In high load call centers (more than 50 concurrent calls) it is recommended to install the second network adapter (NIC) on a recording server.
One NIC will be dedicated to monitoring or listening to the voip network traffic.
Other NIC will be used for a remote access of the server from managers' or agents' computers.
The first NIC shouldn't even be configured with IP address; it will operate in "stealth" mode with TCP/IP unbound from the card and no IP address assigned. This NIC is said to be in promiscuous mode.
Installation of the second NIC on the server is required, if the switch doesn't support a receiving of incoming packets on a destination (analysis) port. The switch is able to forward a copy of packets from source port(s) to a destination port, but it discards packets received from a device, connected to a destination port. That means the port works in "listen only" mode. If the server needs to be accessed from a network, an installation of the second NIC is necessary (see below picture).
