Access point pull dhcp address while on a trunk port

Danny Mainprize · ‎08-18-2016

I have a 3560X switch with a Cisco Meraki 42 access point plugged into it. I need the access point to do vlan tagging so ssid1 =vlan 72 and ssid2 = vlan 73. The port setup is switchmode mode access, switchport access vlan 201, so it will pull DHCP from the 201 management vlan pool.

When I switch it to a trunk port it can no longer pull a DHCP address because it doesn't know which vlan pool to pull from. Am I just missing a step somewhere to help this thing pull from a specific pool while being on a trunk?

Luke Oxley · ‎08-18-2016

Hey dmainprize,

Thanks for the post. There are three ways you can achieve this, I'll divulge...

Method 1:

Set the management VLAN as the native VLAN on that trunk, this way the untagged traffic from the access point (including the initial DHCP discover broadcast) will drop into that VLAN and get an address respectively. Then once it is up and functioning, it'll still be able to drop traffic from the SSIDs into their respective VLAN over the 802.1q connection.

Method 2:

If for any reason you cannot set the management VLAN as the native VLAN on the trunk, you can add an IP helper in on the VLAN that is the native. This has the ability to pipe all DHCP discovers over to a different subnet in order to request an address. I wouldn't recommend this, as without knowing your environment it could affect other factors.

Method 3: (Preferred)

Under the access point configuration in the Meraki Dashboard, the "LAN IP" configuration for the access point can be set to static or DHCP. In DHCP mode, you can specify a VLAN to request the address from, this will tag the packet as opposed to leaving it untagged so when the tagged packet hits the trunk it'll be dropped in to the correct VLAN to get an address from. I've attached a screen dump of this below. To get the same view as me, you may need to click "switch to new view" on the Dashboard as Meraki are going through some GUI changes at the moment.