(Optional) Configuring Strategies for Processing Option 82 Information on a DHCP Relay Agent

Context

To enable a DHCP relay agent to accept, process, and forward DHCP messages that carry Option 82 information, you must configure the DHCP relay agent to trust and process this option.

You are advised to perform the configuration on a user-side device. If the DHCP relay agent connects to a DHCP snooping-enabled device, configure the strategies for processing Option 82 information on the DHCP snooping device. When a device functions as the DHCP snooping device, for details on how to perform the configuration, see Inserting the Option 82 Field in a DHCP Message in "DHCP Snooping Configuration" in the S2720, S5700, and S6700 V200R019C10 Configuration Guide - Security.

If the device functions as the first-hop DHCP relay agent, it can process Option 82 information. If the device functions as the second-hop or subsequent DHCP relay agent, it cannot process Option 82 information.

Procedure

Enter the system view.
```
system-view
```
Enable the DHCP relay agent to trust Option 82.
```
dhcp relay trust option82
```
By default, a DHCP relay agent does not trust Option 82.

When this function is enabled, the DHCP relay agent can receive and forward DHCP messages that carry Option 82. If the DHCP relay agent is disabled from trusting Option 82 using the undo dhcp relay trust option82 command, the device discards the DHCP messages carrying Option 82.
Configure strategies for processing Option 82 information on the DHCP relay agent.
- Configure the DHCP relay agent to insert the Option 82 field to DHCP messages in a VLAN view. This configuration takes effect on all DHCP messages from this VLAN received on the interfaces of the DHCP relay agent.
  1. Enter the VLAN view.
```
vlan vlan-id
```
  2. Enable the DHCP relay agent to insert the Option 82 field to received DHCP messages.
```
dhcp option82 { insert | rebuild } enable interface interface-type interface-number1 [ to interface-number2 ]
```
    By default, a DHCP relay agent is disabled from inserting the Option 82 field to received DHCP messages.
  3. Return to the system view.
```
quit
```
- Configure the DHCP relay agent to insert the Option 82 field to DHCP messages in an interface view. This configuration takes effect on DHCP messages received on the specified interface.
  
  Use the following methods to configure strategies for processing Option 82 information. If both methods are used, method 2 takes effect.
  - Method 1:
    1. Enter the interface view.
```
interface interface-type interface-number
```
    2. Enable the DHCP relay agent to insert the Option 82 field to received DHCP messages.
```
dhcp option82 { insert | rebuild } enable
```
      By default, a DHCP relay agent is disabled from inserting the Option 82 field to received DHCP messages.
      
      DHCP messages received on the DHCP relay agent may carry the Option 82 field. Select a strategy based on network requirements.
      
      When insert is configured: If a DHCP message does not carry the Option 82 field, the DHCP relay agent inserts the Option 82 field. If a DHCP message carries the Option 82 field, the DHCP relay agent checks the Option 82 field. If the field contains remote-id, the Option 82 field remains unchanged. Otherwise, the DHCP relay agent inserts remote-id.
      
      When rebuild is configured: If a DHCP message does not carry the Option 82 field, the DHCP relay agent inserts the Option 82 field. If a DHCP message carries the Option 82 field, the DHCP relay agent deletes the original Option 82 field and inserts the locally configured Option 82 field.
    3. Return to the system view.
```
quit
```
  - Method 2:
    1. Enter the interface view or sub-interface view.
```
interface interface-type interface-number [.subinterface-number ]
```
      Only the S5720-EI, S5720-HI, S5730-HI, S5731-H, S5731S-H, S5731-S, S5731S-S, S6720-HI, S5732-H, S6730-H, S6730S-H, S6730-S, S6730S-S, S6720-EI, and S6720S-EI support sub-interfaces.
    2. Enable the DHCP relay agent to support Option 82.
```
dhcp relay information enable
```
      By default, a DHCP relay agent does not support Option 82.
    3. Configure a strategy for processing Option 82 information on the DHCP relay agent.
```
dhcp relay information strategy { drop | keep | replace }
```
      The default strategy is replace.
      
      DHCP messages received on the DHCP relay agent may carry the Option 82 field. Select a strategy based on network requirements.
      
      When replace is configured: If a DHCP message does not carry the Option 82 field, the DHCP relay agent inserts the Option 82 field. If a DHCP message carries the Option 82 field, the DHCP relay agent deletes the original Option 82 field and inserts the locally configured Option 82 field.
      
      When drop is configured: If a DHCP message does not carry the Option 82 field, the DHCP relay agent forwards the message directly without processing it. If a DHCP message carries the Option 82 field, the DHCP relay agent discards the Option 82 field and forwards the message.
      
      When keep is configured: If a DHCP message does not carry the Option 82 field, the DHCP relay agent forwards the message directly without processing it. If a DHCP message carries the Option 82 field, the DHCP relay agent retains the Option 82 field and forwards the message.
    4. Return to the system view.
```
quit
```
(Optional) Set the format of the Option 82 field.
Configure the format of the Option 82 field in the system or interface view. If the configuration is performed in the system view, it takes effect on all interfaces of the device. If the configuration is performed in an interface view, it takes effect only on the specified interface.

If the strategy for processing Option 82 information is drop or keep on the DHCP relay agent, skip this step.
- All Option82 fields configured in the system view or in the same interface view share a length of 1-255 bytes. If their total length exceeds 255 bytes, some Option82 information will be lost.
- There is no limit on the number of Option 82 fields configured on the device. However, a large number of Option 82 fields will occupy a lot of memory and prolong the device processing time. To ensure device performance, you are advised to configure Option 82 fields based on the service requirements and device memory size.
- In the system view:
  
  Configure the format of the Option 82 field.
```
dhcp option82 [ vlan vlan-id ] [ ce-vlan ce-vlan-id ] [ circuit-id | remote-id ] format { default | common | extend | user-defined text }
```
  By default, the Option 82 field is in the default format.
- In the interface view:
  1. Enter the interface view.
```
interface interface-type interface-number
```
  2. Configure the format of the Option 82 field.
```
dhcp option82 [ vlan vlan-id ] [ ce-vlan ce-vlan-id ] [ circuit-id | remote-id ] format { default | common | extend | user-defined text }
```
    By default, the Option 82 field is in the default format.
  3. Return to the system view.
```
quit
```