Reasons why the Option 82 field in packets sent by other devices is replaced after the function of forcibly appending the Option 82 field is configured on S9700

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S series switches support the Option 82 insertion function. The switch adds the configured Option 82 to received DHCP packets that do not contain the Option 82 field. If the packets received from other devices contain Option 82 fields, the switch deletes their original Option 82 fields and adds the configured Option 82 field to the packets.

Other related questions:
Inner VLAN ID setting for user packets on S series switch when the DHCP Option 82 field contains only one VLAN ID
If the DHCP Option 82 field defined on an S series switch contains only one VLAN ID and specifies the inner VLAN ID value, the switch sets the inner VLAN ID of user packets to 4096. Different carriers process invalid VLAN IDs in the DHCP Option 82 field in different ways. On a network, if the BRAS connected to the switch has specific requirements for invalid inner VLAN IDs in the DHCP Option 82 field, configure the Option 82 format that does not contain the inner VLAN ID. To configure the Option 82 format, run the dhcp option82 format user-defined text command in the system view or interface view.

Method used to configure the DHCP Option field on the AR
Option fields in a DHCP message carry control information and parameters that are not defined in protocols. There are known options and customized options. For details about known options, see RFC 2132. Customized options are defined by vendors. For example, to set Option 64 to the hexadecimal string 0x11 and configure known Option 121 to assign classless static route to clients (destination IP address 10.10.10.10/24 and gateway address 10.11.11.11), perform the following configurations: - Interface address pool [Huawei] interface gigabitethernet1/0/1 [Huawei-GigabitEthernet1/0/1] dhcp server option 64 hex 11 [Huawei-GigabitEthernet1/0/1] dhcp server option121 ip-address 10.10.10.10 24 10.11.11.11 - Global address pool [Huawei] ip pool global1 [Huawei-ip-pool-global1] option 64 hex 11 [Huawei-ip-pool-global1] option121 ip-address 10.10.10.10 24 10.11.11.11 - DHCP option template (applicable to only the scenario where user-defined network parameters are allocated to static clients) [Huawei] dhcp option template template1 [Huawei-dhcp-option-template-template1] option 64 hex 11 [Huawei-dhcp-option-template-template1] option121 ip-address 10.10.10.10 24 10.11.11.11

Configuring the DHCP Option 43 field on an AC
Perform the following operations to configure the DHCP Option 43 field on an AC that functions as a DHCP server: 1. Run the system-view command to enter the system view. 2. Run the dhcp enable command to enable the DHCP function. 3. Run the ip pool ip-pool-name command to enter the global address pool view. 4. Run the option 43 sub-option 2 ip-address ip-address &<1-8> command to set the DHCP Option 43 field to the IP addresses of the active and standby ACs.

In which situation can an S series switch send the option field in Request messages to a client
For S series switches excluding the S1700, the DHCP server returns the corresponding option field to a client only when the corresponding option field is encapsulated in the Request message.

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