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Beginner

WLC-9800 External dhcp guide

Hi

 

Having an issue with the 9800 controller setup in sso, where I cant get clients to get a dhcp reply. The aps are up.. the ssid are up..  but external dhcp not so much

 

I have tried setting it up globally under policy without effect. I have tried setting up the svi with an helper and I can reach the dhcp server . but traffic comes back on the mgmt intf (ap intf) been looking everywhere for some good guides on the 9800 regarding dhcp externally (also the vrf options) does anyone have any good tips here=? 

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VIP Advisor

Re: WLC-9800 External dhcp guide

Do you see any logs

 

follow below gude

 

https://www.cisco.com/c/en/us/td/docs/wireless/controller/9800/config-guide/b_wl_16_10_cg.pdf

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Beginner

Re: WLC-9800 External dhcp guide

Hi,

 

It would be really useful if someone could give a quick breakdown on the difference between AireOS config and IOS XE ....not getting anywhere fast with the documentation. Thanks.

 

ED

Beginner

Re: WLC-9800 External dhcp guide

I agree, but I’ve found the docs here fairly useful. https://www.cisco.com/c/en/us/support/wireless/catalyst-9800-series-wireless-controllers/products-configuration-examples-list.html

Any specific questions feel free to ask in the forums. Once you get the hang of how WLANs are configured through the different GUI screens it gets better. I did stare and compares from our AireOS WLCs and could find most of the same settings in the 9800.
Beginner

Re: WLC-9800 External dhcp guide

I'm also having an issue with a new 9800-L not passing DHCP requests properly.  I'm sure it's a config issue.  On AireOS the relay/proxy setup was all in the interface settings.  You could have it source DHCP requests or ignore and send the requests through the connected switch, which is what I do. 

In the 9800, it looks like the general policy screen has a DHCP text box, but that does nothing.  I've also tried adding SVIs on the 9800 and put in helpers there just to see if it would work and it does not.  A client debug shows a broadcast DHCP request going out, but nothing coming back.  Trunks look good and an AireOS WLC connected to the same switch with the same VLANs is sending DHCP requests fine.

Beginner

Re: WLC-9800 External dhcp guide

Hi,

I am in the same situation on a new 9800 deployment. I tried several configuration, just like kdavison suggests. I did some packet captures on the L3 router and the WLC is clearly not relaying the DHCP request. We had to enable DHCP relay on the L3 router instead. It was working fine with a previous AireOS controller in the same subnet.

DHCP relay however works when using an internal DHCP pool on the 9800 and relaying to the Loopback of the 9800.

We are running version 16.12.1s.

Beginner

Re: WLC-9800 External dhcp guide

J.rambeau,

What is the output of “show run | i option” on the cli of your 9800?
Beginner

Re: WLC-9800 External dhcp guide

I have nothing for this output.

Did you have success with a specific option here?

Beginner

Re: WLC-9800 External dhcp guide

I did have an option statement in there, which I believe was adding the option 82 on the relay as it went to the connected switch. We are connecting our 9800 to a 6807 switch and I also noticed that you can add the command “ip dhcp relay information trust-all” on the switch side to get the relay to work properly. On some Cisco platforms you can trust just the inbound interface, which is more ideal so you’re not inherently trusting all dhcp relay traffic.
Beginner

Re: WLC-9800 External dhcp guide

My problem is that the DHCP Request of the client never makes it out of the controller because I cannot not see any UDP/67 while capturing packet at the L3 router (actually a firewall). Sure you can have issues with option 82 but this is a different matter here.
I will try and replicate the issue on the lab, maybe I missed something on the customer configuration...

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