Hi Muhammed,
I understand what you are trying to achieve but unfortunately a direct solution/feature to address this problem isn't available.
Let's take a look at a few example scenarios:
Case 1:
Primary - MCS-7815-I2
Secondary - C2951-CME
When you enter the configuration for redundancy in this case, you will create a DHCP Pool on the CCM (or extenal DHCP) and additionally will create a SRST Reference in the Call manager with the IP of the CME.
Once you do that the Configuration File for the Phone reflets something like this:
TFTP Server 1 - MCS-7815-I2 (IP ADDR)
Alternate TFTP - C2951-CME (IP ADDR)
You can see the same on the phone as well under Network Configuration once the phone is registered.
Now, when the MCS fails the phone knows that it has a secondary entry for the TFTP to contact and sends a request to the TFTP server which is CME in this case. CME being configured with either CCM Fallback or Telephony configuration is equipped to handle this request and register the stranded phones from MCS.
This is pretty much the normal failover procedure.
Case 2:
Primary - C2951-CME
Secondary - MCS-7815-I2
In Simple terms on the CME we do not have a provision to provide a SRST reference where in we can define the IP of the MCS as the TFTP server. Since that cannot the phones would not be able to fall back automaticall to the MCS.
Other than that, CME has features to handle SRST like auto-registering the phones and preserving the existing DNs from the CCM but MCS would not be able to do that, we would need to have a manually created exact replica of the configuration on MCS that should match CME at all times to cater the failover.
Suggestion:
1. We setup 2 external DHCP servers with the exact IP Pool Range.
2. The only difference would be the Option 150 IP Address.
DHCP_Pool_CME - This would have the Option 150 set to point the CME TFTP
DHCP_Pool_MCS - This would have the Option 150 point to the MCS TFTP
We can however only keep one pool active at a given point of time. Once we know that the CME has failed or the connectivity has broken we can switch the DHCP by turning off the 1st pool and activating the 2nd pool.
This would enable the phones point to the MCS and request registration.
However, in this case we would still need to make sure that MCS has all the configuration and updated configuration that will be needed by the phones to operate.
Hope this helps !
Disclaimer - This has not been tested out in the lab and would not an ideal configuration as per Cisco.
Regards
Yash Joshi
CCIE Voice # 31109
Regards
Yash Joshi
CCIE Voice # 31109
