It is a fast converged version of Spanning Tree Protocol as its name implies. So, the convergence time is lower than STP. But with some additional improvements, It is more useful. It is the backup of Root Port. It is the backup of Designated Port.
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Note: Before reading this article you should understand how STP works. One big disadvantage of STP is the low convergence which is very important in switched network. To overcome this problem, in , the IEEE with document While STP can take 30 to 50 seconds to transit from a blocking state to a forwarding state, RSTP is typically able to respond less than 10 seconds of a physical link failure. These ports are allowed to immediately enter the forwarding state rather than passively wait for the network to converge.
This path is different than using the root port. The alternative port moves to the forwarding state if there is a failure on the designated port for the segment. The backup port applies only when a single switch has two links to the same segment collision domain. To have two links to the same collision domain, the switch must be attached to a hub. The other port will be Backup port according to the definition of Backup port above.
But how does Sw2 select its Designated and Backup port? The decision process involves the following parameters inside the BPDU:. There are only three port states left in RSTP that correspond to the three possible operational states. The RSTP converges with all ports either in forwarding state or discarding state. RSTP provides faster convergence than If a RSTP enabled port receives a legacy It sends and receives Find out more or Sign In.
Note: Alternative Port and Backup Port are in discarding state. STP State Comments 0 Comments. No comments yet. IPv6 Tutorial 9tut.
Understanding Rapid Spanning Tree Protocol (802.1w)
Nowadays we see more and more routing in our networks. To keep up with the speed of these routing protocols another flavor of spanning-tree was created… rapid spanning-tree. Rapid spanning-tree is not a revolution of the original spanning-tree but an evolution. Take a look at the picture below:. Remember the port states of spanning-tree? We have a blocking, listening, learning and forwarding port state.
Rapid Spanning-Tree (RSTP)
As you have learned in the previous sections, the immediate hindrance of STP is convergence. It takes anywhere from 30 to 50 seconds depending on the type of failure to converge the network. For starters, RSTP requires full-duplex point-to-point connection between adjacent switches. Half duplex, generally speaking, denotes a shared medium whereby multiple hosts share the same wire; a point-to-point connection cannot reside in this environment. As a result, RSTP cannot work in a half-duplex mode. Ports not participating in spanning tree are known as edge ports.