Cisco CNS Network Registrar User's Guide, 6.1
Appendix - DHCP Options
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DHCP Options

Table Of Contents

DHCP Options

Option Descriptions

BOOTP Extensions/DHCP Option Field Format

RFC 1497 Vendor Extensions

IP Layer Parameters Per Host

IP Layer Parameters Per Interface

Link Layer Parameters Per Interface

TCP Parameters

Application and Service Parameters

DHCP Extensions

Microsoft Client Options

Option Tables

Options by Number

Options by Network Registrar Name

Options by Category

Option Validation Types


DHCP Options


DHCP provides a framework for passing configuration information to hosts on a TCP/IP network. Configuration parameters and other control information are carried in tagged data items that are stored in the options field of the DHCP message. The data items themselves are also called options.

This appendix contains DHCP options and BOOTP vendor extensions from RFC 2132, and includes the validation type for each option, as indicated in Table B-9.

This appendix also contains the standard Microsoft client options and several tables displaying the options sorted by categories.

Option Descriptions

The following sections describe the DHCP options in detail:

"BOOTP Extensions/DHCP Option Field Format"section

RFC 1497 Vendor Extensions

IP Layer Parameters Per Host

Link Layer Parameters Per Interface

TCP Parameters

Application and Service Parameters

DHCP Extensions

Microsoft Client Options

BOOTP Extensions/DHCP Option Field Format

DHCP options have the same format as the BOOTP vendor extensions defined in RFC 1497. Options can be fixed length or variable length. All options begin with a tag octet, which uniquely identifies the option. Fixed-length options without data consist of only a tag octet. Only options 0 and 255 are fixed length. All other options are variable-length with a length octet following the tag octet. The value of the length octet omits the two octets specifying the tag and length. The length octet is followed by that number of octets of data. Options containing NVT ASCII data should not include a trailing NULL; however, the receiver of such options must be prepared to delete trailing nulls if they exist. The receiver must not require that a trailing null be included in the data. In the case of some variable-length options, the length field must be specified.

Any options defined subsequent to this document must contain a length octet even if the length is fixed or zero. All multi-octet quantities are in network byte-order.

Except for the options in section 9, all options can be used with either DHCP or BOOTP. Many of these options have their default values specified in other documents. In particular, RFC 1122 [4] specifies default values for most IP and TCP configuration parameters.

Many options supply one or more 32-bit IP addresses. Use of IP addresses instead of DNS names can make future service migration more difficult. Use of IP addresses instead of DNS CNAMEs is not recommended.

When used with BOOTP, the first four octets of the vendor information field are reserved for a magic cookie (as suggested in RFC 951). This field identifies the mode in which the succeeding data is to be interpreted. The value of the magic cookie is the 4 octet dotted decimal 99.130.83.99 (or hexadecimal number 63.82.53.63) in network byte order.

All of the vendor extensions defined in RFC 1497 are also DHCP options.

Option codes 128 through 254 (decimal) are reserved for site-specific options.

RFC 1497 Vendor Extensions

Table B-1 lists the vendor extensions as defined in RFC 1497.

Table B-1 RFC 1497 Vendor Extension Options 

Option Name
No.
Length
Description

Pad

0

1 octet

Causes the subsequent fields to align on word boundaries.

End

255

1 octet

End of valid information in the vendor field. Subsequent octets should be filled with the Pad options.

Subnet Mask

1

4 octets

Client's subnet mask, as per RFC 950. If both the Subnet Mask and the Router option are specified in a DHCP reply, the Subnet Mask option must be first.

Time Offset

2

4 octets

Offset of the client's subnet, in seconds, from Universal Time (UT). The offset is expressed as a twos-complement 32-bit integer. A positive offset indicates a location east of the zero meridian and a negative offset indicates a location west of the zero meridian.

Router

3

4 octet minimum; multiples of 4

List of IP addresses for routers on the client's subnet. Routers should be in order of preference.

Time Server

4

4 octet minimum; multiples of 4

List of RFC 868 compliant time servers available to the client. Servers should be in order of preference.

Name Server Option

5

4 octet minimum; multiples of 4

List of IEN 116 name servers available to the client. Servers should be in order of preference.

Domain Name Server

6

4 octet minimum; multiples of 4

List of Domain Name System (STD 13, RFC 1035) name servers available to the client. Servers should be in order of preference.

Log Server

7

4 octet minimum; multiples of 4

List of MIT-LCS UDP log servers available to the client. Servers should be in order of preference.

Cookie Server

8

4 octet minimum; multiples of 4

List of RFC 865-compliant cookie servers available to the client. Servers should be in order of preference.

LPR Server

9

4 octet minimum; multiples of 4

List of RFC 1179-compliant line printer servers available to the client. Servers should be in order of preference.

Impress Server

10

4 octet minimum; multiples of 4

List of Imagen Impress servers available to the client. Servers should be in order of preference.

Resource Location Server

11

4 octet minimum; multiples of 4

List of RFC 887-compliant resource location servers available to the client. Servers should be in order of preference.

Host Name

12

1 octet minimum

Name of the client. The name may or may not be qualified with the local domain name. See RFC 1035 for the character set restrictions.

Boot File Size

13

2 octets

Number of 512-octet blocks in the default boot file.

Merit Dump File

14

1 octet minimum

Path name of a file to which the client's core image should be placed in the event the client crashes. The path is formatted as a character string consisting of characters from the NVT ASCII character set.

Domain Name

15

1 octet minimum

Domain name that the client should use when resolving host names through the Domain Name System.

Swap Server

16

4 octets

IP address of the client's swap server.

Root Path

17

1 octet minimum

Path name that contains the client's root disk. The path is formatted as a character string consisting of characters from the NVT ASCII character set.

Extensions Path

18

1 octet minimum

Uses a string to specify a file, retrievable through TFTP. The file contains information that can be interpreted in the same way as the 64-octet vendor-extension field within the BOOTP response, with these exceptions: the length of the file is unconstrained, and all references to instances of this option in the file are ignored.


IP Layer Parameters Per Host

Table B-2 lists the options that affect the operation of the IP layer on a per-host basis.

Table B-2 IP Layer Parameters Per Host Options 

Option Name
No.
Length
Description

IP Forwarding Enable/Disable

19

1 octet

Specifies whether the client should configure its IP layer for packet forwarding. Values: 0=disable; 1=enable

Non-Local Source Routing Enable/Disable

20

1 octet

Specifies whether the client should configure its IP layer to allow forwarding of datagrams with non-local source routes. Values: 0=disable; 1=enable

Policy Filter

21

8 octet minimum; multiples of 8

Policy filters for non-local source routing. The filters consist of a list of IP addresses and masks that specify destination/mask pairs with which to filter incoming source routes. Any source-routed datagram whose next-hop address does not match one of the filters should be discarded by the client.

Maximum Datagram Reassembly Size

22

2 octets

Maximum size datagram that the client should be prepared to reassemble. Value: 576 minimum

Default IP Time-to-Live

23

1 octet

Default TTL that the client should use on outgoing datagrams. Values: 1 to 255

Path MTU Aging Timeout

24

4 octets

Timeout (in seconds) to use when aging Path MTU values (defined in RFC 1191).

Path MTU Plateau Table

25

2 octets minimum; multiples of 2

Table of MTU sizes to use when performing Path MTU Discovery as defined in RFC 1191. The table is formatted as a list of 16-bit unsigned integers, ordered from smallest to largest. Value: 68 minimum


IP Layer Parameters Per Interface

Table B-3 lists the options that affect the operation of the IP layer on a per-interface basis. A client can issue multiple requests, one per interface, to configure interfaces with their specific parameters.

Table B-3 IP Layer Parameters Per Interface Options 

Option Name
No.
Length
Description

Interface MTU

26

2 octets

Maximum time to live to use on this interface.

All Subnets Are Local

27

1 octet

Specifies whether or not the client can assume that all subnets of the IP network to which the client is connected use the same MTU as the subnet of that network to which the client is directly connected.
Values: 1=all subnets share same MTU; 0=some directly-connected subnets can have smaller MTUs

Broadcast Address

28

4 octets

Broadcast address in use on the client's subnet.

Perform Mask Discovery

29

1 octet

Specifies whether or not the client should perform subnet mask discovery using ICMP. Values: 0=disable; 1=enable

Mask Supplier

30

1 octet

Specifies whether or not the client should respond to subnet mask requests using ICMP.
Values: 0=do not respond; 1=respond

Perform Router Discovery

31

1 octet

Specifies whether or not the client should solicit routers using the Router Discovery mechanism defined in RFC 1256. Values: 0=disable; 1=enable

Router Solicitation Address

32

4 octets

Address to which the client should transmit router solicitation requests.

Static Route

33

8 octet minimum; multiples of 8

List of static routes that the client should install in its routing cache. If multiple routes to the same destination are specified, they are in descending order of priority. The routes consist of a list of IP address pairs. The first address is the destination address, and the second address is the router for the destination. The default route (0.0.0.0) is an illegal destination for a static route.


Link Layer Parameters Per Interface

Table B-4 lists the options that affect the operation of the data link layer on a per-interface basis.

Table B-4 Link Layer Parameters Per Interface Options 

Option Name
No.
Length
Description

Trailer Encapsulation

34

1 octet

Specifies whether or not the client should negotiate the use of trailers (RFC 893) when using the ARP protocol. Values: 0=do not use; 1=use

ARP Cache Timeout

35

4 octets

Timeout in seconds for ARP cache entries.

Ethernet Encapsulation

36

1 octet

Specifies whether or not the client should use Ethernet Version 2 (RFC 894) or IEEE 802.3 (RFC 1042) encapsulation if the interface is an Ethernet.
Value: 0=use RFC 894 encapsulation; 1=use RFC 1042 encapsulation


TCP Parameters

Table B-5 lists the options that affect the operation of the TCP layer on a per-interface basis.

Table B-5 TCP Parameter Options 

Option Name
No.
Length
Description

TCP Default TTL

37

1 octet

Default TTL that the client should use when sending TCP segments. Value: minimum 1

TCP Keepalive Interval

38

4 octets

Interval (in seconds) that the client TCP should wait before sending a keepalive message on a TCP connection. The time is specified as a 32-bit unsigned integer. A value of zero indicates that the client should not generate keepalive messages on connections unless specifically requested by an application. Value: 32-bit unsigned; 0=do not generate keepalive messages unless specifically requested.

TCP Keepalive Garbage

39

1 octet

Specifies the whether or not the client should send TCP keep-alive messages with an octet of garbage for compatibility with older implementations.
Values: 0=do not send; 1=send


Application and Service Parameters

Table B-6 lists some miscellaneous options used to configure miscellaneous applications and services.

Table B-6 Application and Service Parameter Options 

Option Name
No.
Length
Description

Network Information Service (NIS) Domain

40

1 octet minimum

Name of the client's NIS domain. The domain is formatted as a character string consisting of characters from the NVT ASCII character set.

Network Information Service (NIS) Servers

41

4 octet minimum; multiples of 4

List of IP addresses indicating NIS servers available to the client. Servers should be in order of preference.

Network Time Protocol Servers

42

4 octet minimum; multiples of 4

List of IP addresses indicating NTP servers that are available to the client. Servers should be in order of preference.

Vendor-Specific Information

43

1 octet minimum

This option is used by clients and servers to exchange vendor-specific information. The information is an opaque object of n octets, presumably interpreted by vendor-specific code on the clients and servers. The definition of this information is vendor specific. The vendor is indicated in the vendor-class-identifier option. Servers not equipped to interpret the vendor-specific information sent by a client must ignore it (although it can be reported). Clients that do not receive desired vendor-specific information should make an attempt to operate without it, although they can do so (and announce they are doing so) in a degraded mode.

If a vendor potentially encodes more than one item of information in this option, then the vendor should encode the option using encapsulated vendor-specific options as described here.

     

The encapsulated vendor-specific options field should be encoded as a sequence of code/length/value fields of identical syntax to the DHCP options field with these exceptions:

There should not be a magic cookie field in the encapsulated vendor-specific extensions field.

Codes other than 0 or 255 can be redefined by the vendor within the encapsulated vendor-specific extensions field, but should conform to the tag-length-value syntax defined in section 2.

Code 255 (END), if present, signifies the end of the encapsulated vendor extensions, not the end of the vendor extensions field. If no code 255 is present, then the end of the enclosing vendor-specific information field is taken as the end of the encapsulated vendor-specific extensions field.

NetBIOS over TCP/IP Name Server

44

4 octet minimum; multiples of 4

List of RFC 1001/1002 NBNS name servers in order of preference.

NetBIOS over TCP/IP Datagram Distribution Server

45

4 octet minimum; multiples of 4

List of RFC 1001/1002 NBDD servers in order of preference.

NetBIOS over TCP/IP Node Type

46

1 octet

Allows NetBIOS over TCP/IP client, which are configured as described in RFC 1001/1002.
Values: Single octet in hexadecimal that identifies the client type:

0x1=B-node (broadcast node)

0x2=P-node (point-to-point node)

0x4=M-node (mixed node)

0x8=H-node

NetBIOS over TCP/IP Scope

47

1 octet minimum

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

X Window System Font Server

48

4 octet minimum; multiples of 4

List of X Window System Font servers available to the client. Servers should be in order of preference.

X Window System Display Manager

49

4 octet minimum; multiples of 4

List of IP addresses of systems that are running the X Window System Display Manager and are available to the client. Addresses should be in order of preference.

Network Information Service (NIS+) Domain

64

1 octet minimum

Name of the client's NIS+ domain. The domain is formatted as a character string consisting of characters from the NVT ASCII character set.

Network Information Service (NIS+) Servers

65

4 octet minimum; multiples of 4

List of IP addresses indicating NIS+ servers available to the client. Servers should be in order of preference.

Mobile IP Home Agent

68

0 octets minimum; multiples of 4; expected, 4 octets (single home agent's address)

List of IP addresses indicating mobile IP home agents available to the client. Agents should be in order of preference.
Value: 32-bit address; 0=no home agents available

Simple Mail Transport Protocol (SMTP) Server

69

4 octet minimum; multiples of 4

List of SMTP servers available to the client. Servers should be in order of preference.

Post Office Protocol (POP3) Server

70

4 octet minimum; multiples of 4

List of POP3 servers available to the client. Servers should be in order of preference.

Network News Transport Protocol (NNTP) Server

71

4 octet minimum; multiples of 4

List of NNTP servers available to the client. Servers should be in order of preference.

World Wide Web (WWW) Server

72

4 octet minimum; multiples of 4

List of World Wide Web (WWW) servers available to the client. Servers should be in order of preference.

Finger Server

73

4 octet minimum; multiples of 4

List of Finger servers available to the client. Servers should be in order of preference.

Internet Relay Chat Server

74

4 octet minimum; multiples of 4

List of IRC servers available to the client. Servers should be in order of preference.

StreetTalk Server

75

4 octet minimum; multiples of 4

List of StreetTalk servers available to the client. Servers should be in order of preference.

StreetTalk Directory Assistance (STDA) Server

76

4 octet minimum; multiples of 4

List of STDA servers available to the client. Servers should be in order of preference.


DHCP Extensions

This section describes the options that are specific to DHCP.

Table B-7 lists some options used to configure miscellaneous applications and services.

Table B-7 Application and Service Parameter Options 

Option Name
No.
Length
Description

Requested IP Address

50

4 octets

Used in a client request (DHCPDISCOVER) to allow the client to request that a particular IP address be assigned.

IP Address Lease Time

51

4 octets

Used in a client request (DHCPDISCOVER or DHCPREQUEST) to allow the client to request a lease time for the IP address. In a server reply (DHCPOFFER), a DHCP server uses this option to specify the lease time it is willing to offer.
Value: seconds, as 32-bit unsigned integer

Option Overload

52

1 octet

Indicates that the DHCP sname or file fields are being overloaded by using them to carry DHCP options. A DHCP server inserts this option if the returned parameters will exceed the usual space allotted for options. If this option is present, the client interprets the specified additional fields after it concludes interpretation of the standard option fields.
Values: 1=file field is used to hold options; 2=sname field is used to hold options; 3=both fields are used to hold options

DHCP Message Type

53

1 octet

Used to convey the type of DHCP message. The \ is 1 (DHCPDISCOVER).
Values: 1=DHCPDISCOVER; 2=DHCPOFFER; 3=DHCPREQUEST; 4=DHCPDECLINE; 5=DHCPACK; 6=DHCPNAK; 7=DHCPRELEASE; 8=DHCPINFORM

Server Identifier

54

4 octets

Used in DHCPOFFER and DHCPREQUEST messages, and can optionally be included in the DHCPACK and DHCPNAK messages. DHCP servers include this option in the DHCPOFFER in order to allow the client to distinguish between lease offers. DHCP clients use the contents of the server identifier field as the destination address for any DHCP messages unicast to the DHCP server. DHCP clients also indicate which of several lease offers is being accepted by including this option in a DHCPREQUEST message. The identifier is the IP address of the selected server.

Parameter Request List

55

1 octet
minimum

Used by a DHCP client to request values for specified configuration parameters. The list of requested parameters is specified as n octets, where each octet is a valid DHCP option code as defined in this document. The client can list the options in order of preference. The DHCP server does not have to return the options in the requested order, but must try to insert the options in the order that the client requested.

Message

56

1 octet
minimum

Used by a DHCP server to provide an error message to a DHCP client in a DHCPNAK message in the event of a failure. A client can use this option in a DHCPDECLINE message to indicate why the client declined the offered parameters. The message consists of n octets of NVT ASCII text, which the client can display on an available output device.

Maximum DHCP Message Size

57

2 octets

Maximum length DHCP message that a server is willing to accept. The length is specified as an unsigned 16-bit integer. A client can use the maximum DHCP message size option in DHCPDISCOVER or DHCPREQUEST messages, but should not use the option in DHCPDECLINE messages. Value: 576 minimum

Renewal (T1) Time Value

58

4 octets

Time interval from address assignment until the client transitions to RENEWING state.
Value: seconds, as 32-bit unsigned integer

Rebinding (T2) Time Value

59

4 octets

Time interval from address assignment until the client transitions to REBINDING state.
Value: seconds, as 32-bit unsigned integer

Vendor Class Identifier

60

1 octet
minimum

Used by DHCP clients to optionally identify the vendor type and configuration of a DHCP client. The information is a string of n octets, interpreted by servers. Vendors can choose to define specific vendor class identifiers to convey particular configuration or other identification information about a client. For example, the identifier can encode the client's hardware configuration. Servers not equipped to interpret the class-specific information sent by a client must ignore it (although it can be reported). Servers that respond should only use option 43 to return the vendor-specific information to the client.

Client-Identifier

61

2 octet
minimum

Used by DHCP clients to specify their unique identifier. DHCP servers use this value to index their database of address bindings. This value is expected to be unique for all clients in an administrative domain.

DHCP servers should treat identifiers as opaque objects. The client identifier can consist of type-value pairs similar to the htype/chaddr fields. For instance, it can consist of a hardware type and hardware address. In this case, the type field should be one of the ARP hardware types defined in STD2. A hardware type of 0 (zero) should be used when the value field contains an identifier other than a hardware address (for example, a fully qualified domain name).

For correct identification of clients, each client's client-identifier must be unique among the client-identifiers used on the subnet to which the client is attached. Vendors and system administrators are responsible for choosing client-identifiers that meet this requirement for uniqueness.

TFTP Server Name

66

1 octet
minimum

Identifies a TFTP server when the sname field in the DHCP header has been used for DHCP options.

Bootfile Name

67

1 octet
minimum

Identifies a bootfile when the file field is the DHCP header that has been used for DHCP options.


Microsoft Client Options

Table B-8 lists the standard Microsoft client options.

Table B-8 Microsoft DHCP Client Options 

Option Name
No.
Description

dhcp-lease-time

51

14 days

domain-name

15

A domain name such as cisco.com

domain-name-servers

6

IP address of the name servers

netbios-name-servers

44

WINS server address

netbios-node-type

46

Identifies the NetBIOS client type; note that Network Registrar displays a warning if it is not present

routers

3

IP address of the router for this subnet


Option Tables

The following tables display the DHCP options in various ways. They show the options sorted numerically, by Network Registrar name, and by category.

DHCP options have a prescribed format and allowed values for their option parameters. Table B-9 lists each DCHP option and parameter type (in the Validation column). The parameter formats and allowed values come from the DHCP and Internet RFCs. All the DHCP options appear, but clients control only some, and the CLI only others.

Options by Number

Table B-9 shows the DHCP options sorted by option number, and includes the validation type. (See Table B-12 for details on the option validation types found in the Validation column.)

Table B-9 DHCP Options by Number 

No.
Network Registrar Name
Protocol Name
Category
Validation

--

packet-file-name

--

DHCP Packet Fields

STRING

--

packet-server-name

--

DHCP Packet Fields

STRING

--

packet-siaddr

--

DHCP Packet Fields

IPADDR

0

pad (set by protocol)

Pad

--

 

1

subnet-mask (derived)

Subnet Mask

Basic

IPADDR as mask

2

time-offset

Time Offset

BOOTP

INT

3

routers

Router

Basic,
MS DHCP Client

IPADDR_ARRAY

4

time-servers

Time Server

BOOTP

IPADDR_ARRAY

5

name-servers

Name Server

BOOTP

IPADDR_ARRAY

6

domain-name-servers

Domain Name
Server

Basic,
MS DHCP Client

IPADDR_ARRAY

7

log-servers

Log Server

Servers

IPADDR_ARRAY

8

cookie-servers

Cookie Server

BOOTP

IPADDR_ARRAY

9

lpr-servers

LPR Server

Servers

IPADDR_ARRAY

10

impress-servers

Impress Server

BOOTP

IPADDR_ARRAY

11

resource-location-servers

Resource
Location Server

BOOTP

IPADDR_ARRAY

12

host-name

Host Name

Basic

Hostname STRING

13

boot-size

Boot File Size

BOOTP

WORD (512-byte blocks

14

merit-dump

Merit Dump File

BOOTP

STRING

15

domain-name

Domain Name

Basic,
MS DHCP Client

STRING

16

swap-server

Swap Server

BOOTP

IPADDR

17

root-path

Root Path

BOOTP

STRING

18

extensions-path

Extensions Path

BOOTP

STRING

19

ip-forwarding

IP Forwarding
Enable/Disable

Host IP

BOOL

20

non-local-source-routing

Non-Local Source
Routing

Host IP

BOOL

21

policy-filters

Policy Filter

Host IP

Alternating IPADDR_ARRAY address/mask entries

22

max-dgram-reassembly

Maximum Datagram
Reassembly Size

Host IP

WORD

23

default-ip-ttl

Default IP
Time-to-Live

Host IP

BYTE

24

path-mtu-aging-timeout

Path MTU Aging
Timeout

Host IP

UINT

25

path-mtu-plateau-tables

Path MTU Plateau
Table

Host IP

WORD_ARRAY

26

interface-mtu

Interface MTU

Interface

WORD

27

all-subnets-local

All Subnets Are
Local

Interface

BOOL

28

broadcast-address

Broadcast Address

Interface

IPADDR (255.255.255.255)

29

perform-mask-discovery

Perform Mask
Discovery

Interface

BOOL

30

mask-supplier

Mask Supplier

Interface

BOOL

31

router-discovery

Perform Router
Discovery

Interface

BOOL

32

router-solicitation-
address

Router Solicitation
Address

Interface

IPADDR

33

static-routes

Static Route

Interface

IPADDR_ARRAY

34

trailer-encapsulation

Trailer Encapsulation

Interface

BOOL

35

arp-cache-timeout

ARP Cache Timeout

Interface

UINT

36

ieee802.3-encapsulation

Ethernet Encapsulation

Interface

BOOL

37

default-tcp-ttl

TCP Default TTL

Interface

BYTE > 0

38

tcp-keepalive-interval

TCP Keepalive
Interval

Interface

UINT

39

tcp-keepalive-garbage

TCP Keepalive
Garbage

Interface

BOOL

40

nis-domain

NIS Domain

Servers

STRING

41

nis-servers

Network Information Service (NIS) Servers

Servers

IPADDR_ARRAY

42

ntp-servers

NTP Servers

Servers

IPADDR_ARRAY

43

vendor-encapsulated-
options

Vendor-Specific
Information

--

BYTE_ARRAY

44

netbios-name-servers

NetBIOS over TCP/IP
Name Server

WINS/NetBIOS,
MS DHCP Client

IPADDR_ARRAY

45

netbios-dd-servers

NetBIOS over TCP/IP
Datagram Distribution
Server

WINS/NetBIOS

IPADDR_ARRAY

46

netbios-node-type

NetBIOS over
TCP/IP Node Type

WINS/NetBIOS,
MS DHCP Client

BYTE (1, 2, 4, 8)

47

netbios-scope

NetBIOS over
TCP/IP Scope

WINS/NetBIOS,
MS DHCP Client

STRING

48

font-servers

X Window System
Font Server

Servers

IPADDR_ARRAY

49

x-display-managers

X Window System
Display Manager

Servers

IPADDR_ARRAY

50

dhcp-requested-address
(set by DHCP client)

Requested IP Address

--

IPADDR

51

dhcp-lease-time

IP Address Lease
Time

Lease Information,
MS DHCP Client

UINT

52

dhcp-option-overload

Option Overload

--

BYTE

53

dhcp-message-type
(set by protocols)

DHCP Message Type

--

BYTE

54

dhcp-server-identifier
(set by DHCP server)

Server Identifier

--

IPADDR

55

dhcp-parameter-request-
list

Parameter Request
List

--

BYTE_ARRAY

56

dhcp-message

Message

--

STRING

57

dhcp-max-message-size
(set by protocol)

Maximum DHCP
Message Size

--

WORD

58

dhcp-renewal-time

Renewing (T1)
Time Value

Lease Information,
MS DHCP Client

UINT

59

dhcp-rebinding-time

Rebinding (T2)
Time Value

Lease Information,
MS DHCP Client

UINT

60

dhcp-class-identifier
(set by DHCP client)

Vendor Class Identifier

--

STRING

61

dhcp-client-identifier
(set by DHCP client)

Client-Identifier

Basic

BYTE_ARRAY

62

netwareip-domain

NetWare/IP
Domain Name

NetWare Client

STRING

63

netwareip-information

NetWare/IP
Information

NetWare Client

BYTE_ARRAY

64

nis+-domain

NIS+ Domain

Servers

STRING

65

nis+-servers

NIS+ Servers

Servers

IPADDR_ARRAY

66

tftp-server

TFTP Server Name

Servers

STRING

67

boot-file

Bootfile Name

BOOTP

STRING

68

mobile-ip-home-agents

Mobile IP Home Agent

Servers

IPADDR_ARRAY

69

smtp-servers

SMTP Server

Servers

IPADDR_ARRAY

70

pop3-servers

POP3 Server

Servers

IPADDR_ARRAY

71

nntp-servers

NNTP Server

Servers

IPADDR_ARRAY

72

www-servers

WWW Server

Servers

IPADDR_ARRAY

73

finger-servers

Finger Server

Servers

IPADDR_ARRAY

74

irc-servers

IRC Server

Servers

IPADDR_ARRAY

75

streettalk-servers

StreetTalk Server

Servers

IPADDR_ARRAY

76

streettalk-directory-
assistance-servers

STDA Server

Servers

IPADDR_ARRAY

77

dhcp-user-class-id
(set by DHCP client)

--

--

STRING

81

client-fqdn

DHCP Client FQDN

--

BYTE_ARRAY

82

relay-agent-info

DHCP Relay Agent
Information

(for suboptions, see relay-agent-info)

BYTE_ARRAY (

85

nds-servers

NDS Servers

NetWare Client

IPADDR_ARRAY

86

nds-tree

NDS Tree Name

NetWare Client

STRING

87

nds-context

NDS Context

NetWare Client

STRING

122

cablelabs-client-
configuration

CableLabs Client Configuration

(for suboptions, see cablelabs-client- configuration)

BYTE_ARRAY

128

mcns-security-server

--

Servers

IPADDR

185

vpn-id

VPN Identifier

--

BYTE_ARRAY

186

cisco-vpn-id

Cisco VPN Identifier

--

BYTE_ARRAY

251

auto-configure

Autoconfiguration

--

BYTE

255

end (set by protocol)

End

--

 

Options by Network Registrar Name

Table B-10 lists the DHCP options by Network Registrar name. (For each option's validation type, cross-reference it by number to Table B-9 and check the Validation column.)

Table B-10 DHCP Options by Network Registrar Name 

Network Registrar Name
Number
Option Name
Category

all-subnets-local

27

All Subnets Are Local

Interface

arp-cache-timeout

35

ARP Cache Timeout

Interface

boot-file

67

Bootfile Name

BOOTP

boot-size

13

Boot File Size

BOOTP

broadcast-address

28

Broadcast Address

Interface

cablelabs-client-configuration

122

CableLabs Client Configuration

Interface

client-fqdn

81

DHCP Client FQDN

(proposed)

cookie-servers

8

Cookie Server

BOOTP

default-ip-ttl

23

Default IP Time-to-Live

Host IP

default-tcp-ttl

37

TCP Default TTL

Interface

dhcp-class-identifier

60

Vendor Class Identifier

--

dhcp-client-identifier

61

Client-Identifier

Basic

dhcp-lease-time

51

IP Address Lease Time

Lease Information,
MS DHCP Client

dhcp-max-message-size

57

Maximum DHCP
Message Size

--

dhcp-message-type

53

DHCP Message Type

--

dhcp-message

56

Message

--

dhcp-option-overload

52

Option Overload

--

dhcp-parameter-request-list

55

Parameter Request List

--

dhcp-rebinding-time

59

Rebinding (T2)
Time Value

Lease Information,
MS DHCP Client

dhcp-renewal-time

58

Renewing (T1)
Time Value

Lease Information,
MS DHCP Client

dhcp-requested-address

50

Requested IP Address

--

dhcp-server-identifier

54

Server Identifier

--

dhcp-user-class-id

77

--

--

domain-name

15

Domain Name

Basic, MS DHCP Client

domain-name-servers

6

Domain Name Server

Basic, MS DHCP Client

end

255

End

--

extensions-path

18

Extensions Path

BOOTP

finger-servers

73

Finger Server

Servers

font-servers

48

X Window System
Font Server

Servers

host-name

12

Host Name

Basic

ieee802.3-encapsulation

36

Ethernet Encapsulation

Interface

impress-servers

10

Impress Server

BOOTP

interface-mtu

26

Interface MTU

Interface

ip-forwarding

19

IP Forwarding
Enable/Disable

Host IP

irc-servers

74

IRC Server

Servers

log-servers

7

Log Server

Servers

lpr-servers

9

LPR Server

Servers

mask-supplier

30

Mask Supplier

Interface

max-dgram-reassembly

22

Maximum Datagram
m Reassembly Size

Host IP

mcns-security-server

128

--

Servers

merit-dump

14

Merit Dump File

BOOTP

mobile-ip-home-agents

68

Mobile IP Home Agent

Servers

name-servers

5

Name Server

BOOTP

nds-context

87

NDS Context

NetWare Client

nds-servers

85

NDS Servers

NetWare Client

nds-tree

86

NDS Tree Name

NetWare Client

netbios-dd-servers

45

NetBIOS over TCP/IP
Datagram Distribution Server

WINS/NetBIOS

netbios-name-servers

44

NetBIOS over TCP/IP
Name Server

WINS/NetBIOS,
MS DHCP Client

netbios-node-type

46

NetBIOS over TCP/IP
Node Type

WINS/NetBIOS,
MS DHCP Client

netbios-scope

47

NetBIOS over TCP/IP
Scope

WINS/NetBIOS,
MS DHCP Client

netwareip-domain

62

NetWare/IP Domain Name

NetWare Client

netwareip-information

63

NetWare/IP Information

NetWare Client

nis+-domain

64

NIS+ Domain

Servers

nis+-servers

65

Network Information Service (NIS+) Servers

Servers

nis-domain

40

NIS Domain

Servers

nis-servers

41

Network Information Service (NIS) Servers

Servers

nntp-servers

71

NNTP Server

Servers

non-local-source-routing

20

Non-Local Source Routing

Host IP

ntp-servers

42

NTP Servers

Servers

packet-file-name

--

--

DHCP Packet Fields

packet-server-name

--

--

DHCP Packet Fields

packet-siaddr

--

--

DHCP Packet Fields

pad

0

Pad

--

path-mtu-aging-timeout

24

Path MTU Aging Timeout

Host IP

path-mtu-plateau-tables

25

Path MTU Plateau Table

Host IP

perform-mask-discovery

29

Perform Mask Discovery

Interface

policy-filters

21

Policy Filter

Host IP

pop3-servers

70

POP3 Server

Servers

relay-agent-info

82

DHCP Relay Agent
Information

--

resource-location-servers

11

Resource Location Server

BOOTP

root-path

17

Root Path

BOOTP

router-discovery

31

Perform Router Discovery

Interface

router-solicitation-address

32

Router Solicitation Address

Interface

routers

3

Router

Basic, MS DHCP Client

smtp-servers

69

SMTP Server

Servers

static-routes

33

Static Route

Interface

streettalk-directory-
assistance-servers

76

STDA Server

Servers

streettalk-servers

75

StreetTalk Server

Servers

subnet-mask

1

Subnet Mask

Basic

swap-server

16

Swap Server

BOOTP

tcp-keepalive-garbage

39

TCP Keepalive Garbage

Interface

tcp-keepalive-interval

38

TCP Keepalive Interval

Interface

tftp-server

66

TFTP Server Name

Servers

time-offset

2

Time Offset

BOOTP

time-servers

4

Time Server

BOOTP

trailer-encapsulation

34

Trailer Encapsulation

Interface

vendor-encapsulated-options

43

Vendor Specific Information

--

www-servers

72

WWW Server

Servers

x-display-managers

49

X Window System
Display Manager

Servers


Options by Category

Table B-11 list each option by category. (For each option's validation type, cross-reference it by number to Table B-9 and check the Validation column.)

Table B-11 DHCP Options by Category 

Category
Number
Network Registrar Name
Option Name

--

0

pad

Pad

--

43

vendor-encapsulated-options

Vendor Specific Information

--

50

dhcp-requested-address

Requested IP Address

--

52

dhcp-option-overload

Option Overload

--

53

dhcp-message-type

DHCP Message Type

--

54

dhcp-server-identifier

Server Identifier

--

55

dhcp-parameter-request-list

Parameter Request List

--

56

dhcp-message

Message

--

57

dhcp-max-message-size

Maximum DHCP Message Size

--

60

dhcp-class-identifier

Vendor Class Identifier

--

77

dhcp-user-class-id

--

--

82

relay-agent-info

--

--

122

cablelabs-client-configuration

--

--

255

end

End

Basic

1

subnet-mask

Subnet Mask

Basic

3

routers

Router

Basic

6

domain-name-servers

Domain Name Server

Basic

12

host-name

Host Name

Basic

15

domain-name

Domain Name

Basic

61

dhcp-client-identifier

Client-Identifier

BOOTP

2

time-offset

Time Offset

BOOTP

4

time-servers

Time Server

BOOTP

5

name-servers

Name Server

BOOTP

8

cookie-servers

Cookie Server

BOOTP

10

impress-servers

Impress Server

BOOTP

11

resource-location-servers

Resource Location Server

BOOTP

13

boot-size

Boot File Size

BOOTP

14

merit-dump

Merit Dump File

BOOTP

16

swap-server

Swap Server

BOOTP

17

root-path

Root Path

BOOTP

18

extensions-path

Extensions Path

BOOTP

67

boot-file

Bootfile Name

DHCP Packet Fields

--

packet-file-name

--

DHCP Packet Fields

--

packet-server-name

--

DHCP Packet Fields

--

packet-siaddr

--

Host IP

19

ip-forwarding

IP Forwarding Enable/Disable

Host IP

20

non-local-source-routing

Non-Local Source Routing

Host IP

21

policy-filters

Policy Filter

Host IP

22

max-dgram-reassembly

Maximum Datagram Reassembly Size

Host IP

23

default-ip-ttl

Default IP Time-to-Live

Host IP

24

path-mtu-aging-timeout

Path MTU Aging Timeout

Host IP

25

path-mtu-plateau-tables

Path MTU Plateau Table

Interface

26

interface-mtu

Interface MTU

Interface

27

all-subnets-local

All Subnets Are Local

Interface

28

broadcast-address

Broadcast Address

Interface

29

perform-mask-discovery

Perform Mask Discovery

Interface

30

mask-supplier

Mask Supplier

Interface

31

router-discovery

Perform Router Discovery

Interface

32

router-solicitation-address

Router Solicitation Address

Interface

33

static-routes

Static Route

Interface

34

trailer-encapsulation

Trailer Encapsulation

Interface

35

arp-cache-timeout

ARP Cache Timeout

Interface

36

ieee802.3-encapsulation

Ethernet Encapsulation

Interface

37

default-tcp-ttl

TCP Default TTL

Interface

38

tcp-keepalive-interval

TCP Keepalive Interval

Interface

39

tcp-keepalive-garbage

TCP Keepalive Garbage

Lease Information

51

dhcp-lease-time

IP Address Lease Time

Lease Information

58

dhcp-renewal-time

Renewing (T1) Time Value

Lease Information

59

dhcp-rebinding-time

Rebinding (T2) Time Value

Microsoft DHCP Client

3

routers

Router

Microsoft DHCP Client

6

domain-name-servers

Domain Name Server

Microsoft DHCP Client

15

domain-name

Domain Name

Microsoft DHCP Client

44

netbios-name-servers

NetBIOS over TCP/IP Name Server

Microsoft DHCP Client

46

netbios-node-type

NetBIOS over TCP/IP Node Type

Microsoft DHCP Client

47

netbios-scope

NetBIOS over TCP/IP Scope

Microsoft DHCP Client

51

dhcp-lease-time

IP Address Lease Time

Microsoft DHCP Client

58

dhcp-renewal-time

Renewing (T1) Time Value

Microsoft DHCP Client

59

dhcp-rebinding-time

Rebinding (T2) Time Value

NetWare Client

62

netwareip-domain

NetWare/IP Domain Name

NetWare Client

63

netwareip-information

NetWare/IP Information

NetWare Client

85

nds-servers

NDS Servers

NetWare Client

86

nds-tree

NDS Tree Name

NetWare Client

87

nds-context

NDS Context

Servers

7

log-servers

Log Server

Servers

9

lpr-servers

LPR Server

Servers

40

nis-domain

NIS Domain

Servers

41

nis-servers

Network Information Service (NIS) Servers

Servers

42

ntp-servers

NTP Servers

Servers

48

font-servers

X Window System Font Server

Servers

49

x-display-managers

X Window System Display Manager

Servers

64

nis+-domain

NIS+ Domain

Servers

65

nis+-servers

NIS+ Servers

Servers

66

tftp-server

TFTP Server Name

Servers

68

mobile-ip-home-agents

Mobile IP Home Agent

Servers

69

smtp-servers

SMTP Server

Servers

70

pop3-servers

POP3 Server

Servers

71

nntp-servers

NNTP Server

Servers

72

www-servers

WWW Server

Servers

73

finger-servers

Finger Server

Servers

74

irc-servers

IRC Server

Servers

75

streettalk-servers

StreetTalk Server

Servers

76

streettalk-directory-
assistance-servers

STDA Server

Servers

128

mcns-security-server

--

WINS/NetBIOS

44

netbios-name-servers

NetBIOS over TCP/IP Name Server

WINS/NetBIOS

45

netbios-dd-servers

NetBIOS over TCP/IP Datagram Distribution Server

WINS/NetBIOS

46

netbios-node-type

NetBIOS over TCP/IP Node Type

WINS/NetBIOS

47

netbios-scope

NetBIOS over TCP/IP Scope


Option Validation Types

Table B-12 defines the DHCP option validation types.

Table B-12 Validation Types 

Validation
Format and Allowed Values

BOOL

Boolean value. Represents the state of an enabled or disabled option.

BYTE

Unrestricted sequence of octets.

BYTE_ARRAY

List of BYTES.Unrestricted sequence of octets.

INT

32-bit integer value. Maximum range of values: - 2147483648 through 2147483647.

IPADDR

IP address as 32-bit number, entered as a quadruple-octet (numbers ranging from 0-255) with decimal points separating the octet numbers.

Some IP addresses are subnet masks, as per RFC 950. A subnet mask is a 32-bit number, entered in IP Address format, starting with 0 or more bits, with the remaining bits set to zero. Nine numbers can appear in a subnet mask— 0, 128, 192, 224, 240, 248, 252, 254, and 255. The subnet-mask option is an exception: it accepts any valid IP address, even invalid masks.

IPADDR_ARRAY

List containing at least one IP address. See IPADDR for format and allowed values of each list member.

STRING

Unrestricted sequence of ASCII characters (from 1 through 255). A hostname string may or may not be qualified with the local domain name (see RFC 1035). The grammar for hostnames is:

domain ::= <subdomain> | " "

<subdomain> ::= <label> | <subdomain> "." <label>

<label> ::= <ldh-str> <let-dig>

<ldh-str> ::= <let-dig-hyp> | <let-dig-hyp> <ldh-str>

<let-dig-hyp> ::= <let-dig> | `-`

<let-dig> ::= <letter> | <digit>

<letter> ::= any one of the 52 alphabetic characters `A' through `Z' in uppercase and `a' through `z' in lowercase.

<digit> ::= any one of the ten digits `0' through `9'

UINT

32-bit unsigned value. Represents a count, size or duration. Can have a range of allowed values associated with a given option. Maximum range of values: 0 through 4294967295.

WORD

16-bit unsigned value. Represents a count, size or duration. Can have a range of allowed values associated with a given option. Maximum range of values: 0 through 65535.

WORD_ARRAY

List containing at least one WORD. See WORD for format and allowed values of each list member.