Netbackup and DataDomain

https://my.datadomain.com/download/whitepapers/DD-WP-OST-BestPractices.pdf

The network used for optimized duplication is based on network
name resolution on the source Data Domain system. The destination
Data Domain system is known to the source Data Domain
system based on the IP address supplied by DNS, or by a local
hosts file entry. Populating the source Data Domain systems hosts
file with the desired IP address of the destination Data Domain
system is all that is required to use a specific NIC and network.
If this value is not present, NetBackup will perform optimized
duplication using the same network it uses to access the source
and destination Data Domain systems for backup and restore jobs.

If you want to configure replication network, just register host name of DD with IP address of replication network using "net hosts" command. You do it on both DD only, do not edit hosts file on NetBackup server.

# net hosts show
# net hosts delete <public_network_address>  (IF hostname is already registered with public IP)
# net hosts add <replication_network_address> <peer_DD_hostname>