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IP Phones go down and reboot

                   Hi everyone,

I am sooo new to this phone system thing but we are a small business and we hav Cisco IP phones. recently they keep having problems. sometime one of them shut downs and we have to remove the cable and plug it in back to make it come up and re-register, and sometimes some of them reboot them selves, and there was couple of times that all the phones got rebooted together and sometimes all of them go down and we have to restart the router for them to come up.

I go into every phone by typing their IP in the IE and when i go to status message i get this:

No DNS server IP

DNS unknown Host

No CTL installed

TFTP timed out

and somethings like this.

Can anyone help me with this?


paolo bevilacqua
Hall of Fame Master

Probably your network is unstable, so phones loose connection, and reboot.

Can you tell me how can I troubleshoot that? this network is so vague to me and I dont know much abou tphone systems..

Check your switch configurtion, DHCP Server Configuration, and use this doc too might help you:


Leonardo Santana

what should I check on them?

Take a look on the documentation.

Step 1 Check for inline/PoE power issues.

Step 2 Check IP addressing and DHCP.

Step 3 Check for IP network connectivity.

Step 4 Check for CM issues.

What solution you have? CME? CUCM?


Rate this if helps you

Leonardo Santana

Oh i told you I am new to all of these, I dont even know its CME or CUCM and i dont know what they are.

all I know is I get connected to a router named UC520 and from there i can get connected to CUE and I dont even know what they are exactly.

on my phone, the address of DHCP and TFTP server is that same IP as UC520 router.


First you have to unterstand the boot proccess of the ip phones:

Ok check, when then unregister the ip phones lost the ip?

If you wanna to solve you have to understand the problem first, know the ip phone boot process.

Step 1 Check for inline/PoE power issues.

Step 2 Check IP addressing and DHCP.

Step 3 Check for IP network connectivity.

Step 4 Check for CM issues.

Ok Thanks, but two questions:

how can i figure out I am using CUCM or CME?

and what does that mean theat my phone's TFTP and DHCP server is pointing to UC520 router?

and what is the role of that router and of CUE and how can i find my DHCP and TFTP server?is it possible if they are the same router(UC520)


CUCM/CME are another Cisco Solutiion.

What means is that one the TFTP is where the IP Phones requests the config file (extension, permission..), second your UC520 Router seems to be the DHCP Server of your network.

The UC520 is your IP PBX, you can validate using the command sh run on the UC520.

Try to find the dhcp pool configuration, follow an dhcp config example:

ip dhcp excluded-address 

ip dhcp excluded-address


ip dhcp pool 0

 network /16




Thank you so much for your help, I really appreciate it, it is getting more clear to me right now.

Yes I've found out the DHCP config on UC520. Now what is the next step in troubleshooting? what should I check about the DHCP and IP addresses?

It seems like my dns IP is not even operational. and where can I find my TFTP server?

sorry for all the questions

can you post your dhcp config?

you can use the command sh ephone registered to see your ip phones registered.

this is my DHCP config:

ip dhcp relay information trust-all

ip dhcp excluded-address

ip dhcp excluded-address

ip dhcp excluded-address

ip dhcp pool phone



   option 150 ip

And how is that command gonna help me troubleshoot?

Your TFTP Address is

When the IP Phones lost the register see if they lost the ip address, can you post the sh logging of your router.

Your are conected to an switch correct? They are using PoE?

Verify your interface that is using this IP, post he sh interfaces too.

Put the commands output on an notepad an attach to this discussion.


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