Nitro instances-built in encryption in transit

My customer is planning to use Nitro instances as worker nodes in EKS to get the built in encryption in transit between nodes. However they want to understand how they can verify the traffic between the nodes are indeed encrypted. Any documentation or steps to prove that encryption in transit does occur?

https://aws.amazon.com/about-aws/whats-new/2019/10/introducing-amazon-ec2-m5n-m5dn-r5n-and-r5dn-instances-featuring-100-gbps-of-network-bandwidth/