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Cisco IP Phone 7821 unkown registration status

Hi Guys,

Hope find you all well! Since I'm running out of ideas, I decide to open this new discussion. My end customer has a CUCM cluster with one Publisher and two Subscribers, version

For some reason, some IP Phones model 7821 (SIP) are not getting registered on the CUCM and I can see that they have the "Unknow" status. This is what I already tried to solve the issue:

- delete the phones from the CUCM and add them again;

- reboot the CUCM cluster

- install the last available firmware version on all nodes and restart the TFTP

- factory reset the phones

Now comes the funnest part: the end customer has a separated CUCM cluster that is running version 12.0. If I change the voice vlan (Voice VLAN here the new CUCM cluster is) on the switch ports where this phones are connected the phones are able to get register on the new CUCM.

Question: Can this be an issue related with firewall or something like that? It's strange because I'm able to ping the IP address of the affects IP Phones from all the nodes (old cluster).

Any help will be much appreciated.

Thank you!


Bruno Marques

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