Cisco IP Phone 6921 not registered

[Ahmed habib]

I have two IP Phones 6921 when I connect them to the network they show phone not registered or network unavailable and when I go to the network settings the phone suddenly take an IP and become registered and can make calls then become not registered again and so on.

I make factory reset to them but nothing change.

I want to know what is the problem !

[R0g22]

Where are you trying to register these phones ? So per you the phones do not take an IP until you go into the settings ?
When the phones don't register, instead of network settings, can you look at the status messages ?

[M02@rt37]

Hi,

SIP or SCCP firmware for your 6921 IP phone?

Try to mirror your IP phone port with wireshark to check the deconnection cause.

Do U check the settings of the dhcp server?

I think the fact that you go to the network settting on your 6921 is not the reason why thé phone can be registered and had an IP@.

Stay on the main screen of your IP phone and check if it restart again even if registration is OK few seconds.

Check also the "status messages" on your IP phone.

Regards