16 EtherChannel
This chapter covers
- How EtherChannel combines redundant links into a single logical link
- Static and dynamic EtherChannel configuration
- How traffic is load-balanced over the physical links of an EtherChannel
- Using layer-3 EtherChannel to provide redundant layer-3 connections
In the previous two chapters on STP, we emphasized the essential role of STP in preventing layer-2 loops in a LAN with redundant connections. However, the downside of STP is that all redundant links are disabled; they provide essential redundancy in aLAN, but will only be used to forward traffic if an active link fails.
In this chapter we will cover EtherChannel, a technology that helps to overcome this limitation, allowing multiple physical links to be combined into a single logical one. As a result, STP and frame-forwarding logic will treat the group of links as a single unit, allowing the whole group of links to remain active without causing layer-2 loops. This not only maximizes usage of the available bandwidth, but also improves network resilience and simplifies management — advantages that we’ll delve into in this chapter. EtherChannel is CCNA exam topic 2.4: Configure and verify (Layer 2/Layer 3) EtherChannel (LACP).