Network Resiliency – EtherChannel

Part 4 – EtherChannel

Resilient plant-wide network architectures play a pivotal role in maintaining overall plant uptime and productivity. Industrial Automation and Control System (IACS) application requirements such as availability and performance drive the choice of resiliency technology.

When selecting resiliency technology, various plant application factors should be evaluated, including physical layout of IACS devices (geographic dispersion), resiliency performance, uplink media type, tolerance to data latency and jitter and future-ready requirements.

In this network resiliency series, we will highlight the various network resiliency protocols, such as DLR, REP, FlexLinks, EtherChannel, and see how they may be applied in various IACS applications.

This week we will look at EtherChannel for redundant star topologies.

What is EtherChannel?

An EtherChannel (or port group) is a group of two or more Fast Ethernet or Gigabit Ethernet switch ports bundled into a single logical link, creating a higher bandwidth link between two switches. Each EtherChannel can consist of up to eight compatible, configured Ethernet ports. The switch supports up to six EtherChannels.

EtherChannels are also referred to as Port Channels and support both LACP and PAgP:

  • LACP – Link Aggregation Control Protocol (IEEE802.3ad standard)
  • PAgP – Port Aggregation Protocol (Cisco proprietary protocol)

EtherChannel Operation

Strictly speaking, EtherChannel and Link Aggregation Control Protocol (LACP) are not resiliency protocols. They are designed to provide additional bandwidth between two devices by aggregating multiple Ethernet connections into a higher bandwidth virtual connection. However, these protocols need to quickly recover from the loss of one or more channel members. This fast recovery from a failure of an individual channel member can be used to provide link redundancy between two devices.

EtherChannel bundles multiple Ethernet links between two switches into a single logical link and balances the traffic load across the physical links. As shown in the figure below, when a physical link is lost, the EtherChannel load-balancing algorithm stops using the lost link and uses the other available links. When the link is restored, EtherChannel resumes balancing the load across the available link. In this way, EtherChannel can be used as a resiliency protocol when multiple links exist between two switches. To be used as a resiliency protocol, the switches must have redundant links between each other, such as in the redundant star topology.

LACP as defined in the IEEE 802.3ad standard. LACP facilitates the automatic creation of EtherChannels by exchanging LACP packets between Ethernet ports. As interoperability is a key requirement for the CPwE solution, Cisco, Panduit and Rockwell Automation recommend the use of LACP to establish EtherChannel links between switches when multiple physical links exist. The CPwE Resiliency CVD design guidance below assumes the use of LACP.

All ports in an EtherChannel must have the same characteristics:

  • All are applied with the Smartports IE Switch port role and belong to the same VLAN.
  • All are either 10/100 ports, or all are 10/100/1000 ports. You cannot group a mix of 10/100 and 10/100/1000 ports in an EtherChannel.
  • All are enabled. A disabled port in an EtherChannel is treated as a link failure, and its traffic is transferred to one of the remaining ports in the EtherChannel.

What Stratix switches support EtherChannel?

  • Stratix 8000 and 8300 support up to 6 EtherChannels
  • Stratix 5700 (full firmware only) supports up to 6 EtherChannels
  • Stratix 5400 and 5410 support up to 10 EtherChannels

Advantages of EtherChannel

  • Bandwidth — EtherChannel uses all available links simultaneously, adding bandwidth to uplink capacity
  • Standards-based — As LACP is defined in an IEEE standard, infrastructure from various vendors can be configured in a topology and interoperate
  • Configurable via Device Manager web interface on IES

Disadvantages of EtherChannel

  • Performance — Although EtherChannel uses multiple links and converges quickly when a link-loss is detected, it does not converge as quickly on average as does Flex Links

EtherChannel Resources

CPwE Resources:

Stratix Resources:

Looking for more information?
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