Provided by: isc-dhcp-relay_4.4.1-2.2ubuntu6_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 ] 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.

       -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)