498 CHAPTER 25: V OICE VLAN C ONFIGURATIONn ■ As the first 24 bits of a MAC address (in binary format), an OUI address is aglobally unique identifier assigned to a vendor by IEEE (Institute of Electricaland Electronics Engineers).■ The default OUI address can be configured/removed manually.Working Modes of VoiceVLANA voice VLAN can operate in two working modes: automatic mode and manualmode (the mode here refers to the way of adding a port to a voice VLAN).■ In automatic mode, the system identifies the source MAC address contained inthe protocol packets (untagged packets) sent when the IP phone is powered onand matches it against the OUI addresses. If a match is found, the system willautomatically add the port into the Voice VLAN and apply ACL rules to ensurethe packet precedence. An aging time can be configured for the voice VLAN.The system will remove a port from the voice VLAN if no voice packet isreceived from it after the aging time. The adding and deleting of ports areautomatically realized by the system.■ In manual mode, the IP phone access port needs to be added to the voiceVLAN manually. It then identifies the source MAC address contained in thepacket, matches it against the OUI addresses. If a match is found, the systemissues ACL rules and configures the precedence for the packets. In this mode,the operation of adding ports to the voice VLAN and removing ports from thevoice VLAN are carried out by the administrators.■ Both modes forward tagged packets according to their tags.The following table lists the co-relation between the working modes of a voiceVLAN, the voice traffic type of an IP phone, and the interface modes of a VLANinterface.Voice VLANoperating mode Voice traffic type Interface link typeAutomatic mode Tagged voice traffic Access: the traffic type is not supportedTrunk: supported provided that the defaultVLAN of the access port exists and is not avoice VLAN and that the access port belongsto the voice VLANHybrid: supported provided that the defaultVLAN of the access port exists and is not avoice VLAN. Besides, the default VLAN need tobe in the list of tagged VLANs whose packetscan pass through the access portUntagged voice traffic Access, Trunk, Hybrid: not supported
