[Asterisk-Users] DHCP, the TFTP Server setting and the Cisco 79xx phones

[Paul Rodan]

The thing I dislike the most about the 79xx phones is that in DHCP mode,
they expect the DHCP server to tell them their TFTP server address. They
won't let you set it manually. So if I don't have  DHCP server that gives
TFTP server info, which is most of the DHCP servers at out there, then the
phone won't be able to download any updates made to the SIP000*.cnf file. 

 

Using dhcpd on my full blown linux, I've added:

 

  next-server 10.5.5.1;

  option tftp-server-name "10.5.5.1";

 

to dhcpd.conf and that makes the phones take it fine. Initially I only
needed the "next-server" option, but I found the oldest firmware's of the
79xx sometimes ignored this parameter, I added "option tftp-server-name" and
that seems to have fixed the problem. It's probably only in my head, but you
never know.

 

Anyways, I'm playing with the LinkSys WRT54G router now with OpenWRT
installed. I'm trying to use dnsmasq to give the same parameters. In
dnsmasq.conf I've added:

 

"dhcp-option=66,10.5.5.1"

 

But the Cisco phones are ignoring it. According to RFC2132, DHCP Option/Code
66 is the TFTP server name. But the Cisco 79xx phones I've tested are
ignoring this.

 

My question is this, does the Cisco 79xx IP Phones use a different DHCP Code
(other than 66) to define its TFTP server?

 

Also, does the Cisco 79xx honor DHCP Option 42, which defines the NTP
server? Or does it only honor the "sntp_server=" option in its config file?

 

 

Maybe there's a way to query the dhcp server on my Linux server and figure
out which DHCP codes it's offering. I can then mimick it with dnsmasq?

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