Cisco Catalyst LAN Switching

This chapter covers the following key topics:

• Why Trunks? Describes the advantages of trunks and compares various trunk connection methods for interconnecting Catalysts, routers, and servers.

• Ethernet Trunks Details the trunk options over Fast Ethernet and Gigabit Ethernet. EtherChannel technologies are also discussed. Also describes ISL and 802.1Q encapsulation over trunks. Automatic methods of establishing trunks through DISL and DTP are also considered.

• FDDI Trunks and 802.10 Encapsulation Provides an overview of trunking technology over FDDI in a Cisco environment and the associated encapsulation technology, 802.10.

• ATM Trunks Offers an overview of LANE and MPOA for trunking over ATM. Both LANE and MPOA are detailed in subsequent chapters.

• Trunk Options Provides guidelines for choosing an appropriate trunk technology by comparing the advantages and disadvantages of each.

Except for the simplest of network configurations, a network comprises multiple Catalysts. Although each Catalyst can stand autonomously, they usually interconnect through ATM, FDDI, or Ethernet technologies. Administrators often face the challenge of choosing the best method to interconnect geographically disbursed members of a VLAN. Some of the issues involved in the decision include the following: technology availability, resources, bandwidth, and resiliency.

This chapter reviews the advantages of trunks and discusses the various technologies available for Catalyst trunks. Specifically, the following sections describe trunks for Fast and Gigabit Ethernet, FDDI, and ATM. The sections also explain Inter-Switch Link (ISL), 802.1Q, Dynamic ISL (DISL), Dynamic Trunk Protocol (DTP), Token Ring ISL (TRISL), 802.10, LAN Emulation (LANE), and Multiprotocol over ATM (MPOA). Guidelines for choosing a method are included at the end of the chapter.