An EtherChannel is comprised of physical, individual FastEthernet, GigabitEthernet, or Ten-GigabitEthernet (10Gbps) links that are bundled together into a single logical link, as illustrated in Figure 33.1 below. An EtherChannel comprised of FastEthernet links is referred to as a FastEtherChannel (FEC); an EtherChannel comprised of GigabitEthernet links is referred to as a GigabitEtherChannel (GEC); and, finally, an EtherChannel comprised of Ten-GigabitEthernet links is referred to as a Ten-GigabitEtherChannel (10GEC):
Figure 33.1 – EtherChannel Physical and Logical Views
Each EtherChannel can consist of up to eight ports. Physical links in an EtherChannel must share similar characteristics, such as be defined in the same VLAN or have the same speed and duplex settings, for example. When configuring EtherChannels on Cisco Catalyst switches, it is important to remember that the number of supported EtherChannels will vary between the different Catalyst switch models.
For example, on the Catalyst 3750 series switches, the range is 1 to 48; on the Catalyst 4500 series switches, the range is 1 to 64; and on the flagship Catalyst 6500 series switches, the number of valid values for EtherChannel configuration depends on the software release. For releases prior to Release 12.1(3a)E3, valid values are from 1 to 256; for Releases 12.1(3a)E3, 12.1(3a)E4, and 12.1(4)E1, valid values are from 1 to 64. Release 12.1(5c)EX and later support a maximum of 64 values, ranging from 1 to 256.
NOTE: You are not expected to known the values supported in each different IOS version.
There are two link aggregation protocol options that can be used to automate the creation of an EtherChannel group: Port Aggregation Protocol (PAgP) and Link Aggregation Control Protocol (LACP). PAgP is a Cisco proprietary protocol, while LACP is part of the IEEE 802.3ad specification for creating a logical link from multiple physical links. These two protocols will be described in detail throughout this module.