Avaya 9608 Administrator's Manual page 68

Server Administration
Options 58 and 59 are received. Expired leases cause Avaya IP Telephones to
reboot. Avaya recommends providing enough leases so an IP Address for an IP
deskphone does not change if it is briefly taken offline.
Note:
The DHCP standard states that when a DHCP lease expires, the device should
Note:
immediately cease using its assigned IP Address. However, if the network has
problems and the only DHCP server is centralized or if the DHCP server itself
has problems, the deskphone will not receive responses to its request for a
renewal of the lease. In this case the deskphone is not usable until the server can
respond.
Avaya recommends that once assigned an IP Address, the deskphone continues
using that address after the DHCP lease expires, until a conflict with another
device is detected. As indicates, the system parameter DHCPSTD allows an
administrator to specify that the deskphone will either:
a). Comply with the DHCP standard by setting DHCPSTD to "1", or
b). 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 deskphone 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 deskphone receives a DHCPACK, a
DHCPNAK, or an ARP Reply. After receiving a DHCPNAK or ARP Reply, the
deskphone displays an error message, sets its IP Address to 0.0.0.0, and
attempts to contact the DHCP server again. Log events are generated for either
case.
Depending on the DHCP application you choose, be aware that the application
most likely does not immediately recycle expired DHCP leases. An expired lease
might remain reserved for the original client a day or more. For example,
Windows NT
period protects a lease for a short time. 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 two IP Addresses, therefore two possible DHCP leases. Assume three
IP deskphones, two of which are using the two available IP Addresses. When the
lease for the first two deskphones expires, the third deskphone cannot get a
lease until the reservation period expires. Even if the other two deskphones are
removed from the network, the third deskphone remains without a lease until the
reservation period expires.
- Option 52 - Overload Option, if desired.
If this option is received in a message, the deskphone interprets the sname and file
fields in accordance with IETF RFC 2132, Section 9.3.
68 Deskphone SIP 9608, 9611G, 9621G, 9641G Administrator Guide Release 6.0.1
®
DHCP reserves expired leases for about one day. This reservation