Compaq TCP/IP Services for OpenVMS
Management

7.7.2.1 DHCPCAP Configuration Syntax

The DHCPCAP. configuration file uses two-character, case-sensitive symbols that represent host parameters. Colons (:) follow and separate parameters from one another. For example, gw specifies gateway. For a list of the available symbols, see Section 7.7.2.5.

The following is the format of a configuration file entry:

entryname:symbol=value:symbol=value:symbol=value:

In this format:

entryname is usually the name of the BOOTP or DHCP client.
symbol is the two-character symbol that describes the parameters to be associated with the client.
value is a valid entry that represents the symbol. For more information, see Section 7.7.2.4.

Example 7-8 shows a sample DHCPCAP file entry.

Example 7-8 Sample Single-Host DHCPCAP File Entry

mypc:\ :ht=ether:\ :ha=112233445566:\ :ip=143.32.3.10:\ :gw=143.32.3.1:\ :dn=acme.com:

7.7.2.2 DHCPCAP Configuration Rules

When you create the DHCPCAP file, entries must conform to the following rules:

Start each new host entry on a new line. You can make a single entry span multiple lines by ending each line with a backslash (\).
Terminate each entry name and each symbol/value pair with a colon (:). For readability, you can leave blank spaces between symbol/value pairs.
Enter the entry name in the first field in the configuration file entry.
Make sure that the host hardware type ( ht ) precedes the host hardware address ( ha ).

You can delete symbol values associated with a particular client by entering an at sign (@) immediately following the symbol. For example, gw@.

Both BOOTP and DHCP interpret lines that begin with any of the following as comments:

The pound sign (#)
One or more blank spaces followed by #
A blank line

7.7.2.3 DHCPCAP Configuration Examples

Example 7-9 shows a sample single-host DHCPCAP. file entry. This entry, mypc , describes the configuration for a BOOTP client. It describes the client itself, its IP address, the default gateway, and the domain name.

Example 7-9 Sample Single Host DHCPCAP Entry

mypc:\ :ht=ether:\ :ha=112233445566:\ :ip=143.32.3.10:\ :gw=143.32.3.1:\ :dn=acme.com:

Example 7-10 shows a subnet DHCPCAP. file entry. This entry, subnet5, describes the parameters for all the clients on a particular subnet, 143.32.5.0. It describes the default gateway, subnet mask, domain name, DNS server address, and lease time of the address.

Example 7-10 Sample Subnet DHCPCAP Entry

subnet5:\ :nw=143.32.5.0:\ :gw=143.32.5.1:\ :sm=255.255.255.0:\ :dn=engr.acme.com:\ :ds=143.32.5.10:\ :lt=3600:

7.7.2.4 Symbol Value Formats

The symbol values require specific formats. Use only the following formats:

ASCII string
Enclose this string in quotation marks ("string") if it contains any of the special characters: colon (:), pound sign (#), tab, or space.
ASCII integer list
A list of integers separated by white space consisting of ASCII-format characters that represent an unsigned hexadecimal, octal, or decimal integer.
- Begin the string with 0X or 0x if this is a hexadecimal integer.
- Begin the string with zero (0) if this is an octal integer.
IP address list
ASCII string representing an IP address in dotted-decimal notation (for example, 128.119.95.2).
An IP address list is a string of one or more IP addresses, with the addresses separated by spaces. For example:
tg=128.119.91.2 128.119.95.42 128.119.95.8
You can also use IP address lists to define DHCP address ranges, routing policy filters, and static routes.
ASCII-format representation of a hexadecimal integer that DHCP and BOOTP interpret as a hardware address.
The ASCII string must have the correct number of digits for the specified hardware type; for example, twelve digits for a 48-bit Ethernet address. To improve readability, you can:
- Separate the two-digit sequences (bytes) with hyphens (-).
- Separate the two-digit sequences (bytes) with periods (.).
- Add a 0x prefix to each byte (or only some bytes) of the address.
- Add a hyphen between some bytes and 0x prefixes before others.
- Add a period between some bytes and 0x prefixes before others.
Examples of valid hexadecimal ASCII strings are:
ha=7F-FF-81-00-0A-47 ha=0X7F0XFF0X81000A47 ha=0X7F-FF0XF8-1000A47
Booleans and switches
A boolean symbol performs a function just by its presence. A switch is the value 0 or 1, and it associates one of two functions to those values (usually, disable and enable, respectively).
:ms=1:\ #This is an example of switch type field :hn:\ #This is an example of a boolean type field

7.7.2.5 DHCP Configuration Symbols

Table 7-8 describes each DHCP configuration file symbol and indicates whether you use the symbol in DHCP configuration only or in BOOTP and DHCP configuration.

Table 7-8 BOOTP/DHCP Configuration File Symbols
Symbol Function Value Format Description

as Maximum datagram reassembly size ASCII integer Specifies the maximum size datagram that the client should be prepared to reassemble. The minimum value is 576.

at ARP cache timeout ASCII integer Specifies the timeout (in seconds) for ARP cache entries.

ba Broadcast address IP address Specifies the broadcast address in use on the client's subnet.

bf Boot file ASCII string Specifies the fully qualified path name of the client's default boot image.

br IP forwarding Boolean Specifies whether the client should configure its IP layer for packet forwarding. A value of 0 means disable IP forwarding, and a value of 1 means enable IP forwarding.

bs Boot file size ASCII integer or auto Specifies the length in 512-octet blocks of the default boot image for the client.

bw NetBIOS name servers IP address list Specifies a list of RFC 1001/1002 NBNS name servers listed in order of preference.

bx NetBIOS over TCP/IP datagram distribution server IP address list Specifies a list of RFC 1001/1002 NBDD servers listed in order of preference.

by NetBIOS over TCP/IP node type ASCII integer Specifies whether clients can be configured as described in RFC 1001 and 1002. The NetBIOS node type option allows NetBIOS over TCP/IP configurable clients to be configured as described in RFC 1001 and 1002. Specify the value as a single octet (from 0 to 255) that identifies the client type.

bz NetBIOS over TCP/IP scope ASCII string Specifies the NetBIOS over TCP/IP scope text parameter for the client as specified in RFC 1001/1002. There can be character-set restrictions.

ck Client identifier Opaque

cs Cookie server address list IP address list Specifies a list of RFC 865 cookie servers available to the client. Enter servers in order of preference.

ct Vendor class String Specifies the vendor type and configuration of a DHCP client. The information is a string of n octets, interpreted by servers. Vendors may choose to define specific vendor class identifiers to convey particular configuration or other identification information about a client. For example, the identifier may encode the client's hardware configuration. Servers not equipped to interpret the class-specific information sent by a client must ignore it (although it may be reported).

da STDA servers IP address list Specifies a list of StreetTalk Directory Assistance (STDA) servers available to the client. Servers should be listed in order of preference.

df Merit dump file ASCII string Specifies the path name of a file to which the client's core image should be dumped in the event the client fails. The path is formatted as a character string consisting of characters from the NVT ASCII character set.

dn DNS domain name ASCII String Specifies the domain name that the client should use when resolving host names via the Domain Name System.

ds DNS servers IP address list Specifies a list of Domain Name System (RFC 1035) name servers available to the client. Enter servers in order of preference.

ec Ethernet encapsulation 0 or 1 Specifies whether the client should use Ethernet Version 2 (RFC 894) or IEEE 802.3 (RFC 1042) encapsulation if the interface is an Ethernet. The switch values are:

0 - Use RFC 894 encapsulation
1 - Use RFC 1042 encapsulation

ef Extensions path ASCII string Specifies a file, retrievable through TFTP, that contains information that can be interpreted in the same way as the 64-octet vendor-extension field in the BOOTP response. The length of the file is unconstrained.

fi Finger servers IP address list Specifies a list of finger servers available to the client. Servers should be listed in order of preference.

fn Forward nonlocal datagarams 0 or 1 Specifies whether the client should configure its IP layer to allow forwarding of datagrams with nonlocal source routes.

gw Gateway address list IP address list Specifies a list of the IP addresses of gateways for the specified subnet. This list consists of the default routes.

ha Client's hardware address ASCII string Specifies whether host names can be assigned by the hardware address. If so specified, the client host, provided it remains in the same domain, retains the same name, even if its IP address changes.

hn Host name Boolean Specifies that the DHCP server should write the client's host name to the vend field of the DHCP reply packet and send the packet to the client. Can appear only in the format hn: or hn@:.

ho Host name ASCII string Specifies the name of the client. The name may or may not be qualified with the local domain name.

ht Client's hardware type ASCII string or ASCII integer Specifies the hardware type code as assigned in the ARP section of RFC 1340, Assigned Numbers.

hr Forwarding enable/disable 0 or 1 Specifies whether the client should configure its IP layer for packet forwarding. The values are:

0 - Disable
1 - Enable

im Impress server address list IP address list Specifies a list of Imagen Impress servers available to the client. Enter servers in order of preference.

ip Client IP address IP address Specifies the IP address of the BOOTP client or a single IP address to assign the DHCP client.

it IP time to live ASCII string Specifies the default time to live that the client should use on outgoing datagrams.

ki TCP keepalive interval ASCII integer Specifies the interval (in seconds) that the client TCP should wait before sending a keepalive message on a TCP.

ko TCP keepalive garbage 0 or 1 Specifies whether the client should send TCP keepalive messages with an octet of garbage for compatibility with older implementations.

lg Log server IP address list Specifies a list of MIT-LCS UDP log servers available to the client. Enter servers in order of preference.

lp LPR server address list IP address list Specifies a list of RFC 1179 line printer servers available to the client. Enter servers in order of preference.

lt Lease time ASCII integer Specifies in a client request, that a client is allowed to request a lease time for the IP address. In a server reply, specifies the lease time the server is willing to offer. Enter the time in seconds.

md Perform mask discovery 0 or 1 Specifies whether the client should perform subnet mask discovery using ICMP.

mm Maximum DHCP message size Integer Specifies the maximum length DHCP message that it is willing to accept. The length is specified as an unsigned 16-bit integer. A client may use the maximum DHCP message size option in DHCPDISCOVER or DHCPREQUEST messages, but should not use the option in DHCPDECLINE messages.

ms Mask supplier 0 or 1 Specifies whether the client should respond to subnet mask requests using ICMP.

nn NNTP IP address list Specifies the NNTP server.

no NetWare options Opaque

ns IEN-116 name server address list IP address list Specifies a list of IEN 116 name servers available to the client. Enter servers in order of preference.

nt NTP servers IP address list Specifies a list of NNTP (Network Time Protocol) servers.

ov Overload file/sname Integer Specifies 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.

pf Policy filter IP address list Specifies policy filters for nonlocal 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.

pl Path MTU plateau table ASCII integer list Specifies a table of MTU sizes to use when performing Path MTU Discovery as defined in RFC 1191. The minimum value is 68.

pt Path MTU aging timeout Integer Specifies the timeout (in seconds) to use when aging Path MTU values are discovered by the mechanism defined in RFC 1191 [12]. The timeout is specified as a 32-bit unsigned integer.

rd Perform router discovery 0 or 1 Specifies whether the client should solicit routers using the Router Discovery mechanism defined in RFC 1256.

rl Resource location protocol server address list IP address list Specifies a list of RFC 887 Resource Location servers available to the client. Servers should be listed in order of preference.

rp Root path ASCII string Specifies the path name that contains the client's root directory or partition. The path is formatted as a character string consisting of characters from the NVT ASCII character set.

rs Router solicitation address IP address Specifies the address to which the client should transmit router solicitation requests.

sa Boot server address IP address Specifies the IP address of the TFTP server the client uses.

sl All subnets are local 0 or 1 Specifies whether 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.

sn Boot file server name ASCII string Specifies the host name of the bootfile server.

sm Subnet mask IP address Specifies the client's subnet mask as per RFC 950. A subnet mask allows the addition of subnetwork numbers to an address and provides more complex address assignments. If both the subnet mask and the router option are specified in a DHCP reply, the subnet mask option must be first.

sp SMTP servers IP address list Specifies a list of SMTP (Simple Mail Transport Protocol) servers available to the client. Servers should be listed in order of preference.

sr Static route IP address list Specifies a list of static routes that the client should install in its routing cache. If multiple routes to the same destination are specified, they are listed 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.

st StreetTalk servers IP address list Specifies a list of StreetTalk servers available to the client. Servers should be listed in order of preference.

sw Swap server IP address Specifies the IP address of the client's swap server.

sv Server IP IP address Specifies the server ID in a DHCOFFER and DHCPREQUEST message and optionally in a 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.

t1 DHCP renewal time Integer Specifies the time interval (in seconds) from address assignment until the client transitions to the RENEWING state. The value is specified as a 32-bit unsigned integer.

t2 DHCP rebinding time Integer Specifies the time interval (in seconds) from address assignment until the client transitions to the REBINDING state. The value is specified as a 32-bit unsigned integer.

to Time offset ASCII integer or auto Specifies (in seconds) the offset of the client's subnet in seconds from Coordinated Universal Time (UTC). 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.

tr Trailer encapsulation 0 or 1 Specifies whether the client should negotiate the use of trailers (RFC 893) when using the ARP protocol.

tu Interface MTU ASCII integer Specifies the MTU to use on this interface.

ts Time server address list IP address list Specifies a list of RFC 868 time servers available to the client. Servers should be listed in order of preference.

tt TCP default TTL ASCII integer Specifies the default time to live that the client should use when sending TCP segments.

uc User class ASCII string Specifies the type or category of user or application the client represents. This option is used by a DHCP client to optionally identify the type or category of user or application it represents. The format of this option is an NVT ASCII text object of varying length which represents a user class of which the client host is a member.
DHCP administrators may define specific user class identifiers to convey information about a host's software configuration or about its user's preferences. For example, an identifier may specify that a particular DHCP client is a member of the class "accounting auditors", which have special service needs such as a particular database server.

vm Vendor's magic cookie selector ASCII string Specifies a vendor magic cookie for the client.

xd X Window System display manager IP address list Specifies a list of IP addresses of systems that are running the X Window System display manager that are available to the client. Enter addresses in order of preference.

xf X Window System font server IP address list Specifies a list of X Window System font servers available to the client. Enter addresses in order of preference.

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

ys NIS servers IP address list Specifies a list of IP addresses indicating NIS servers available to the client. Servers should be listed in order of preference.

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

zs NIS+ server IP address list Specifies a list of IP addresses indicating NIS+ servers available to the client. Servers should be listed in order of preference.

**Table 7-8 BOOTP/DHCP Configuration File Symbols**
Symbol	Function	Value Format	Description
as	Maximum datagram reassembly size	ASCII integer	Specifies the maximum size datagram that the client should be prepared to reassemble. The minimum value is 576.
at	ARP cache timeout	ASCII integer	Specifies the timeout (in seconds) for ARP cache entries.
ba	Broadcast address	IP address	Specifies the broadcast address in use on the client's subnet.
bf	Boot file	ASCII string	Specifies the fully qualified path name of the client's default boot image.
br	IP forwarding	Boolean	Specifies whether the client should configure its IP layer for packet forwarding. A value of 0 means disable IP forwarding, and a value of 1 means enable IP forwarding.
bs	Boot file size	ASCII integer or auto	Specifies the length in 512-octet blocks of the default boot image for the client.
bw	NetBIOS name servers	IP address list	Specifies a list of RFC 1001/1002 NBNS name servers listed in order of preference.
bx	NetBIOS over TCP/IP datagram distribution server	IP address list	Specifies a list of RFC 1001/1002 NBDD servers listed in order of preference.
by	NetBIOS over TCP/IP node type	ASCII integer	Specifies whether clients can be configured as described in RFC 1001 and 1002. The NetBIOS node type option allows NetBIOS over TCP/IP configurable clients to be configured as described in RFC 1001 and 1002. Specify the value as a single octet (from 0 to 255) that identifies the client type.
bz	NetBIOS over TCP/IP scope	ASCII string	Specifies the NetBIOS over TCP/IP scope text parameter for the client as specified in RFC 1001/1002. There can be character-set restrictions.
ck	Client identifier	Opaque
cs	Cookie server address list	IP address list	Specifies a list of RFC 865 cookie servers available to the client. Enter servers in order of preference.
ct	Vendor class	String	Specifies the vendor type and configuration of a DHCP client. The information is a string of n octets, interpreted by servers. Vendors may choose to define specific vendor class identifiers to convey particular configuration or other identification information about a client. For example, the identifier may encode the client's hardware configuration. Servers not equipped to interpret the class-specific information sent by a client must ignore it (although it may be reported).
da	STDA servers	IP address list	Specifies a list of StreetTalk Directory Assistance (STDA) servers available to the client. Servers should be listed in order of preference.
df	Merit dump file	ASCII string	Specifies the path name of a file to which the client's core image should be dumped in the event the client fails. The path is formatted as a character string consisting of characters from the NVT ASCII character set.
dn	DNS domain name	ASCII String	Specifies the domain name that the client should use when resolving host names via the Domain Name System.
ds	DNS servers	IP address list	Specifies a list of Domain Name System (RFC 1035) name servers available to the client. Enter servers in order of preference.
ec	Ethernet encapsulation	0 or 1	Specifies whether the client should use Ethernet Version 2 (RFC 894) or IEEE 802.3 (RFC 1042) encapsulation if the interface is an Ethernet. The switch values are: 0 - Use RFC 894 encapsulation 1 - Use RFC 1042 encapsulation
ef	Extensions path	ASCII string	Specifies a file, retrievable through TFTP, that contains information that can be interpreted in the same way as the 64-octet vendor-extension field in the BOOTP response. The length of the file is unconstrained.
fi	Finger servers	IP address list	Specifies a list of finger servers available to the client. Servers should be listed in order of preference.
fn	Forward nonlocal datagarams	0 or 1	Specifies whether the client should configure its IP layer to allow forwarding of datagrams with nonlocal source routes.
gw	Gateway address list	IP address list	Specifies a list of the IP addresses of gateways for the specified subnet. This list consists of the default routes.
ha	Client's hardware address	ASCII string	Specifies whether host names can be assigned by the hardware address. If so specified, the client host, provided it remains in the same domain, retains the same name, even if its IP address changes.
hn	Host name	Boolean	Specifies that the DHCP server should write the client's host name to the vend field of the DHCP reply packet and send the packet to the client. Can appear only in the format hn: or hn@:.
ho	Host name	ASCII string	Specifies the name of the client. The name may or may not be qualified with the local domain name.
ht	Client's hardware type	ASCII string or ASCII integer	Specifies the hardware type code as assigned in the ARP section of RFC 1340, Assigned Numbers.
hr	Forwarding enable/disable	0 or 1	Specifies whether the client should configure its IP layer for packet forwarding. The values are: 0 - Disable 1 - Enable
im	Impress server address list	IP address list	Specifies a list of Imagen Impress servers available to the client. Enter servers in order of preference.
ip	Client IP address	IP address	Specifies the IP address of the BOOTP client or a single IP address to assign the DHCP client.
it	IP time to live	ASCII string	Specifies the default time to live that the client should use on outgoing datagrams.
ki	TCP keepalive interval	ASCII integer	Specifies the interval (in seconds) that the client TCP should wait before sending a keepalive message on a TCP.
ko	TCP keepalive garbage	0 or 1	Specifies whether the client should send TCP keepalive messages with an octet of garbage for compatibility with older implementations.
lg	Log server	IP address list	Specifies a list of MIT-LCS UDP log servers available to the client. Enter servers in order of preference.
lp	LPR server address list	IP address list	Specifies a list of RFC 1179 line printer servers available to the client. Enter servers in order of preference.
lt	Lease time	ASCII integer	Specifies in a client request, that a client is allowed to request a lease time for the IP address. In a server reply, specifies the lease time the server is willing to offer. Enter the time in seconds.
md	Perform mask discovery	0 or 1	Specifies whether the client should perform subnet mask discovery using ICMP.
mm	Maximum DHCP message size	Integer	Specifies the maximum length DHCP message that it is willing to accept. The length is specified as an unsigned 16-bit integer. A client may use the maximum DHCP message size option in DHCPDISCOVER or DHCPREQUEST messages, but should not use the option in DHCPDECLINE messages.
ms	Mask supplier	0 or 1	Specifies whether the client should respond to subnet mask requests using ICMP.
nn	NNTP	IP address list	Specifies the NNTP server.
no	NetWare options	Opaque
ns	IEN-116 name server address list	IP address list	Specifies a list of IEN 116 name servers available to the client. Enter servers in order of preference.
nt	NTP servers	IP address list	Specifies a list of NNTP (Network Time Protocol) servers.
ov	Overload file/sname	Integer	Specifies 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.
pf	Policy filter	IP address list	Specifies policy filters for nonlocal 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.
pl	Path MTU plateau table	ASCII integer list	Specifies a table of MTU sizes to use when performing Path MTU Discovery as defined in RFC 1191. The minimum value is 68.
pt	Path MTU aging timeout	Integer	Specifies the timeout (in seconds) to use when aging Path MTU values are discovered by the mechanism defined in RFC 1191 [12]. The timeout is specified as a 32-bit unsigned integer.
rd	Perform router discovery	0 or 1	Specifies whether the client should solicit routers using the Router Discovery mechanism defined in RFC 1256.
rl	Resource location protocol server address list	IP address list	Specifies a list of RFC 887 Resource Location servers available to the client. Servers should be listed in order of preference.
rp	Root path	ASCII string	Specifies the path name that contains the client's root directory or partition. The path is formatted as a character string consisting of characters from the NVT ASCII character set.
rs	Router solicitation address	IP address	Specifies the address to which the client should transmit router solicitation requests.
sa	Boot server address	IP address	Specifies the IP address of the TFTP server the client uses.
sl	All subnets are local	0 or 1	Specifies whether 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.
sn	Boot file server name	ASCII string	Specifies the host name of the bootfile server.
sm	Subnet mask	IP address	Specifies the client's subnet mask as per RFC 950. A subnet mask allows the addition of subnetwork numbers to an address and provides more complex address assignments. If both the subnet mask and the router option are specified in a DHCP reply, the subnet mask option must be first.
sp	SMTP servers	IP address list	Specifies a list of SMTP (Simple Mail Transport Protocol) servers available to the client. Servers should be listed in order of preference.
sr	Static route	IP address list	Specifies a list of static routes that the client should install in its routing cache. If multiple routes to the same destination are specified, they are listed 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.
st	StreetTalk servers	IP address list	Specifies a list of StreetTalk servers available to the client. Servers should be listed in order of preference.
sw	Swap server	IP address	Specifies the IP address of the client's swap server.
sv	Server IP	IP address	Specifies the server ID in a DHCOFFER and DHCPREQUEST message and optionally in a 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.
t1	DHCP renewal time	Integer	Specifies the time interval (in seconds) from address assignment until the client transitions to the RENEWING state. The value is specified as a 32-bit unsigned integer.
t2	DHCP rebinding time	Integer	Specifies the time interval (in seconds) from address assignment until the client transitions to the REBINDING state. The value is specified as a 32-bit unsigned integer.
to	Time offset	ASCII integer or auto	Specifies (in seconds) the offset of the client's subnet in seconds from Coordinated Universal Time (UTC). 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.
tr	Trailer encapsulation	0 or 1	Specifies whether the client should negotiate the use of trailers (RFC 893) when using the ARP protocol.
tu	Interface MTU	ASCII integer	Specifies the MTU to use on this interface.
ts	Time server address list	IP address list	Specifies a list of RFC 868 time servers available to the client. Servers should be listed in order of preference.
tt	TCP default TTL	ASCII integer	Specifies the default time to live that the client should use when sending TCP segments.
uc	User class	ASCII string	Specifies the type or category of user or application the client represents. This option is used by a DHCP client to optionally identify the type or category of user or application it represents. The format of this option is an NVT ASCII text object of varying length which represents a user class of which the client host is a member. DHCP administrators may define specific user class identifiers to convey information about a host's software configuration or about its user's preferences. For example, an identifier may specify that a particular DHCP client is a member of the class "accounting auditors", which have special service needs such as a particular database server.
vm	Vendor's magic cookie selector	ASCII string	Specifies a vendor magic cookie for the client.
xd	X Window System display manager	IP address list	Specifies a list of IP addresses of systems that are running the X Window System display manager that are available to the client. Enter addresses in order of preference.
xf	X Window System font server	IP address list	Specifies a list of X Window System font servers available to the client. Enter addresses in order of preference.
yd	NIS domain name	ASCII string	Specifies the name of the client's NIS domain. The domain is formatted as a character string consisting of characters from the NVT ASCII character set.
ys	NIS servers	IP address list	Specifies a list of IP addresses indicating NIS servers available to the client. Servers should be listed in order of preference.
zd	NIS+ domain name	ASCII string	Specifies the name of the client's NIS+ domain. The domain is formatted as a character string consisting of characters from the NVT ASCII character set.
zs	NIS+ server	IP address list	Specifies a list of IP addresses indicating NIS+ servers available to the client. Servers should be listed in order of preference.

Table 7-9 Vendor Specific Options
Symbol Function Value Format Description

For Join DHCP clients:

cb Client binary ASCII string Refer to the JOIN documentation at the following URL: http://www.join.com/doc/

mf NFS mounted file systems ASCII string list Refer to the JOIN documentation at the following URL: http://www.join.com/doc/

pr Printers ASCII string list Refer to the JOIN documentation at the following URL: http://www.join.com/doc/

ps SVR4 printer setup ASCII string list Refer to the JOIN documentation at the following URL: http://www.join.com/doc/

ss Name service switch ASCII string Refer to the JOIN documentation at the following URL: http://www.join.com/doc/

For OpenVMS DHCP clients:

sd SMTP substitute domain ASCII string

sg SMTP gateway ASCII string

sn SMTP substitute domain not local Boolean

sz SMTP zone ASCII string

For SUN DHCP clients:

aa Sun Vendor Option #2 IP address list Refer to the JOIN documentation at the following URL:
http://www.join.com/doc/

**Table 7-9 Vendor Specific Options**
Symbol	Function	Value Format	Description
For Join DHCP clients:
cb	Client binary	ASCII string	Refer to the JOIN documentation at the following URL: `http://www.join.com/doc/`
mf	NFS mounted file systems	ASCII string list	Refer to the JOIN documentation at the following URL: `http://www.join.com/doc/`
pr	Printers	ASCII string list	Refer to the JOIN documentation at the following URL: `http://www.join.com/doc/`
ps	SVR4 printer setup	ASCII string list	Refer to the JOIN documentation at the following URL: `http://www.join.com/doc/`
ss	Name service switch	ASCII string	Refer to the JOIN documentation at the following URL: `http://www.join.com/doc/`
For OpenVMS DHCP clients:
sd	SMTP substitute domain	ASCII string
sg	SMTP gateway	ASCII string
sn	SMTP substitute domain not local	Boolean
sz	SMTP zone	ASCII string
For SUN DHCP clients:
aa	Sun Vendor Option #2	IP address list	Refer to the JOIN documentation at the following URL: http://www.join.com/doc/

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