Controller Based WLANs

What is the use of option-82 and how to configure it

by on ‎04-05-2015 09:38 PM

Introduction- The DHCP Information option (Option 82) is commonly used in metro or large enterprise deployments to provide additional information on “physical attachment” of the client. Option 82 is supposed to be used in distributed DHCP server/relay environment, where relays insert additional information to identify the client’s point of attachment.

Feature Notes- DHCP relay is supposed to insert the “giaddr” field in the relayed DHCP packets, so that DHCP server may identify the pool to be used for the request. The choice of the pool is made based on the “giaddr” field or the incoming interface, if the “giaddr” is missing or zero . Option 82 serves as refinement to the request, allowing the DHCP server to select a “sub-range” in the pool.

Environment- 

The controller, when acting as a DHCP relay agent, inserts information about the AP and SSID through which a client is connecting into the DHCP request.

The MAC address is the hardware address and ESSID is an alphanumeric name that uniquely identifies a wireless network. For configuring Option-82, select the VLAN interface mapped for the VAP profile and do the following configurations.

Network Topology- DHCP Server  -->Gateway--> Controller (DHCP Relay Agent)  --> AP --> Client

Configuration Steps- 

  • Navigate to Configuration > Network > IP >IP Interfaces.
  • Click Edit next to the VLAN ID for which you want to configure Option 82.
  • Under DHCP Helper Address select Mac or Mac Essid from the Option-82 drop-down menu.
  • Click Apply

This example enables Option 82 for VLAN 5 using ESSID. You can include only the MAC address or MAC address and ESSID.

(host) (config) #interface vlan 5
(host) (config-subif)#option-82
(host) (config-subif)#option-82 mac essid
(host) (config-subif)#

Troubleshooting- Enable Debugging for network

logging level debugging network subcat dhcp 

 

Comments
shujun.chen@ericsson

Hi,

We configured AC 7030 following your guide, but option-82 is not included in DHCP. DHCP discovery message path is : client -->AP-->AC-->EoGRE-> Gateway (DHCP server). If we configured dhcp helper address and vlan IP address, we can see option 82 is in DHCP discovery message, but this is not in EoGRE, it goes to Gateway from L3. It looks that DHCP discovery with option 82 can not be encapsulated in EoGRE, is it true? 

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