[Serusers] Notes on converting a Cisco CM phone for SIP

[Niall O'Reilly]

FWIW.  I hope this may save someone some time and effort.

Cisco provides documentation on how to convert a Cisco model 79XX phone
from a CM configuration to a SIP configuration.

I've recently converted two phones.  With the first one, everything went
deceptively easily.  As I discovered later, this was because my TFTP
server was the same system which had answered the DHCP request from the
phone.  This was accidental, as the LAN where the phone was connected
was served by two DHCP servers: one on the same LAN, the other further
away.  The local one responded more quickly to the DHCP request, and
happened also to be the relevant TFTP server.

For the second phone, on a different LAN, a suitable local server was
found which could provide the TFTP service.  The DHCP servers, however,
were on remote LANs.  The following configuration statements were used
with ISC dhcpd to point the phone at the local TFTP service.

	# Top of file, among global configuration statements
	# Define an option called 'option-150'

	option option-150 code 150 = ip-address;

	# This host is the 'first phone' mentioned above

	host blower {
		hardware ethernet 00:0f:23:00:13:3f;
		fixed-address 192.168.2.108;
	}

	# This host is the 'second phone' mentioned above

	host squawk {
		hardware ethernet 00:11:5c:93:ab:69;
		fixed-address 192.168.150.33;
		option tftp-server-name "local-server.example.com";
		server-name "local-server.example.com";
		next-server local-server.example.com;
		option option-150 local-server.example.com;
	}

This section of the configuration file was developed incrementally
until the phone loaded its SIP configuration.  The 'server-name'
and 'next-server' statements probably have no useful effect. It
was simply convenient to leave them in place rather than to edit
the configuration again.

The 'option tftp-server-name' statement is needed once the phone
has been configured for SIP, as the SIP firmware (?) uses option
66, which is set by this command, to identify the TFTP server.

The 'option option-150' statement is needed before the phone has
been configued for SIP, as the CM firmware uses option 150 for
the same purpose.

Although the Cisco document mentions option 66 as specifying the
_address_ of the TFTP server,  Droms' and Lemon's book describes
this option as specifying the _name_ of the server; this is what
the ISC server expects.

Bear in mind that domain names to be passed as names in DHCP options
are specified to the ISC server as quoted strings; in contrast,
domain names to be passed as addresses in DHCP options are specified
without quotes.

Web searches for 'converting call manager phone sip' and 'droms lemon'
will probably find the Cisco document and book mentioned above.

Best regards,

Niall O'Reilly

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