From Cisco VLAN (Virtual Local Area Network) is a logical LAN that have separate broadcast domain. VLAN is often called LAN virtualization. VLAN groups ports of the switch and each group are given different VLAN-ID and VLAN name. The groups acts like different switch logically. You can extend the VLAN capability of one switch by interconnecting two or more switches via trunk ports. Trunk ports are type of ports that pass multiple VLAN traffic between switches. Trunk ports are also called tagged ports and operates IEEE 802.1Q protocol. Configuring VLANs in JunOS can be difficult if you are configuring it for the first time.
In Juniper switches, there is no VTP (VLAN Trunking Protocol) or DTP (Dynamic Trunking Protocol) protocols. For managing VLANs GVRP (GARP VLAN Registration Protocol) is used in Juniper switches. If you are connecting Cisco switches with Juniper switches then disable VTP mode in Cisco switch.