Assume you have a Media Agent on client name media_agent.com, the official hostname, and there is a second LAN on the same host with the address media_agent_bkup.com which you which to use to perform backups.
Ensure the Data Protector client is installed on media_agent.com and media_agent_bkup.com is imported as a virtual host. Configure a Media Agent for both client names media_agent.com and media_agent_bkup.com. When configuring a backup, choose the Media Agent configured on the client which corresponds to the LAN you which to use for backing up the data. The Session Manager will tell the Disk Agent to connect to the Media Agent via the backup LAN. It is possible to configure a backup so that multiple objects on a backup host can be backed up across both LANs concurrently by configuring both Media Agents in the same backup.
It is important to note the client name of the Disk Agent does not determine which LAN is used for data backup. The LAN used for data backup is based on the client name configured for the Media Agent. Also, when a session is run, the Media Agent is reported as starting on the official hostname even if connections are via a different LAN.