- You need to configure spanning tree on a cisco switch Pc#
- You need to configure spanning tree on a cisco switch mac#
To do that, we go on the command line on Core2, and we enter the command: We always want traffic to be going through the core. If we didn't do that and Core1 went down, when we had that outage we would be back to the warehouse being the Root Bridge again and we want to avoid that. To do that, we need to configure Core2 to be the next most preferred Root Bridge. Using the same example, if the Core1 switch fails, we want to ensure that traffic still goes through the most direct centralised path. So, that is much more optimal Root Bridge placement. It's going along the most direct path which is going through the core. Now, you see it's only five hops as compared to the seven hops that we had before.
You need to configure spanning tree on a cisco switch Pc#
If we now send traffic from a PC connected into Access1, sending it to another PC if it's connected to Access3, the path it will go along is Access1 to Distribution2, to Core1, to Distribution4, to Access3. I've taken out all of the links that have got blocking parts on there. If we now look at the Spanning Tree in the diagram here, again, we've set the core bridge as the Root Bridge. It will show the message, "This bridge is the root," and I can see the priority is 24576. To verify it, I go to Core1, enter the commands: It is manipulating the elections so that this switch will be elected as the Root Bridge. When you put that command, it sets a Bridge Priority of 24576 which is better than the default Bridge Priority. Here, we're using VLAN 1 for our example. Now, you can have different switches being the Root Bridge for different VLANs. The way that you set this is that, at global config on the switch that you want to be the Root Bridge, enter the command: What we should have done was configure the Root Bridge to be sitting on one of our core switches so that all traffic is going to go through that path instead. That's likely to congest some links overwhelmed with CPU and RAM, and of course, lead to suboptimal performance. All traffic between different pairs of distribution switches will go over an indirect path and transit that old switch in the warehouse.
That's the suboptimal Root Bridge selection.
It's pinging around all over the network and going via the warehouse switch, and it's seven hops in total. It will then go at Core1, then to Distribution3, then Access4, then the Warehouse, and then Access3. The PC connected to Access1 sends some traffic in with a destination address of the other PC. Let's see what would happen if we had a PC that was connected into the Access1 switch on the left and it sent traffic to the Access3 switch over near the right-hand side. It only shows the Spanning Tree where the traffic is going to be forwarded over. I've removed links that have got blocking ports on them in the diagram. Now, we'll look at the actual paths that traffic will take throughout our network. I can see here that this bridge is the root and the priority is the default of 32768. If we check this, I go on to the warehouse switch and enter the command: It has fast Ethernet links compared to Gigabit Ethernet and it's old so it's got limited GPU and memory resources. That old warehouse switch has got little bandwidth links.
You need to configure spanning tree on a cisco switch mac#
In the example, the switch with the lowest MAC address becomes the Root Bridge and that happens to be the old switch that we've got in the warehouse down in the bottom right. They just leave it as is and that can lead to the problem as you see in our example.
That is because Spanning Tree works just fine straight out of the box and on a lot of networks, therefore, administrators don't touch it at all. You'd be surprised at how often this does actually happen in production networks. In on our example below, all switches have been left with the default Bridge Priority.
That is likely to give you suboptimal Root Bridge selection. So, the lowest MAC address is probably going to be the oldest switch. If you think about it, whenever Cisco makes a new switch, we're going to increment the MAC address. The switch with the lowest MAC address will be the Root Bridge and that is liable to be the oldest switch in your network. If you do not manually set the Bridge priority on your switches, they're all going to default to 32768. In the case of a tie, the switch with the lowest MAC address will be selected. The default value is 32768, and the lowest number is preferred. You can manipulate the Root Bridge Election by setting Bridge priority on your switches. Best practice is to ensure that a pair of high-end core switches are selected as the first and second most preferred Root Bridge. Since Spanning Tree selects paths pointing towards and away from the Root Bridge for forwarding traffic along, the Root Bridge acts as a center point of the LAN.
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