DHCP Options 569■ Option 66: TFTP server name option. It specifies a TFTP server to be assigned tothe client.■ Option 67: Bootfile name option. It specifies the bootfile name to be assignedto the client.■ Option 150: TFTP server IP address option. It specifies the TFTP server IP addressto be assigned to the client.For more information about DHCP options, refer to RFC 2132.Self-Defined Options Some options, such as Option 43, have no unified definitions in RFC 2132. Theformats of some self-defined options are introduced as follows.Vendor-specific option (Option 43)DHCP servers and clients exchange vendor-specific information through messagescontaining the vendor-specific option (Option 43). Upon receiving a DHCPmessage requesting Option 43 (in Option 55), the DHCP server returns a responsemessage containing Option 43 to assign vendor-specific information to the DHCPclient.The DHCP client can obtain the preboot executive environment (PXE) serveraddress through Option 43, to further obtain the bootfile or other controlinformation from the PXE server.Figure 165 shows the format of Option 43.Figure 165 Format of Option 43For scalability sake, the PXE server address is configured as a sub-option of Option43 so that the DHCP client can obtain more information through Option 43. Thevalue of the sub-option type is 0x80.Figure 166 shows the format of the PXE server address list. Currently, the value ofthe PXE server type can only be 0.Figure 166 Format of PXE server address listPXE server list (variable)Sub-option type (0x80)23 31Option type (0x2B) Option length Sub-option length...0 7 15Server IP addresses (variable)PXE server type (0x0000)Server number0 157
