dhcp_network(4)

NAME

     dhcp_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,
     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 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 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  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 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:

     Client_ID
           The client identifier field, Client_ID,  is  an  ASCII
           hexadecimal  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 charac-
           ters. Valid characters are 0 - 9 and A-F. Entries with
           values  of 00 are freely available for dynamic alloca-
           tion to requesting clients. BOOTP clients are  identi-
           fied  by  the  concatenation of the network's hardware
           type  (as  defined  by  RFC  1340,  titled   "Assigned
           Numbers") and the client's hardware address. For exam-
           ple, 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 binding  (can-
                 not  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 (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 respon-
           sible 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 hexadecimal  (if  0x  pre-
           fixes  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  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.

     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  attri-
     bute:

     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | Availability                | SUNWdhcsu                   |
    |_____________________________|_____________________________|
    | Interface Stability         | Evolving                    |
    |_____________________________|_____________________________|

dhcp_network(4)

NAME

DESCRIPTION

ATTRIBUTES

SEE ALSO