server.pcy(4) Kernel Interfaces Manual server.pcy(4)
NAME
server.pcy - BOOTP and DHCP server policy
DESCRIPTION
The server.pcy file is a text database that governs the behavior of BOOTP and DHCP servers. If the joind daemon is invoked to use text
databases, it reads the server.pcy file on startup. If the JOINCONFIG variable is present in the joind environment, it specifies the
directory for the server.pcy file; otherwise, joind searches the /etc/join directory. Defaults exist for all parameters and switches, so
it is not an error if the file does not exist.
Format
Blank lines are ignored. The number sign character (#) introduces a comment, which continues to the next newline. Each new policy option
must begin and end on a separate line. Policy options are introduced by a keyword, and may be Boolean, or may take a value separated from
the keyword by whitespace (but not a newline). If an option is present more than once, only the value attached to the last occurrence is
used; earlier value(s) are ignored.
Keywords and Values
This Boolean tells the server that if a DHCP client needs a boot file, send the name of that file in the BOOTP file field and not as a DHCP
option (option 67). BOOTP clients always receive a boot file name in the file field. This is disabled by default. This Boolean tells the
server to ignore the value of the broadcast bit and always broadcast a reply, even when the client can receive a pseudo unicast reply.
This was needed by some Cabletron smart bridges. This is disabled by default. This Boolean is for clients that do not use DHCP client
identifiers. The parameter tells the server to use the client's hardware address as its identifier, but to ignore the hadware type field.
In the JOIN database, the identifier is stored with a type field of zero (which is also the type for those clients that are using client
idetfifiers). This is disabled by default. For each subnet that the BOOTP and DHCP server administers, two lists are maintained in mem-
ory: a "free" list containing IP addresses available for allocation and a "provisional" list containing addresses that have been tenta-
tively assigned, which are awaiting client approval in the form of a DHCPREQUEST packet.
The value of seconds determines how long an address will remain on the free list before the server determines that the client does
not want the offered address. The free list does not contain every address available to the server; instead it acts as a cache of
addresses which the server can offer without reading the disk.
If a new client makes a DHCPDISCOVER, and no IP address exists for the client in permanent store, the server first goes to the free
list for an unused address. If the free list is exhausted, the server first reclaims any addresses on the provisional list which
have expired. It then extends this list to be free_list_size in length by reading from the disk. This has a benefit in that
addresses are usually offered in numerically increasing order. Making the ttl too short will not give clients an opportunity to con-
firm offered addresses; making it too long will waste memory.
Default: 60 See the explanation under provisional_ttl. If this number is too low, server response time will suffer. If it is too
large it has the undesirable effect of requiring the server to reclaim expired leases before they are actually needed for realloca-
tion to new clients. Although this is not an error, a desirable feature of server operation is that, whenever possible, a client
requesting a new IP address should get back its old address, unless that address has been leased to a new client.
Default: 8 This option and the "assign_name_by_ipaddr" option are mutually exclusive. They govern how the server assigns names to
hosts. This option tells the server to bind a name to the MAC address. That way, if the client moves to a new address, it keeps the
same name. This tells the server that if a lookup to the name service (gethostbyaddr(3)) succeeds, the client should receive the
name that was found at the IP address. This Boolean option is compatible with previous options. It instructs the server that if it
is not able to find a name for the client by application of the two previous policies, it can accept the name the client suggests
for itself providing that this is not in contradiction with values currently in the name service. If a contradiction exists, or
this policy is not enabled, joind consults its namepool or prefix. (See namepool(4)). This Boolean tells joind to support BOOTP
clients. When replying to BOOTP clients, the server does not use the DHCP extensions to the BOOTP protocol. This is enabled by
default. This Boolean is only valid if the support_bootp option is enabled. When on support_bootp permits the server to perma-
nently assign an IP address from its free pool to a BOOTP client in the event that no permanent binding exists in bootptab. Nor-
mally the BOOTP and DHCP server can only service BOOTP clients for which such a binding pre-exists. Before the server offers an IP
address to a client it may first check that the address is not in use by sending an ICMP echo request. If an echo is received, it
means that the address is in use, and the server selects another. This parameter specifies the time (in milliseconds) that the
server waits for the echo. If this value is zero or negative, the server does not perform this check. Disabling this check may be
necessary in certain environments to decrease server response time to an acceptable level; this release of joind is not multi-
threaded, so the server idles while awaiting the response.
RELATED INFORMATION
Files: namepool(4)
Specifications: RFC 1541, RFC 1542 delim off
server.pcy(4)