VLAN-1 is the default VLAN in Cisco switches. After initial boot up process, the switch loads the default configuration and all switch ports became a part of the default VLAN (VLAN-1). The switch port that is the part of the default VLAN work in the same broadcast domain. The figure below illustrates the default VLAN of a Cisco switch, the show VLAN brief command was executed on a switch running the default configuration. You can see that all ports are assigned to VLAN 1 by default. There is no difference between the features and function of VLAN1 and other VLAN; excluding that it cannot be renamed or deleted. By default, all Layer 2 control traffic is associated with VLAN 1.
A data VLAN is also referred to as a user VLAN. It is used to separate the network into different groups of users or devices. Data VLAN is used to forward user-generated traffic. It is also separate voice and management traffic from data traffic.
A native VLAN is assigned to an 802.1Q trunk port that was created for backward compatibility with old devices that don’t support VLANs just like a hub. Frames belonging to the native VLAN are not tagged when sent out on the trunk links so older devices can simply understand these frames. Frames received untagged on the trunk links are set to the native VLAN. The trunk is the links between switches that maintain the transmission of traffic connected with more than one VLAN. An 802.1Q trunk port supports traffic coming from many VLANs (tagged traffic); with traffic that does not come from a VLAN. Tagged traffic is traffic that has a 4-byte tag inserted in the original Ethernet frame header; specifying the VLAN to which the frame belongs. The 802.1Q trunk port places untagged traffic on the native VLAN, which by default is VLAN 1.
The separate VLAN for management like monitoring, system logging, SNMP, and other sensitive management jobs is best practice in networking. It also ensures that bandwidth for management will also be available even when user traffic is high. VLAN 1 is the management VLAN by default. To create the management VLAN, the switch virtual interface of that VLAN is assigned an IP address and subnet mask, which management remotely via HTTP, Telnet, SSH, or SNMP. Because the out-of-the-box configuration of a Cisco switch has VLAN 1 as the default VLAN, VLAN 1 would be a bad choice for the management VLAN.
If your organization uses voice over IP (VoIP), a separate VLAN is needed. This will save bandwidth for other applications and ensure VoIP quality. The Voice Over Internet Protocol (VoIP) traffic requires, assured bandwidth to ensure quality, transmission priority, ability to be routed around congested areas on the network and delay of less than 150ms across the network. To meet these requirements, the entire network has to be designed to support VoIP.