I checked vpp behavior when Nat is enabled to face packets with Time To Live (TTL) value of 1. I'm using vpp version of v19.08-rc0 on master branch.

I configured a simple nat scenario with static mapping when client send an icmp packet with TTL 1, vpp drops the packets without generating any reject icmp message.

hint:

Nat plugin checks TTL and redirect packets to error drop node but related icmp reject message is not generated and sent to client. Isn't it due to bypassing ip4-rewrite node in some arcs in packet flow? ( one of its responsibility is checking packet TTL and decreasing it one unit )