EtherChannel
Encyclopedia
Link aggregation
Link aggregation or trunking or link bundling or Ethernet/network/NIC bonding or NIC teaming are computer networking umbrella terms to describe various methods of combining multiple network connections in parallel to increase throughput beyond what a single connection could sustain, and to provide...
technology or port-channel architecture used primarily on Cisco switches
Network switch
A network switch or switching hub is a computer networking device that connects network segments.The term commonly refers to a multi-port network bridge that processes and routes data at the data link layer of the OSI model...
. It allows grouping of several physical Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
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
Computer port (hardware)
In computer hardware, a port serves as an interface between the computer and other computers or peripheral devices. Physically, a port is a specialized outlet on a piece of equipment to which a plug or cable connects...
, 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
Backbone network
A backbone network or network backbone is a part of computer network infrastructure that interconnects various pieces of network, providing a path for the exchange of information between different LANs or subnetworks. A backbone can tie together diverse networks in the same building, in different...
, but can also be used to connect end user machines.
EtherChannel technology was invented by Kalpana
Kalpana (company)
Kalpana was a computer networking equipment manufacturer, located in Silicon Valley during the 1980s and 1990s.Kalpana is considered to be the inventor of Ethernet switching as the company was the first to introduce the concept of a multi-port network switch with its seven-port EtherSwitch in 1990...
in the early 1990s. They were later acquired by Cisco Systems
Cisco Systems
Cisco Systems, Inc. is an American multinational corporation headquartered in San Jose, California, United States, that designs and sells consumer electronics, networking, voice, and communications technology and services. Cisco has more than 70,000 employees and annual revenue of US$...
in 1994. In 2000 the IEEE passed 802.3ad
Link aggregation
Link aggregation or trunking or link bundling or Ethernet/network/NIC bonding or NIC teaming are computer networking umbrella terms to describe various methods of combining multiple network connections in parallel to increase throughput beyond what a single connection could sustain, and to provide...
which is an open standard
Open standard
An open standard is a standard that is publicly available and has various rights to use associated with it, and may also have various properties of how it was designed . There is no single definition and interpretations vary with usage....
version of EtherChannel.
Benefits
Using an EtherChannel has numerous advantages, and probably the most desirable aspect is the bandwidth. Using the maximum of 8 active ports a total bandwidth of 800 Mbit/s, 8 Gbit/s or 80 Gbit/s is possible depending on port speed. This assumes there is a traffic mixture, as those speeds do not apply to a single application only. It can be used with Ethernet running on twisted pair wiring, single-mode and multimode fiber.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.
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.
EtherChannel aggregates the traffic across all the available active ports in the channel. The port is selected using a Cisco-proprietary hash algorithm, based on source or destination MAC address
MAC address
A Media Access Control address is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies, including Ethernet...
es, IP address
IP address
An Internet Protocol address is a numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing...
es or TCP and UDP port
TCP and UDP port
In computer networking, a port is an application-specific or process-specific software construct serving as a communications endpoint in a computer's host operating system. A port is associated with an IP address of the host, as well as the type of protocol used for communication...
numbers. The hash function gives a number between 0 and 7, and the following table shows how the 8 numbers are distributed among the 2 to 8 physical ports. In the hypothesis of real random hash algorithm, 2, 4 or 8 ports configurations lead to fair load-balancing, whereas other configurations lead to unfair load-balancing.
| Number of Physical Links | |||||||
| Link # | 8 | 7 | 6 | 5 | 4 | 3 | 2 |
| 1 | 1 | 2 | 2 | 2 | 2 | 3 | 4 |
| 2 | 1 | 1 | 2 | 2 | 2 | 3 | 4 |
| 3 | 1 | 1 | 1 | 2 | 2 | 2 | |
| 4 | 1 | 1 | 1 | 1 | 2 | ||
| 5 | 1 | 1 | 1 | 1 | |||
| 6 | 1 | 1 | 1 | ||||
| 7 | 1 | 1 | |||||
| 8 | 1 | ||||||
Fault-tolerance is another key aspect of EtherChannel. 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
Spanning tree protocol
The Spanning Tree Protocol is a network protocol that ensures a loop-free topology for any bridged Ethernet local area network. The basic function of STP is to prevent bridge loops and ensuing broadcast radiation...
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. Without the use of an EtherChannel, STP would effectively shutdown any redundant links between switches until one connection goes down. This is where an EtherChannel is most desirable, it allows full use of all available links between two devices.
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. Cisco ISL
Cisco Inter-Switch Link
Cisco Inter-Switch Link is a Cisco Systems proprietary protocol that maintains VLAN information in Ethernet frames as traffic flows between switches and routers, or switches and switches....
, VTP
VTP
VLAN Trunking Protocol is a Cisco proprietary protocol that propagates the definition of Virtual Local Area Networks on the whole local area network. To do this, VTP carries VLAN information to all the switches in a VTP domain. VTP advertisements can be sent over ISL, 802.1q, IEEE 802.10 and...
and IEEE 802.1Q
IEEE 802.1Q
IEEE 802.1Q is the networking standard that supports Virtual LANs on an Ethernet network. The standard defines a system of VLAN tagging for Ethernet frames and the accompanying procedures to be used by bridges and switches in handling such frames...
are compatible with EtherChannel.
Limitations
A limitation of EtherChannel is that all the physical ports in the aggregation group must reside on the same switch except in the case of a switch stack, where they can reside on different switches on the stack. Avaya'sAvaya
Avaya Inc. is a privately held computer networking, information technology and telecommunications company that is a global provider of business communications systems. The international head quarters is in Basking Ridge, New Jersey, United States...
SMLT protocol removes this limitation by allowing the physical ports to be split between two switches in a triangle configuration or 4 or more switches in a mesh configuration. Cisco's Virtual Switching System allows the creation of a Multichassis Etherchannel (MEC) similar to the DMLT protocol allowing ports to be aggregated towards different physical chassis that conform a single "virtual switch" entity.
Components
EtherChannel is made up of the following key elements:
- Ethernet links — EtherChannel works over links defined by the IEEE 802.3IEEE 802.3IEEE 802.3 is a working group and a collection of IEEE standards produced by the working group defining the physical layer and data link layer's media access control of wired Ethernet. This is generally a local area network technology with some wide area network applications...
standard, including all sub-standards. All links in a single EtherChannel must be the same speed.
- Compatible hardware — The entire line of Cisco Catalyst switchesCatalyst switchCatalyst is the brand name for a variety of network switches sold by Cisco Systems. While commonly associated with Ethernet switches, a number of different interfaces have been available throughout the history of the brand. Cisco acquired several different companies and rebranded their products...
as well as Cisco IOSCisco IOSCisco IOS is the software used on the vast majority of Cisco Systems routers and current Cisco network switches...
software-based routers support EtherChannel. Configuring an EtherChannel between a switch and a computer would either require special network interface cards (NICs) such as the model pictured here, or support built into the operating system. FreeBSD, for example, supports EtherChannel via LACP on standard NICs. Multiple EtherChannels per device are supported; the number depends on the type of equipment. Catalyst 6500Catalyst 6500The Catalyst 6500 is a modular chassis network switch manufactured by Cisco Systems since 1999, capable of delivering speeds of up to "400 million packets per second"....
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 ProtocolPort Aggregation ProtocolPort Aggregation Protocol is a Cisco Systems proprietary networking protocol, which is used for the automated, logical aggregation of Ethernet switch ports, known as an etherchannel. This means it can only be used between Cisco switches and/or switches from licensed vendors...
(PAgP) for the automated aggregation of Ethernet ports.
EtherChannel vs. 802.3ad
EtherChannel and IEEE 802.3adLink aggregation
Link aggregation or trunking or link bundling or Ethernet/network/NIC bonding or NIC teaming are computer networking umbrella terms to describe various methods of combining multiple network connections in parallel to increase throughput beyond what a single connection could sustain, and to provide...
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:
| EtherChannel | IEEE 802.3ad |
|---|---|
| Requires switch configuration. | Little, if any, configuration of switch required to form aggregation. Some initial setup of the switch may be required. |
| Supports different packet distribution modes. | Supports only standard distribution mode. |
Both technologies are capable of automatically configuring this logical link. EtherChannel supports both LACP and Cisco's PAgP
Port Aggregation Protocol
Port Aggregation Protocol is a Cisco Systems proprietary networking protocol, which is used for the automated, logical aggregation of Ethernet switch ports, known as an etherchannel. This means it can only be used between Cisco switches and/or switches from licensed vendors...
, whereas 802.3ad uses LACP.
See also
- Link aggregationLink aggregationLink aggregation or trunking or link bundling or Ethernet/network/NIC bonding or NIC teaming are computer networking umbrella terms to describe various methods of combining multiple network connections in parallel to increase throughput beyond what a single connection could sustain, and to provide...
- Link Aggregation Control Protocol
- Multi-link trunkingMulti-link trunkingMulti-Link Trunking is a link aggregation or IEEE 802.3ad port trunking technology designed by Nortel . It allows grouping several physical Ethernet links into one logical Ethernet link to provide fault-tolerance and high-speed links between routers, switches, and servers...
- R-SMLTR-SMLTRouted-SMLT is a computer networking protocol designed by Nortel as an enhancement to SMLT enabling the exchange of Layer 3 information between peer nodes in a Switch Cluster for unparalleled resiliency and simplicity for both L3 and L2.In many cases, core network convergence-times after a...
- Distributed Split Multi-Link TrunkingDistributed Split Multi-Link TrunkingDistributed Split Multi-Link Trunking or Distributed SMLT is a computer networking technology designed by Avaya to enhance the Split Multi-Link Trunking protocol...