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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  TCP/IP Network Configuration and Management Protocols (BOOTP, DHCP, SNMP and RMON)
           9  Host Configuration and TCP/IP Host Configuration Protocols (BOOTP and DHCP)
                9  TCP/IP Dynamic Host Configuration Protocol (DHCP)
                     9  DHCP Messaging, Message Types and Formats

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DHCP Options, Option Format and "Option Overloading"
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DHCP Client/Server Implementation, Features and Issues
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Summary Of DHCP Options / BOOTP Vendor Information Fields
(Page 2 of 6)

RFC 1497 Vendor Extensions

Table 192 shows the DHCP/BOOTP options that were originally defined in RFC 1497.


Table 192: DHCP/BOOTP Options: RFC 1497 Vendor Extensions

Code Value

Data Length (bytes)

Name and Description

0

0

Pad: A single byte used as “filler” to align a subsequent field on a word (two-byte) boundary. Contains no information.

One of two options that is a single byte in length, having no Data subfield (the other being the End option below.)

1

4

Subnet Mask: A 32-bit subnet mask being supplied for the client to use on the current network. Must appear in the option list before the Router option if both are present.

2

4

Time Offset: Specifies the time offset of the client's subnet in seconds from Coordinated Universal Time (UTC, formerly Greenwich Mean Time or GMT). Positive values represent areas east of the prime meridian (in the United Kingdom), negative values areas west. Essentially, this is used to indicate the time zone of the subnet.

3

Variable (Multiple of 4)

Router: Specifies a list of 32-bit router addresses for the client to use on the local network. Routers are listed in the order of preference for the client to use.

4

Variable (Multiple of 4)

Time Server: Specifies a list of time server addresses (per RFC 868) for the client to use on the local network. Servers are listed in the order of preference for the client to use.

5

Variable (Multiple of 4)

IEN-116 Name Server: Specifies a list of IEN-116 name server addresses for the client to use on the local network. Servers are listed in the order of preference for the client to use.

Note that this option is not used for DNS name servers; see below.

6

Variable (Multiple of 4)

DNS Name Server: Specifies a list of DNS name server addresses for the client to use on the local network. Servers are listed in the order of preference for the client to use.

7

Variable (Multiple of 4)

Log Server: Specifies a list of MIT-LCS UDP log server addresses for the client to use on the local network. Servers are listed in the order of preference for the client to use.

8

Variable (Multiple of 4)

Cookie Server: Specifies a list of RFC 865 “cookie” server addresses for the client to use on the local network. Servers are listed in the order of preference for the client to use.

9

Variable (Multiple of 4)

LPR Server: Specifies a list of RFC 1179 line printer server addresses for the client to use on the local network. Servers are listed in the order of preference for the client to use.

10

Variable (Multiple of 4)

Impress Server: Specifies a list of Imagen Impress server addresses for the client to use on the local network. Servers are listed in the order of preference for the client to use.

11

Variable (Multiple of 4)

Resource Location Server: Specifies a list of RFC 887 resource location server addresses for the client to use on the local network. Servers are listed in the order of preference for the client to use.

12

Variable

Host Name: Specifies a host name for the client. This may or may not be a DNS host name; see option #15 below.

13

2

Boot File Size: Specifies the size of the default boot image file for the client, expressed in units of 512 bytes.

14

Variable

Merit Dump File: Specifies the path and filename of the file to which the client should dump its core image in the event that it crashes.

15

Variable

Domain Name: Specifies the DNS domain name for the client. Compare to option #12.

16

4

Swap Server: Specifies the address of the client's swap server.

17

Variable

Root Path: Specifies the path name of the client's root disk. This allows the client to access files it may need, using a protocol such as NFS.

18

Variable

Extensions Path: Specifies the name of a file that contains vendor-specific fields that the client can interpret in the same way as the Options or Vend field in a DHCP/BOOTP message. This was defined to allow a client and server to still exchange vendor-specific information even though the Option/Vend field is now used for the general-purpose fields described in this topic.

Also see option #43 below.

255

0

End: Placed after all other options to mark the end of the option list.

One of two options that is a single byte in length, having no Data subfield (the other being the Pad option above.)


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DHCP Client/Server Implementation, Features and Issues
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