dhcp_network(4) File Formats dhcp_network(4)NAMEdhcp_network - 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 dhcp_network.
The DHCP network tables can exist as ASCII text files or binary text
files, 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 dhcp_network 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
dhcp_network file for that network. To set the DHCP server in informa‐
tional mode, where it responds to INFORM messages but does not lease
addresses on that network, create an empty dhcp_network file for that
network. For normal operations, where the DHCP server both leases
addresses and responds to INFORM packets, create a dhcp_network file
using dhcpmgr(1M) or pntadm(1M) and populate 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:
Client_ID The client identifier field, Client_ID, is an ASCII hexa‐
decimal representation of the unique octet string value
of the DHCP Client Identifier Option (code 61) which
identifies a DHCP client. In the absence of the DHCP
Client Identifier Option, the DHCP client is identified
using the form given below for BOOTP 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 avail‐
able for dynamic allocation to requesting clients. BOOTP
clients are identified by the concatenation of the net‐
work's hardware type (as defined by RFC 1340, titled
"Assigned Numbers") and the client's hardware address.
For example, the following BOOTP client has a hardware
type of '01' (10mb ethernet) 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 bind‐
ing (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 unus‐
able. Can also be used by the network
administrator to prevent a certain
client from booting, if used in con‐
junction with the MANUAL flag.
8 (BOOTP) This entry is reserved for allocation
to BOOTP clients only.
Client_IP The Client_IP field holds the IP address for this entry.
This value must be unique in the database.
Server_IP This field holds the IP address of the DHCP server which
owns this client IP address, and 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 expi‐
ration time, and is in seconds since January 1, 1970. It
can be decimal, or hexadecimal (if 0x prefixes number).
The special value -1 is used to denote a permanent lease.
Macro This ASCII text field contains the dhcptab macro name
used to look up this entry's configuration parameters in
the dhcptab(4) database.
Comment This ASCII text field contains an optional comment.
TREATISE ON LEASES
This section describes how the DHCP/BOOTP server calculates a client's
configuration lease using information contained in the dhcptab(4) and
DHCP network tables. The server consults the LeaseTim and LeaseNeg sym‐
bols 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 net‐
work 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 network 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
extension is ignored, and the lease is set to be the time remaining 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.
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).
ATTRIBUTES
See attributes(5) for a description of the following attribute:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Availability │service/network/dhcp │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Committed │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOdhcpconfig(1M), dhcpmgr(1M), dhtadm(1M), in.dhcpd(1M), pntadm(1M),
dhcptab(4), dhcp(5), dhcp_modules(5), attributes(5)
System Administration Guide: IP Services
Reynolds, J. and J. Postel, Assigned Numbers, STD 2, RFC 1340,
USC/Information Sciences Institute, July 1992.
SunOS 5.11 10 Dec 2009 dhcp_network(4)
