The role of the mesh gateway or cross-cluster gateway is very important as it provides a flat network that we can use to connect multiple Consul clusters, regardless of their location in a zero-trust network environment through mutual TLS. 

This can be seen in the following diagram:

Two Consul servers are running in a Kubernetes environment and one Consul server is running in a VM. server-2 is the leader in both data centers.

The mesh gateway works as follows: 

1. The Consul web service receives traffic through the Ingress gateway from the internet.
2. service-defaults for the api Consul service (residing on DC2) is defined using the local mode of the mesh gateway.
3. service-resolver for api redirects the traffic to DC2.
4. When the web application invokes the api service, it goes through the mesh gateway of DC1, and the service resolves to the api service on DC2.
5. The traffic is mTLS between two configured gateways and between services and the mesh gateway.
6. The mesh gateway does not decrypt network traffic.

This concludes the mesh gateway, which is used to securely connect Consul clusters.