Page 114 - Asterisk™: The Future of Telephony

option time-offset -18000;
range dynamic-bootp 192.168.1.128 192.168.1.254;
default-lease-time 21600;
max-lease-time 43200;
}
Keep in mind that this assumes that the only things on this network are devices that
belong to the phone system (this setup will hand out an IP address to any device that
requests it). If you have a more complex environment, you will need to configure the
DHCP daemon to handle the various devices it is serving. For example, you might want
to devise a scope that restricts IP addresses in your voice LAN to Polycom phones. Since
all Polycom IP desk phones have 00:04:f2 as their OUI (Organizationally Unique Iden-
tifier), you might choose to restrict scope based on that.

In a Microsoft DHCP environment, the tftp-server-name is referred to
as Boot server host name. It is defined under option 66.

The DHCP protocol is far more flexible than is often realized, because in most envi-
ronments it is not used for complex provisioning tasks. With a little care and attention,
you can devise a DHCP environment that serves both your voice and data devices and
greatly simplifies administrative workload when adding new devices.

FTP server
†
FTP is currently our favorite way to configure Polycom sets. We would recommend it
over TFTP for any set that allows for both. To install it on your CentOS system, the
following command will install VSFTPD, the Very Secure FTP Daemon:
# yum -y install vsftpd
Then, in order to lock things down, we need to prevent anonymous logins with a simple
change to the vsftpd config file, /etc/vsftpd/vsftpd.conf:

# anonymous_enable=NO
Restart the server with service vsftpd restart. To ensure that the daemon runs after
every reboot, run chkconfig vsftpd on.
Now, we have to create a user account and group for the sets to use. In this case, we
will create an account for the Polycom sets:

† FTP is preferred over TFTP due to the ability of a Polycom phone to see timestamps on FTP files. This allows
the phone to avoid redownloading configuration files and firmware updates that it already has—thus
shortening boot time.

86 | Chapter 4: Initial Configuration of Asterisk