Chapter 3. Trunking and Bandwidth Aggregation
So far you have learned how to essentially configure a switch as a single independent device. However, such a configuration is not a very valid representation of the real world, because the size of many networks dictates that more than one switch is required to service the connectivity needs of the network. You've also learned about virtual LANs (VLANs) and how each switch can service multiple logical LANs simultaneously, maintaining separation between each VLAN.
Trunking refers to the interconnection of switches to allow devices attached to a particular switch to communicate with devices attached to another switch. Trunking allows switches to transmit traffic from multiple VLANs configured locally across the trunk, thus allowing a VLAN to be distributed over multiple switches. Cisco routers and other devices also support trunking, which ensures they can communicate over multiple VLANs without requiring a physical interface per VLAN. The configuration of the multiple VLANs transported by trunks requires VLAN trunking protocol (VTP), a protocol that propagates VLAN information across multiple switches, to be enabled. VTP also controls whether or not trunks form under certain conditions.
Bandwidth aggregation refers to the bundling of multiple physical interfaces to create a single virtual interface that supports the combined bandwidth of each physical interface. Not only does this offer a performance increase over using just a single physical interface to connect to a device, but it also offers redundancy because a physical interface failure does not take down the virtual interface (other physical interfaces are still operational). Cisco Catalyst switches and routers support EtherChannel, a well established proprietary protocol that enables the bundling of up to eight physical interfaces between Cisco Catalyst switches, routers and other devices.
In this chapter, you learn how to interconnect switches and routers using trunks and how to configure bandwidth aggregation between switches and routers.
After some initial introductory material, this chapter presents the following configuration scenarios, which enable you to learn how to implement the technologies and concepts discussed in this chapter: