OpenBSD manual page server

NAME

dhcpd.leases — DHCP server lease database

DESCRIPTION

The Internet Software Consortium DHCP Server keeps a persistent database of leases that it has assigned. This database is a free-form ASCII file containing a series of lease declarations. Every time a lease is acquired, renewed or released, its new value is recorded at the end of the lease file. So if more than one declaration appears for a given lease, the last one in the file is the current one.

FORMAT

Lease descriptions are stored in a format that is parsed by the same recursive descent parser used to read the dhcpd.conf(5) and dhclient.conf(5) files. Currently, the only declaration that is used in the dhcpd.leases file is the lease declaration.

Each lease declaration includes the single IP address that has been leased to the client. The statements within the braces define the duration of the lease and to whom it is assigned.

The start and end time of a lease are recorded using the starts and ends statements:

Dates are specified as follows:

The weekday is present to make it easy for a human to tell when a lease expires - it's specified as a number from zero to six, with zero being Sunday. The day of week is ignored on input. The year is specified with the century, so it should generally be four digits except for really long leases. The month is specified as a number starting with 1 for January. The day of the month is likewise specified starting with 1. The hour is a number from 0 to 23, the minute a number from 0 to 59, and the second also a number from 0 to 59.

Lease times are specified in Coordinated Universal Time (UTC), not in the local time zone.

The MAC address of the network interface that was used to acquire the lease is recorded with the hardware statement:

The MAC address is specified as a series of hexadecimal octets, separated by colons.

If the client uses a client identifier to acquire its address, the client identifier is recorded using the uid statement:

The client identifier is recorded as a series of hexadecimal octets, regardless of whether the client specifies an ASCII string or uses the newer hardware type/MAC address format.

If the client sends a hostname using the Client Hostname option, as specified in some versions of the DHCP-DNS Interaction draft, that hostname is recorded using the client-hostname statement.

If the client sends its hostname using the Hostname option, it is recorded using the hostname statement.

The DHCP server may determine that a lease has been misused in some way, either because a client that has been assigned a lease NAKs it, or because the server's own attempt to see if an address is in use prior to reusing it reveals that the address is in fact already in use. In that case, the abandoned statement will be used to indicate that the lease should not be reassigned.

Abandoned leases are reclaimed automatically. When a client asks for a new address, and the server finds that there are no new addresses, it checks to see if there are any abandoned leases, and allocates the least recently abandoned lease. The standard mechanisms for checking for lease address conflicts are still followed, so if the abandoned lease's IP address is still in use, it will be reabandoned.

If a client requests an abandoned address, the server assumes that the reason the address was abandoned was that the lease file was corrupted, and that the client is the machine that responded when the lease was probed, causing it to be abandoned. In that case, the address is immediately assigned to the client.

FILES

/var/db/dhcpd.leases

 

SEE ALSO

dhcp-options(5), dhcpd.conf(5), dhcpd(8)

STANDARDS

R. Droms, Dynamic Host Configuration Protocol, RFC 2131, March 1997.

S. Alexander and R. Droms, DHCP Options and BOOTP Vendor Extensions, RFC 2132, March 1997.

AUTHORS

dhcpd(8) was written by Ted Lemon <mellon@vix.com> under a contract with Vixie Labs.

The current implementation was reworked by Henning Brauer <henning@openbsd.org>.