11.What are Types of BPDU?
Two types of BPDU exist -
1. Configuration BPDU - Used for Spanning-Tree Computation.
2. Topology Change Notification (TCN) BPDU - Used to announce changes in the Network Topology.
12.How Root bridge is elected?
The Bridge ID is used to elect the root bridge in the STP domain. This ID is 8 bytes long and includes both the priority and the MAC address of the device. Switch with the lowest Bridge ID is elected as the Root bridge which means Switch with the lowest priority will become Root Bridge if two or more switches have same priority than switch with lowest mac address will become Root Bridge.
13.Explain Root path cost?
Root path cost is the Cumulative Cost of all links to the Root Bridge.
14.How Root Ports are elected?
Non Root Bridges use Root path cost to determine which port will be the Root port. The port with the lowest root path cost is elected as the root port and is placed in the forwarding state.
15.What is the difference between Path cost and Root Path cost?
Path cost is the value assigned to each port. It is added to BPDUs received on that port to calculate the root path cost. Root path cost is defined as the cumulative cost to reach the root bridge. This value is calculated by adding the receiving port's path cost to the value contained in the BPDU. In a BPDU, Root path cost is transmitted not the path cost.
16.What is Path Cost or Spanning Tree Path Cost value?
The Spanning Tree Cost Value is inversely proportional to the associated bandwidth of the link and therefore a path with a low cost value is more preferable than a path with high cost value.
Link Bandwidth Cost Value
10 Gbps 2
1 Gbps 4
100 Mbps 19
10 Mbps 100
17.What is Root Port?
Once the Root Switch is elected, every other Switch in the network must select a single port on itself to reach the Root Switch. The single selected port on a Switch with least Path Cost to reach the Root Bridge is called the Root Port. Root Bridge will never have a Root Port.
18.What is Extended System ID?
The Extended System ID is utilized by spanning-tree to include the VLAN ID information inside 16-bit STP Bridge Priority value. Extended System ID is the least significant 12-bits in 16-bit STP Bridge Priority value.
19.Explain Root Guard ?
Root guard is used to protect root bridge. Root Guard stops a new switch introduced in the network with a lower bridge ID to become the root bridge. If a port with Root Guard feature enabled receives a superior BPDU, it moves the port into a root-inconsistent state (equal to a listening state) thus maintaining the current Root Bridge status. It is enabled on interface level.switch(config-if)# spanning-tree guard root
20.What is BPDU Guard ?
When we enable portfast on a port , we do not expect BPDU's on that port. Suppose a switch is connected by mistake on the port where portfast is enabled, loop can form. An even greater consequence is that connected switch has potential to become root bridge. The BPDU Guard feature was developed to protect the integrity of switch ports that have PortFast enabled. If any BPDU (superior to the current root or not) is received on a port where BPDU Guard is enabled, that port immediately is put into the error-disable state. The port is shut down in an error condition and must be either manually re-enabled or automatically recovered through the error-disable timeout function.
BPDU Guard can be enabled on both interface & global level. It is basically enabled on access layer switches. In this all vlans are effected.
Switch(config)# spanning-tree portfast bpduguard default Switch(config-if)# spanning-tree bpduguard enable
Read More Questions:
STP Interview Questions Part1
STP Interview Questions Part2
STP Interview Questions Part3
Two types of BPDU exist -
1. Configuration BPDU - Used for Spanning-Tree Computation.
2. Topology Change Notification (TCN) BPDU - Used to announce changes in the Network Topology.
12.How Root bridge is elected?
The Bridge ID is used to elect the root bridge in the STP domain. This ID is 8 bytes long and includes both the priority and the MAC address of the device. Switch with the lowest Bridge ID is elected as the Root bridge which means Switch with the lowest priority will become Root Bridge if two or more switches have same priority than switch with lowest mac address will become Root Bridge.
13.Explain Root path cost?
Root path cost is the Cumulative Cost of all links to the Root Bridge.
14.How Root Ports are elected?
Non Root Bridges use Root path cost to determine which port will be the Root port. The port with the lowest root path cost is elected as the root port and is placed in the forwarding state.
15.What is the difference between Path cost and Root Path cost?
Path cost is the value assigned to each port. It is added to BPDUs received on that port to calculate the root path cost. Root path cost is defined as the cumulative cost to reach the root bridge. This value is calculated by adding the receiving port's path cost to the value contained in the BPDU. In a BPDU, Root path cost is transmitted not the path cost.
16.What is Path Cost or Spanning Tree Path Cost value?
The Spanning Tree Cost Value is inversely proportional to the associated bandwidth of the link and therefore a path with a low cost value is more preferable than a path with high cost value.
Link Bandwidth Cost Value
10 Gbps 2
1 Gbps 4
100 Mbps 19
10 Mbps 100
17.What is Root Port?
Once the Root Switch is elected, every other Switch in the network must select a single port on itself to reach the Root Switch. The single selected port on a Switch with least Path Cost to reach the Root Bridge is called the Root Port. Root Bridge will never have a Root Port.
18.What is Extended System ID?
The Extended System ID is utilized by spanning-tree to include the VLAN ID information inside 16-bit STP Bridge Priority value. Extended System ID is the least significant 12-bits in 16-bit STP Bridge Priority value.
19.Explain Root Guard ?
Root guard is used to protect root bridge. Root Guard stops a new switch introduced in the network with a lower bridge ID to become the root bridge. If a port with Root Guard feature enabled receives a superior BPDU, it moves the port into a root-inconsistent state (equal to a listening state) thus maintaining the current Root Bridge status. It is enabled on interface level.switch(config-if)# spanning-tree guard root
20.What is BPDU Guard ?
When we enable portfast on a port , we do not expect BPDU's on that port. Suppose a switch is connected by mistake on the port where portfast is enabled, loop can form. An even greater consequence is that connected switch has potential to become root bridge. The BPDU Guard feature was developed to protect the integrity of switch ports that have PortFast enabled. If any BPDU (superior to the current root or not) is received on a port where BPDU Guard is enabled, that port immediately is put into the error-disable state. The port is shut down in an error condition and must be either manually re-enabled or automatically recovered through the error-disable timeout function.
BPDU Guard can be enabled on both interface & global level. It is basically enabled on access layer switches. In this all vlans are effected.
Switch(config)# spanning-tree portfast bpduguard default Switch(config-if)# spanning-tree bpduguard enable
Read More Questions:
STP Interview Questions Part1
STP Interview Questions Part2
STP Interview Questions Part3
No comments:
Post a Comment