Question for using a specific VLAN in DHCP Client

Hello,

I have a interface ether1 which is a trunk port oin switchA to another switchB carrying vlan 10 and 500.

On the other switchB there is ether1 as well the trunk port and on ether2 (tagged vlan 500) there is a cable modem in bridge mode which gives me the public cable modem ip by dhcp.

I want that cable incoming in ether2 be tagged as 500 so that i can use it in switchA in a DHCP Client.

The other ports on switchB should be vlan 10.

switchA is actually here the router with firewall etc.

Reason:

My internet access is in room A (switchB) but i want for reasons my firewall/router etc in room B (switchA/router)

So i want to put the cable modem signal into a vlan only for that to roomB and there a dhcp client using that vlan 500 as my WAN and all other ports in roomB are then vlan 10 and back to roomA to switchB also vlan 10 for the other free ports.

I don’t know if its clear what i want.

Is that possible and what is the best way?

Thank you very much

Yes, why do you explain your network in a backwards way…
It would appear you have an ISP modem in the entry room to the house.
It would appear you have attached the ethernet cable to a smart switch in the entry room to the house.
It would appear you have a cable coming from the initial switch to your Mikrotik Router.

A diagram would have made this much clearer!!!

q1. Why is ether2 on the switch tagged for vlan500? Does the modem provide a public IP on that vlan??
q2. Just to be sure, the ISP gives you a public IP? ( their device is not a modem/router creating a subnet and thus a private IP on ether2)
q3. What is brand of switch?

Solution.
Ether1 on router is a trunk port carrying vlans 10 and 500 and 99.
VLAN99 should be the managment vlan and where the switch gets its IP address.
VLAN 10 as stated will be access ports on all other ports of switch besides ether1 - trunk to router ( carrying 10,99,500), and ether2 from ISP modem.

MT
ether1 is a trunk port carrying all three vlans
ether2-X either access ports or trunk ports as required down the line to other devices.
vlan500 is terminated at IP DHCP CLient

Bridge carries ports 1-X
add bridge=bridge ingress filtering=yes frame-types=admit-only-vlan-tagged interface=ether1
add bridge=bridge ingress-filtering=yes frame-types=admit-priority-and-untagged interface=ether2 vlan-id=10
etc…

add bridge=bridge tagged=bridge,ether1 vlan-id=99
add bridge=bridge tagged=bridge,ether1 untagged=ether2 vlan-id=10
add bridge=bridge tagged=ether1 vlan-id=500