File Formats dhcpnetwork(4)
NAME
dhcpnetwork - DHCP network tables
DESCRIPTION
The Dynamic Host Configuration Protocol (DHCP) network
tables are used to map the client identifiers of DHCP
clients to IP addresses and the associated configuration
parameters of that address. One DHCP network table exists
for each network served by the DHCP server, and each table
is named using the network's IP address. There is no table
or file with the name dhcpnetwork.
The DHCP network tables can exist as ASCI text files,
binary text files, or NIS] tables, depending on the data
store used. Since the format of the file could change, the
preferred method of managing the DHCP network tables is
through the use of dhcpmgr(1M) or the pntadm(1M) command.
The dhcpnetwork file is used as a policy mechanism for
whether in.dhcpd(1M) leases addresses on a given network. If
the DHCP server is not serving leases or information to a
network, there should be no dhcpnetwork file for that net-
work. To set the DHCP server in informational mode, where it
responds to INFORM messages but does not lease addresses on
that network, create an empty dhcpnetwork file for that
network. For normal operations, where the DHCP server both
leases addresses and responds to INFORM packets, create a
dhcpnetwork file using dhcpmgr(1M) or pntadm(1M) and popu-
late it with leasable addresses.
The format of the records in a DHCP network table depends on
the data store used to maintain the table. However, an entry
in a DHCP network table must contain the following fields:
ClientID The client identifier field, ClientID, is an
ASCI hexadecimal representation of the unique
octet string value of the DHCP Client Identif-
ier Option (code 61) which identifies a DHCP
client. In the absence of the DHCP Client
Identifier Option, the DHCP client is identi-
fied using the form given below for BOTP
clients. The number of characters in this
field must be an even number, with a maximum
length of 64 characters. Valid characters are
0 - 9 and A-F. Entries with values of 00 are
freely available for dynamic allocation to
requesting clients. BOTP clients are identi-
fied by the concatenation of the network's
hardware type (as defined by RFC 1340, titled
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File Formats dhcpnetwork(4)
"Assigned Numbers") and the client's hardware
address. For example, the following BOTP
client has a hardware type of '01' (10mb eth-
ernet) and a hardware address of
8:0:20:11:12:b7, so its client identifier
would be: 010800201112B7
Flags The Flags field is a decimal value, the bit
fields of which can have a combination of the
following values:
1 (PERMANENT) Evaluation of the Lease
field is turned off (lease
is permanent). If this bit
is not set, Evaluation of
the Lease field is enabled
and the Lease is DYNAMIC.
2 (MANUAL) This entry has a manual
client ID binding (cannot be
reclaimed by DHCP server).
Client will not be allocated
another address.
4 (UNUSABLE) When set, this value means
that either through ICMP
echo or client DECLINE, this
address has been found to be
unusable. Can also be used
by the network administrator
to prevent a certain client
from booting, if used in
conjunction with the MANUAL
flag.
8 (BOTP) This entry is reserved for
allocation to BOTP clients
only.
ClientIP The ClientIP field holds the IP address for
this entry. This value must be unique in the
database.
ServerIP This field holds the IP address of the DHCP
server which owns this client IP address, and
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File Formats dhcpnetwork(4)
thus is responsible for initial allocation to
a requesting client. On a multi-homed DHCP
server, this IP address must be the first
address returned by gethostbyname(3NSL).
Lease This numeric field holds the entry's absolute
lease expiration time, and is in seconds since
January 1, 1970. It can be decimal, or hexade-
cimal (if 0x prefixes number). The special
value -1 is used to denote a permanent lease.
Macro This ASCI text field contains the dhcptab
macro name used to look up this entry's confi-
guration parameters in the dhcptab(4) data-
base.
Comment This ASCI text field contains an optional
comment.
TREATISE ON LEASES
This section describes how the DHCP/BOTP server calculates
a client's configuration lease using information contained
in the dhcptab(4) and DHCP network tables. The server con-
sults the LeaseTim and LeaseNeg symbols in the dhcptab, and
the Flags and Lease fields of the chosen IP address record
in the DHCP network table.
The server first examines the Flags field for the identified
DHCP network table record. If the PERMANENT flag is on, then
the client's lease is considered permanent.
If the PERMANENT flag is not on, the server checks if the
client's lease as represented by the Lease field in the net-
work table record has expired. If the lease is not expired,
the server checks if the client has requested a new lease.
If the LeaseNeg symbol has not been included in the client's
dhcptab parameters, then the client's requested lease exten-
sion is ignored, and the lease is set to be the time remain-
ing as shown by the Lease field. If the LeaseNeg symbol has
been included, then the server will extend the client's
lease to the value it requested if this requested lease is
less than or equal to the current time plus the value of the
client's LeaseTim dhcptab parameter.
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File Formats dhcpnetwork(4)
If the client's requested lease is greater than policy
allows (value of LeaseTim), then the client is given a lease
equal to the current time plus the value of LeaseTim. If
LeaseTim is not set, then the default LeaseTim value is one
hour.
For more information about the dhcptab symbols, see
dhcptab(4).
ATRIBUTES
See attributes(5) for a description of the following attri-
bute:
ATRIBUTE TYPE ATRIBUTE VALUE
Availability SUNWdhcsu
Interface Stability Evolving
SEE ALSO
dhcpconfig(1M), dhcpmgr(1M), dhtadm(1M), in.dhcpd(1M),
pntadm(1M), dhcptab(4), dhcp(5), dhcpmodules(5), attri-
butes(5)
Solaris DHCP Service Developer's Guide
System Administration Guide: IP Services
Reynolds, J. and J. Postel, Assigned Numbers, STD 2, RFC
1340, USC/Information Sciences Institute, July 1992.
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