Note For all Lync Server roles, one network adapter is required, but two network adapters are recommended. Each network adapter should have a bandwidth of 1 gigabit per second (Gbps) or greater.
For more information about Lync Server hardware requirements, see the following TechNet article:
An additional network adapter can be added to the Windows Server-based computer as a teamed network adapter solution. Teamed network adapters let you use dual port configurations that effectively double the throughput of network traffic that the Lync Server front-end server can send and receive. This generates more available network bandwidth for the additional SIP signaling and audio media traffic that's created by the collocated Lync Server Mediation Server role.
Note Teamed network adapter solutions are supported by the server or hardware vendor. For more information, see the "More Information" section.