dhclient.conf分析

    xiaoxiao2022-06-30  73

    NAME      dhclient.conf - DHCP client configuration file DESCRIPTION      The dhclient.conf file contains configuration information for      dhclient(8), the Internet Software Consortium DHCP Client.      The dhclient.conf file is a free-form ASCII text file.  It is parsed by      the recursive-descent parser built into dhclient(8).  The file may      contain extra tabs and newlines for formatting purposes.  Keywords in the      file are case-insensitive.  Comments may be placed anywhere within the      file (except within quotes).  Comments begin with the `#' character and      end at the end of the line.      The dhclient.conf file can be used to configure the behaviour of the      client in a wide variety of ways: protocol timing, information requested      from the server, information required of the server, defaults to use if      the server does not provide certain information, values with which to      override information provided by the server, or values to prepend or      append to information provided by the server.  The configuration file can      also be preinitialized with addresses to use on networks that do not have      DHCP servers. PROTOCOL TIMING      The timing behaviour of the client need not be configured by the user.      If no timing configuration is provided by the user, a fairly reasonable      timing behaviour will be used by default - one which results in fairly      timely updates without placing an inordinate load on the server.      The following statements can be used to adjust the timing behaviour of      the DHCP client if required, however:      timeout time;              The timeout statement determines the amount of time that must              pass between the time that the client begins to try to determine              its address and the time that it decides that it is not going to              be able to contact a server.  By default, this timeout is sixty              seconds.  After the timeout has passed, if there are any static              leases defined in the configuration file, or any leases remaining              in the lease database that have not yet expired, the client will              loop through these leases attempting to validate them, and if it              finds one that appears to be valid, it will use that lease's              address.  If there are no valid static leases or unexpired leases              in the lease database, the client will restart the protocol after              the defined retry interval. 超时语句确定的时间必须在客户端开始,尝试确定其地址,否则超时后就不能链接服务器。默认情况下,这个超时时间为六十秒。超时过后,如果有尚未到期的配置文件中定义任何静态租约,或留在租赁数据库中的任何租约,客户端会遍历这些租赁试图验证他们,如果找到一个似乎是有效的,它将使用租赁的地址。如果在租期数据库中没有有效的静态或租约未到期租约,客户端将重新定义重试间隔后的协议。      retry time;              The retry statement determines the time that must pass after the              client has determined that there is no DHCP server present before              it tries again to contact a DHCP server.  By default, this is              five minutes. 重试语句确定客户端再次试图联系DHCP服务器之前必须经过的时间。默认情况下,这是五分钟。      select-timeout time;              It is possible (some might say desirable) for there to be more              than one DHCP server serving any given network.  In this case, it              is possible that a client may be sent more than one offer in              response to its initial lease discovery message.  It may be that              one of these offers is preferable to the other (e.g., one offer              may have the address the client previously used, and the other              may not).              The select-timeout is the time after the client sends its first              lease discovery request at which it stops waiting for offers from              servers, assuming that it has received at least one such offer.              If no offers have been received by the time the select-timeout              has expired, the client will accept the first offer that arrives.              By default, the select-timeout is zero seconds - that is, the              client will take the first offer it sees. 这是可能的(有些人可能会说希望)多个DHCP服务器服务于任何给定的网络。在这种情况下,可能的是,客户机收到多个回复响应初始租赁发现消息。这可能是因为这些回复中的一个是优选的其他(例如,一个回复可具有以前使用的客户端的地址,而另一个可能不是) 。 选择超时是客户端发送它的第一个租约发现请求时到假设它已收到至少一个这样的回复之后,它停止等待来自服务器的回复之间的时间。如果在选择超时已到期的时间内没有收到回复,客户端将接受第一个收到的回复。 默认情况下,选择超时为0秒 - 也就是说,客户端将采取它认为第一次回复。      reboot time;              When the client is restarted, it first tries to reacquire the              last address it had.  This is called the INIT-REBOOT state.  If              it is still attached to the same network it was attached to when              it last ran, this is the quickest way to get started.  The reboot              statement sets the time that must elapse after the client firsttatries to reacquire its old address before it gives up and tries              to discover a new address.  By default, the reboot timeout is ten              seconds. 当客户端重启后,首先尝试重新获取它重启之前的地址。这就是所谓的INIT- REBOOT状态。如果客户端仍连接在它最后一次运行的同一个网络上,这是开始的最快方法。重启语句设置的时间就是,客户端首先尝试重新获得它的旧地址必须经历的时间,超时后客户端将试图发现一个新的地址。默认情况下,重新启动超时是十秒钟。      backoff-cutoff time;              The client uses an exponential backoff algorithm with some              randomness, so that if many clients try to configure themselves              at the same time, they will not make their requests in lockstep.              The backoff-cutoff statement determines the maximum amount of              time that the client is allowed to back off.  It defaults to two              minutes. 客户端使用一个拥有一些随机性的指数退避算法,因此,如果许多客户端尝试在同一时间来配置他们自己,他们不会让自己同时请求服务器。退避截止语句确定了客户端允许后退的最长时间。它默认为两分钟。      initial-interval time;              The initial-interval statement sets the amount of time between              the first attempt to reach a server and the second attempt to              reach a server.  Each time a message is sent, the interval              between messages is incremented by twice the current interval              multiplied by a random number between zero and one.  If it is              greater than the backoff-cutoff amount, it is set to that amount.              It defaults to ten seconds. 初始间隔语句是设置第一次尝试与第二次尝试到达服务器的之间的一段时间。每个发送的消息的时间,消息之间的时间间隔由当前间隔乘以0和1之间的随机数的两倍加一。如果它比退避截止量大时,它将被设置。它默认为十秒钟。 LEASE REQUIREMENTS AND REQUESTS      The DHCP protocol allows the client to request that the server send it      specific information, and not send it other information that it is not      prepared to accept.  The protocol also allows the client to reject offers      from servers if they do not contain information the client needs, or if      the information provided is not satisfactory.      There is a variety of data contained in offers that DHCP servers send to      DHCP clients.  The data that can be specifically requested is what are      called DHCP Options.  DHCP Options are defined in dhcp-options(5).      request [option] [, ... option];              The request statement causes the client to request that any              server responding to the client send the client its values for              the specified options.  Only the option names should be specified              in the request statement - not option parameters.      require [option] [, ... option];              The require statement lists options that must be sent in order              for an offer to be accepted.  Offers that do not contain all the              listed options will be ignored.      send { [option declaration] [, ... option declaration] }              The send statement causes the client to send the specified              options to the server with the specified values.  These are full              option declarations as described in dhcp-options(5).  Options              that are always sent in the DHCP protocol should not be specified              here, except that the client can specify a dhcp-lease-time option              other than the default requested lease time, which is two hours.              The other obvious use for this statement is to send information              to the server that will allow it to differentiate between this              client and other clients or kinds of clients. OPTION MODIFIERS      In some cases, a client may receive option data from the server which is      not really appropriate for that client, or may not receive information      that it needs, and for which a useful default value exists.  It may also      receive information which is useful, but which needs to be supplemented      with local information.  To handle these needs, several option modifiers      are available.      default { [option declaration] [, ... option declaration] }              If for some set of options the client should use the value              supplied by the server, but needs to use some default value if no              value was supplied by the server, these values can be defined in              the default statement.      supersede { [option declaration] [, ... option declaration] }              If for some set of options the client should always use its own              value rather than any value supplied by the server, these values              can be defined in the supersede statement. 如果由于某些选项,客户端应该总是使用本地配置的一个或多个值,而不是任何由服务器提供的,这些值可以在优先于语句来定义。      prepend { [option declaration] [, ... option declaration] }              If for some set of options the client should use a value you              supply, and then use the values supplied by the server, if any,              these values can be defined in the prepend statement.  The              prepend statement can only be used for options which allow more              than one value to be given.  This restriction is not enforced -              if violated, the results are unpredictable. 如果因为某些设置选项的客户端应该使用您提供的值,然后使用由服务器提供的,如果有的话,这些值可以在前置语句中定义的值。该前置语句只能用于允许给予一个以上的值的选择。此限制并不强制执行 - 如果你忽视它,其行为将不可预知。      append { [option declaration] [, ... option declaration] }              If for some set of options the client should first use the values              supplied by the server, if any, and then use values you supply,              these values can be defined in the append statement.  The append              statement can only be used for options which allow more than one              value to be given.  This restriction is not enforced - if you              ignore it, the behaviour will be unpredictable. LEASE DECLARATIONS      The lease declaration:            lease { lease-declaration [... lease-declaration] }      The DHCP client may decide after some period of time (see PROTOCOL      TIMING) that it is not going to succeed in contacting a server.  At that      time, it consults its own database of old leases and tests each one that      has not yet timed out by pinging the listed router for that lease to see      if that lease could work.  It is possible to define one or more fixed      leases in the client configuration file for networks where there is no      DHCP or BOOTP service, so that the client can still automatically      configure its address.  This is done with the lease statement.      NOTE: the lease statement is also used in the dhclient.leases file in      order to record leases that have been received from DHCP servers.  Some      of the syntax for leases as described below is only needed in the      dhclient.leases file.  Such syntax is documented here for completeness.      A lease statement consists of the lease keyword, followed by a left curly      brace, followed by one or more lease declaration statements, followed by      a right curly brace.  The following lease declarations are possible:      bootp;  The bootp statement is used to indicate that the lease was              acquired using the BOOTP protocol rather than the DHCP protocol.              It is never necessary to specify this in the client configuration              file.  The client uses this syntax in its lease database file.      interface "string";              The interface lease statement is used to indicate the interface              on which the lease is valid.  If set, this lease will only be              tried on a particular interface.  When the client receives a              lease from a server, it always records the interface number on              which it received that lease.  If predefined leases are specified              in the dhclient.conf file, the interface should also be              specified, although this is not required.      fixed-address ip-address;              The fixed-address statement is used to set the IP address of a              particular lease.  This is required for all lease statements.              The IP address must be specified as a dotted quad (e.g.,              12.34.56.78). 固定地址语句用来设置特定租约的IP地址。这是必需的所有租赁的语句。 IP地址必须被指定为一个点分四组(例如, 12.34.56.78 ) 。      filename "string";              The filename statement specifies the name of the boot filename to              use.  This is not used by the standard client configuration              script, but is included for completeness. 文件名语句指定引导文件名使用的名称。但为了保持完整性,这是不使用的标准的客户端配置脚本。      server-name "string";              The server-name statement specifies the name of the boot server              name to use.  This is also not used by the standard client              configuration script. 服务器名语句指定要使用的引导服务器名称的名称。这也是不使用标准的客户端配置脚本。      option option-declaration;              The option statement is used to specify the value of an option              supplied by the server, or, in the case of predefined leases              declared in dhclient.conf, the value that the user wishes the              client configuration script to use if the predefined lease is              used. 选项​​语句用于指定由服务器,或者,在dhclient.conf声明预定租约的情况下,用户希望在客户端配置脚本如果使用预定义的租赁使用的值提供的选项的值。      script "script-name";              The script statement is used to specify the pathname of the DHCP              client configuration script.  This script is used by the DHCP              client to set each interface's initial configuration prior to              requesting an address, to test the address once it has been              offered, and to set the interface's final configuration once a              lease has been acquired.  If no lease is acquired, the script is              used to test predefined leases, if any, and also called once if              no valid lease can be identified.  For more information, see              dhclient.leases(5).      medium "media setup";              The medium statement can be used on systems where network              interfaces cannot automatically determine the type of network to              which they are connected.  The media setup string is a system-              dependent parameter which is passed to the DHCP client              configuration script when initializing the interface.  On UNIX              and UNIX-like systems, the argument is passed on the ifconfig(8)              command line when configuring the interface.              The DHCP client automatically declares this parameter if it used              a media type (see the media statement) when configuring the              interface in order to obtain a lease.  This statement should be              used in predefined leases only if the network interface requires              media type configuration.      renew date;      rebind date;      expire date;              The renew statement defines the time at which the DHCP client              should begin trying to contact its server to renew a lease that              it is using.  The rebind statement defines the time at which the              DHCP client should begin to try to contact any DHCP server in              order to renew its lease.  The expire statement defines the time              at which the DHCP client must stop using a lease if it has not              been able to contact a server in order to renew it.      These declarations are automatically set in leases acquired by the DHCP      client, but must also be configured in predefined leases - a predefined      lease whose expiry time has passed will not be used by the DHCP client.      Dates are specified as follows:            _weekday_ _year_/_month_/_day__hour_:_minute_:_second_      The weekday is present to make it easy for a human to tell when a lease      expires - it is specified as a number from zero to six, with zero being      Sunday.  When declaring a predefined lease, it can always be specified as      zero.  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 between 0 and 23, the      minute a number between 0 and 59, and the second also a number between 0      and 59. ALIAS DECLARATIONS      alias { declarations ... }      Some DHCP clients running TCP/IP roaming protocols may require that in      addition to the lease they may acquire via DHCP, their interface also be      configured with a predefined IP alias so that they can have a permanent      IP address even while roaming.  The Internet Software Consortium DHCP      client does not support roaming with fixed addresses directly, but in      order to facilitate such experimentation, the DHCP client can be set up      to configure an IP alias using the alias declaration.      The alias declaration resembles a lease declaration, except that options      other than the subnet-mask option are ignored by the standard client      configuration script, and expiry times are ignored.  A typical alias      declaration includes an interface declaration, a fixed-address      declaration for the IP alias address, and a subnet-mask option      declaration.  A medium statement should never be included in an alias      declaration. OTHER DECLARATIONS      reject ip-address;              The reject statement causes the DHCP client to reject offers from              servers who use the specified address as a server identifier.              This can be used to avoid being configured by rogue or              misconfigured DHCP servers, although it should be a last resort -              better to track down the bad DHCP server and fix it. 拒绝语句使DHCP客户端拒绝来自使用指定的地址作为服务器标识符的服务器的应答。这可以用来避免被恶意的或配置错误的DHCP服务器配置,尽管它应该是 更好地追查不良DHCP服务器并修复它的最后的手段 。      interface "name" { declarations ... }              A client with more than one network interface may require              different behaviour depending on which interface is being              configured.  All timing parameters and declarations other than              lease and alias declarations can be enclosed in an interface              declaration, and those parameters will then be used only for the              interface that matches the specified name.  Interfaces for which              there is no interface declaration will use the parameters              declared outside of any interface declaration, or the default              settings.      media "media setup" [, "media setup", ...];              The media statement defines one or more media configuration              parameters which may be tried while attempting to acquire an IP              address.  The DHCP client will cycle through each media setup              string on the list, configuring the interface using that setup              and attempting to boot, and then trying the next one.  This can              be used for network interfaces which are not capable of sensing              the media type unaided - whichever media type succeeds in getting              a request to the server and hearing the reply is probably right              (no guarantees).              The media setup is only used for the initial phase of address              acquisition (the DHCPDISCOVER and DHCPOFFER packets).  Once an              address has been acquired, the DHCP client will record it in its              lease database and will record the media type used to acquire the              address.  Whenever the client tries to renew the lease, it will              use that same media type.  The lease must expire before the              client will go back to cycling through media types. EXAMPLES      The following configuration file is used on a laptop which has an IP      alias of 192.5.5.213, and has one interface, ep0 (a 3Com 3C589C).      Booting intervals have been shortened somewhat from the default, because      the client is known to spend most of its time on networks with little      DHCP activity.  The laptop does roam to multiple networks.            timeout 60;            retry 60;            reboot 10;            select-timeout 5;            initial-interval 2;            reject 192.33.137.209;            interface "ep0" {                send host-name "andare.fugue.com";                send dhcp-client-identifier 1:0:a0:24:ab:fb:9c;                send dhcp-lease-time 3600;                supersede domain-name "fugue.com rc.vix.com home.vix.com";                prepend domain-name-servers 127.0.0.1;                request subnet-mask, broadcast-address, time-offset, routers,                        domain-name, domain-name-servers, host-name;                require subnet-mask, domain-name-servers;                script "/etc/dhclient-script";                media "media 10baseT/UTP", "media 10base2/BNC";            }            alias {              interface "ep0";              fixed-address 192.5.5.213;              option subnet-mask 255.255.255.255;            }      This is a very complicated dhclient.conf file - in general, yours should      be much simpler.  In many cases, it is sufficient to just create an empty      dhclient.conf file - the defaults are usually fine. SEE ALSO      dhclient.leases(5), dhcpd.conf(5), dhcp-options(5), dhclient(8), dhcpd(8)      RFC 2132, RFC 2131. AUTHORS      The dhclient(8) utility 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>. FreeBSD 11.0-PRERELEASE         January 1, 1997        FreeBSD 11.0-PRERELEASE NAME | DESCRIPTION | PROTOCOL TIMING | LEASE REQUIREMENTS AND REQUESTS | OPTION MODIFIERS | LEASE DECLARATIONS | ALIAS DECLARATIONS | OTHER DECLARATIONS | EXAMPLES | SEE ALSO | AUTHORS Want to link to this manual page? Use this URL: <https://www.freebsd.org/cgi/man.cgi?query=dhclient.conf&sektion=5&manpath=FreeBSD+10.3-RELEASE+and+Ports>
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