I am discussing this topic with my cooworker, and I need to clarify these questions to determine who is correct.

My position is that if you have a CAPWAP tunnel, you don’t need to assign an IP address to the AP; you just need to have the controller's IP and set up a DHCP server on the controller.

The other position is that it is necessary to assign an IP address to the AP.

Could you please let me know who is correct?

Please tell me who has the reason 

[Flavio Miranda]

@athan1234 

 Unfortunatelly you are wrong. The AP need to get an IP address first. Only after it gets its IP address, it will be able to join the WLC in order to stablish the capwap tunnel in the first place. 

 Most of time, is during the DHCP process that the AP discovery the WLC IP address but even in situation where the WLC IP address if discovery by other method, the AP need to get IP address before anything. 

In the event of the WLC is actiing as DHCP server, which is very rare, the AP will use the WLC as DHCP service first, and then will join to the WLC after getting the IP address. 

[athan1234]

Thanks, so how does the AP get its IP for the first time? Is it mandatory to assign an IP in the CAPWAP tunnel?

For example, if I set up a CAPWAP tunnel, imagine my controller management has a range of 10.0.0.5 255.255.255.0.

I set up a CAPWAP tunnel with 10.0.0.5 255.255.255.0 .

I also set up a DHCP opn the controller  for the AP management range of 10.0.0.10–10.0.0.50.

It is not working.

I set up a capwap tunnel 10.0.0.5 255.255.255.0 10.0.0.1 

I sett up a dhcp for the AP managment range 10.0.0.10 -10.0.0.50 .

It is not working 

[Flavio Miranda · Accepted solution]

@athan1234 

AP can get the IP via DHCP or static via capwap command

If you choose the do It statically, there a few comands you need to use 

You need to assing IP ,mask and Gateway

After that the WLC 

[Leo Laohoo]

---

@athan1234 wrote:
you don’t need to assign an IP address to the AP

---

Wut?

How is the AP going to join the controller?

Think of a CAPWAP tunnel similar to a VPN tunnel.  Each ends needs to have an IP address.

[athan1234]

Thanks @Flavio Miranda 

[athan1234]

@Flavio Miranda  One more thing: you don’t need to use a CAPWAP tunnel if you want to have DHCP , for example  on the switch with Option 43 for the controller. It’s not necessary to have a CAPWAP tunnel, is it? CAPWAP tunnel is only required if you want to assign a static IP to the AP. isent ´it 

[marce1000]

 - Negative the AP and controller can only communicate through a CAPWAP tunnel in both scenarios

 M.

[MHM Cisco World]

No friend 

There are WLC and AP and discover method and capwap 

AP use discover method to detect wlc ip

One of discover method is dhcp 

After AP detect wlc ip it use IP to build capwap tunnel to wlc

For which this tunnel use ?

If AP is local mode it use for push config from wlc to AP and AP forward traffic from wifi to wire via wlc 

If AP is flex it only use to push config and/or authc of wifi clients.

Only one condition you not need capwap

If AP is standalone then you can do config on AP directly 

MHM

[athan1234]

Thanks  @MHM Cisco World 

[MHM Cisco World]

You are so welcome friend 

MHM

[Rich R]

- AP always needs a CAPWAP tunnel to join the WLC.  UDP 5246  is for the CAPWAP control tunnel and UDP 5247 is for the CAPWAP data tunnel (client data).

- AP can use static IP or DHCP - DHCP is recommended.  AP can fall back to using DHCP automatically if it can't discover a WLC using static IP.

- AP can use a number of different methods to discover the WLC.  Recommended to use Option 43 with DHCP.  This allows to specify multiple WLC IPs (primary/secondary/tertiary) for resilience.

DHCP with option 43 means AP installation and replacement (in case of failure or upgrade) is made much quicker and easier - no specific AP config required, just plug in the AP.

See:
https://www.cisco.com/c/en/us/support/docs/wireless/catalyst-9120axe-access-point/221056-understand-the-ap-join-process-with-the.html
https://www.cisco.com/c/en/us/support/docs/wireless-mobility/wireless-lan-wlan/97066-dhcp-option-43-00.html