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

[Kristian Kielhofner]

Paul Rodan wrote:

> 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?

Paul,

	Try DHCP option 150.  I don't know what is about about those Cisco's, 
but they sure are picky (and evidently not RFC Compliant).

--
Kristian Kielhofner