This specifies which local interface's address should be used as the source IP for outgoing key synchronization packets when the session type is manual. This lets an administrator control which physical or logical interface a peer sees the key-sync session originating from, which matters on devices with several management or line interfaces. For example, on a node with both an in-band data port and a dedicated management port, setting keySyncSessionSourceAddressFrom to the management interface keeps encryption-key traffic off the customer-facing data path.