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help 4 DHCP Cable modem on Vlan SF 300-8

I have Multiwan router with 1 port WAN and 4 DHCP Cable modem connected to SF 300-8. I want to connect 4 modem via VLAN through switch. I define Vlan2,3,4,5 on router also in Switch. port 1 on the router as trunk and the other port 2,3,4,5 as Vlan2,3,4,5 with VLAN mode Access. I tag port 1 on every VLAN also Untagged for each port. I having problem when I check the status from multiwan router. all IP address is the same (duplicate). what I want is each VLAN has own DHCP Address. Is that any miss configuration ?

Your help is really appreciate.

Thank you

interface setting.JPGport to vlan.JPG

Alejandro Gallego
Cisco Employee

This is a pretty crazy configuration you are trying to do. When you say they all get the same address are you saying they all receive an address on the same network or the exact same ip address?

Aside from above, you need to have separate DHCP scopes for each VLAN, and the router needs to be able to either maintain multiple DHCP scopes or needs to be able to DHCP relay the dhcp discovery frames. From what you wrote, it does not sound like you have all the required components.

Dear Alejandro,

Thank you for your response. please see below configuration :

as you can see above configuration VLAN port 3,4,5 should have own DHCP, but the reality I got DHCP1  on each Qbalancer VLAN port 3,4,5. I think DHCP broadcast on all port that shouldn't happen. I can't figure out why this happen.

can you tell me what components should I provide?

Thank you

I do not have first hand experience with the Q Balancer but it should not be behind the switch as shown in your diagram. The Q-Balancer is a router and technically so are the modems, so by placing the switch in between you are defeating the purpose of the balancer. I may be completely wrong...

The other thing is that you are trying to IP the modems but you are not routing anything. This will be a very long response and what I will try to do is create a Visio showing how it should be laid out. The basics is that the connection between the Qbalancer and the switch should be Point-to-point with a route statement for all your subnets. The switch should be a L3 switch with DHCP relay enabled and pointing to your DHCP server (Qbalancer?). But the thing is that now we create a problem, how is the traffic coming in from the cloud. I mean is the destination a single subnet behind the QBal. or what?

I just do not understand why you would have the switch between the Modems and the Qbal.? Where is your LAN? Are you provisioning the modems like an ISP? Are you providing a service or is the internet service being provided to you?

The basic idea I'm doing this, because of limited WAN port on Qbalancer. So I need to create virtual lan to make  connection bonding.  All 4 modem has own Public DHCP from the ISP. The Qbalancer should get different ip address on each port..

If you create a single connection to Qbal. even though it would be a trunk there is no way to balance your traffic. The Qbal. is a router not a switch, so it may be able to understan multiple LAN subnets but I do not believe it will understand trunking from the WAN. As this would mean something completely different. Also, the Qbal. will not be able to send DHCP out its WAN ports which is probably why you stated earlier that all modems had the same IP. By default most cable modems have an IP of which I would guess is what you were seein.

In short, this configuration will not work for what you are trying to accomplish. I may be wrong so give a call to Qbal. and see if they have any suggestions.

Thanks, I did check to Qbalancer vendor, they succeed config qbalancer with zyxel ES 3024 through VLAN, but they never try on Cisco. I though it will be similar configuration, but is not.

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