It's completely removed from the bandwidth equation and half of the bandwidth across the horizontal link and going up into the left from the bottom, that's removed as well. So we want the ability to augment bandwidth and going faster is an option. But there is another option and that is, figure out a way to marry the fact that spanning tree needs to run in our environment still. With the technology that we're about to show you, that is going to allow us to fix spanning tree out a little bit and essentially give us our cake and allow us to eat it as well.
Focus your attention on the topology. Notice EtherChannel. What are we doing? We're bundling the links together, aggregating them together, improving the bandwidth and the distribution of traffic in our topology. But I really want you to focus on spanning tree protocol's blocked port. Is it just a port it's blocking? No, not in this case, it's blocking the entire EtherChannel bundle. So it sees it as a bundle here of all those physical ports, instead of individual physical ports.
So what's our ratio now? Well out of these six links we're using four. It's better than what we originally had, which was only two out of the six we were using. Now you may be thinking out there, this is dangerous, OK? You might be thinking that this is dangerous because what happens if one of the member links of an EtherChannel bundle goes down? I want to have stability in my network.
Well this is one of the most amazing things about EtherChannel: if a member link goes down, the EtherChannel bundle endures. And how many ports can you stick in an EtherChannel bundle? Turns out that only eight can be active at any given time. But let's say, we had eight in an EtherChannel bundle. How they differ from each other when aggregating links and redistributing the load in case of a link fail for any network?
It provides a method to control the bundling of several physical ports together to form a single logical channel. It enables a network device, typically a data switch , to negotiate an automatic bundling of links by sending LACP packets to the peer. In practice, LACP protocol serves the general principle of link aggregation, which describes the effort of setting up parallel network structures to provide redundancy, or to improve performance.
However, they don't support entering the aggregation port to configure various parameters. This helps ensure things are working properly. Static will form without any verification, so you have to make sure things are good to go. To configure an EtherChannel using LACP negotiation, each side must be set to either active or passive; only interfaces configured in active mode will attempt to negotiate an EtherChannel.
Passive interfaces merely respond to LACP requests. PAgP behaves the same, but its two modes are refered to as desirable and auto. Increased bandwidth is especially useful between switches. Think of a case where you have two switches with 1Gbps ports.
That means that you will have 1Gbps of bandwidth down to your hosts, which means that you may require more than 1Gbps of bandwidth between the switches. An EtherChannel work very well in this scenario. The second reason for etherchannels is for resiliency.
If you have four links in an EtherChannel and one is lost, the other three will keep on working although at a reduced capacity. This can be especially useful in cases of long cable runs that can be dug up or damaged in some way. So why bundle several links together into a virtual interface, and not just plug in a few extra links between switches? If you connect two or more links without bundling them together, one of two things will happen. The first scenario is that spanning-tree will block all but one link.
The other links can still be used for resiliency, but there will be no bandwidth gains. The second scenario is that spanning-tree is not running, and the additional links create a loop in the network.
This could result in a broadcast storm, which would be catastrophic to the network. Etherchannels can be configured as layer-2 links which are the most common or layer-3 links. The difference between the two is that the Layer-3 link has an IP address, while the layer-2 link does not. Depending on the model of switch, additional licensing may be required to use an L3 EtherChannel.
Etherchannels are used with physical switches, virtual switches, and other network devices. Examples of etherchannels with virtual switching is connecting a hypervisor host to the network or connecting a NetScaler. Layer-3 capable devices such as routers and ASA firewalls can also be configured with an EtherChannel.
Even with a layer-3 device, L2 etherchannels are still quite common. One very important factor to remember is that etherchannels are meant to be connected to a single switch. An EtherChannel by default cannot be spread across multiple switch chassis.
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