Provided by: isc-dhcp-relay_4.4.3-P1-4ubuntu2_amd64 bug

NAME

       dhcrelay - Dynamic Host Configuration Protocol Relay Agent

SYNOPSIS

       dhcrelay  [  -4  ] [ -dqaD ] [ -p port | -rp relay-port ] [ -c count ] [ -A length ] [ -pf
       pid-file ] [ --no-pid ] [ -m append | replace | forward | discard ] [ -i interface0 [  ...
       -i  interfaceN  ] ] [ -iu interface0 [ ...  -iu interfaceN ] ] [ -id interface0 [ ...  -id
       interfaceN ] ] [ -U interface ] [ -g ipaddr ] server0 [ ...serverN ]

       dhcrelay -6 [ -dqI ] [ -p port | -rp relay-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.  Incompatible with
              -rp.

       -rp relay-port
              Alternative source port for upstream (i.e toward the server) messages  with  DHCPv4
              RAI relay-port sub-option or DHCPv6 relay-source-port option. Relay port support is
              only available if the code was compiled with (./configure --enable-relay-port)  and
              requires LPF or BPF link layer access.

       -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.

       -g ipaddr
              When  a  package  gets  sent  back  to the client, replace the gateway's IP address
              (giaddr) with the given ipaddr. This can be used as a workaround for bogus  clients
              like  Solaris  11 grub, which use the giaddr instead of the announced router (3) to
              setup its default route.

       -i ifname
              Listen for DHCPv4/BOOTP traffic 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.

       -iu ifname
              Specifies  an  upstream  network  interface:  an  interface from which replies from
              servers and other relay agents  will  be  accepted.   Multiple  interfaces  may  be
              specified by using more than one -iu option.  This argument is
               intended to be used in conjunction with one or more -i or -id arguments.

       -id ifname
              Specifies  a  downstream  network  interface: an interface from which requests from
              clients and other relay agents  will  be  accepted.   Multiple  interfaces  may  be
              specified  by using more than one -id option.  This argument is intended to be used
              in conjunction with one or more -i or -iu arguments.

       -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.

       -U ifname
              Enables the addition of a RFC 3527 compliant link selection suboption  for  clients
              directly  connected to the relay.  This RFC allows a relay to specify two different
              IP addresses: one for the server to use when communicating with the relay  (giaddr)
              the  other  for  choosing  the  subnet for the client (the suboption).  This can be
              useful if the server is unable to send packets to the relay via  the  address  used
              for the subnet.

              When enabled, dhcrelay will add an agent option (as per -a above) that includes the
              link selection suboption to the forwarded  packet.   This  will  only  be  done  to
              packets received from clients that are directly connected to the relay (i.e. giaddr
              is zero).  The address used in the suboption will be that of the  link  upon  which
              the  inbound  packet  was  received (which would otherwise be used for giaddr). The
              value of giaddr will be set to that of interface ifname.

              Only one interface should be marked  in  this  fashion.   Currently  enabling  this
              option  on an interface causes the relay to process all DHCP traffic similar to the
              -i option, in the future we may split the two more completely.

              This option is off by  default.   Note  that  enabling  this  option  automatically
              enables the -a option.

              Keep in mind that using options such as -m replace or -m discard on relays upstream
              from one using -U can pose problems.  The upstream relay will wipe out the  initial
              agent  option  containing  the  link selection while leaving the re-purposed giaddr
              value in place, causing packets to go astray.

       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)