#Switch loop in r default software#

It will through you the error in the log. What happens in this case if if by mistake or intentionally someone configure SW3 to be root bridge for vlan 10 (by lowering the priority) SW1 will put the ports into root-inconsistent port hence this BPDU will not have any affect. What you need to do is configure root guard feature on F0/1 of SW1. In the above topology SW2 is root bridge for VLan 10 and you dont want any other switch in the network to become the root bridge for this vlan 10 other than SW2.

Even if you receive a superior BPDU from another switch, root guard will prevent that switch from becoming the root bridge. Root guard for spanning tree can be used to prevent a certain switch from becoming the root bridge. Hence it is layer 1 cable issue STP would not be able to detect it automatically, hence you would use the loopguard feature. Hence when you confiugre the loopguard/udld then the port would go blocked. what happens when it stopped reciving the BPDU's? (Considering the example that there is some issue with the fiber cable and Tx is haiving issue hence port T0/2 is not reciving it hence it waits for the max age timer to expire after which the port transition from Blocking to forwarding mode which is not supposed to hence there would be loop. The Sw2 and Sw3 is connected through fiber cable, One end would be tx and other end would be rx.ДЄs you know that blocked port would be recieving the BPDU's. Think SW1 is the Root bridge hence the port T0/2 will be in blocking state.( To have the loopfree topology) Hence consider the above topology one of the link will be block. Taking 3 switchs as a example: connecting in a triangle. Loop guard will ensure that if a blocked interface no longer receives BPDUs from the other side that it will be shut down to prevent a layer 2 loop. If one of these links fails it's possible that interfaces that are currently in 'blocking' mode go to forwarding. Fibre links have a transmit and receive connector. Please study them and then if you have something which is unclear you can ask here.ДЎ) LoopGuard: Spanning Tree Loop Guard helps to prevent loops when you use fibre links. Maybe you didn't found the right documentation, so here are some links that explain clear and straightforward how this features work: To explain here how each of this features work, would mean to either copy / paste from or to write about 5-10 pages to really capture of all aspects, which is a high effort for this topic which is explained very well at Just to know for future questions related to STP Since STP is more a LAN topic than a WAN one, this thread should be opened there. Loopguard, BPDUguard and Rootguard are Spanning-Tree enhancements.

Rootguard:- It is enabled on the designated ports of root switch, so that if those ports listen to the superior BPDU then put that port in inconsistent state. Now imagine if some other customer switch sends a superior BPDU then the STP need to be converged again and lead of serious issues. In case of metro ethernet, SP puts switches at customer building and make that switch ar root bridge. If the port is receiving BPDUs, the loop guard feature puts the port into an inconsistent state until it starts receiving BPDUs again.Д«PDU Guard:-BPDUGuard enables on access port which helps the switches to put the port in shut down mode once it receives the superior BPDU. The loop guard feature checks if a root port or an alternate root port receives BPDUs.

#Switch loop in r default software#

Some software failures may introduce temporary loops in the network. Loopguard:- Unidirectional link failures may cause a root port or alternate port to become designated as root if BPDUs are absent.