Data Domain Replication Proxy

Hello everyone.
We want to set up DataDomain replications. The problem is that the two DataDomains cannot communicate directly with each other, but have to go through a proxy.
A proxy can also be specified in the DDOS GUI under "Add System". However, we cannot find anything about the proxy in any DELLEMC documentation. What kind of proxy is required or can it be used as a proxy? A Squid web proxy? A VMware Reverse Proxy (UAG)? At DELLEMC there is also no software component that can serve as a proxy.
Thank you for your feedback.