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dhcrelay(8)		    System Manager's Manual		   dhcrelay(8)

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 ] -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	speci-
       fied  on	 the  command  line, to	which DHCP/BOOTP queries should	be re-
       layed.

       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 run-
	      ning  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 de-
	      bugging  purposes.  Default is port 67 for DHCPv4/BOOTP, or port
	      547 for DHCPv6.

       -q     Quiet mode.  Prevents dhcrelay6 from printing its	 network  con-
	      figuration 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  re-
	      sponses 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 addi-
	      tion of relay agent options while	still fitting into the	Ether-
	      net MTU size.

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

       -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 gi-
	      addr  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.

       Options available in DHCPv6 mode	only:

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

       -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  in-
	      cluded in	the command line when running in DHCPv6	mode.  The in-
	      terface 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 in-
	      cluded in	the command line when running in DHCPv6	mode.  The in-
	      terface  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)

NAME | SYNOPSIS | DESCRIPTION | OPERATION | COMMAND LINE | SEE ALSO | BUGS | AUTHOR

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