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How does an IP Telephone achieve conciousness?

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leopard96

MIS
Apr 18, 2004
43
US
I'm currently managing an AVVID IP Tel system with about 500 users in three locations. I'm doing alright so far but I have been trying to find a good explanation about how a telephone comes up and knows where to go. Does the phone wake up and use CDP to discover the switches around it and the switches put it in an AUX VLAN or does it just power on and issue a BOOTP/DHCP Req to whatever is listening and then a Call Manager who already has the phone's MAC and knows what to send it? This is the best I've got so far but I'd like to know a little more about the specifics of the process if anyone has this. Its not critical but I'd just like to understand it a little more. I could be way off for all I know. No one else around me seems to know how the phone wakes up and gets going.
Thanks in advance!
 
The cisco phones use CDP to determine the "voice vlan"

its call AUX vlan on the Catalyst OS based switches.
voice vlan for IOS based switches.


Then once they know the vlan, they start broadcasting for DHCP requests, in the dhcp lease, tehre is option 150 which is the TFTP server and then it uses that address to pull its config file from the CCM servers...

Then in the config file, the rest of the info comes down.


BuckWeet
 
One thing I've learned...

If using a non-Cisco managed switch, it can't use CDP to find the voice vlan.

In the menu of the phone itself, you can go to Settings, **# (star star pound) and then hit 3 (Network Settings). Scroll down and you can edit the Admin VLAN ID to whatever voice vlan you need.

It's manual, yes, and probably not the ideal solution, but it does work and the phone does know how to go get the info it needs.

--DW
 
Can't you just change the native VLAN of the port to the voice vlan? I would think that would do the same thing. I run all Cisco infrastructure so i don't have the problem.


It is what it is!!
__________________________________
A+, Net+, I-Net+, Certified Web Master, MCP, MCSA, MCSE, CCNA, CCDA, and few others (I got bored one day)
 
Yup, that works too... but here's the part I left off...

vlan3 is our data vlan... "native" vlan if you will.

vlan10 is our voice vlan...

on the Cisco, an IP phone port would look like this...

interface FastEthernet0/1
description Connection to IP Phone
switchport trunk encapsulation dot1q
switchport trunk native vlan 3
switchport mode trunk
switchport voice vlan 10
spanning-tree portfast
!

and the phone magically works, get's an IP from teh vlan 10 (different subnet 172.l6.x.x) and then the passthrough port on the 7960/7940 phone gets an IP from subnet 3 (192.168.x.x).

With the non-Cisco managed switches I use, I set things up equiv. to that, trunk... dot1q... native 3... and then allow access to vlan 10... I still need the passthrough to be vlan3, but must allow access to vlan10 for the phones. CDP won't find the voice vlan, so I have to manually tell the phone where to go...

I should have been more clear :)

--DW
 
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