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4.4 DHCP client behavior Connected: An Internet Encyclopedia
4.4 DHCP client behavior

Up: Connected: An Internet Encyclopedia
Up: Requests For Comments
Up: RFC 2131
Up: 4. Specification of the DHCP client-server protocol
Prev: 4.3.6 Client messages
Next: 4.4.1 Initialization and allocation of network address

4.4 DHCP client behavior

4.4 DHCP client behavior

Figure 5 gives a state-transition diagram for a DHCP client. A client can receive the following messages from a server:

  • DHCPOFFER

  • DHCPACK

  • DHCPNAK

The DHCPINFORM message is not shown in figure 5. A client simply sends the DHCPINFORM and waits for DHCPACK messages. Once the client has selected its parameters, it has completed the configuration process.

Table 5 gives the use of the fields and options in a DHCP message by a client. The remainder of this section describes the action of the DHCP client for each possible incoming message. The description in the following section corresponds to the full configuration procedure previously described in section 3.1, and the text in the subsequent section corresponds to the abbreviated configuration procedure described in section 3.2.

 --------                               -------
|        | +-------------------------->|       |<-------------------+
| INIT-  | |     +-------------------->| INIT  |                    |
| REBOOT |DHCPNAK/         +---------->|       |<---+               |
|        |Restart|         |            -------     |               |
 --------  |  DHCPNAK/     |               |                        |
    |      Discard offer   |      -/Send DHCPDISCOVER               |
-/Send DHCPREQUEST         |               |                        |
    |      |     |      DHCPACK            v        |               |
 -----------     |   (not accept.)/   -----------   |               |
|           |    |  Send DHCPDECLINE |           |                  |
| REBOOTING |    |         |         | SELECTING |<----+            |
|           |    |        /          |           |     |DHCPOFFER/  |
 -----------     |       /            -----------   |  |Collect     |
    |            |      /                  |   |       |  replies   |
DHCPACK/         |     /  +----------------+   +-------+            |
Record lease, set|    |   v   Select offer/                         |
timers T1, T2   ------------  send DHCPREQUEST      |               |
    |   +----->|            |             DHCPNAK, Lease expired/   |
    |   |      | REQUESTING |                  Halt network         |
    DHCPOFFER/ |            |                       |               |
    Discard     ------------                        |               |
    |   |        |        |                   -----------           |
    |   +--------+     DHCPACK/              |           |          |
    |              Record lease, set    -----| REBINDING |          |
    |                timers T1, T2     /     |           |          |
    |                     |        DHCPACK/   -----------           |
    |                     v     Record lease, set   ^               |
    +----------------> -------      /timers T1,T2   |               |
               +----->|       |<---+                |               |
               |      | BOUND |<---+                |               |
  DHCPOFFER, DHCPACK, |       |    |            T2 expires/   DHCPNAK/
   DHCPNAK/Discard     -------     |             Broadcast  Halt network
               |       | |         |            DHCPREQUEST         |
               +-------+ |        DHCPACK/          |               |
                    T1 expires/   Record lease, set |               |
                 Send DHCPREQUEST timers T1, T2     |               |
                 to leasing server |                |               |
                         |   ----------             |               |
                         |  |          |------------+               |
                         +->| RENEWING |                            |
                            |          |----------------------------+
                             ----------
          Figure 5:  State-transition diagram for DHCP clients


Next: 4.4.1 Initialization and allocation of network address

Connected: An Internet Encyclopedia
4.4 DHCP client behavior

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