(Optional) Configuring the Abnormal Packet Detection Function
Context
Devices from different vendors may use different DHCP implementation mechanisms. After detecting that the UDP header checksum or magic cookie field in a received DHCP packet fails the check, a device may not allow the DHCP packet to pass through and discards the packet. As a result, DHCP becomes unavailable. In this case, you can configure the device not to check the UDP header checksum or magic cookie field in received DHCP packets, so that DHCP packets with an incorrect UDP header checksum or incorrect value of the magic cookie field can still be properly forwarded.
According to the protocol, if the UDP header checksum is 0, the peer device does not verify the checksum in DHCP packets. If the peer device does not comply with the protocol, the peer device still verifies the checksum even if the UDP header checksum in DHCP packets sent by the local device is 0. In this case, you need to configure the local device to add the UDP header checksum to DHCP packets to be sent, so that the locally sourced DHCP packets can pass the checksum verification of the peer device.
- A device, functioning as a DHCP server, DHCP relay agent, DHCP client, or DHCP snooping-enabled device, can be configured not to check the UDP header checksum or magic cookie field in received DHCP packets.
- Only a device functioning as a DHCP server can be configured to add the UDP header checksum to DHCP packets to be sent.
- After DHCP is enabled on a device, the device checks the IP header checksum and UDP header checksum in received DHCP packets by default. In addition, the function of checking the IP header checksum cannot be disabled.