DHCP configuration in cisco WLC 9800 for DHCP external server

[King_1988]

Dear All,

We have a below scenario : 

Our expectation is the user will get ip address from DHCP server while connecting to SSID. All SVI  for service ip is configured in Core Switch except WMI ip, that's why we have created just service VLAN in L2 on WLC-9800. 

WLC -Trunk-> L2 Switch -> Trunk- > Core Switch (L3). Also DHCP server is connected to L3 Core switch and in separate SVI. In this case we have just configured.

We have enable DHCP like above. Any other configuration is needed or it should work?

[MHM Cisco World]

What is WLC exact  model

40 or 80 or cl?

MHM

[MHM Cisco World]

Config->layer2->vlan 

Then select SVI

In advance tab of SVI 

Go to dhcp relay 

Add your dhcp serve-IP

Do this and update me

MHM

[Kasun Bandara]

@King_1988 try disabling DHCP proxy setting in WLC.

[balaji.bandi · Accepted solution]

If you have Layer3 SVI - then add IP-helper address on that SVI for the DHCP Server.

then you need to do below :  untick ipv4 DHCP Required and other option

[King_1988]

SVI is configured in Core switch and in WLC we will keep the service vlans as L2 and pass via trunk

[MHM Cisco World · Accepted solution]

so there is no need any DHCP config in your WLC, the WLC bridge the DHCP
config the ip helper under the SVI in Core SW 
interface vlan x
ip add x.x.x.x
ip helper-address y.y.y.y
no shut

MHM

[King_1988]

Ok. So, for the external DHCP server there is no need of any DHCP configuration in WLC 9800 if we keep service vlan L2, right? 

[MHM Cisco World]

Correct.

Since no SVI and dhcp external then wlc can not relay the dhcp' 

The Core SW with it SVI can relay the dhcp

MHM

[King_1988]

Thanks. 

[Rich R · Accepted solution]

> then you need to do below :  untick ipv4 DHCP Required
I disagree @balaji.bandi - "ipv4 DHCP required" setting is independent of the other DHCP settings.  It prevents clients from using static IP addresses, regardless of how DHCP is configured.  So the decision on ticking that is really just about whether or not you allow users to configure their own IP address or force them to use DHCP when joining the WLAN.
https://www.cisco.com/c/en/us/products/collateral/wireless/catalyst-9800-series-wireless-controllers/guide-c07-743627.html#DHCPRequiredoption

[balaji.bandi]

I disagree @balaji.bandi - "ipv4 DHCP required" setting is independent of the other DHCP settings. 

@Rich R  - may have lost communication due to non-follow last 3days due to other works.

[marce1000]

 - Checkout best practices for DHCP here : https://www.cisco.com/c/en/us/products/collateral/wireless/catalyst-9800-series-wireless-controllers/guide-c07-743627.html#DHCPbridgingandDHCPrelay

       Appendix : always evaluate the configuration of the WLC-9800 with the CLI command show tech wireless  and feed the output into Wireless Debug Analyzer  , checkout all advisories ! 

 M.

[Rich R]

Before giving the right answer - is your WLAN configured for:
- Flexconnect Local Switching? or
- Central Switching?

Your screenshot shows you've ticked DHCP Required (Good) but you've then filled in a DHCP server IP below.  I'm not completely clear what that is supposed to do but the config guide shows that only being used if you are using 9800 internal DHCP server.

If you're using standard layer 2 forwarding, which Cisco recommends as best practice, with layer 3 handled by next hop layer 3 gateway, then you do not need to configure a DHCP IP anywhere on the WLC because it's handled by the switch/router/firewall.

If you want to use DHCP relay on the WLC for centrally switched WLANs then you need to configure SVI interface:
https://www.cisco.com/c/en/us/products/collateral/wireless/catalyst-9800-series-wireless-controllers/guide-c07-743627.html#DHCPbridgingandDHCPrelay

So for a start I would remove that DHCP Server IP Address from your policy profile config and refer to the link above for configuring DHCP relay with option 82 if needed.

[King_1988]

Ok thanks. I will follow this. DHCP is configured in a external server.