I have a trunk (Non-gatekeeper) between the legacy CCM 4.12 system and the new CCM 6.0. The trunk on the CCM 4 has the SUB then PUB listed, same on the CCM 6 side. Calls flow from the CCM 4 side to CCM 6 side no problem. Calls do not work from the CCM 6 to the CCM 4. Now here is the interesting part. This was working when I only had the PUB running on the CCM 6 side. I just added the SUB. So, I changed the server group to have the SUB listed first and moved the PUB to second. But I have updated the trunk config to match. But if I move the PUB up in the list and leave everything else the same and do a reset everything starts working again.