Port 111 is the RPC portmapper port. See here for details.

Since years, NW uses an internal portmapper (especially on Windows).

If this port is blocked in firewall what will be the impact?

NW uses its own portmapper.  If you use version which uses system portmapper, you won't be able to initiate communication between server and client as portmapper is used to allocate/register ports used by host side daemons.

Hello!

Port 111 is used for client direct function.

If you need to use this function than port 111 needs to be opened between Data-Domain and all clients that are using this function.

Also this is a port mapper used to communicate with Storage node, vCenter ESXi hosts etc.