User guide

DHCP client Dynamic Host Configuration Protocol
5-5
iMG/RG Software Reference Manual (System Administration)
Addresses allocated by DHCP expire after the specified lease time runs out. If this happens, the DHCP client
must relearn its configuration by repeating the process described above. The client will attempt to initiate
renewal of a held lease well before it is due to expire (approximately half way through the total duration of the
lease). This avoids the problem of an active interface being unexpectedly disabled and dropping normal IP traffic.
The DHCP client on the AT-RG624/634 DHCP conforms to most of the specification given in RFC2131. A sub-
set of the DHCP options described in RFC2132 is supported.
The residential Gateway DHCP client accepts and makes use of the following information:
• IP address
• Subnet mask
• Default route (one only)
• Domain name servers (up to two can be usefully supported by DNS relay)
• Host name or DHCP-client-identifier. This option can be used to specify a client identifier in a host declara-
tion, so that a DHCP server can find the host record by matching against the client identifier. This option
can be useful when attempting to operate the DHCP client with a Microsoft DHCP server.
Note: When attempting to use a DHCP client with a Microsoft DHCP server, then send dhcpclient-identifier is
mandatory, and must be specifically set to the MAC address of the device upon which the client is
running; otherwise DHCP will not work at all.
5.1.3.1 Lease requirements and requests
The DHCP protocol allows the client to request that the server send it specific information, and not send it
other information that it is not prepared to accept. The protocol also allows the client to reject offers from
servers if they do not contain information the client needs, or if the information provided is not satisfactory.
Using the DHCPCLIENT INTERFACE CONFIG ADD REQUESTED OPTION command causes the client to
request that any server responding to the client send the client its values for the specified options. Only the
option names should be specified in the request statement - not option parameters.
Using the DHCPCLIENT INTERFACE CONFIG ADD REQUIRED OPTION command configures a list of
options that must be sent in order for an offer to be accepted. Offers that do not contain all the listed options
will be ignored.
Using the DHCPCLIENT INTERFACE CONFIG ADD SENT OPTION command causes the client to send the
specified options to the server with the specified values. Options that are always sent in the DHCP protocol
should not be specified here, except that the client can specify a requested-lease-time option other than the
default requested lease time, which is two hours. The other obvious use for this statement is to send informa-
tion to the server that will allow it to differentiate between this client and other clients or kinds of clients.