request for a renewal of the lease. In this case the device is not usable until the server can respond.
Configure system such that once the IP address is assigned to the device, the device continues
using that address after the DHCP lease expires, until a conflict with another device is detected.
The system parameter DHCPSTD allows an administrator to specify that the device will either:
• Comply with the DHCP standard by setting DHCPSTD to 1.
• Continue to use its IP address after the DHCP lease expires by setting DHCPSTD to 0.
The latter case is the default. If the default is invoked, after the DHCP lease expires the phone
continues to broadcast DHCPREQUEST messages for its current IP address, and it sends an ARP
Request for its own IP address every five seconds.
The messages continue to be sent until the device receives a DHCPACK, a DHCPNAK, or an ARP
reply. After receiving a DHCPNAK or ARP reply, the device immediately stops using the current IP
address. The device displays the DHCPNAK: message for five seconds and then, sets the IP
address to 0.0.0.0. Duplicate address detection is no longer performed and the device enters the
DHCP INT state.
Depending on the DHCP application you choose, the application might not immediately recycle
expired DHCP leases. An expired lease might remain reserved for the original client a day or more.
If the client and the DHCP server are in two different time zones, the clocks of the computers are not
in sync, or the client is not on the network when the lease expires, there is time to correct the
situation.
The following example shows the implication of having a reservation period.
Assume that there are two IP addresses, therefore two possible DHCP leases. Assume that there
are three IP devices in the network, two of which are using the two available IP addresses. When
the lease for the first two devices expires, the third device cannot get a lease until the reservation
period expires. Even if the other two devices are removed from the network, the third device
remains without a lease until the reservation period expires.
Parameter configuration through DHCPACK
Parameter
Set to
DHCP lease
time
Option 51, if received
DHCP lease
renew time
Option 58, if received
DHCP lease
rebind time
Option 59, if received
DOMAIN
Option 15, if received
DNSSRVR
Option 6, if received, which might be a list of IP addresses
HTTPSRVR
The siaddr parameter, if that parameter is non-zero
Table continues…
DHCP options
September 2017
Installing and Administering Avaya J129 IP Phone
33
