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:

• Windows NT^® 4.0 DHCP Server
• Windows 2000^® DHCP Server
• Windows 2003^® DHCP Server

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:
• IP addresses available for the 9600 Series IP Telephones.
• The following DHCP options:
• Option 1 - Subnet mask.
  As described in Table 3, item 3.
• Option 3 - Gateway (router) IP address(es).
  As described in Table 3, item 1. If using more than one address, the total list can contain up to 255 total ASCII characters. You must separate IP addresses with commas with no intervening spaces.
• Option 6 - DNS server(s) address list.
  If using more than one address, the total list can contain up to 127 total ASCII characters. You must separate IP addresses with commas with no intervening spaces. At least one address in Option 6 must be a valid, non zero, dotted decimal address.
• Option 12 - Host Name.
  Value is AVohhhhhh, where: o is “A” if the OID (first three octets) of the MAC address for the telephone is 00-04-0D. “E” if the OID is 00-09-6E, “L” if the OID is 00-60-1D, and “X” if the OID is anything else and where hhhhhh are ASCII characters for the hexadecimal representation of the last three octets of the MAC address for the telephone.
• Option 15 - DNS Domain Name.
  This string contains the domain name to be used when DNS names in system parameters are resolved into IP addresses. This domain name is appended to the DNS name before the 9600 IP Telephone attempts to resolve the DNS address. Option 15 is necessary if you want to use a DNS name for the HTTP server. Otherwise, you can specify a DOMAIN as part of customizing HTTP as indicated in DNS Addressing.
• 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: 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 7:  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.

• 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])
    15 (domain name)
    NVSSON (site-specific option number)
• Option 57 - Maximum DHCP message size.
• Option 58 - DHCP lease renew time.
  If not received or if this value is greater than that for Option 51, the default value of T1 (renewal timer) is used as per IETF RFC 2131, Section 4.5, listed in Related Documentation.
• Option 59 - DHCP lease rebind time.
  If not received or if this value is greater than that for Option 51, the default value of T2 (rebinding timer) is used as per RFC 2131, Section 4.5

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 DNS administration include:

• Option 6: “aaa.aaa.aaa.aaa”
• Option 15: “dnsexample.yourco.com,zzz.zzz.zzz.zzz”
• Option 242: “MCIPADD=xxxx.xxx.xxx.xxx”

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 5, the 9600 Series IP Telephone sets the system values to the DHCPACK message field values shown.