Self-Defined Options - 3Com MSR 50 Series Configuration Manual

Self-Defined Options

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