Content

| 3.9 |  | EtherChannel |
| 3.9.1 |  | EtherChannel explained |

EtherChannel is a Cisco-proprietary technology that, by aggregating links into a single logical link, provides incremental trunk speeds ranging from 10 Mbps to 160 Gbps (full duplex). EtherChannel comes in four flavors:

- Standard EtherChannel
- Fast EtherChannel (FEC)
- Gigabit EtherChannel (GEC)
- 10-Gigabit EtherChannel

The term EtherChannel encompasses all these technologies. Ether-Channel combines up to eight standard Ethernet links (160 Mbps on a Catalyst 3000), up to eight Fast Ethernet links (1.6 Gbps), up to eight Gigabit Ethernet links (16 Gbps), and up to eight 10-Gigabit Ethernet links (160 Gbps).

EtherChannel provides fault-tolerant, high-speed links between switches, routers, and servers. The term heard most often in the context of EtherChannel is "resiliency". Cisco defines resiliency as “the ability to recover from any network failure or issue, whether it is related to a disaster, link, hardware, design, or network services.” Recall STP and how it handles link failures within a Layer 2 topology. With EtherChannel, resiliency refers to the ability of the EtherChannel to continue to operate when one of the links in a “bundle” goes down and also the ability to restore the full bundle should the downed link come back into service. Module 2 discussed trunking technologies, in particular, we looked at the IEEE 802.1Q and ISL Ethernet trunking technologies. What might not have been made clear at that time is that Ethernet trunks frequently go hand in hand with EtherChannel links. The reason for this should be clear. Trunk links carry more traffic and require more bandwidth than access links.

EtherChannel bundles segment into groups of two to eight links. This lets links scale at rates between 100 Mbps and a healthy fraction of 1 Tbps. Remember when T1 or 1.544 Mbps was the fastest WAN link available. Now it is at least 16 Tbps for up to a 50-kilometer stretch with single-mode fiber, using the Catalyst 6500 10GBASE-EX4 Metro 10-Gigabit Ethernet module. EtherChannel operates as either an access link or trunk link. For example, EtherChannel can be deployed between the wiring closet and the data center. In the data center, EtherChannel links can be deployed between servers and the network backbone to provide scalable incremental bandwidth.

Some of the benefits of EtherChannel are:

- EtherChannel does not require any changes as it is transparent to networked applications. For support of EtherChannel on enterprise-class servers and network interface cards, smart software drivers can coordinate distribution of loads across multiple network interfaces.
- When EtherChannel is used within the campus, switches and routers provide load balancing transparently across multiple links to network users. Unicast, multicast, and broadcast traffic is distributed across the links in the channel.
- EtherChannel provides automatic recovery for loss of a link by redistributing loads across remaining links. If a link does fail, EtherChannel redirects traffic from the failed link to the remaining links in less than a second. This convergence is transparent to the end user. No host protocol timers expire, so no sessions are dropped.

Figure shows a typical EtherChannel network configuration. Now that we have introduced EtherChannel, we can investigate how it works and how to configure it in a network. Next, we explain how EtherChannel utilizes frame distribution.