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SG300 and DHCP Issues

We are having issues with DHCP and our SG300-52 and SG300-28P. Our set-up is as follows:

Firewall --> SG300-52 (Direct connect to firewall) -->SG300-28P (Direct connect to SG300-52)

The firewall and SG300-52 are both physically located in the same room while the SG300-28P is in a different location. The firewall connects directlyu to the SG300-52 with 3 VLANs. The SG300-28P is connected to the SG300-52 from two separate ethernet wires with its own respective VLAN.

Each box on its own works without issue when directly hooked up to the firewall as DHCP addresses are assigned.

However, DHCP does not work on the SG300-28P when it is hooked up to the SG300-52. Devices hooked up to the SG300-28P in this instance *are not* able to get an IP address for ONE of the VLANs. The second VLAN on the SG200-28P is able to retrieve the DHCP addresses. It appears as though the firewall is not receiving the DHCP request for the VLAN in question. Keep in mind that when the SG300-28P is hooked up directly to the firewall the same VLAN works properly.

Having checked the wiring, firewall and devices through a process of elimination, it would appear that the two SG300 boxes are somehow blocking DHCP requests from being sent to the firewall when they are hooked up together. Both boxes have Layer 3 turned on and both boxes have the latest firmware.

I would appreciate any insights on how I can have the VLAN in question be able to properly function with DHCP.

Thank you.


Jeff Van Houten

You said both switches have l3 turned on. Are they routing to each other or configured as trunks? If routing you're going to need an ip helper address somewhere. Hard to say exactly without a map or some configs.

Sent from Cisco Technical Support iPad App


Think Jeff pretty much hit it on the head wherever those vlans are being routed from you will need helper addresses pointing to the firewall if thats whats handing out the ip addresses .  Otherwise the dhcp broadcast stops at your l3 boundary where it is routed.