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DHCP Generic Setup

This document is limited to describing a generic administration that works with the 9600 Series IP Telephones. Three DHCP software alternatives are common to Windows operating systems:

Any other DHCP application might work. It is the responsibility of the customer to install and configure the DHCP server correctly.

DHCP server setup involves:

  1. Installing the DHCP server software according to vendor instructions.
  2. Configuring the DHCP server with:

NOTE: 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, 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 9:  9600 Series IP Telephone Customizable 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.

The 9600 Series IP Telephones do not support Regular Expression Matching, and therefore, do not use wildcards. For more information, see Administering Options for the 9600 Series IP Telephones.

In configurations where the upgrade script and application files are in the default directory on the HTTP server, do not use the HTTPDIR=<path>.

You do not have to use Option 242. If you do not use this option, you must ensure that the key information, especially HTTPSRVR and MCIPADD, is administered appropriately elsewhere.

Avaya recommends that you administer DHCP servers to deliver only the options specified in this document. Administering additional, unexpected options might have unexpected results, including causing the IP telephone to ignore the DHCP server.

The media server name and HTTP server name must each be no more than 32 characters in length.

Examples of good DHCP administration include:

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® DHCP reserves expired leases for about one day. This reservation 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 telephones, two of which are using the two available IP Addresses. When the lease for the first two telephones expires, the third telephone cannot get a lease until the reservation period expires. Even if the other two telephones are removed from the network, the third telephone remains without a lease until the reservation period expires.

In Table 7, the 9600 Series IP Telephone sets the system values to the DHCPACK message field values shown.

Table 7:  DHCPACK Setting of System Values 
System Value
Set to
IPADD
The yiaddr field.
NETMASK
Option #1 (if received).
GIPADD
Option #3 (if received, which might be a list of IP Addresses).
TLSSRVR
The siaddr field, if that field is non-zero.
HTTPSRVR
The siaddr field, if that field is non-zero.
DNSSRVR
Option #6 (if received, which might be a list of IP Addresses).
DOMAIN
Option #15 (if received).
DHCP lease time
Option #51 (if received).
DHCP lease renew time
Option #58 (if received).
DHCP lease rebind time
Option #59 (if received).

The system values L2Q, L2QVLAN, and PHY2VLAN are not set from a name=value pair if those system values were previously set by LLDP. For more information, see Link Layer Discovery Protocol (LLDP).


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