Provided by: dhcp-probe_1.3.0-8_amd64 bug

NAME

       dhcp_probe.cf - configuration file for dhcp_probe

SYNPOSIS

       /etc/dhcp_probe.cf

DESCRIPTION

       The  file  /etc/dhcp_probe.cf contains configuration information used by the dhcp_probe(8)
       daemon.  dhcp_probe reads the file when it begins  (and  whenever  it  receives  a  SIGHUP
       signal).

       The  location  of  this  file  defaults  to /etc/dhcp_probe.cf, but may be overridden by a
       command-line option to dhcp_probe(8).

       The file consists of a series of statements, one per line.  Each statement begins  with  a
       keyword  followed  by  one  or  more  arguments  (depending  on the keyword); keywords and
       arguments are separated by spaces or tabs.  Statements may be specified in any order.

       Some keywords take an ethernet-address argument.  Ethernet address values must be  written
       in a form that ether_aton(3) recognizes; e.g.  1:2:3:4:5:6 or 00:A5:b2:0:BB:c.

       Some  keywords take an ip-address as a value.  IP address values must be written in a form
       that inet_aton(3) recognizes; e.g.  192.168.1.2.

       Blank lines are ignored.  Lines for which the first  non-blank  character  is  a  '#'  are
       treated as comments.  Trailing comments on statements are not supported.

       Because  all  presently-defined  keywords are optional, the file may be empty, however, it
       must exist.

KEYWORDS

       The keywords are as follows:

   chaddr
              The chaddr statement is optional, and is used to specify the value  of  the  chaddr
              field  in  the  request  packets  sent  by the program.  This value is also used to
              compute the DHCP Client Identifier option in some of the request  packets  sent  by
              the program (by prepending x'01').

              Specify:

                     chaddr ethernet-address

              If  not specified, this value defaults to the Ethernet address corresponding to the
              interface you specified on the commandline.

              You might want to use the chaddr statement if the interface is also a DHCP  client,
              so  that  sending  requests  with the interface's own chaddr/DHCP Client Identifier
              will not interfere with that functionality.

              If you specify a value, be sure to specify a unicast Ethernet address that does not
              belong to any valid client on your network.

              Correctly-functioning  BootP  and DHCP servers that respond will send any responses
              to the chaddr address, or  in  some  cases,  to  the  Ethernet  broadcast  address.
              Therefore,  if  you  specify  a  value  here  (and it differs from your interface's
              Ethernet address), the program will have to place the  interface  into  promiscuous
              mode to be sure it hears unicast responses.

              Note  that  the  chaddr  value  does  not affect the Ethernet source address of the
              Ethernet frames sent by the program.

              If you specify this value, you may also wish to  specify  the  same  value  in  the
              ether_src statement.  See the description of that statement for further discussion.

   ether_src
              The  ether_src  statement  is  optional,  and  is  used to specify the value of the
              ether_src field in the Ethernet frames sent by the program.

              Specify:

                     ether_src ethernet-address

              If not specified, this value defaults to the Ethernet address corresponding to  the
              interface you specified on the commandline.

              If you specify a value, be sure to specify a unicast Ethernet address that does not
              belong to any valid client on your network.

              Note that this value does not affect the chaddr field or the DHCP Client Identifier
              option field in request packets sent by the program.

              If  you  specified  a chaddr value, you may also wish to specify an equal ether_src
              value.  While not strictly necessary, doing so will cause any Layer 2  switches  on
              the  network  to learn that this hardware address is on your leg of the network, so
              they will not need to flood response packets directed to that hardware address, but
              instead can direct the response packets only to your leg of the network.

              Additionally, specifying the same ether_src value could help you discover any buggy
              BootP or DHCP servers that  mistakenly  direct  their  responses  to  the  sender's
              ether_src (instead of to the sender's bootp_chaddr).

   server_id
              The  server_id  statement is optional, and is used to specify the value of the DHCP
              Server Identifer option in some of the request packets sent by the program.

              Specify:

                     server_id ip-address

              If not specified, this value defaults to 10.254.254.254.

              The DHCP Server Identifer option appears in the packets the program sends  when  it
              mimics a DHCP client in the SELECTING state.

              It's  best that the DHCP Server Identifier option the program uses not match the IP
              address of any valid DHCP server on your network, to avoid confusing  them.   Other
              than  that,  any IP address is a reasonable value; you may wish to specify one that
              could never be a valid address on your network.

   client_ip_address
              The client_ip_address statement is optional, and is used to specify the IP  address
              that the program should request, or claim to have a lease on.

              Specify:

                     client_ip_address ip-address

              If not specified, this value defaults to 172.31.254.254.

              When  the  program generates a DHCPREQUEST packet that mimics a DHCP client that is
              in the INIT-REBOOT or SELECTING state, the packet contains a Requested  IP  Address
              option containing this value.  When the program generates a DHCPREQUEST packet that
              mimics a DHCP client that is in the REBINDING state, the packet contains  a  ciaddr
              field containing this value.

              It's  best  that  the  value the program uses not match the IP address of any valid
              DHCP client on your network, to avoid confusing valid DHCP servers.

              It's extremely useful if the value the program uses  not  be  valid  (topologically
              speaking) for the physical network on which the program sends the packets.  Sending
              a topologically inappropriate value may stimulate some DHCP servers to respond with
              a DHCPNAK, which helps the program flush out DHCP servers.

   response_wait_time
              The  response_wait_time  statement is optional, and is used to specify how long the
              program should wait for responses after sending a single request packet.

              Specify

                     response_wait_time num_milliseconds

              If not specified, this value defaults to 5000 milliseconds (5 seconds).

              The value is specified in milliseconds, and must fit into an 'int'  on  your  host.
              (Values  larger  than an 'int' may be silently misinterpreted.)  Typical values are
              on the order of a few thousand milliseconds; i.e. several seconds.

   cycle_time
              The cycle_time statement is optional, and is used to specify how long  the  program
              should sleep between each probe cycle.

              Specify

                     cycle_time num_seconds

              If not specified, this value defaults to 300 seconds.

              The  value  is  specified  in seconds, and must into into an 'unsigned int' on your
              host.  (Values larger than an  'unsigned  int'  may  be  silently  misinterpreted.)
              Typical  valus range from several hundred to several thousand seconds (i.e. several
              minutes to several hours).

              During each probe cycle, the program sends  one  of  the  request  packet  flavors,
              captures any responses that arrive during the response_wait_time, then repeats this
              for each of the other request packet flavors.  After doing this for each flavor  of
              request  packet,  the  probe  cycle  is  complete,  and  the program sleeps for the
              cycle_time.

   legal_server
              The legal_server statement is optional, and  is  used  to  specify  the  IP  source
              address  of  responses that come from a legal BootP or DHCP server on your network.
              The statement may be specified multiple times.

              Specify

                     legal_server ip-address

              If not specified, the program assumes there are no legal BootP and DHCP servers  on
              your network; all responses will be treated as coming from an unknown DHCP server.

              When  the  program  receives  a response packet, it compares the packet's IP source
              address to all the addresses you have specified in legal_server statements.  If the
              IP  source address matches one of these values, the response is deemed to have come
              from a known DHCP server, and is ignored.  If the IP source address does not  match
              any of these values (or you do not specify any legal_server), then the program logs
              a message that reports the packet's IP source address and Ethernet source  address.
              Additionally, if the program was started with the -o commandline option, the packet
              is also written to a packet capture file.

              If both legal_server and legal_server_ethersrc statements appear, then  a  response
              must  have  both  a valid IP source and a valid ethernet source to be considered to
              have come from a known DHCP server.

              When relaying a response from a server to a client, some  BootP  Relay  Agents  may
              change  the  response's  IP  source address, replacing the server's IP address with
              that of the BootP Relay Agent.  If BootP Relay Agents on your network do this,  you
              will need to specify their IP addresses here instead.

   legal_server_ethersrc
              The  legal_server_ethersrc  statement  is  optional,  and  is  used  to specify the
              Ethernet source address of responses that come from a legal BootP or DHCP server on
              your network.  The statement may be specified multiple times.

              Specify

                     legal_server_ethersrc ethernet-address

              If  not  specified,  the  program  does  not  check  the Ethernet source address of
              responses.

              If you have specified at least one legal_server_ethersrc value,  when  the  program
              receives  a  response  packet,  the  program  compares the packet's Ethernet source
              address  to  all  the  addresses  you  have  specified   in   legal_server_ethersrc
              statements.   If  the  Ethernet  source  does  not  match  one of these values, the
              response is deemed to have come from an unknown DHCP server;  the  program  logs  a
              message  that  reports  the packet's IP source address and Ethernet source address.
              Additionally, if the program was started with the -o commandline option, the packet
              is also written to a packet capture file.

              If  both  legal_server and legal_server_ethersrc statements appear, then a response
              must have both a valid IP source and a valid ethernet source to  be  considered  to
              have come from a known DHCP server.

              Each  router on the path from the DHCP server to the DHCP client will overwrite the
              Ethernet source  address  field.   So  if  you  specify  any  legal_server_ethersrc
              statements,  also  list the Ethernet source value(s) for the last hop router(s).  A
              BootP Relay Agent on the path  from  the  DHCP  server  to  the  DHCP  client  will
              overwrite  the  Ethernet  field.  So also list the Ethernet source value(s) for the
              BootP Relay Agent.  (The BootP Relay Agent is often co-resident in the last-hop  IP
              router,  so  you  may  have already taken care of this when you listed the last-hop
              router(s).

              The legal_server_ethersrc statement is considered experimental in version 1.3.0, as
              it has received only limited testing.

   lease_network_of_concern
              The  lease_network_of_concern  statement is optional, and may be specified multiple
              times.  The statement is used to specify one or more network  ranges  that  are  of
              concern relative to the IP addresses distributed by a rogue BootP/DHCP server.

              Specify

                     lease_network_of_concern network-ip-address network-mask

              Specifying  one  or  more  lease_network_of_concern statements activates the "Lease
              Networks of Concern" feature.

              When the program receives a response packet that it determines to be from  a  rogue
              BootP/DHCP  server,  if  the  "Lease  Networks  of  Concern" feature is active, the
              program will examine the packet further.  If the packet's yiaddr field is non-zero,
              the  value  in  that  field  is tested to see if it falls within any of the "Leases
              Networks of Concern."  If it does, then the message the program logs is extended to
              also  report this fact, and to include the value of the yiaddr field.  Furthermore,
              if an alert_program_name2 was specified, when that program is called, it is  called
              with   an   additional   -y   yiaddr   option.    (This  is  not  supported  if  an
              alert_program_name was specified, as the older  alert_program_name  uses  a  syntax
              that cannot be extended.)

              The  "Lease Networks of Concern" feature does not change the way the program probes
              for or detects rogue BootP/DHCP servers.  Upon  detection  of  a  rogue  BootP/DHCP
              server,  the  feature  only  may  cause  additional  information to be added to the
              message logged (and passed to alert_program_name2).

              This feature may be used, for example,  by  specifying  your  networks'  legitimate
              address ranges as "Lease Networks of Concern".  While most rogue BootP/DHCP servers
              distribute private IP addresses, or send DHCPNAKs to legitimate clients, other more
              damaging rogue BootP/DHCP servers may distribute IP addresses that fall within your
              legitimate network ranges.   This  will  help  differentiate  those  more  damaging
              incidents from the more common ones.

   alert_program_name
              The  alert_program_name  statement is optional, and may be used to specify the name
              of an external program that should be run every time a response packet is  received
              from an unexpected server.

              Note that using the newer alert_program_name2 statement is preferrable.

              Specify

                     alert_program_name /absolute/path/name

              Unexpected  response  packets  are  reported  as a matter of course, and optionally
              written to a packet capture file.  You may use  an  alert_program_name  to  provide
              additional  handling  of  the event, for example, to alert an appropriate party via
              mail or paging.  The alert_program_name you specify is called with  four  arguments
              in  the  following  order:  the name of the calling program (e.g.  dhcp_probe), the
              name of the interface on which the unexpected response packet was received, the  IP
              source address of the packet, and the Ethernet source address of the packet.

              As  the  alert_program_name  is called with the same privileges as dhcp_probe (i.e.
              root), you should exercise caution to ensure that the alert program is safe  for  a
              privileged user to execute.

              Because  the syntax supported by the external program is not extensible, the use of
              alert_program_name2 is preferrable.

              You may not specify both alert_program_name and alert_program_name2.

   alert_program_name2
              The alert_program_name2 statement is optional, and may be used to specify the  name
              of  an external program that should be run every time a response packet is received
              from an unexpected server.

              Specify

                     alert_program_name2 /absolute/path/name

              Unexpected response packets are reported as a  matter  of  course,  and  optionally
              written  to  a  packet capture file.  You may use an alert_program_name2 to provide
              additional handling of the event, for example, to alert an  appropriate  party  via
              mail  or  paging.  The alert_program_name2 you specify is called with the following
              required options:

                     -p the name of the calling program (e.g. dhcp_probe),
                     -I the name of the interface on which the unexpected response packet was received
                     -i the IP source address of the packet
                     -m Ethernet source address of the packet

              The following non-required options may also be passed:

                     -y the non-zero yiaddr value from the packet, when it falls inside a "Lease Network of Concern"

              The alert_program_name2 program you specify must ignore  options  or  arguments  it
              does  not  recognize;  this  is to ensure it remains forward-compatible with future
              enhancements to dhcp_probe.  It must be prepared to accept options in any order.

              As the alert_program_name2 is called with the same privileges as  dhcp_probe  (i.e.
              root),  you  should exercise caution to ensure that the alert program is safe for a
              privileged user to execute.

              You may not specify both alert_program_name and alert_program_name2.

EXAMPLE

       An example /etc/dhcp_probe.cf file follows:

              # dhcp_probe.cf: config file for dhcp_probe
              #
              # General syntax:
              #  Comment lines start with '#' (trailing comments not permitted).
              #  Blank lines are OK.
              #  Tokens within a line should be separated with spaces and/or tabs.
              #  Entries in the file may be in any order.
              #  Any 'ethernet-address' must be written in a form that ether_aton(3) recognizes; e.g.
              #      1:2:3:4:5:6   00:A5:b2:0:BB:c
              #  Any 'ip-address' must be written in a form that inet_aton(3) recognizes; e.g.
              #      192.168.1.2
              #
              # ----------------------------------------------------------------------------------
              #
              # CLIENT HARDWARE ADDRESS
              #
              # By default, for the 'chaddr' field in the BootP header, we use the Ethernet
              # address corresponding to the interface you specified.
              # We also use this value to compute the DHCP Client Identifier option (by prepending x'01').
              # You may optionally override this value.
              # (Note that this does not override the Ethernet Src address in the Ethernet frame we send.)
              #
              # You might want to do this if our interface is also a DHCP client, so
              # sending requests with the interface's own chaddr/DHCP Client Identifier would interfere with
              # that functionality.
              #
              # If you specify a value, be sure to specify an Ethernet address that does not belong to
              # any valid client on your network.  Be sure to specify a unicast Ethernet address.
              #
              # Syntax:
              #    chaddr enet-addr

              chaddr 0:0:0:1:2:3

              # ----------------------------------------------------------------------------------
              #
              # ETHERNET SOURCE ADDRESS
              #
              # By default, for the 'ether_shost' field in the Ethernet header, we use the Ethernet
              # address corresponding to the interface you specified.
              # You may optionally override this value.
              # (Note that this does not override the 'chaddr' in the BootP header, nor the DHCP Client Identifier.)
              #
              # If you are specify the 'chaddr' statement, you might want to also do this, so you don't miss buggy
              # DHCP servers that respond (incorrectly) to ether_src instead of to chaddr.
              #
              # If you specify a value, be sure to specify an Ethernet address that does not belong to
              # any valid client on your network.  Be sure to specify a unicast Ethernet address.
              #
              # Syntax:
              #    ether_src enet-addr

              ether_src 0:0:0:1:2:3

              # ----------------------------------------------------------------------------------
              #
              # DHCP SERVER IDENTIFIER
              #
              # When we generate a DHCPREQUEST packet corresponding to a client that is in the SELECTING
              # state, the options field must contain a 'DHCP Server Identifier' option, indicating the
              # IP address of the DHCP server the client is selecting.   It's best that the value we use
              # not match the IP address of any valid DHCP server, to avoid confusing them.  The program
              # provides a default value of 10.254.254.254, which you may override here.
              #
              # Syntax:
              #    server_id ip-addr

              server_id 10.1.2.3

              # ----------------------------------------------------------------------------------
              #
              # CLIENT IP ADDRESS
              #
              # When we generate a DHCPREQUEST packet corresponding to a client that is in the INIT-REBOOT
              # or SELECTING state, the options field must containg a 'Requested IP Address' option, indicating
              # the IP address the client is requesting.    When we generate a DHCPREQUEST packet corresponding
              # to a client that is in the REBINDING state, the 'ciaddr' field in the BootP header must contain
              # the IP address that the DHCP client presently has leased and wishes to renew.
              #
              # In all these cases, it's best that the value we use not match the IP address of any valid DHCP client,
              # to avoid confusing the valid DHCP servers.
              #
              # Furthermore, it is extremely useful if the value we use *not* be valid (topologically speaking) for the
              # physical network on which we send the packets.  Sending a topologically inappropriate value
              # may stimulate some DHCP servers to respond with a DHCPNAK, which helps us flush out DHCP servers.
              # (This will probably happen only in response to the packets we sending when pretending to be in REBINDING state.)
              #
              # The program provides a default value of 172.31.254.254, which you may override here.
              #
              # Syntax:
              #   client_ip_address ip-addr

              # client_ip_address 172.31.254.254

              # ----------------------------------------------------------------------------------
              #
              # RESPONSE WAIT TIME
              #
              # After sending one packet, we wait for responses.  The length of time we wait
              # is the 'response_wait_time'.  The program provides a default value of 5000, which you
              # may override here.  The value is measured in milliseconds, and must fit into
              # an 'int' on your host.  (Values larger than an 'int' may be silently misinterpreted.)
              # Typical values are on the order of a few thousand milliseconds; i.e. several seconds.
              #
              # Syntax:
              #    response_wait_time num_milliseconds

              # response_wait_time 5000

              # ----------------------------------------------------------------------------------
              #
              # CYCLE WAIT TIME
              #
              # For each flavor packet, we send the packet and listen for responses to that packet.
              # After doing this for all flavor packets, we go to sleep for the "cycle_time",
              # then repeat the process.  The program provides a default value of 300, which you
              # may override here.  The value is measured in seconds, and must fit into an
              # 'unsigned int' on your host.  (Values larger than an 'unsigned int' may be silently
              # misinterpreted.)  Typical valus range from several hundred to several thousand
              # seconds (i.e. several minutes to several hours).
              #
              # Syntax:
              #    cycle_time num_seconds

              cycle_time 1200

              # ----------------------------------------------------------------------------------
              #
              # LEGAL SERVERS' IP SOURCE ADDRESSES
              #
              # After sending one packet, we wait for responses.  Responses from legal BootP or DHCP
              # servers are ignored; presumably you aren't interesting in discovering them.
              # Specify a legal server's IP source address with the 'legal_server' statement.
              # The value you specify is compared to the IPsrc field in each response's IP header.
              #
              # If you have multiple legal servers, specify each in a separate statement.
              # If your BootP Relay Agents overwrite the server's IP address in the IPsrc field
              # with their own IP addresses, you will need to list the IP addresses of the
              # BootP Relay Agents.
              #
              # Alternatively, do not specify any legal_server statements at all, so *no* responses
              # will be considered legal.
              # (This is different from the way legal_server_ethersrc statements are handled.)
              #
              # If both legal_server and legal_server_ethersrc statements appear, then a response
              # must have both a valid IP source and a valid ethernet source to be considered legal.
              #
              # Syntax:
              #   legal_server ip-addr

              legal_server 192.168.1.2
              legal_server 192.168.3.4

              # ----------------------------------------------------------------------------------
              #
              # LEGAL SERVERS' ETHERNET SOURCE ADDRESSES
              #
              # Specify a legal server's Ethernet source address with the 'legal_server_ethersrc' statement.
              # The value you specify is compared to the ethernet_src field in each response's IP header.
              #
              # If you have multiple legal ethernet sources, specify each in a separate statement.
              # Each router on the path from the DHCP server to the DHCP client will overwrite
              # the ethernet_src field.  So also list the ethernet_src value(s) for the last hop router(s).
              # The BootP Relay Agent on the path from the DHCP server to the DHCP client will overwrite
              # the ethernet_src field.  So also list the ethernet_src value(s) for the BootP Relay Agent.
              # (This is often co-resident in the last-hop IP router, so you may have already taken care
              # of this when you listed the last-hop router(s).
              #
              # Alternatively, do not specify any legal_server_ethersrc statements at all.
              # If none are specified, then all ethernet_src values are considered legal.
              # (This is different from the way legal_server statements are handled.)
              #
              # If both legal_server and legal_server_ethersrc statements appear, then a response
              # must have both a valid IP source and a valid ethernet source to be considered legal.
              #
              # Syntax:
              #   legal_server_ethersrc enet-addr

              # legal_server_ethersrc 0:2:4:ab:cd:ef
              # legal_server_ethersrc 0:17:30:1:0A:3

              # ----------------------------------------------------------------------------------
              #
              # ALERT PROGRAM NAME
              #
              # In addition to logging a response received from an unexpected server, we will optionally
              # call a user-specified 'alert program' if one is specified here.  To use this feature,
              # specify the absolute pathname of a program we should execute for each unexpected response.
              # Either specify it using the older 'alert_program_name' statement, or (preferrably) using
              # the newer 'alert_program_name2' statement.  (The newer statement is preferrable because
              # it calls the alert program with a more extensible syntax.)  You may not specify
              # both alert_program_name and alert_program_name2.
              #
              # Old style alert program:
              #
              # Syntax:
              #   alert_program_name /absolute/path/name
              #
              # The program specified via 'alert_program_name' will be called as follows:
              #   /absolute/path/name  name_of_calling_program  name_of_interface_on_which_the_response_was_received  IP_source_of_the_response  ether_src_of_the_response
              #
              #
              # Newer style alert program:
              #
              # Syntax:
              #   alert_program_name2 /absolute/path/name
              #
              # The program specified via 'alert_program_name2' will be called as follows:
              #   /absolute/path/name  -p name_of_calling_program  -I name_of_interface_on_which_the_response_was_received  -i IP_source_of_the_response  -m ether_src_of_the_response [-y yiaddr_when_in_lease_networks_of_concern]
              # The options may appear in any order.
              # The program must silently ignore any options or arguments it does not recognize,
              # so as to be forward-compatible with future enhancements to dhcp_probe.

              alert_program_name2 /usr/local/etc/dhcp_probe_notify2

              # ----------------------------------------------------------------------------------
              #
              # LEASE NETWORKS OF CONCERN
              #
              # Optionally define one or more network ranges that are to be treated as
              # being of special concern when a rogue BootP/DHCP server is detected sending response
              # that contains a 'yiaddr' value that falls into any of these ranges.
              # Specify each such network ranges of concern in a separate statement.
              # When the yiaddr value in a rogue server's response falls into any of these ranges,
              # the message logged will contain additional text remarking on this fact.
              # And if an alert_program_name2 is used, that alert program
              # will be called with an extra option so it can also act on that fact.
              #
              # If you specify all your networks' legitimate IP ranges, this can help you
              # take additional notice of rogue BootP/DHCP servers that distribute *your*
              # network addresess, rather than simply distribute private IP address or
              # send DHCPNAKs to legitimate clients.
              #
              # Syntax:
              #    lease_network_of_concern  IP-network-address network-mask

              lease_network_of_concern 128.112.0.0 255.255.0.0
              lease_network_of_concern 140.180.0.0 255.255.0.0

SEE ALSO

       dhcp_probe(8)