Etherchannel

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Etherchannel and Fast Etherchannel are registered trademarks of Cisco and are derived from ether net and Channel (Engl. Channel ) from. Etherchannel is the technical term for an invention of the company Kalpana (now Cisco) and refers to a method for bundling a plurality of physical Ethernet - interfaces into one logical channel, wherein Fast etherchannel several fast Ethernet interfaces are bundled. Etherchannel has partly established itself as an everyday expression for the bundling of Ethernet channels and is colloquially used not only for Cisco products ( generic term similar to Tempo and paper handkerchiefs). The technology originally served exclusively to increase the data throughput between two Ethernet switches (also invented by Kalpana). Soon after the introduction of Etherchannel, there were also implementations for connecting servers and other systems.

Other names

Although there are incompatibilities and technical differences, the following expressions are used as synonyms for the bundling of Ethernet interfaces (depending on the manufacturer or context) :

functionality

In general, several physical Ethernet interfaces are interconnected to connect two devices, which means 2 bundled interfaces can transport twice the amount of data, 4 consequently four times the amount. It makes sense to bundle the fastest possible interfaces, 2 times Ethernet (half duplex) correspond to 20 Mbit / s, 3 times Fast Ethernet (full duplex) as Fast Etherchannel are already 600 Mbit / s. A maximum increase in performance can be achieved with many bundling methods if the number of bundled ports is a power of two. For example, by interconnecting eight Fast Ethernet interfaces, almost the bandwidth of a Gigabit Ethernet interface can be achieved. Another advantage is increased reliability. With some methods, one or more interfaces can fail without the logical channel being interrupted. Only the data throughput is reduced according to the missing connections.

Bundling procedure

  • Round robin: Here all available lines are used alternately one after the other.
  • DA trunking: The elementary interface is selected here based on the modulo of the destination MAC address.
  • SA trunking: The elementary interface is selected here based on the modulo of the source MAC address.
  • SA-DA trunking: The elementary interface is selected here based on the modulo of the source MAC address and the destination MAC address.
  • Adaptive trunking: Here, a further interface is only switched on when the first elementary interface is fully utilized.
  • Dynamic trunking: With the help of the proprietary Arif or the IEEE compliant LACP , dynamic Etherchannels can be defined.

Basic implementation

The basic implementation of channel bundling between two Ethernet switches requires surprisingly few changes (compared to a normal switch). Of course, the management interface has to be expanded to define the trunk. Then the way in which a switch learns its SAT (source address table - table with the MAC addresses of the senders) is affected, and finally broadcasts and packets directed to unknown destination MAC addresses are affected . treated separately from the drink.

  • Management Interface: The fact that the menu structures are affected certainly doesn't need much explanation.
  • Address learning phase: If a switch receives an unknown sender address on a trunk port, this is not automatically assigned to the address stack (SAT) of this port, rather the switch tries to assign the same network load to all members of the trunk and therefore becomes new Distribute sender addresses evenly on all ports belonging to the trunk. As a result, the port that currently has the fewest entries in its SAT receives the new address.
  • Broadcasts and unknown addresses: In the case of a trunk, these are not sent over all ports, but only over one line per trunk; in general, the port with the lowest port number is selected.

No further measures are necessary to implement a simple implementation. The implementation of the transport mechanisms ( cut through , store and forward etc.) do not require any changes. Nevertheless, this implementation is far from ideal and is actually only suitable for coupling two networks. One disadvantage is that only one port of the trunk is used per MAC address. For a single station this means that it has no advantages - only the network as a whole benefits. It can also happen that the most active stations are all randomly assigned to the same port, which means that the load is not evenly distributed within the trunk. There are also bundling processes that can connect powerful servers. All these facts have led to the fact that many manufacturers offer different, but also more developed implementations, but these are usually not compatible with each other.