Chapter Summary | CCNP CIT Exam Cram 2 (Exam Cram 642-831)

When thinking of VLANs, most administrators who merely support an already configured network think of switches, because the switch is both the access point for the workstations and the location where the VLANs are created.

After a VLAN is created, inter-VLAN routing enables nodes in one VLAN to talk to a node in another VLAN. An access port leading to the end user can be assigned only to one VLAN, sometimes referred to as a color . In this chapter, you learned that trunking using certain protocols enables you to send the traffic of more than one VLAN down a single pipe between wiring closet devices such as switches or routers. Here are those protocols:

IEEE 802.10 ” A Cisco proprietary protocol used primarily to transport VLAN information over FDDI.
IEEE 802.1Q ” The standard protocol used for inserting a frame tag VLAN identifier in the frame header. As a frame enters the switch fabric, it is tagged with additional information regarding the VLAN properties. The tag remains in the frame as it is forwarded between switches, and is removed prior to exiting the access link to the destination interface. This process is completely transparent to the end user.
Inter-Switch Link (ISL) ” A special Cisco proprietary Ethernet protocol that assigns a 26-byte header and a 4-byte checksum, sometimes referred to as the FCS or the CRC, to an encapsulated frame header.
LAN Emulation (LANE) ” An IEEE standard for transporting VLANs over ATM networks. This process uses no encapsulation or frame tagging. ATM and LANE are beyond the scope of this book and thus were not covered in great detail.

This chapter also covered the VLAN Trunking Protocol (VTP), which is used to enable a single server operating in a VTP domain to configure all the switches in the domain with VLAN information to keep them consistent in the network. VTP enables you to configure one device and have the same configuration propagated to all the devices in the switch block. The different VTP modes ”Server, Client, and Transparent ”were also discussed.