A.3 DHCP Option Descriptions

The following table describes the DHCP option codes and names:

Table A-1 DHCP Option Codes and Names

Code

Option Name

2

Time Offset

3

Router

4

Time Server

5

Name Server

6

Domain Name Server

7

Log Server

8

Cookie Server

9

LPR Server

10

Impress Server

11

Resource Location Server

13

Boot File Size

14

Merit Dump File

16

Swap Server

17

Root Path

18

Extension Paths

19

IP Forwarding Enable/Disable

20

Non-Local Source Routing

21

Policy Filter

22

Maximum Datagram Re-assembly size

23

Default IP Time-to-live

24

Path MTU Aging Time-out

25

Path MTU Plateau Table

26

Interface MTU

27

All subnets are local

28

Broadcast Address

29

Perform Mask Discovery

30

Mask Supplier

31

Perform Router Discovery

32

Router Solicitation Address

33

Static Route

34

Trailer Encapsulation

35

ARP Cache Time-out

36

Ethernet Encapsulation

37

TCP Default TTL

38

TCP Keep-alive interval

39

TCP Keep-alive garbage

40

NIS Domain

41

NIS Servers

42

Network Time Protocol Servers

43

Vendor Specific Option

44

NetBIOS over TCP/IP options-name server

45

NetBIOS over TCP/IP options-datagram distribution server

46

NetBIOS over TCP/IP options-node type

47

NetBIOS over TCP/IP options-Scope

48

X Window System Font Server

49

X Window System Display Manager

58

Renewal (T1) Time

59

Renewal (T2) Time

60

Vendor Class Identifier

62

NWIP Domain Name

63-05

Perform NSQ Broadcast

63-06

Preferred DSS

63-07

Nearest NWIP Server(s)

63-08

Number of Auto Retries

63-09

Auto Retry Interval

63-10

Support NWIP 1.1

63-11

Primary DDS

63-12

IPX Network Number

63-13

IPX Stale Time

63-14

Migration Agents

64

NIS+ Domain

65

NIS Servers

66

TFTP Server Name

67

Boot File Name

68

Mobile IP Home Agent

69

SMTP Server

70

POP3 Server

71

NNTP Server

72

WWW Server

73

Default Finger Server

74

Default IRC Server

75

Street Talk Server

76

Street Talk Directory Assistance server

78

SLP Directory Agent

79

SLP Service Scope

85

NDS Servers

86

NDS Tree Name

87

NDS Context

The DHCP Options are described as follows:

Time Offset: Specifies the offset time of client's subnet in seconds. This is expressed as a two's complement 32-bit integer preference value. Two types of offset can be set: positive and negative. A positive offset indicates a location to the east of the zero meridian and a negative offset indicates a location to the west of the zero meridian.

Router: Specifies the routers on the client's subnet as a list of IP addresses. The routers should be listed in the order of preference.

Time Server: Specifies a list of RFC time servers available to the client. The servers should be listed in the order of preference.

Name Server: Specifies a list of IEN 116 [7] name servers available to the client. The name servers should be listed in the order of preference.

Domain Name Server: Specifies a list of DNS name servers available to the client. The DNS servers should be listed in the order of preference.

Log Server: Specifies a list of MIT-LCS UDP log servers available to the client. The log servers should be listed in the order of preference.

Cookie Server: Specifies a list of RFC 865 cookie servers available to the client. The cookie servers should be listed in the order of preference.

LPR Server: Specifies a list of RFC 1179 line printer servers available to the client. The LPR servers should be listed in the order of preference.

Impress Server Option: Specifies a list of Imagen Impress servers available to the client. The impress servers should be listed in the order of preference.

Resource Location Server: Specifies a list of RFC 887 resource location servers available to the client. The resource location servers should be listed in the order of preference.

Boot File Size: Specifies the length in 512-octet blocks of the boot image for the client. The length is specified as an unsigned 16-bit integer.

Merit Dump File: Specifies the location of a file where the core image of the client should be dumped if the client crashes.

Swap Server: Specifies the IP address of the swap server for the client.

Root Path: Specifies the path name for the client's root disk.

IP Forwarding Enable/Disable: Specifies whether the client should forward an IP address. Values can be either True or False. True indicates that IP forwarding should be enabled and False indicates that IP forwarding should be disabled.

Nonlocal Source Routing Enable/Disable: Specifies whether the client should forward datagrams with non-local source routing. Values can be either True or False. True indicates to enable datagram forwarding and False indicates to disable datagram forwarding.

Policy Filter: Specifies the policy filters for non-local source routing. The policy filters consist of a list of IP addresses and masks that filter the incoming source routes.

Maximum Datagram Reassembly Size: Specifies the maximum size of the datagram that the client should reassemble.

Default IP TTL: Specifies the time-to-live used by the client on outgoing datagrams.

Path MTU Aging Time-out: Specifies the time-out (in seconds) used when the aging path MTU values are discovered by the mechanism defined in RFC 1191.

Path MTU Plateau Table Option: Specifies a table of MTU sizes used when performing path MTU discovery as defined in RFC 1191.

Interface MTU: Specifies the MTU used on this interface. The minimum value for MTU is 68.

All subnets are local: Specifies whether the client can assume that all subnets of IP network connected to the client use the same MTU as the subnet of the network to which the client is directly connected. Values can be either True or False. True indicates that all subnets share the same MTU. False indicates that some subnets of the network that is directly connected have smaller MTU values.

Broadcast Address: Specifies the broadcast address being used on the client's subnet.

Perform Mask Discovery: Specifies whether the client should perform subnet mask discovery by using ICMP. Values can be either True or False. True indicates that the client should perform subnet mask discovery. False indicates that the client should not perform subnet mask discovery.

Mask Supplier: Specifies whether the client should respond to subnet mask requests by using ICMP. Values can be either True or False. True indicates that the client should respond and False indicates that the client should not respond.

Perform Router Discovery: Specifies whether the client should solicit routers by using the Router Discovery mechanism as defined in RFC 1256. Values can be either True or False. True indicates that the client should perform router discovery and False indicates that the client should not perform router discovery.

Router Solicitation Address: Specifies the IP address to which the client can send router solicitation requests.

Static Route: Specifies a list of static routes that the client can install in its routing cache. Multiple routes to the same destination are listed in descending order. Static routes consists of a list of IP address in pairs. The first address in the pair is the destination address and the second is the router for the destination.

Trailer Encapsulation: Specifies whether the client can negotiate encapsulating trailers when using the ARP protocol. Values can be either True or False. True indicates that the client should use trailers and False indicates that the client should not use trailers.

ARP Cache Time-out: Specifies the time-out (in seconds) for ARP cache entries.

Ethernet Encapsulation: Specifies whether the client can use Ethernet version 2.0 (RFC 894) or IEE 802.3 (RFC 1042) encapsulation if it is an Ethernet interface. Values can be either True or False. True indicates that the client should use RFC 1042 encapsulation and False indicates that the client should use RFC 894 encapsulation.

TCP Default TTL: Specifies the default TTL that the client should use when sending TCP™ segments.

TCP Keep-alive interval: Specifies the interval (in seconds) that the TCP client should wait before sending a keep-alive message on a TCP connection.

TCP Keep-alive Garbage: Specifies whether the client should send TCP keep-alive messages with a garbage octet for compatibility with older implementations. Values can be either True or False. True indicates that a garbage octet should be sent and False indicates that a garbage octet should not be sent.

NIS Domain: Specifies the NIS domain name of the client.

NIS Servers: Specifies a list of the NIS server's IP addresses available to the client. The NIS servers should be listed in the order of preference.

Network Time Protocol Servers: Specifies a list of IP addresses indicating Network Time Protocol Servers (NTP servers) available to the client. The NTP servers should be listed in the order of preference.

Vendor-Specific Information: Specifies the vendor-specific information that can be used by the clients and servers.

NetBIOS over TCP/IP Name Server: Specifies a list of RFC 1001 and RFC 1002 NetBIOS over TCP/IP Name Servers listed in order of preference.

NetBIOS over Datagram Distribution Server: Specifies a list of RFC 1001 and RFC 1002 NetBIOS over Datagram Distribution servers listed in order of preference.

NetBIOS over TCP/IP Node Type: Allows NetBIOS over TCP/IP clients that can be configured as described in RFC 1001 and RFC 1002. Node types include B-node, P-node, M-node, and H-node.

NetBIOS over TCP/IP Scope: Specifies the NetBIOS over TCP/IP scope parameter for the client as specified in RFC 1001 and RFC 1002.

X Window System Font Server: Specifies a list of X Window System* Font servers available to the client. These servers should be listed in order of preference.

X Window System Display Manager: Specifies a list of IP addresses of systems that use the X Window System Display Manager and are available to the client. The IP addresses should be listed in order of preference.

T1 Time Value: Specifies the time interval from the address assignment until the client reaches the renewing state.

T2 Time Value: Specifies the time interval from the address assignment until the client reaches the rebinding state.

Vendor Class Identifier: Specifies the vendor type and configuration of a DHCP client.

NetWare/IP Domain: Enables the server to convey the NetWare/IP domain name used by the NetWare/IP product.

Preferred NSQ Broadcast: Specifies whether the client should perform a NetWare Nearest Server Query (NSQ) to find out its nearest NetWare/IP server. Values can be either True or False. True indicates that the client should perform a NetWare NSQ and False indicates that the client should not perform a NetWare NSQ.

Preferred DSS: Specifies a list of addresses for a NetWare Domain SAP/RIP Server (DSS).

Nearest NWIP Server(s): Specifies a list of addresses for the Nearest NetWare/IP (NWIP) servers.

Number of Auto Retries: Specifies the number of times a NetWare/IP client can attempt to communicate with a DSS server at startup.

Auto Retry Interval: Specifies the delay interval (in seconds) that each NetWare/IP client uses when attempting to communicate with a DSS server at startup.

Support NWIP 1.1: Specifies whether the NetWare/IP client should support NetWare/IP version 1.1. This is required only when it contacts a NetWare/IP version 1.1 server. Values can either be True or False. True indicates that the client should support NetWare/IP version 1.1 and False indicates that the client should not support NetWare/IP version 1.1.

Primary DDS: Specifies the Primary Domain SAP/RIP Service server (DSS) for the NetWare/IP domain. The NetWare/IP administration utility uses this as the Primary DSS server when configuring a secondary DSS server.

NIS+ Domain: Specifies the name of the client’s NIS+ domain.

NIS+ Servers: Specifies a list of IP addresses indicating Network Information Service (NIS)+ servers available to the client. The NIS+ servers should be listed in order of preference.

TFTP Server Name: Specifies the name of the TFTP server for the client.

Boot File Name: Specifies the name of the boot file for the client.

Mobile IP Home Agent: Specifies a list of IP addresses that indicates the mobile IP home agents available to the client. These agents should be listed in order of preference.

SMTP Server: Specifies a list of Simple Mail Transport Protocol (SMTP) servers available to the client. The SMTP servers should be listed in order of preference.

POP3 Server: Specifies a list of POP3 servers available to the client. The POP3 servers should be listed in order of preference.

NNTP Server: Specifies a list of Network News Transport Protocol (NNTP) servers available to the client. The NNTP servers should be listed in order of preference.

WWW Server: Specifies a list of World Wide Web (WWW) servers available to the client. The WWW servers should be listed in order of preference.

Default Finger Server: Specifies a list of Finger servers available to the client. The Finger servers should be listed in order of preference.

Default IRC Server: Specifies a list of Internet Relay Chat (IRC) servers available to the client. The IRC servers should be listed in order of preference.

StreetTalk Server: Specifies a list of StreetTalk* servers available to the client. The StreetTalk servers should be listed in order of preference.

StreetTalk Directory Assistance Server: Specifies a list of StreetTalk Directory Assistance (STDA) servers available to the client. The STDA servers should be listed in order of preference.

Directory Agent: Specifies a list of IP addresses for Directory Agents. The Directory Agents should be listed in order of preference.

Service Scope: Specifies the scope that an SLP agent is configured to use.

NDS Servers: Specifies one or more NDS® servers for the client to contact to access the NDS database. The NDS servers should be listed in order of preference.

NDS Tree Name: Specifies the name of the NDS tree that the client contacts.

NDS Context: Specifies the initial NDS context that the client should use.

A.3.1 Assigning Options

DHCP and BOOTP options can be assigned at three levels:

  • Globally

  • At the subnet level

  • At the IP address level

The DHCP server’s options inheritance rules specify that options assigned at the lowest level override options set at a higher level. For example, options have been assigned at all three levels for the client on the subnet, as shown in the following table.

Table A-2 DHCP and BOOTP options at three levels

Level

Option

Value

Global

1, Subnet Mask

255.255.0.0

 

3, Router

132.57.3.8

 

4, Time Server

129.23.120.5

Subnet

1, Subnet Mask

255.254.0.0

 

5, Name Server

10.73.57.251

 

7, Log Server

10.73.58.2

 

13, Boot File Size

1024

IP Address

7, Log Server

Null

 

13, Boot File Size

256

The following table lists the effective options for the client with the IP address referred to in the preceding table.

Table A-3 Options for the Client with the IP Addresses

Option

Value

1, Subnet Mask

255.254.0.0

3, Router

132.57.3.8

4, Time Server

129.23.120.5

5, Name Server

10.73.57.251

7, Log Server

Null

13, Boot File Size

256