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DHCP Server Administration
Issue 2 December 2007 57
- Option 42 - SNTP Server.
This option specifies a list of IP Addresses indicating NTP servers available to the
telephone. List servers in the order of preference.The minimum length is 4, and the
length must be a multiple of 4.
- Option 51 - DHCP lease time.
If this option is not received, the DHCPOFFER is not be accepted. Avaya
recommends a lease time of six weeks or greater. If this option has a value of
FFFFFFFF hex, the IP Address lease is assumed to be infinite as per RFC 2131,
Section 3.3, so that renewal and rebinding procedures are not necessary even if
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 telephone
does not change if it is briefly taken offline.
Note:
Note: Regarding Option 51: The DHCP standard states that when a DHCP lease
expires, the device should immediately cease using its assigned IP Address. If
the network has problems and the only DHCP server is centralized, the server is
not accessible to the given telephone. In this case the telephone is not usable
until the server can be reached. Avaya recommends that once assigned an IP
Address, the telephone continues using that address after the DHCP lease
expires, until a conflict with another device is detected. As Table 11:
9600 Series
SIP IP Telephones Customizeable System Parameters indicates, the system
parameter DHCPSTD allows an administrator to specify that the telephone 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 telephone sends an ARP Request for its own IP Address
every five seconds. The request continues either forever, or until the telephone
receives an ARP Reply. After receiving an ARP Reply, the telephone displays an
error message, sets its IP Address to 0.0.0.0, and attempts to contact the DHCP
server again.
- Option 52 - Overload Option, if desired.
If this option is received in a message, the telephone interprets the sname and file
fields in accordance with IETF RFC 2132,
Section 9.3, listed in Appendix B: Related Documentation
.
- Option 53 - DHCP message type.
Value is 1 (DHCPDISCOVER) or 3 (DHCPREQUEST).
- Option 55 - Parameter Request List.
Acceptable values are:
1 (subnet mask),
3 (router IP Address[es])
6 (domain name server IP Address[es])
7 (log server)
15 (domain name)
26 (Interface MTU)
42 (NTP servers)
SSON (site-specific option number)