Avaya SIP Software 3.2 for 1200 Series User Manual Page 84

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The DHCP request contains standard IP Deskphone IP DHCP option requests
from the point when the IP Deskphone does not receive the VLAN information.
These options include the Vendor Specific and all Site Specific options.
2. The DHCP server receives the request. If the server is configured, the DHCP server
returns a DHCP Offer message with a special text string in the Vendor Specific
option or one of the Site Specific options.
Following is the format of the text in the option:
VLAN-A:XXX+YYY+ZZZ+…
where VLAN-A is a substring followed with VLAN information. XXX, YYY, ZZZ are
the numbers of the supported VLANs. They can be from 1 to 10 different VLANs;
each VLAN is separated with the symbol +.
3. After receiving the DHCP Offer message, the IP Deskphone scans each Vendor
and Site Specific options for the string VLAN-A.
4. If the IP Deskphone finds the VLAN-A string, it tries each VLAN, and in turn XXX,
YYY, ZZZ searches for a DHCP server.
5. The search is done by sending a DHCP Discover message looking for a DHCP Offer
message as a response.
6. If the IP Deskphone finds a response, it discontinues its DHCP exchange on the
untagged channel and continues its DHCP exchange on the “discovered” VLAN.
7. If there is no response, the initial untagged Discover message assumes there is no
VLAN configuration information available from the DHCP server and continues
using untagged packets. When the IP Deskphone sends its first DHCP Discover
message, it does not know if it can find VLAN configuration information. If it does
discover VLAN information, it continues the VLAN configuration as described
above. If it does not find any VLAN information, then it assumes there is only a
Configuration Phase.
DHCP options
The DHCP protocol provides option mechanisms for the client and server to exchange
information in addition to the standard Bootstrap Protocol (BOOTP) information. This section
describes the client and server options supported by the IP Deskphone.
IP Deskphone to Server options on page 85
Server to IP Deskphone options on page 86
Configure the DHCP Server
84 SIP Software for Avaya 1200 Series IP Deskphones-Administration January 2012
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