MR - Mandatory DHCP

[RaphaelL]

Hi ,

We had issues with Zebra wireless scanners. After days of troubleshooting we found that article : 

https://supportcommunity.zebra.com/s/article/000026799?language=en_US#:~:text=The%20%22Mandatory%20D....

and that post : 

https://community.meraki.com/t5/Wireless/Mandatory-DHCP/m-p/102573

https://documentation.meraki.com/MR/Access_Control#Mandatory_DHCP

which is not required by AOSP or IEEE standards and Zebra devices do not support this.

Why would Meraki go that way ?

Still running MR28 , does anyone knows if that behavior has changed with MR29 or MR30 ?

I can't test it at the moment.

[alemabrahao]

I don't understand, are you trying to set a static IP on a Zebra device to try to connect to a network where the mandatory DHCP is enabled?

If so, it is normal for the connection to drop, the WLC itself works that way.

[RaphaelL]

No that wouldn't make any sense.

Devices are DHCP. but Mandatory DHCP requires a DHCP transaction per roaming , which is not part of the IEEE standards so some devices do not have to support it. Zebra are one of those devices and they won't support it like mentionned in their KB

[alemabrahao]

I understand, well I believe that on Meraki's side they are unlikely to make any changes, so the only alternative is to disable the feture itself, or create an exclusive SSID for these devices (I'm not particularly a fan of this approach).

[K2_Josh]

Thanks for posting about this. But I'm a little unclear on the context: Is mandatory DHCP a requirement for this SSID/network/org?

And was mandatory DHCP enabled by default on a SSID/network/org? I'm pretty sure that it's always been off by default for me.

Meanwhile, I would recommend three sets of changes to the Meraki team:

1. Update all documentation related to mandatory DHCP

2. Update applicable best practices and CVD-like docs with a note about this
3. Add an 'i' with a  circle hover label near the toggles for this setting to link to the appropriate documentation and not potential compatibility issues with roaming on some devices.

I'm going to make internal notes to keep this feature disabled for VLANs with wireless devices.

[RaphaelL]

Hi ,

This is not enabled by default. It was a special request from our security teams. This has been working perfectly in 99.9% of our sites expect for the ones which contains Zebra devices ( however this issue can be replicated with other devices )

It is specified in the documentation , but can still bite you ( like it did for me )

[AFC-IT]

We've been banging our heads against the wall for the last couple days trying to solve the issue with our Zebra scanners and roaming between APs. Support advised us to disable Mandatory DHCP and it worked, the first thing we said after that is that that setting needs an 'i' info bubble! 

I found this in the documentation today, and it's exactly what needs to be in that info bubble.

"Enabled: Wireless clients associated to an AP (either new associations or clients that roamed from another AP) that have not requested a DHCP address are placed in a blocked state and are not able to send any traffic on LAN and WAN."

[thomasthomsen]

I was "caught" in the exact same situation a few years back. The exact same thing. 🙂

I was also quite "surprised" until I, almost by chance, read the documentation, and thought about it.

I mean, in theory, the Meraki APs could exchange the information with the other APs on the site, that a client already had done DHCP once, and the problem would be "solved".

[RaphaelL]

That's why I'm wondering if that behavior has changed in recent firmwares like MR30

[thomasthomsen]

I know the network i was working on at the time was running MR29 (dont know the exact release).

[AFC-IT]

I just found this thread after experiencing the exact same issue with Zebra scanners and our brand new Meraki APs. Meraki support advised us to disable Mandatory DHCP and it fixed the issue right away. We're on MR30.6 firmware, so I can report that it hasn't changed. Extremely happy that we figured out what was causing our problems and how to fix it though.