User Guide for Cisco Network Registrar, 7.1
Appendix: DHCP Options
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DHCP Options

Table Of Contents

DHCP Options

Option Descriptions

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

DHCPv4 Extension Options

DHCPv6 Options

Microsoft Client Options

Option Tables

Options by Number

Options by Network Registrar Name

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-10.

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:

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

DHCPv4 Extension Options

DHCPv6 Options

Microsoft Client Options

Options by Number

Options by Network Registrar Name

Option Validation Types

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 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 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 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 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 hostnames through the Domain Name System.

Swap Server

16

4 octets

IP address of the client swap server.

Root Path

17

1 octet minimum

Path name that contains the client 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 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 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 dhcp-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, and 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 the code 255 is not 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 hexadecimal octet 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 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 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.


DHCPv4 Extension Options

Table B-7 lists the DHCPv4 extension options.

Table B-7 DHCPv4 Extensions 

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 preset value is 1 (DHCPDISCOVER). Values:
1=DHCPDISCOVER; 2=DHCPOFFER; 3=DHCPREQUEST; 4=DHCPDECLINE; 5=DHCPACK; 6=DHCPNAK; 7=DHCPRELEASE; 8=DHCPINFORM; 13=LEASEQUERY

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 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-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.

Relay Agent Information

82

 

Identifies the DHCP relay agent information.

iSNS

83

14 bytes
minimum

Identifies the Internet Storage Name Service (see RFC 4174)

BCMS Controller Domain

88

Variable

List of Broadcast and Multicast Service (BCMS) controller domains (see RFC 4280)

BCMS Address

89

4 octets minimum

List of IP addresses for the BCMS controller (see RFC 4280)

Lease Query Client Last Transaction Time

91

4 octets

Time of the most recent access of the client sending a DHCPLEASEQUERY (see RFC 4388).

Lease Query Associated IP Addresses

92

4 octets minimum

All IP addresses associated with the client specified in a particular DHCPLEASEQUERY message (see RFC 4388).


DHCPv6 Options

Table B-8 lists the DHCPv6 options, along with their defined data types. All the option packets include at least an option length (option-len) and a variable length data field. There can also be additional parameter settings, as described in the table. Mod in the Description column indicates that the option is modifiable. Many of these options are described in RFC 3315.

Table B-8 DHCPv6 Options 

Network Registrar Name
(Type)
No.
Description (Mod=modifiable)

client-identifier
AT_BLOB

1

DUID identifying a client between a client and a server.

server-identifier
AT_BLOB

2

DUID identifying a server between a client and a server.

ia-na
AT_BLOB

3

Nontemporary Addresses option with the associated parameters and addresses. Parameters are the unique ID, time the client contacts the addresses in the IA to extend the lifetime, and time the client contacts any available server to extend the lifetime of the addresses.

ia-ta
AT_BLOB

4

Temporary Addresses option with the associated parameters and addresses.

iaaddr
AT_BLOB

5

IPv6 addresses associated with an IA_NA or IA_TA. (The IAADRR must be encapsulated in the options field of an IA_NA or IA_TA option.) The IAADDR option includes preferred and valid lifetime fields, and the options field that encapsulates the options specific to this address.

oro
AT_SHORT

6

Option Request option (ORO) that identifies a list of options in a message between a client and a server. A client can include this option in a Solicit, Request, Renew, Rebind, Confirm, or Information-request message to inform the server about options the client wants from the server. A server can include this option in a Reconfigure message to indicate which option updates the client should request.

preference
AT_INT8

7

A server sends this option to a client to affect what server the client selects (Mod).

elapsed-time
AT_SHORT

8

A client sends this option to a server to indicate how long the client has been trying to complete a message exchange (Mod).

relay-message
AT_BLOB

9

DHCP message in a Relay-forward or Relay-reply message.

auth
AT_BLOB

11

Authenticates the identity and contents of a DHCP message. The parameters are the authentication protocol, the authentication algorithm, the replay detection method (RDM), and the authentication information.

server-unicast
AT_IP6ADDR

12

The server sends this option to a client to indicate that the client can unicast messages to the server.

status-code
AT_BLOB

13

Returns a status indication related to the DHCP message or option in which it appears. The parameters are the status code and status message.

rapid-commit
AT_ZEROSIZE

14

Signals use of the two-message exchange for address assignment.

user-class
AT_TYPECNT

15

Clients use this option to identify the type or category of user or applications it represents. A zero type count value field followed by user data (as a blob).

vendor-class
AT_VENDOR_CLASS

16

Clients use this option to identify the vendor that manufactured the hardware on which they are running.

vendor-opts
AT_VENDOR_OPTS

17

Clients and servers use this option to exchange vendor-specific information. The enterprise ID for the CableLabs vendor is 4491; the suboptions for CableLabs are listed in Table C-4 on page C-7.

interface-id
AT_BLOB

18

Relay agents use this option to identify the interface on which the client message is received.

reconfigure-message
AT_INT8

19

The server includes this in a Reconfigure message to indicate whether the client should respond with a Renew or Information-request message.

reconfigure-accept
AT_ZEROSIZE

20

Clients use this option to announce to the server whether the client is willing to accept Reconfigure messages.

sip-servers-name
AT_DNSNAME

21

Domain names of the SIP outbound proxy servers for the client (Mod). See RFC 3319.

sip-servers-address
AT_IP6ADDR

22

IPv6 addresses of the SIP outbound proxy servers for the client (Mod).

dns-servers
AT_IP6ADDR

23

IPv6 addresses of DNS recursive name servers (Mod).

domain-list
AT_DNSNAME

24

Domain names in the domain search list (Mod).

ia-pd
AT_BLOB

25

IPv6 prefix delegation identity association and its associated parameters and prefixes. Parameters are the unique ID, time the client contacts the addresses in the IA to extend the lifetime, and time the client contacts any available server to extend the lifetime of the addresses.

iaprefix
AT_BLOB

26

IPv6 prefixes associated with an IA_PD. The prefix must be encapsulated in the options field of an IA_PD option. Parameters are the valid and preferred lifetimes, prefix length, and the prefix.

nis-servers
AT_IP6ADDR

27

List of IPv6 addresses of Network Information Service (NIS) servers available to the client (see RFC 3898) (Mod).

nisp-servers
AT_IP6ADDR

28

List of IPv6 addresses of NIS+ servers available to the client (Mod).

nis-domain-name
AT_DNSNAME

29

Conveys the NIS domain name to the client (Mod).

nisp-domain-name
AT_DNSNAME

30

Conveys the NIS+ domain name to the client (Mod).

sntp-servers
AT_IP6ADDR

31

List of Simple Network Time Protocol (SNTP) servers available to the client (see RFC 4075) (Mod).

info-refresh-time
AT_TIME

32

Sets an upper bound for how long a client should wait before refreshing DHCPv6 information (see RFC 4242) (Mod).

bcms-server-d
AT_DNSNAME

33

List of BCMS controller domains (see RFC 4280) (Mod).

bcms-server-a
AT_IP6ADDR

34

List of IPv6 addresses for the Broadcast and Multicast Service (BCMS) controller (see RFC 4280) (Mod).

geoconf-civic
AT_BLOB

36

DHCP civic addresses configuration (Mod).

remote-id
AT_BLOB

37

Relay agents that terminate switched or permanent circuits can add this option to identify remote hosts (see RFC 4649) (Mod).

relay-agent-subscriber-id
AT_BLOB

38

Allows assignment and activation of subscriber-specific actions (see RFC 4580) (Mod).

client-fqdn
AT_BLOB

39

DHCP client FQDN (Mod).

new-posix-timezone
AT_BLOB

41

POSIX time zone, for example, EST5EDT4, M3.2.0/02:00,M11.1.0/02:00.

new-tzdb-timezone
AT_BLOB

42

POSIX time zone database name, for example, Europe/Zurich.

ero
AT_BLOB

43

Relay agent Echo Request option to inform the server of the list of relay agent options to echo back.

lq-query
AT_BLOB

44

Used only in a LEASEQUERY message; identifies the query being performed. The option includes the query type, link-address (or 0::0), and options to provide data needed for the query.

client-data
AT_BLOB

45

Encapsulates the data for a single client on a single link in a LEASEQUERY-REPLY message.

clt-time
AT_TIME

46

Client last transaction time encapsulated in the client-data option; identifies how long ago the server last communicated with the client (in seconds).

lq-relay-data
AT_BLOB

47

Used only in a LEASEQUERY-REPLY message; provides the relay agent data used when the client last communicated with the server.

lq-client-link
AT_IP6ADDR

48

Used only in a LEASEQUERY-REPLY message; identifies the links on which the client has one or more bindings. It is used in reply to a query when no link-address was specified and the client is found to be on more than one link.

lost-server
AT_DNSNAME

51

A DHCPv6 client will request a LoST server domain name in an Options Request Option (ORO) (see RFC3315) (Mod).

This option contains a single domain name and must contain precisely one root label.


Microsoft Client Options

Table B-9 lists the standard Microsoft client options.

Table B-9 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-10 lists each DHCP 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-10 shows the DHCPv4 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.) A 0+ in the Comments column means a repeat count of zero or more occurrences, 1+ means one or more occurrences, 2n means multiple occurrences in multiples of 2. Comments also indicate whether the option includes suboptions, and, if so, how many, and whether the option is nonmodifiable (NM).


Tip For the syntax for adding more complex option data values for suboptions, see the "Adding Complex Values for Suboptions" section on page 21-7.


Table B-10 DHCPv4 Options by Number 

No.
Network Registrar Name
Protocol Name
Validation
Comments

0

pad

Pad

AT_NOLEN

NM

1

subnet-mask

Subnet Mask

AT_IPADDR

 

2

time-offset

Time Offset

AT_STIME

Replaced by tz- options (RFC 4833)

3

routers

Router

AT_IPADDR

1+

4

time-servers

Time Server

AT_IPADDR

1+

5

name-servers

Name Server

AT_IPADDR

1+

6

domain-name-servers

Domain Server

AT_IPADDR

1+

7

log-servers

Log Server

AT_IPADDR

1+

8

cookie-servers

Quotes Server

AT_IPADDR

1+

9

lpr-servers

LPR Server

AT_IPADDR

1+

10

impress-servers

Impress Server

AT_IPADDR

1+

11

resource-location-servers

RLP Server

AT_IPADDR

1+

12

host-name

Host Name

AT_NSTRING

 

13

boot-size

Boot File Size

AT_SHORT

 

14

merit-dump

Merit Dump File

AT_NSTRING

 

15

domain-name

Domain Name

AT_NSTRING

 

16

swap-server

Swap Server

AT_IPADDR

 

17

root-path

Root Path

AT_NSTRING

 

18

extensions-path

Extension File

AT_NSTRING

 

19

ip-forwarding

Forward On/Off

AT_BOOL

 

20

non-local-source-routing

SrcRte On/Off

AT_BOOL

 

21

policy-filters

Policy Filter

AT_IPADDR

2n

22

max-dgram-reassembly

Maximum DG Assembly

AT_SHORT

 

23

Default-ip-ttl

Default IP TTL

AT_RANGEBYTE

 

24

path-mtu-aging-timeout

MTU Timeout

AT_TIME

 

25

path-mtu-plateau-tables

MTU Plateau

AT_RANGESHORT

2n

26

interface-mtu

MTU Interface

AT_RANGESHORT

 

27

all-subnets-local

MTU Subnet

AT_BOOL

 

28

broadcast-address

Broadcast Address

AT_IPADDR

 

29

perform-mask-discovery

Mask Discovery

AT_BOOL

 

30

mask-supplier

Mask Supplier

AT_BOOL

 

31

router-discovery

Router Discovery

AT_BOOL

 

32

router-solicitation-address

Router Request

AT_IPADDR

 

33

static-routes

Static Route

AT_IPADDR

2n

34

trailer-encapsulation

Trailers

AT_BOOL

 

35

arp-cache-timeout

ARP Timeout

AT_TIME

 

36

ieee802.3-encapsulation

Ethernet

AT_BOOL

 

37

default-tcp-ttl

Default TCP TTL

AT_RANGEBYTE

 

38

tcp-keepalive-interval

Keepalive Time

AT_TIME

 

39

tcp-keepalive-garbage

Keepalive Data

AT_BOOL

 

40

nis-domain

NIS Domain

AT_STRING

 

41

nis-servers

NIS Servers

AT_IPADDR

1+

42

ntp-servers

NTP Servers

AT_IPADDR

1+

43

vendor-encapsulated-
options

Vendor Specific

AT_BLOB

NM

44

netbios-name-servers

NetBIOS Name Server

AT_IPADDR

1+

45

netbios-dd-servers

NetBIOS Distribution Server

AT_IPADDR

1+

46

netbios-node-type

NetBIOS Node Type

AT_RANGEBYTE

 

47

netbios-scope

NetBIOS Scope

AT_NSTRING

 

48

font-servers

X Window Font

AT_IPADDR

1+

49

x-display-managers

X Window Manager

AT_IPADDR

1+

50

dhcp-requested-address

Address Request

AT_IPADDR

 

51

dhcp-lease-time

Address Time

AT_TIME

NM

52

dhcp-option-overload

Overload

AT_OVERLOAD

 

53

dhcp-message-type

DHCP Message Type

AT_MESSAGE

NM (See the DHCP Message Type option in Table B-7)

54

dhcp-server-identifier

DHCP Server ID

AT_IPADDR

 

55

dhcp-parameter-request-
list

Parameter List

AT_INT8

0+

56

dhcp-message

DHCP Message

AT_NSTRING

NM

57

dhcp-max-message-size

DHCP Maximum Message Size

AT_SHORT

NM

58

dhcp-renewal-time

Renewing Time

AT_TIME

NM

59

dhcp-rebinding-time

Rebinding Time

AT_TIME

NM

60

dhcp-class-identifier

Class Identifier

AT_NSTRING

 

61

dhcp-client-identifier

Client Identifier

AT_BLOB

 

62

netwareip-domain

NetWare/IP Domain

AT_NSTRING

 

63

netwareip-information

NetWare/IP Option

AT_BLOB

 

64

nis+-domain

NIS Domain Name

AT_NSTRING

 

65

nis+-servers

NIS Server Address

AT_IPADDR

1+

66

tftp-server

TFTP Server Name

AT_NSTRING

 

67

boot-file

Bootfile Name

AT_NSTRING

 

68

mobile-ip-home-agents

Mobile IP Home Agent

AT_IPADDR

0+

69

smtp-servers

SMTP Server

AT_IPADDR

1+

70

pop3-servers

POP3 Server

AT_IPADDR

1+

71

nntp-servers

NNTP Server

AT_IPADDR

1+

72

www-servers

WWW Server

AT_IPADDR

1+

73

finger-servers

Finger Server

AT_IPADDR

1+

74

irc-servers

IRC Server

AT_IPADDR

1+

75

streettalk-servers

StreetTalk Server

AT_IPADDR

1+

76

streettalk-directory-
assistance-servers

STDA Server

AT_IPADDR

1+

77

dhcp-user-class-id

User Class ID

AT_TYPECNT

Suboptions (2)

78

slp-directory-agent

Service Location Protocol Directory Agent

AT_BLOB

Suboptions (2)

79

slp-service-scope

SLP Service Scope

AT_BLOB

Suboptions (2)

80

rapid-commit

Rapid Commit

AT_ZEROSIZE

 

81

client-fqdn

Client FQDN

AT_BLOB

Suboptions (4)

82

relay-agent-info

Relay Agent Information

AT_BLOB

For suboptions, see Table C-3 on page C-2

83

iSNS

Internet Storage Name Service (RFC4174)

AT_BLOB

Suboptions (7)

85

nds-servers

NDS Servers

AT_IPADDR

1+

86

nds-tree

NDS Tree Name

AT_NSTRING

 

87

nds-context

NDS Context

AT_NSTRING

 

88

bcms-servers-d

BCMS Controller Domain (RFC 4280)

AT_DNSNAME

1+

89

bcms-servers-a

BCMS Address

AT_IPADDR

1+

90

authentication

Authentication

AT_BLOB

Suboptions (5)

91

client-last-transaction-
time

Lease Query Client Last Transaction Time

AT_TIME

 

92

associated-ip

Lease Query Associated IP Addresses

AT_IPADDR

1+

93

pxe-client-arch

 

AT_SHORT

 

94

pxe-client-network-id

 

AT_BLOB

Suboptions (2)

95

ldap-url

 

AT_NSTRING

 

97

pxe-client-machine-id

 

AT_BLOB

Suboptions (2)

98

user-auth

 

AT_NSTRING

 

99

geoconf-civic

Civic Addresses Configuration

AT_BLOB

 

100

tz-posix

IEEE 1003.1 String

AT_NSTRING

 

101

tz-database

Time Zone Database

AT_NSTRING

 

112

netinfo-parent-server-addr

 

AT_IPADDR

 

113

netinfo-parent-server-tag

 

AT_NSTRING

 

114

initial-url

 

AT_NSTRING

 

116

auto-configure

Autoconfiguration

AT_RANGEBYTE

 

117

name-service-search

Name Service Search

AT_SHORT

1+

118

subnet-selection

Subnet Selection

AT_IPADDR

 

119

domain-search

Domain Search

AT_BLOB

 

120

sip-servers

SIP Servers

AT_BLOB

Suboptions (2)

121

classless-static-route

Classless Static Route

AT_BLOB

 

122

cablelabs-client-
configuration)

CableLabs Client Configuration

AT_BLOB

Suboptions (10) (see cablelabs-client- configuration, page C-3)

123

geo-conf

GeoConf Option

AT_BLOB

 

124

v-i-vendor-class

Vendor-Identifying Vendor Class

AT_VENDOR_CLASS

NM

125

v-i-vendor-info

Vendor-Identifying Vendor-Specific Info

AT_VENDOR_OPTS

See also the cablelabs-125 suboptions in Table C-3 on page C-2

128

mcns-security-server

--

AT_IPADDR

 

161

cisco-leased-ip

Cisco

AT_IPADDR

 

162

cisco-client-requested-
host-name

Cisco

AT_NSTRING

 

163

cisco-client-last-
transaction-time

Cisco

AT_INT

 

185

vpn-id

VPN Identifier

AT_BLOB

NM: Suboptions (2)

220

subnet-alloc

Subnet Allocation

AT_BLOB

Suboptions (5)

221

cisco-vpn-id

Cisco VPN Identifier

AT_BLOB

Suboptions (2)

251

cisco-auto-configure

Cisco Autoconfiguration

AT_RANGEBYTE

 

255

end

End

AT_NOLEN

NM


Options by Network Registrar Name

Table B-11 lists the DHCP options by Network Registrar name. (For each option validation type, cross-reference it by number to Table B-10 and check the Validation column.)

Table B-11 DHCP Options by Network Registrar Name 

Network Registrar Name
No.
Option Name
Category

all-subnets-local

27

All Subnets Are Local

Interface

arp-cache-timeout

35

ARP Cache Timeout

Interface

associated-ip

92

Lease Query Associated IP

DHCPv4

auth

11

Authentication

DHCPv6

authentication

90

Authentication

--

auto-configuration

116

Auto-Configuration

DHCPv4

bcms-server-a

34

BCMS Address v6

DHCPv6

bcms-servers-a

89

BCMS Address

DHCPv4

bcms-server-d

33

BCMS Controller Domain v6

DHCPv6

bcms-servers-d

88

BCMS Controller Domain

DHCPv4

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

cisco-autoconfigure

251

Cisco Autoconfiguration

DHCPv4

cisco-client-last-transaction-time

163

Cisco Client Last Transaction Time

DHCPv4

cisco-client-requested-host-name

162

Cisco Client Requested Host Name

DHCPv4

cisco-leased-ip

161

Cisco Leased IP Address

DHCPv4

cisco-vpn-id

221

Cisco VPN Identifier

DHCPv4

classless-static-route

121

Classless Static Route

DHCPv4

client-data

45

Leasequery Reply Client Data

DHCPv6

client-fqdn

81

DHCP Client FQDN

DHCPv4

client-fqdn

39

DHCP Client FQDN

DHCPv6

client-identifier

1

Client Identifier

DHCPv6

client-last-transaction-time

91

Leasequery Client Last Transaction Time

DHCPv4

clt-time

46

Leasequery Client Last Transaction Time

DHCPv6

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

DHCPv4

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

DHCPv4

dhcp-message-type

53

DHCP Message Type

DHCPv4

dhcp-message

56

Message

DHCPv4

dhcp-option-overload

52

Option Overload

DHCPv4

dhcp-parameter-request-list

55

Parameter Request List

DHCPv4

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

DHCPv4

dhcp-server-identifier

54

Server Identifier

DHCPv4

dhcp-user-class-id

77

User Class ID

DHCPv4

dns-servers

23

DNS Recursive Name Server

DHCPv6

domain-list

24

Domain Search List

DHCPv6

domain-name

15

Domain Name

Basic, MS DHCP Client

domain-name-servers

6

Domain Name Server

Basic, MS DHCP Client

domain-search

119

Domain Search

DHCPv4

elapsed-time

8

Elapsed Time

DHCPv6

end

255

End

--

ero

43

Relay Agent Echo Request Option

DHCPv6

extensions-path

18

Extensions Path

BOOTP

finger-servers

73

Finger Server

Servers

font-servers

48

X Window System
Font Server

Servers

geo-conf

123

GeoConf

DHCPv4

geoconf-civic

99

Civic Addresses Configuration

DHCPv4

geoconf-civic

36

Civic Addresses Configuration

DHCPv6

host-name

12

Host Name

Basic

ia-na

3

Identity Association for Nontemporary Addresses

DHCPv6

ia-pd

25

Prefix Delegation

DHCPv6

ia-ta

4

Identity Association for Temporary Addresses

DHCPv6

iaaddr

5

IA Address

DHCPv6

iaprefix

26

IA Prefix

DHCPv6

ieee802.3-encapsulation

36

Ethernet Encapsulation

Interface

impress-servers

10

Impress Server

BOOTP

info-refresh-time

32

Information Refresh Time

DHCPv6

interface-id

18

Interface Identifier

DHCPv6

interface-mtu

26

Interface MTU

Interface

ip-forwarding

19

IP Forwarding
Enable/Disable

Host IP

irc-servers

74

IRC Server

Servers

isns

83

iSNS

DHCPv4

log-servers

7

Log Server

Servers

lpr-servers

9

LPR Server

Servers

lq-client-link

48

Leasequery Client Link Reply

DHCPv6

lq-query

44

Leasequery

DHCPv6

lq-relay-data

47

Leasequery Relay Agent Reply

DHCPv6

mask-supplier

30

Mask Supplier

Interface

max-dgram-reassembly

22

Maximum Datagram 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

name-service-search

117

Name Service Search

DHCPv4

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

new-posix-timezone

41

POSIX time zone string

DHCPv6

new-tzdb-timezone

42

POSIX time zone database name

DHCPv6

nis+-domain

64

NIS+ Domain

Servers

nis+-servers

65

Network Information Service (NIS+) Servers

Servers

nis-domain

40

NIS Domain

Servers

nis-domain-name

29

NIS Domain Name

DHCPv6

nis-servers

41

Network Information Service (NIS) Servers

Servers

nis-servers

27

NIS Servers

DHCPv6

nisp-domain-name

30

NIS+ Domain Name

DHCPv6

nisp-servers

28

NIS+ Servers

DHCPv6

nntp-servers

71

NNTP Server

Servers

non-local-source-routing

20

Non-Local Source Routing

Host IP

ntp-servers

42

NTP Servers

Servers

option-time

8

Option Time

DHCPv6

oro

6

Option Request Option

DHCPv6

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

preference

7

Preference

DHCPv6

rapid-commit

80

Rapid Commit

DHCPv4

rapid-commit

14

Rapid Commit

DHCPv6

reconfigure-accept

20

Reconfigure Accept

DHCPv6

reconfigure-message

19

Reconfigure Message

DHCPv6

relay-agent-info

82

DHCP Relay Agent
Information

DHCPv4

relay-agent-subscriber-id

38

Relay Agent Subscriber ID

DHCPv6

relay-message

9

Relay Message

DHCPv6

remote-id

37

Relay Agent Remote ID

DHCPv6

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

server-identifier

2

DHCPv6 Server Identifier

DHCPv6

server-unicast

12

Server Unicast

DHCPv6

sip-servers

120

SIP Servers

DHCPv4

sip-servers-name

21

SIP Servers Domain Name List

DHCPv6

sip-servers-address

22

SIP Servers IPv6 Address List

DHCPv6

slp-directory agent

78

SLP Directory Agent

DHCPv4

slp-service-scope

79

SLP Service Scope

DHCPv4

smtp-servers

69

SMTP Server

Servers

sntp-servers

31

SNTP Configuration

DHCPv6

static-route

33

Static Route

Interface

status-code

13

Status Code

DHCPv6

streettalk-directory-
assistance-servers

76

STDA Server

Servers

streettalk-servers

75

StreetTalk Server

Servers

subnet-mask

1

Subnet Mask

Basic

subnet-selection

118

Subnet Selection

DHCPv4

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

tz-database

101

TZ Database String

DHCPv4

tz-posix

100

IEEE 1003.1 String

DHCPv4

user-auth

98

User Authentication

DHCPv4

user-class

15

User Class

DHCPv6

vendor-class

16

Vendor Class

DHCPv6

vendor-encapsulated-options

43

Vendor Specific Information

DHCPv4

vendor-opts

17

Vendor Specific Information

DHCPv6

v-i-vendor-class

124

Vendor Identifying Vendor Class

DHCPv4

v-i-vendor-opts

125

Vendor Identifying Vendor Options

DHCPv4

vpn-id

185

VPN Identifier

DHCPv4

www-servers

72

WWW Server

Servers

x-display-managers

49

X Window System
Display Manager

Servers


Option Validation Types

Table B-12 defines the DHCP option validation types. Note that you cannot use some of them to define custom options.

Table B-12 Validation Types 

Validation
Description—Web UI Equivalent)

AT_BLOB

List of binary bytes—binary

AT_BOOL

Boolean—boolean

AT_DATE

Bytes representing a date—date

AT_DNSNAME

DNS name—DNS name

AT_INT

Unsigned 32-bit integer—unsigned 32-bit

AT_INT8

8-bit integer—unsigned 8-bit

AT_INTI

Unsigned 32-bit integer (Intel)—unsigned 32-bit (Intel)

AT_IPADDR

32-bit IP address—IP address

AT_IP6ADDR

32-bit IPv6 address—IPv6 address

AT_MACADDR

Bytes representing a MAC address—MAC address

AT_MESSAGE

Unsigned 8-bit message (not usable for custom options)

AT_NOLEN

No length (used for PAD and END only)

AT_NSTRING

Sequence of ASCII characters—string

AT_OVERLOAD

Overload bytes (not usable for custom options)

AT_RANGEBYTE

Range of bytes (not usable for custom options)

AT_RANGESHORT

Range of shorts (not usable for custom options)

AT_RDNSNAME

Relative DNS name—relative DNS name

AT_SHORT

Unsigned 16-bit integer—unsigned 16-bit

AT_SHRTI

Unsigned 16-bit integer (Intel)—unsigned 16-bit (Intel)

AT_SINT

Signed 32-bit integer—signed 32-bit

AT_SINT8

8-bit integer—signed 8-bit

AT_SINTI

Signed 32-bit integer (Intel)—signed 32-bit (Intel)

AT_SSHORT

Signed 16-bit integer—signed 16-bit

AT_SSHRTI

Signed 16-bit integer (Intel)—signed 16-bit (Intel)

AT_STIME

Signed 32-bit signed integer representing time—signed time

AT_STRING

Unrestricted sequence of ASCII characters—string

AT_TIME

Unsigned 32-bit integer representing time—unsigned time

AT_TYPECNT

Type requiring two child definition: size of the type field, and type of data—counted-type:

For the DHCPv4 dhcp-user-class-id option (77), the repeating pattern is:

[ len (1 byte) ] [ data, of single type ]

For the DHCPv6 user-class option (15), the repeating pattern is:

[ len (2 byte) ] [ data, of single type ]

AT_VENDOR_CLASS

Vendor-class option (enterprise ID followed by opaque data; if DHCPv4, enterprise ID is followed by EID length)—vendor-class

AT_VENDOR_OPTS

Vendor-specific options data (enterprise ID followed by TLVs of vendor-specific data; if DHCPv4, enterprise ID is followed by EID length)—vendor-opts

AT_ZEROSIZE

32 bits of zero size (no longer used for PAD and END)