Aastra 9000i Series Administrator's Manual page 185

Multiple DHCP Servers
The IP Phones can receive messages from multiple DHCP servers.
After the phone receives its first DHCP message, it listens for a specific time period, for more
DHCP messages. If the first DHCP offer contains configuration server information (Options 43,
66, 159 or 160), then the phone times out and continues using the first DHCP offer, without
listening for more DHCP offers. If the first DHCP message contains no configuration server
information, the phone continues to listen for other DHCP messages. If the second DHCP
message contains configuration server information and other conditions, the phone chooses the
second DHCP message over the initial DHCP message.
IMPORTANT NOTE
Users currently using multiple DHCP servers on a single network could be affected by this
feature.
DNS Caching
The IP phones have the ability to cache DNS requests according to RFC1035 and RFC2181. The
phone caches DNS lookups according to the TTL field, so that the phone only performs another
lookup for an address when the TTL expires.
4-22
Note: If the DHCP Download Options parameter is enabled with a
value (Option 43, Option 66, Option 159, or Option 160), the phone
checks the override option setting before timing out.
41-001343-01 Rev 02, Release 3.2.2