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mscarpitti
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DHCP Server on Bridge Interface Issue

Tue Feb 18, 2020 6:25 pm

Recently received our first Mikrotik CCR1036 +6.41 OS and are working to get it configured for deployment. We are a Cisco Trained organization and have hit a stumbling block.

I've read through all the Mikrotik Configuration documentation (as well as about 50 forum threads) surrounding this but can't seem to get this to work.

First question - Being as that we are trying to configure a DHCP Server on a Bridge interface, I understand it requires an IP address on the Bridge interface itself to enable the functionality. As the configuration we are running will include several VLANs attached to the Bridge on a single interface (to enable InterVLAN routing - Router on a Stick basically), which IP subnet should the Bridge interface be associated to if the DHCP server will be providing IPs for multiple Subnets?

Initially the DHCP server would show invalid if no IP address was assigned to the bridge, but it still won't issue IPs whether I assign an IP in the same subnet as one of the VLANs in the bridge or just a dummy network IP address.

I have validated connectivity between the client and the Interface IP Address which the server resides on.

Thanks,
Michael
 
quackyo
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Re: DHCP Server on Bridge Interface Issue

Wed Feb 19, 2020 4:34 pm

If it is a bridge with multiple VLANs, make VLAN interfaces for each VLAN (with the bridge as "backend interface), and set the dhcp servers for each VLAN on the VLAN interface.
 
mscarpitti
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Re: DHCP Server on Bridge Interface Issue

Wed Feb 19, 2020 6:06 pm

I've set it up exactly per the examples given in this thread, which seems to be the general consensus on how to configure this. See scenario 2 of the ROAS configuration for the Router config download.

viewtopic.php?f=13&t=143620

Not sure exactly what you are referring to as using the bridge as a "backend interface". If I assign the DHCP server to the VLAN interface in this configuration, it will remain INVALID. If I assign an IP address to the Bridge interface (in the same subnet as one of the member VLANs), the DHCP server will become VALID but will not issue IP addresses, and I lose connectivity to the VLAN IP Gateway itself and can only reach the Bridge IP.

Conversely, if I remove the VLAN as a bridge member, the DHCP server will become VALID but then I lose Layer3 communication as well.

Thoughts? I can post config as well if that helps.
 
quackyo
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Re: DHCP Server on Bridge Interface Issue

Thu Feb 20, 2020 9:56 am

the VLAN interfaces are "virtual interfaces" so you have to define the interface it should get connection from. see attached image.
Also - did you set IP address on the VLAN interface?

You have to make VLAN interfaces for each VLAN you need connectivity from a dhcp server on.
And you have to make a new dhcp server for each vlan/pool you want to serve.
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mscarpitti
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Re: DHCP Server on Bridge Interface Issue  [SOLVED]

Thu Feb 20, 2020 10:07 pm

Well, after about 20 mins on the phone with a consultant - it seems I ran into a bug straight out of the gate.

I setup the DHCP Servers, Pools, and Networks manually via Webfig. Confirmed all configuration in Terminal was correct but the Servers would not activate. Rebuilt the servers using the DHCP server wizard that resulted in the same exact configurations and now it works.

Thanks for the assistance quackyo.

Michael

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