Provided by: isc-dhcp-relay_4.3.3-5ubuntu12_amd64 bug

NAME

       dhcrelay - Dynamic Host Configuration Protocol Relay Agent

SYNOPSIS

       dhcrelay  [ -4 ] [ -dqaD ] [ -p port ] [ -c count ] [ -A length ] [ -pf pid-file ] [ --no-
       pid ] [ -m append | replace | forward | discard ] [ -i interface0 [ ...  -i interfaceN ] ]
       server0 [ ...serverN ]

       dhcrelay  -6  [  -dqI  ]  [  -p  port  ]  [  -c count ] [ -pf pid-file ] [ --no-pid ] [ -s
       subscriber-id ] -l lower0 [ ...  -l lowerN ] -u upper0 [ ...  -u upperN ]

DESCRIPTION

       The Internet Systems Consortium DHCP Relay Agent, dhcrelay, provides a means for  relaying
       DHCP and BOOTP requests from a subnet to which no DHCP server is directly connected to one
       or more DHCP  servers  on  other  subnets.   It  supports  both  DHCPv4/BOOTP  and  DHCPv6
       protocols.

OPERATION

       The  DHCP  Relay  Agent  listens  for DHCPv4 or DHCPv6 queries from clients or other relay
       agents on one or more interfaces, passing them along  to  ``upstream''  servers  or  relay
       agents  as  specified  on the command line.  When a reply is received from upstream, it is
       multicast or unicast back downstream to the source of the original request.

COMMAND LINE

       Protocol selection options:

       -6     Run dhcrelay as a DHCPv6 relay agent.  Incompatible with the -4 option.

       -4     Run dhcrelay as a DHCPv4/BOOTP relay agent.  This is the default mode of operation,
              so  the  argument is not necessary, but may be specified for clarity.  Incompatible
              with -6.

       Specifying DHCPv4/BOOTP servers

       In DHCPv4 mode, a list of one or more server addresses must be specified  on  the  command
       line, to which DHCP/BOOTP queries should be relayed.

       Options available for both DHCPv4 and DHCPv6:

       -c COUNT
              Maximum  hop  count.  When forwarding packets, dhcrelay discards packets which have
              reached a hop count of COUNT.  Default is 10.  Maximum is 255.

       -d     Force dhcrelay to run as a foreground process.  Useful when running dhcrelay  under
              a debugger, or running out of inittab on System V systems.

       -p PORT
              Listen  and  transmit  on port PORT.  This is mostly useful for debugging purposes.
              Default is port 67 for DHCPv4/BOOTP, or port 547 for DHCPv6.

       -q     Quiet mode.  Prevents dhcrelay6 from printing its network configuration on startup.

       -pf pid-file
              Path to alternate pid file.

       --no-pid
              Option to disable writing pid files.  By default the program will write a pid file.

       Options available in DHCPv4 mode only:

       -a     Append an agent option field to each request before forwarding it  to  the  server.
              Agent  option  fields  in  responses  sent from servers to clients will be stripped
              before forwarding such responses back to the client.  The agent option  field  will
              contain  two  agent  options: the Circuit ID suboption and the Remote ID suboption.
              Currently, the Circuit ID will be the printable name of the interface on which  the
              client  request  was  received.   The  client  supports  inclusion  of  a Remote ID
              suboption as well, but this is not used by default.

       -A LENGTH
              Specify the maximum packet size to send to a DHCPv4/BOOTP server.   This  might  be
              done  to  allow  sufficient  space  for addition of relay agent options while still
              fitting into the Ethernet MTU size.

       -D     Drop packets from upstream servers if they contain Relay Agent Information  options
              that  indicate they were generated in response to a query that came via a different
              relay agent.  If this option is not specified, such packets will be relayed anyway.

       -i ifname
              Listen for DHCPv4/BOOTP queries on interface ifname.  Multiple  interfaces  may  be
              specified  by using more than one -i option.  If no interfaces are specified on the
              command line, dhcrelay will  identify  all  network  interfaces,  eliminating  non-
              broadcast interfaces if possible, and attempt to listen on all of them.

       -m append|replace|forward|discard
              Control  the  handling of incoming DHCPv4 packets which already contain relay agent
              options.  If such a packet does not  have  giaddr  set  in  its  header,  the  DHCP
              standard  requires  that  the  packet be discarded.  However, if giaddr is set, the
              relay agent may handle the situation in four ways:  It may append its  own  set  of
              relay  options  to  the  packet,  leaving  the supplied option field intact; it may
              replace the existing agent option field; it may forward the packet  unchanged;  or,
              it may discard it.

              To use this option you must also enable the -a option.

       Options available in DHCPv6 mode only:

       -I     Force  use  of  the  DHCPv6 Interface-ID option.  This option is automatically sent
              when there are two or more downstream interfaces in use,  to  disambiguate  between
              them.   The  -I option causes dhcrelay to send the option even if there is only one
              downstream interface.

       -s subscriber-id
              Add an option with the specified subscriber-id into the packet.   This  feature  is
              for  testing  rather than production as it will put the same subscriber-id into the
              packet for all clients.

       -l [address%]ifname[#index]
              Specifies the ``lower'' network interface for DHCPv6 relay mode: the  interface  on
              which  queries  will be received from clients or from other relay agents.  At least
              one -l option must be included in the command line when  running  in  DHCPv6  mode.
              The  interface  name  ifname  is  a  mandatory  parameter.  The link address can be
              specified by address%; if it isn't, dhcrelay  will  use  the  first  non-link-local
              address  configured  on the interface.  The optional #index parameter specifies the
              interface index.

       -u [address%]ifname
              Specifies the ``upper'' network interface for DHCPv6 relay mode: the  interface  to
              which  queries  from  clients and other relay agents should be forwarded.  At least
              one -u option must be included in the command line when  running  in  DHCPv6  mode.
              The  interface  name  ifname  is  a mandatory parameter. The destination unicast or
              multicast address can be specified by address%; if not specified, the  relay  agent
              will forward to the DHCPv6 All_DHCP_Relay_Agents_and_Servers multicast address.

       It  is possible to specify the same interface with different addresses more than once, and
       even, when the system supports it, to use the same  interface  as  both  upper  and  lower
       interfaces.

SEE ALSO

       dhclient(8), dhcpd(8), RFC3315, RFC2132, RFC2131.

BUGS

       Using  the  same  interface on both upper and lower sides may cause loops, so when running
       this way, the maximum hop count should be set to a low value.

       The loopback interface is not (yet) recognized as a valid interface.

AUTHOR

       dhcrelay(8) To learn more about Internet Systems Consortium, see https://www.isc.org

                                                                                      dhcrelay(8)