Types of Spanning Tree Protocol (Part 1)
Let's talk today in this post about an important topic in which some may find many difficulties and complications, which are the types of Spanning Tree Protocol that are available. Through a small statistic that I did, I counted at least six types of this protocol, namely CST, RSTP, MSTP, PVST, PVST+, RPVST. Differences between STP, RSTP, MSTP and my IEEE
At the outset, I would like to point out that these protocols have one function, which is to prevent the occurrence of what is known as the loop at the level of the second layer, Data Link, in addition to that the topic will not be about the mechanism of action of each one of them, because, according to my belief, they are known to everyone. Let's start with my IEEE protocols:
CST: Or Common Spanning Tree, or STP that we hear about, which is known through the IEEE organization as 802.1D. This protocol is characterized as working on all types of devices, whether Cisco or Juniper, without discrimination. What distinguishes it is the presence of a single Spanning Tree or One Instance network that includes all Vlans and is exchanged The BPDU is between the switches through the Native Vlan, and it works through a single Instance that includes all the ports and includes all the Vlans in the network (we will understand the idea of the Instance more when it reaches MSTP) and this is an illustration.
RSTP: or Rapid Spanning Tree Protocol, which is a developed form of STP and is known as 802.1w. Through its name, we can conclude that this protocol is faster than the normal protocol, and there are many reasons.
1- The Blocking and Listening modes were merged into one mode, which is Discarding, and it is known that the Listening mode used to take 15 seconds.
2- The time required to transfer the port from Discarding to Learning is 6 seconds, which means that the BPDU is not received 3 times because the BPDU is sent every two seconds, and this gives us only 6 seconds, while we find that the STP needs 20 seconds from you to enter the listening phase, i.e. it must wait for the BPDU to stop Ten times (the idea of transmission depends on the number of times the BPDU is received and not on a specific time, so the protocol looks at the number of times and through it we deduce the required time).
3- Through this comparison, we find that the STP takes about 50 seconds to change from the block state to the forward state, while the RSTP takes about 21 seconds.
4- Two new names have replaced the Blocking Port, which are Alternate Port & Backup Port. The first is a backup port for each segment present in the network, and the second is an alternative port to the Root Port.
5- In the STP, the root bridge was the only one that sent the BPDU, and then the rest of the switches alternated on it. With the RSTP, all existing switches can send the BPDU. If we had two switches located within a large network, and a Down event occurred to one of the ports, the switch would send the BPDU to the other switch in order to It activates the backup port directly.
6- Introducing new names for the types of ports on the switch, such as Edge Port, which means that this port has activated the Fast Port feature, which converts the port directly from Discarding to Forwarding, and it is usually used in ports that do not contain switches that could lead to a loop in the network Or with computers, in addition to another name, which is Shared Port, which means that this port is connected to Hup, and finally another name, Point-to-Point Port, which indicates that the port is connected to another switch.
One final note, since 2004 RSTP has been adopted as the default for STP and has been defined by 802.1D and retired STP, so when you hear STP think of it as RSTP.
MSTP: or Multi Spanning Tree Protocol, which is known by IEEE 802.1S. The idea of this protocol aims to reduce the number of existing Instances so that we can include more than one Vlan in one Instance, as I mentioned that the STP will perform an Instance for all Vlans in the network, which does not There is no doubt that this process reduces pressure on the processor as a positive curve, but it will prevent the network from doing Load Balancing between the VLANs as a negative curve, and from this standpoint, MSTP was found, which allowed us to divide the Vlans into groups, each of which works independently of the other, and through an isolated instance As a small example about this process, suppose we have 40 Vlans in the network, and of course all these Vlans will work in the form of one Instance as we mentioned in the STP, but with MSTP the issue is a little different because it will simply allow us to create an STP for each group of them and let us assume the first 10 Vlans are present while it will We put the rest of the Vlan in another Instance, and in this way, certain ports will be closed for each group of the Vlan, while these ports will be open in the other group. Note the next image to understand the process more
So here the topic for today has ended, hoping that we will later complete the protocols for Cisco, which are PVST, PVST+, RPVST, which I will present soon, God willing, and you will be friendly
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