+++ /dev/null
-
-
-
-dhcpd(8) dhcpd(8)
-
-
-N\bNA\bAM\bME\bE
- dhcpd - Dynamic Host Configuration Protocol Server
-
-S\bSY\bYN\bNO\bOP\bPS\bSI\bIS\bS
- d\bdh\bhc\bcp\bpd\bd [ -\b-p\bp _\bp_\bo_\br_\bt ] [ -\b-f\bf ] [ -\b-d\bd ] [ -\b-c\bcf\bf _\bc_\bo_\bn_\bf_\bi_\bg_\b-_\bf_\bi_\bl_\be ] [ -\b-l\blf\bf
- _\bl_\be_\ba_\bs_\be_\b-_\bf_\bi_\bl_\be ] [ _\bi_\bf_\b0 [ _\b._\b._\b._\bi_\bf_\bN ] ]
-
-D\bDE\bES\bSC\bCR\bRI\bIP\bPT\bTI\bIO\bON\bN
- The Internet Software Consortium DHCP Server, dhcpd,
- implements the Dynamic Host Configuration Protocol (DHCP)
- and the Internet Bootstrap Protocol (BOOTP). DHCP allows
- hosts on a TCP/IP network to request and be assigned IP
- addresses, and also to discover information about the net-
- work to which they are attached. BOOTP provides similar
- functionality, with certain restrictions.
-
-O\bOP\bPE\bER\bRA\bAT\bTI\bIO\bON\bN
- The DHCP protocol allows a host which is unknown to the
- network administrator to be automatically assigned a new
- IP address out of a pool of IP addresses for its network.
- In order for this to work, the network administrator allo-
- cates address pools in each subnet and enters them into
- the dhcpd.conf(5) file.
-
- On startup, dhcpd reads the _\bd_\bh_\bc_\bp_\bd_\b._\bc_\bo_\bn_\bf file and stores a
- list of available addresses on each subnet in memory.
- When a client requests an address using the DHCP protocol,
- dhcpd allocates an address for it. Each client is
- assigned a lease, which expires after an amount of time
- chosen by the administrator (by default, one day). Before
- leases expire, the clients to which leases are assigned
- are expected to renew them in order to continue to use the
- addresses. Once a lease has expired, the client to which
- that lease was assigned is no longer permitted to use the
- leased IP address.
-
- In order to keep track of leases across system reboots and
- server restarts, dhcpd keeps a list of leases it has
- assigned in the dhcpd.leases(5) file. Before dhcpd
- grants a lease to a host, it records the lease in this
- file and makes sure that the contents of the file are
- flushed to disk. This ensures that even in the event of
- a system crash, dhcpd will not forget about a lease that
- it has assigned. On startup, after reading the
- dhcpd.conf file, dhcpd reads the dhcpd.leases file to
- refresh its memory about what leases have been assigned.
-
- New leases are appended to the end of the dhcpd.leases
- file. In order to prevent the file from becoming arbi-
- trarily large, from time to time dhcpd creates a new
- dhcpd.leases file from its in-core lease database. Once
- this file has been written to disk, the old file is
- renamed _\bd_\bh_\bc_\bp_\bd_\b._\bl_\be_\ba_\bs_\be_\bs_\b~, and the new file is renamed
- dhcpd.leases. If the system crashes in the middle of
-
-
-
- 1
-
-
-
-
-
-dhcpd(8) dhcpd(8)
-
-
- this process, whichever dhcpd.leases file remains will
- contain all the lease information, so there is no need for
- a special crash recovery process.
-
- BOOTP support is also provided by this server. Unlike
- DHCP, the BOOTP protocol does not provide a protocol for
- recovering dynamically-assigned addresses once they are no
- longer needed. It is still possible to dynamically
- assign addresses to BOOTP clients, but some administrative
- process for reclaiming addresses is required. By
- default, leases are granted to BOOTP clients in perpetu-
- ity, although the network administrator may set an earlier
- cutoff date or a shorter lease length for BOOTP leases if
- that makes sense.
-
- BOOTP clients may also be served in the old standard way,
- which is to simply provide a declaration in the dhcpd.conf
- file for each BOOTP client, permanently assigning an
- address to each client.
-
- Whenever changes are made to the dhcpd.conf file, dhcpd
- must be restarted. To restart dhcpd, send a SIGTERM
- (signal 15) to the process ID contained in
- _\b/_\bv_\ba_\br_\b/_\br_\bu_\bn_\b/_\bd_\bh_\bc_\bp_\bd_\b._\bp_\bi_\bd, and then re-invoke dhcpd. Because the
- DHCP server database is not as lightweight as a BOOTP
- database, dhcpd does not automatically restart itself when
- it sees a change to the dhcpd.conf file.
-
-C\bCO\bOM\bMM\bMA\bAN\bND\bD L\bLI\bIN\bNE\bE
- The names of the network interfaces on which dhcpd should
- listen for broadcasts may be specified on the command
- line. This should be done on systems where dhcpd is
- unable to identify non-broadcast interfaces, but should
- not be required on other systems. If no interface names
- are specified on the command line dhcpd will identify all
- network interfaces which are up, elimininating non-broad-
- cast interfaces if possible, and listen for DHCP broad-
- casts on each interface.
-
- If dhcpd should listen on a port other than the standard
- (port 67), the -\b-p\bp flag may used. It should be followed by
- the udp port number on which dhcpd should listen. This is
- mostly useful for debugging purposes.
-
- To run dhcpd as a foreground process, rather than allowing
- it to run as a daemon in the background, the -\b-f\bf flag
- should be specified. This is useful when running dhcpd
- under a debugger, or when running it out of inittab on
- System V systems.
-
- To have dhcpd log to the standard error descriptor, spec-
- ify the -\b-d\bd flag. This can be useful for debugging, and
- also at sites where a complete log of all dhcp activity
- must be kept but syslogd is not reliable or otherwise
-
-
-
- 2
-
-
-
-
-
-dhcpd(8) dhcpd(8)
-
-
- cannot be used. Normally, dhcpd will log all output
- using the syslog(3) function with the log facility set to
- LOG_DAEMON.
-
- Dhcpd can be made to use an alternate configuration file
- with the -\b-c\bcf\bf flag, or an alternate lease file with the -\b-l\blf\bf
- flag. Because of the importance of using the same lease
- database at all times when running dhcpd in production,
- these options should be used o\bon\bnl\bly\by for testing lease files
- or database files in a non-production environment.
-
-C\bCO\bON\bNF\bFI\bIG\bGU\bUR\bRA\bAT\bTI\bIO\bON\bN
- The syntax of the dhcpd.conf(8) file is discussed seper-
- ately. This section should be used as an overview of the
- configuration process, and the dhcpd.conf(8) documentation
- should be consulted for detailed reference information.
-
-
-S\bSu\bub\bbn\bne\bet\bts\bs
- dhcpd needs to know the subnet numbers and netmasks of all
- subnets for which it will be providing service. In addi-
- tion, in order to dynamically allocate addresses, it must
- be assigned one or more ranges of addresses on each subnet
- which it can in turn assign to client hosts as they boot.
- Thus, a very simple configuration providing DHCP support
- might look like this:
-
- subnet 239.252.197.0 netmask 255.255.255.0 {
- range 239.252.197.10 239.252.197.250;
- }
-
- Multiple address ranges may be specified like this:
-
- subnet 239.252.197.0 netmask 255.255.255.0 {
- range 239.252.197.10 239.252.197.107;
- range 239.252.197.113 239.252.197.250;
- }
-
- If a subnet will only be provided with BOOTP service and
- no dynamic address assignment, the range clause can be
- left out entirely, but the subnet statement must appear.
-
-
-L\bLe\bea\bas\bse\be L\bLe\ben\bng\bgt\bth\bhs\bs
- DHCP leases can be assigned almost any length from zero
- seconds to infinity. What lease length makes sense for
- any given subnet, or for any given installation, will vary
- depending on the kinds of hosts being served.
-
- For example, in an office environment where systems are
- added from time to time and removed from time to time, but
- move relatively infrequently, it might make sense to allow
- lease times of a month of more. In a final test environ-
- ment on a manufacturing floor, it may make more sense to
-
-
-
- 3
-
-
-
-
-
-dhcpd(8) dhcpd(8)
-
-
- assign a maximum lease length of 30 minutes - enough time
- to go through a simple test procedure on a network appli-
- ance before packaging it up for delivery.
-
- It is possible to specify two lease lengths: the default
- length that will be assigned if a client doesn't ask for
- any particular lease length, and a maximum lease length.
- These are specified as clauses to the subnet command:
-
- subnet 239.252.197.0 netmask 255.255.255.0 {
- range 239.252.197.10 239.252.197.107;
- default-lease-time 600;
- max-lease-time 7200;
- |
-
- This particular subnet declaration specifies a default
- lease time of 600 seconds (ten minutes), and a maximum
- lease time of 7200 seconds (two hours). Other common
- values would be 86400 (one day), 604800 (one week) and
- 2592000 (30 days).
-
- Each subnet need not have the same lease--in the case of
- an office environment and a manufacturing environment
- served by the same DHCP server, it might make sense to
- have widely disparate values for default and maximum lease
- times on each subnet.
-
-B\bBO\bOO\bOT\bTP\bP S\bSu\bup\bpp\bpo\bor\brt\bt
- Each BOOTP client must be explicitly declared in the
- dhcpd.conf file. A very basic client declaration will
- specify the client network interface's hardware address
- and the IP address to assign to that client. If the
- client needs to be able to load a boot file from the
- server, that file's name must be specified. A simple
- bootp client declaration might look like this:
-
- host haagen {
- hardware ethernet 08:00:2b:4c:59:23;
- fixed-address 239.252.197.9;
- filename "/tftpboot/haagen.boot";
- }
-
-O\bOp\bpt\bti\bio\bon\bns\bs
- DHCP (and also BOOTP with Vendor Extensions) provide a
- mechanism whereby the server can provide the client with
- information about how to configure its network interface
- (e.g., subnet mask), and also how the client can access
- various network services (e.g., DNS, IP routers, and so
- on).
-
- These options can be specified on a per-subnet basis, and,
- for BOOTP clients, also on a per-client basis. In the
- event that a BOOTP client declaration specifies options
- that are also specified in its subnet declaration, the
-
-
-
- 4
-
-
-
-
-
-dhcpd(8) dhcpd(8)
-
-
- options specified in the client declaration take prece-
- dence. An reasonably complete DHCP configuration might
- look something like this:
-
- subnet 239.252.197.0 netmask 255.255.255.0 {
- range 239.252.197.10 239.252.197.250;
- default-lease-time 600 max-lease-time 7200;
- option subnet-mask 255.255.255.0;
- option broadcast-address 239.252.197.255;
- option routers 239.252.197.1;
- option domain-name-servers 239.252.197.2, 239.252.197.3;
- option domain-name "isc.org";
- }
-
- A bootp host on that subnet that needs to be in a differ-
- ent domain and use a different name server might be
- declared as follows:
-
- host haagen hardware ethernet 08:00:2b:4c:59:23 {
- fixed-address 239.252.197.9;
- filename "/tftpboot/haagen.boot";
- option domain-name-servers 192.5.5.1;
- option domain-name "vix.com";
- }
-
- A more complete description of the dhcpd.conf file syntax
- is provided in dhcpd.conf(5).
-
-F\bFI\bIL\bLE\bES\bS
- /\b/e\bet\btc\bc/\b/d\bdh\bhc\bcp\bpd\bd.\b.c\bco\bon\bnf\bf,\b, /\b/v\bva\bar\br/\b/d\bdb\bb/\b/d\bdh\bhc\bcp\bpd\bd.\b.l\ble\bea\bas\bse\bes\bs,\b, /\b/v\bva\bar\br/\b/r\bru\bun\bn/\b/d\bdh\bhc\bcp\bpd\bd.\b.p\bpi\bid\bd,\b,
- /\b/v\bva\bar\br/\b/d\bdb\bb/\b/d\bdh\bhc\bcp\bpd\bd.\b.l\ble\bea\bas\bse\bes\bs~\b~.\b.
-
-S\bSE\bEE\bE A\bAL\bLS\bSO\bO
- dhclient(8), dhcrelay(8), dhcpd.conf(5), dhcpd.leases(5)
-
-A\bAU\bUT\bTH\bHO\bOR\bR
- d\bdh\bhc\bcp\bpd\bd(\b(8\b8)\b) was written by Ted Lemon <mellon@vix.com> under a
- contract with Vixie Labs. Funding for this project was
- provided by the Internet Software Corporation. Informa-
- tion about the Internet Software Consortium can be found
- at h\bht\btt\btp\bp:\b:/\b//\b/w\bww\bww\bw.\b.i\bis\bsc\bc.\b.o\bor\brg\bg/\b/i\bis\bsc\bc.\b.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
- 5
-
-
projects / thirdparty / dhcp.git / commitdiff
