Etherchannels

Etherchannel Concept and configuration

EtherChannel is a port link aggregation technology or port-channel architecture used primarily on Cisco switches. It allows grouping of several physical Ethernet links to create one logical Ethernet link for the purpose of providing fault-tolerance and high-speed links between switches, routers and servers. An EtherChannel can be created from between two and eight active Fast, Gigabit or 10-Gigabit Ethernet ports, with an additional one to eight inactive (failover) ports which become active as the other active ports fail. EtherChannel is primarily used in the backbone network, but can also be used to connect end user machines.

Using an EtherChannel has many advantages

• Larger bandwidth. By using the maximum of 8 active ports, a total bandwidth is increased 8 fold comparing to a single port. 
• Scalable. Because EtherChannel takes advantage of existing wiring it makes it very scalable. It can be used at all levels of the network to create higher bandwidth links as the traffic needs of the network increase. All Cisco switches have the ability to support EtherChannel.
• transparent to network applications. When an EtherChannel is configured, all adapters that are part of the channel share the same Layer 2 (MAC) address. This makes the EtherChannel transparent to network applications and users because they only see the one logical connection; they have no knowledge of the individual links.
• Fault-tolerance. Should a link fail, the EtherChannel technology will automatically redistribute traffic across the remaining links. This automatic recovery takes less than one second and is transparent to network applications and the end user. This makes it very resilient and desirable for mission-critical applications.

Spanning tree protocol (STP) can be used with an EtherChannel. STP treats all the links as a single one and BPDUs are only sent down one of the links.

EtherChannels can be also configured as VLAN trunks. If any single link of an EtherChannel is configured as a VLAN trunk, the entire EtherChannel will act as a VLAN trunk.

EtherChannel is made up of the following key elements:

• Ethernet links — EtherChannel works over links defined by the IEEE 802.3 standard, including all sub-standards. All links in a single EtherChannel must be the same speed.
• Compatible hardware — the entire line of Cisco Catalyst switches as well as Cisco IOS software-based routers support EtherChannel. Multiple EtherChannels per device are supported (Catalyst 6500 and 6000 switches support a maximum of 64 EtherChannels).
• Configuration — an EtherChannel must be configured using the Cisco IOS on switches and router, and using specific drivers when connecting a server. There are two main ways an EtherChannel can be set up. The first is by manually issuing a command on each port of the device that is part of the EtherChannel. This must be done for the corresponding ports on both sides of the EtherChannel. The second way is using Cisco Port Aggregation Protocol (PAgP) for the automated aggregation of Ethernet ports.

EtherChannel vs. 802.3ad

EtherChannel and IEEE 802.3ad standards are very similar and accomplish the same goal. There are a few differences between the two, other than the fact that EtherChannel is Cisco proprietary and 802.3ad is an open standard, listed below:

Both technologies are capable of automatically configuring this logical link. EtherChannel supports both LACP and Cisco's PAgP, whereas 802.3ad uses LACP.

LACP allows for up to 8 active and 8 standby links, whereas PAgP only allows for 8 active links.

Cisco Lab

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