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-dhcrelay(8) dhcrelay(8)
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-N\bNA\bAM\bME\bE
- dhcrelay - Dynamic Host Configuration Protocol Relay Agent
-
-S\bSY\bYN\bNO\bOP\bPS\bSI\bIS\bS
- d\bdh\bhc\bcr\bre\bel\bla\bay\by [ -\b-p\bp _\bp_\bo_\br_\bt ] [ -\b-d\bd ] [ -\b-q\bq ] [ -\b-i\bi _\bi_\bf_\b0 [ .\b..\b..\b. -\b-i\bi _\bi_\bf_\bN
- ] ] [ -\b-a\ba ] [ -\b-A\bA _\bl_\be_\bn_\bg_\bt_\bh ] [ -\b-D\bD ] [ -\b-m\bm _\ba_\bp_\bp_\be_\bn_\bd | _\br_\be_\bp_\bl_\ba_\bc_\be |
- _\bf_\bo_\br_\bw_\ba_\br_\bd | _\bd_\bi_\bs_\bc_\ba_\br_\bd ] _\bs_\be_\br_\bv_\be_\br_\b0 [ _\b._\b._\b._\bs_\be_\br_\bv_\be_\br_\bN ]
-
-D\bDE\bES\bSC\bCR\bRI\bIP\bPT\bTI\bIO\bON\bN
- The Internet Software Consortium DHCP Relay Agent, dhcre
- lay, provides a means for relaying DHCP and BOOTP requests
- from a subnet to which no DHCP server is directly con
- nected to one or more DHCP servers on other subnets.
-
-O\bOP\bPE\bER\bRA\bAT\bTI\bIO\bON\bN
- The DHCP Relay Agent listens for DHCP and BOOTP queries
- and responses. When a query is received from a client,
- dhcrelay forwards it to the list of DHCP servers specified
- on the command line. When a reply is received from a
- server, it is broadcast or unicast (according to the relay
- agent's ability or the client's request) on the network
- from which the original request came.
-
-C\bCO\bOM\bMM\bMA\bAN\bND\bD L\bLI\bIN\bNE\bE
- The names of the network interfaces that dhcrelay should
- attempt to configure may be specified on the command line
- using the -\b-i\bi option. If no interface names are specified
- on the command line dhcrelay will identify all network
- interfaces, elimininating non-broadcast interfaces if pos
- sible, and attempt to configure each interface.
-
- If a relay agent is running on a system that is connected
- to one or more networks on which no DHCP servers are pre
- sent, and is also connected to one or more networks on
- which DHCP servers _\ba_\br_\be connected, it is may not be helpful
- for the relay agent to relay requests from those networks
- on which a DHCP server already exists. To avoid such a
- situation, the interfaces on which the relay agent should
- listen should be specified with the -\b-i\bi flag.
-
- Note that in some cases it _\bi_\bs helpful for the relay agent
- to forward requests from networks on which a DHCP server
- is running to other DHCP servers. This would be the case
- if two DHCP servers on different networks were being used
- to provide backup service for each other's networks.
-
- If dhcrelay should listen and transmit on a port other
- than the standard (port 67), the -\b-p\bp flag may used. It
- should be followed by the udp port number that dhcrelay
- should use. This is mostly useful for debugging purposes.
-
- Dhcrelay will normally run in the foreground until it has
- configured an interface, and then will revert to running
- in the background. To run force dhcrelay to always run as
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-dhcrelay(8) dhcrelay(8)
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- a foreground process, the -\b-d\bd flag should be specified.
- This is useful when running dhcrelay under a debugger, or
- when running it out of inittab on System V systems.
-
- Dhcrelay will normally print its network configuration on
- startup. This can be annoying in a system startup script
- - to disable this behaviour, specify the -\b-q\bq flag.
-
-R\bRE\bEL\bLA\bAY\bY A\bAG\bGE\bEN\bNT\bT I\bIN\bNF\bFO\bOR\bRM\bMA\bAT\bTI\bIO\bON\bN O\bOP\bPT\bTI\bIO\bON\bNS\bS
- If the -\b-a\ba flag is set the relay agent will 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 Agent ID suboption. Cur
- rently, the Circuit ID will be the printable name of the
- interface on which the client request was received. The
- Agent ID will be the value that the relay agent stores in
- the DHCP packet's giaddr field. The client supports
- inclusion of a Remote ID suboption as well, but this is
- not used by default.
-
- _\bN_\bo_\bt_\be_\b: The Agent ID suboption is not defined in the current
- Relay Agent Information Option draft (draft-ietf-dhc-
- agent-options-03.txt), but has been proposed for inclusion
- in the next draft.
-
- Relay Agent options are added to a DHCP packet without the
- knowledge of the DHCP client. The client may have filled
- the DHCP packet option buffer completely, in which case
- there theoretically isn't any space to add Agent options.
- However, the DHCP server may be able to handle a much
- larger packet than most DHCP clients would send. The
- current Agent Options draft requires that the relay agent
- use a maximum packet size of 576 bytes.
-
- It is recommended that with the Internet Software Consor
- tium DHCP server, the maximum packet size be set to about
- 1400, allowing plenty of extra space in which the relay
- agent can put the agent option field, while still fitting
- into the Ethernet MTU size. This can be done by specify
- ing the -\b-A\bA flag, followed by the desired maximum packet
- size (e.g., 1400).
-
- Note that this is reasonably safe to do even if the MTU
- between the server and the client is less than 1500, as
- long as the hosts on which the server and client are run
- ning support IP fragmentation (and they should). With
- some knowledge as to how large the agent options might get
- in a particular configuration, this parameter can be tuned
- as finely as necessary.
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-dhcrelay(8) dhcrelay(8)
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- It is possible for a relay agent to receive a packet which
- already contains an agent option field. If this packet
- does not have a giaddr set, the standard requires that the
- packet be discarded.
-
- If giaddr is set, the server may handle the situation in
- one of four ways: it may _\ba_\bp_\bp_\be_\bn_\bd its own set of relay
- options to the packet, leaving the supplied option field
- intact. It may _\br_\be_\bp_\bl_\ba_\bc_\be the existing agent option field.
- It may _\bf_\bo_\br_\bw_\ba_\br_\bd the packet unchanged. Or, it may _\bd_\bi_\bs_\bc_\ba_\br_\bd
- it.
-
- Which of these behaviours is followed by the Internet
- Software Consortium DHCP Relay Agent may be configured
- with the -\b-m\bm flag, followed by one of the four keywords
- specified in _\bi_\bt_\ba_\bl_\bi_\bc_\bs above.
-
- When the relay agent receives a reply from a server that
- it's supposed to forward to a client, and Relay Agent
- Information option processing is enabled, the relay agent
- scans the packet for Relay Agent Information options and
- removes them. As it's scanning, if it finds a Relay
- Agent Information option field containing an Agent ID sub
- option that matches one of its IP addresses, that option
- is recognized as its own. If no such option is found,
- the relay agent can either drop the packet, or relay it
- anyway. If the -\b-D\bD option is specified, all packets that
- don't contain a match will be dropped.
-
-S\bSP\bPE\bEC\bCI\bIF\bFY\bYI\bIN\bNG\bG D\bDH\bHC\bCP\bP S\bSE\bER\bRV\bVE\bER\bRS\bS
- The name or IP address of at least one DHCP server to
- which DHCP and BOOTP requests should be relayed must be
- specified on the command line.
-
-S\bSE\bEE\bE A\bAL\bLS\bSO\bO
- dhclient(8), dhcpd(8), RFC2132, RFC2131, draft-ietf-dhc-
- agent-options-03.txt.
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-B\bBU\bUG\bGS\bS
- It should be possible for the user to define the Circuit
- ID and Remote ID values on a per-interface basis.
-
- The relay agent should not relay packets received on a
- physical network to DHCP servers on the same physical net
- work - if they do, the server will receive duplicate pack
- ets. In order to fix this, however, the relay agent
- needs to be able to learn about the network topology,
- which requires that it have a configuration file.
-
-A\bAU\bUT\bTH\bHO\bOR\bR
- d\bdh\bhc\bcr\bre\bel\bla\bay\by(\b(8\b8)\b) has been written for the Internet Software
- Consortium by Ted Lemon <mellon@fugue.com> in cooperation
- with Vixie Enterprises. To learn more about the Internet
- Software Consortium, see h\bht\btt\btp\bp:\b:/\b//\b/w\bww\bww\bw.\b.v\bvi\bix\bx.\b.c\bco\bom\bm/\b/i\bis\bsc\bc.\b. To learn
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-dhcrelay(8) dhcrelay(8)
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- more about Vixie Enterprises, see h\bht\btt\btp\bp:\b:/\b//\b/w\bww\bww\bw.\b.v\bvi\bix\bx.\b.c\bco\bom\bm.\b.
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projects / thirdparty / dhcp.git / commitdiff
