Dublin,
VLAN is an ICND2 topic...especially for config.
CCENT tests on ICND1...the most you would have to know truly is what a VLAN's function is...see the following which are exam topics to know off the ICND1 exam on Cisco's website under "Implement a Small Switched Network".
Pay attention to the bullets starting with "Explain..."
Select the appropriate media, cables, ports, and connectors to connect switches to other network devices and hosts
*
Explain the technology and media access control method for Ethernet technologies
*
Explain network segmentation and basic traffic management concepts
*
Explain the operation of Cisco switches and basic switching concepts
*
Perform, save and verify initial switch configuration tasks including remote access management
*
Verify network status and switch operation using basic utilities (including: ping, traceroute,telnet,SSH,arp, ipconfig), SHOW & DEBUG commands
*
Implement and verify basic security for a switch (port security, deactivate ports)
*
Identify, prescribe, and resolve common switched network media issues, configuration issues, autonegotiation, and switch hardware failures
I hope this is helpful.
-HH