DHCP Server Administration
-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:
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
Issue 2 December 2007 57
