Symptom:
when we have this setup and sending traffic from left to right as shown below
TestTool ----PE1----P1----P2---P3(NCS5500)---PE2----TestTool (using wireShark capture to capture before and after changing the TTL value at TestTool on the left.)
we observed the TTL value was not propagate properly end to end. There is No traffic lost.

Conditions:
1st, we send as default TTLin the TestTool (255) from left, and capture the packets at the right, save the capture as results_before.pcap, Then, we change the TTL value to 100 at the TestTool and let it run for some time and capture the packets at the right side, it's called results_after.pcap. We found that, the TTL value is still 252.