21.Explain Sudden Loss of BPDUs?
Suppose switch does not receive BPDUs, it will think that the topology must have changed, so blocked ports can be unblocked again. What if the absence of BPDUs is actually a mistake and not a topology change, bridging loops easily can form.
There are two features that help detect or prevent the unexpected loss of BPDUs:-
1. Loop Guard
2. Unidirectional Link Detection (UDLD)
22.What is Loop Guard?
Loop Guard keeps track of the BPDU activity on non-designated ports. It does not allow non-designated ports to become designated ports in case of sudden loss of BPDUs. While BPDUs are received, the port is allowed to behave normally. When BPDUs go missing, Loop Guard moves the port into the loop-inconsistent state (port is effectively blocking at this point to prevent a loop from forming and to keep it in the non-designated role). When BPDUs are received on the port again, Loop Guard allows the port to move through the normal STP states and become active.
It can be enabled on both interface & global level. It affects per vlan basis.
Switch(config)# spanning-tree loopguard default
Switch(config-if)# spanning-tree guard loop
23.What is BPDU Filter?
STP runs on a switch to prevent loops. However, in special cases when we need to prevent BPDUs from being sent or processed on one or more switch ports, we can use BPDU filtering to effectively disable STP on those ports. It prevents port from sending and receiving BPDUs. It can be enabled on both interface & global level.
Switch(config)# spanning-tree portfast bpdufilter default
Switch(config-if)# spanning-tree bpdufilter { enable | disable }
24.What is the difference between BPDU Guard and BPDU Filter?
BPDU Guard works aggresively and puts the port in error-disable state while BPDU filter does not
shut the port, it only filters BPDU. BPDU Guard only prevents receiving BPDUs while BPDU filter
prevents both sending and receiving BPDU.If Both BPDU Guard and BPDU Filter is enabled on a port than only BPDU filter will work.
Read More Questions:
STP Interview Questions Part1
STP Interview Questions Part2
STP Interview Questions Part3
Suppose switch does not receive BPDUs, it will think that the topology must have changed, so blocked ports can be unblocked again. What if the absence of BPDUs is actually a mistake and not a topology change, bridging loops easily can form.
There are two features that help detect or prevent the unexpected loss of BPDUs:-
1. Loop Guard
2. Unidirectional Link Detection (UDLD)
22.What is Loop Guard?
Loop Guard keeps track of the BPDU activity on non-designated ports. It does not allow non-designated ports to become designated ports in case of sudden loss of BPDUs. While BPDUs are received, the port is allowed to behave normally. When BPDUs go missing, Loop Guard moves the port into the loop-inconsistent state (port is effectively blocking at this point to prevent a loop from forming and to keep it in the non-designated role). When BPDUs are received on the port again, Loop Guard allows the port to move through the normal STP states and become active.
It can be enabled on both interface & global level. It affects per vlan basis.
Switch(config)# spanning-tree loopguard default
Switch(config-if)# spanning-tree guard loop
23.What is BPDU Filter?
STP runs on a switch to prevent loops. However, in special cases when we need to prevent BPDUs from being sent or processed on one or more switch ports, we can use BPDU filtering to effectively disable STP on those ports. It prevents port from sending and receiving BPDUs. It can be enabled on both interface & global level.
Switch(config)# spanning-tree portfast bpdufilter default
Switch(config-if)# spanning-tree bpdufilter { enable | disable }
24.What is the difference between BPDU Guard and BPDU Filter?
BPDU Guard works aggresively and puts the port in error-disable state while BPDU filter does not
shut the port, it only filters BPDU. BPDU Guard only prevents receiving BPDUs while BPDU filter
prevents both sending and receiving BPDU.If Both BPDU Guard and BPDU Filter is enabled on a port than only BPDU filter will work.
Read More Questions:
STP Interview Questions Part1
STP Interview Questions Part2
STP Interview Questions Part3
No comments:
Post a Comment