Cisco Cucm - Block OffNet To OffNet Transfer

I got called to look into an issue for a customer who were in the process of migrating users from an old 8.6 to a new 11.0 cluster. PSTN access was being routed through the new cluster and calls worked fine, however there were issues with transfers failing in certain scenarios. 

The call flow was as follows - 

PSTN ----> SIP GW ----> V11 CUCM ----> V11 User ----> V8.6 CUCM ----> V8.6 User

After making a number of test calls and taking the appropriate traces I found the following in the SDL logs on the V11 cluster.

69285831.001 |15:11:13.743 |AppInfo |Transferring - Cannot Complete Transfer with PrimaryTransferredIsOffnetDevice =1, SecondaryTransferDestinationIsOffnetDevice =1

The message is clear that CUCM believes this to be an "OffNet To OffNet Transfer" which on this particular cluster was blocked in the service parameters for Toll Fraud prevention, however in my view this appeared to be an OffNet originated call, with a fully On-Net transfer and therfore shouldnt have met the block criteria.

I decided to look at the Sip Trunk between the cluster, which on investigation had been correctly classified as "On-Net"

I then looked at the route pattern that was being used to route from V11 to the 8.6 and found the culprit.

As you can see, the call classification is incorrectly set as "offnet". Once changed to "OnNet" transfers worked as expected.