These commands are not needed for the IP phones if the automated setup is used because the setup will prompt for these setting and configure a DHCP scope automatically. ■ Request configuration from TFTP server - The IP phone will use the value received in option 150 to attempt to get a configuration file from the TFTP server ( Cisco CME router is always the TFTP server in Cisco CME) ■ IP phone initialized DHCP settings - The IP phone will take the values received from the DHCP response and apply them to the IP stack of the IP phone ■ DHCP Offer -The Scope setting will be sent to the DHCP client (the IP phone) using the broadcast address of 255.255.255.255 ■ DHCP server assigns an IP address - If this broadcast is heard by a local DHCP server, the server will assign a free IP address, the subnet mask for the scope, the default gateway for the scope, the DNS server (optional) for the scope, and a TFTP server ( option 150) for the scope ■ Send DHCP Discover - By default, the IP phone (DHCP client) will then send a DHCP request to the 255.255.255.255 broadcast address The process of a phone booting up continues with the following: The IP phone requests it configuration file from the TFTP server The IP phone initializes applies the IP configuration to the IP stack IP phone send DHCP Discover broadcast requesting an IP addressĭHCP server selects a free IP address from the pool and sends along with the other scope parameters as a DHCP Offer ■ Initialize the IP stack - The IP phone will then initialize a basic IP stack. ■ Discover the Voice VLAN - Learn which VLAN is the voice VLAN through the layer 2 Cisco Discovery Protocol (CDP).
■ Boot - The IP phone will then bootstrap ■ POST - The phone will perform some basic tests called a Power On Self Test (POST). ■ Receives power - The IP phone receives power When an IP phone first receives power, the following steps happen: On the Cisco CME router a DHCP Scope can be configured. Through CDP the IP phone learns what the auxiliary VLAN is The phone performs a Power on Self Test (POST)
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