DHCP and IP unnumbered

RouterOS General
1

Hi

I’m trying to migrate a Cisco router to Mikrotik.
It currently runs a DHCP server over multiple VLANs with each VLAN configured as ip unnumbered, something like below. Can Mikrotik support this? or do I need to assign an IP address to each VLAN? Thanks in advance.


interface Loopback0
ip address 172.17.12.1 255.255.255.0
!
interface FastEthernet0/1.101
encapsulation dot1Q 101
ip unnumbered Loopback0
ip helper-address 172.17.11.3
!
interface FastEthernet0/1.102
encapsulation dot1Q 102
ip unnumbered Loopback0
ip helper-address 172.17.11.3
!
interface FastEthernet0/1.103
encapsulation dot1Q 103
ip unnumbered Loopback0
ip helper-address 172.17.11.3
…

2

You need to assign an IP address to each VLAN. If they exist on the same router then the IPs need to be unique.

3

Thank you for your reply. Yes I know it’s possible with having an IP for each VLAN but if there are hundreds of VLANs it’s not very practical. Also if only one IP needs to be assigned by DHCP to a VLAN, a /30 needs to be assigned and wasting IP address resource.

Is there any other way of having DHCP running over hundreds of interfaces/VLANs without having IP on each interface in Mikrotik Router OS?

4

No, not unless you bridge them all into one another forming one large broadcast domain, which presumably defeats the purpose. RouterOS doesn’t have the concept of unnumbered interfaces. If you need that feature stick with a platform that supports it.

5

What you can do is put all the VLANs into a bridge, with a shared non-0 horizon value, and then run your DHCP server (and IP address) on the bridge.

The non-0 horizon will prevent L2 forwarding from one VLAN to another, while allowing you to treat the aggregate of them collectively.

One other option would be to look for a ‘private’ or ‘protected’ port-based VLAN option on your switches.

–Eric