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DHCP client on bridge interface with a VLAN DHCP not working

Posted: Wed Jan 06, 2021 11:31 pm
by swisstico
Hello everyone,

We have a strange issue that we didn't find the answer...

We have a router (RouterOS 6.47.8) with VLANs and DHCP on each of VLANs, everything works fine (computers, phones, tablets, wired and wireless).

However if we connect a second MikroTik device, reset it without configuration, create a simple bridge, add a port and configure an "/ip dhcp-client" (enabled yes), the new MikroTik never receive the IP address. Then we delete the bridge (tested as well to reset de device and try again without bridge), and use the same dhcp-client config directly on the etherX port, and work perfectly.

We tried to downgrade to RouterOS 6.46.8 thinking of a bug, but we get the same result.
The strange thing is that we have this issue only with a MikroTik with VLANs and DHCP on VLANs, no issue with config without VLANs, but at the same time we know that the DHCP server is working well as the other devices works fine.

Any idea?

Best Regards,

Re: DHCP client on bridge interface with a VLAN DHCP not working

Posted: Thu Jan 07, 2021 9:30 am
by erlinden
It should be working...can you please share your configs: /export hide-sensitive file=anythingyoulike?
And please use the [] tags to make it readable.

Re: DHCP client on bridge interface with a VLAN DHCP not working

Posted: Thu Jan 07, 2021 10:05 am
by sindy
Start by showing the configuration export from both devices when the client doesn't work. There's a similar topic here, but there multiple RouterOS versions and a complex topology are involved, your setup seems much simpler. Anonymize the configurations, following the suggestion in my automatic signature below, before posting them.

Re: DHCP client on bridge interface with a VLAN DHCP not working

Posted: Sun Mar 07, 2021 9:42 pm
by Guscht
Any idea?
Make sure the bridge is untagged! If the bridge itself is tagged (or admit only tagged frames is selected), the DHCP-client will never work.

Re: DHCP client on bridge interface with a VLAN DHCP not working

Posted: Tue Mar 16, 2021 10:28 am
by torgr2019
Any idea?
Make sure the bridge is untagged! If the bridge itself is tagged (or admit only tagged frames is selected), the DHCP-client will never work.
Thank you so much for your reply, it helped me a lot.
Actually i have the classic topology ISP>>router (4011) with vlans, dhcp etc >> access point with multiple SSIDs in different vlans (hAP ac2).
Many days wasted due to poor documentation from Mikrotik.
1. First DO NOT USE the default wizards. Its a crap.
2. Always assign ADMIN MAC ADDRESS and auto-mac=no to the bridge of the AP, otherwise you will be locked out even with Winbox.
3. Bridge should be Vlan filtering yes, VLAN ID at the bridge = the same as the vlan id of the main network the wanted the dhcp to find.
4. Accept all at the bridge.
5. Then create a static IP at DHCP client, and a network for that IP and voila: The AP is accessible from the web and the Winbox and working as it should.

Re: DHCP client on bridge interface with a VLAN DHCP not working

Posted: Tue Mar 16, 2021 4:39 pm
by anav
Agreed documentation is poor but tis slowly improving day by day.
As far as being a strange occurrence, not really. When one understands how the MT handles packet flow etc, it becomes crystal clear and ordinary.
However it will take me a lifetime to get there, considering I started at 55, I have to cram that learning into less years LOL.