What does a BPDU contain?

What does a BPDU contain?

A bridge protocol data unit (BPDU) is a data message transmitted across a local area network to detect loops in network topologies. A BPDU contains information regarding ports, switches, port priority and addresses. BPDUs contain the information necessary to configure and maintain spanning tree topology.

What is the difference between Pvst and Pvst+?

Per VLAN Spanning Tree (PVST) is a Cisco proprietary protocol that allows a Cisco device to have multiple spanning trees. PVST+ is an extension of PVST that allows a Cisco device to also interoperate with devices that are running a single spanning tree (IEEE 802.1Q).

What is the difference between RSTP Pvst Pvst+ and MSTP?

Rapid Per-VLAN Spanning Tree (Rapid PVST+)—Rapid PVST+ is a Cisco enhancement of RSTP that uses PVST+ and provides a separate instance of 802.1w for each VLAN. Multiple Spanning Tree Protocol (MSTP)—MSTP, defined in IEEE 802.1s, maps multiple VLANs into the same spanning-tree instance.

What is root ID in switch?

The root ID is the mac-address of the switch that is the root bridge for that vlan. So if the bridge ID and root ID are the same then you are on the root bridge for that vlan.

What is BPDU on a switch?

D. P. U. (Bridge Protocol Data Unit) A spanning tree protocol (STP) message unit that describes the attributes of a switch port such as its MAC address, priority and cost to reach. BPDUs enable switches that participate in a spanning tree protocol to gather information about each other.

What are the different types of BPDU?

There are two kinds of BPDUs for 802.1D Spanning Tree:

• Configuration BPDU, sent by root bridges to provide information to all switches.
• TCN (Topology Change Notification), sent by bridges towards the root bridge to notify changes in the topology, such as port up or port down.

What is Pvst mode in the switch?

With mode ‘pvst’, the switch uses Per-VLAN Spanning-Tree (PVST). Each VLAN runs its own instance of STP using the original 802.1d rules (non-rapid). With mode ‘rapid-pvst’, the switch also uses Per-VLAN Spanning-Tree (PVST). Each VLAN runs its own instance of STP using the updated Rapid STP rules (802.1w).

What is the difference between Pvst and MST?

MST (Multiple Spanning Tree) and PVST+ (Per VLAN Spanning Tree) both offer loop-free layer two topologies but they each use a different approach: MST maps multiple VLANs to an instance, reducing the number of spanning-tree instances. PVST+ calculates an instance for each spanning-tree instance.

What is the difference between STP and MSTP?

The differences between Spanning Tree Protocol (STP), Rapid Spanning Tree Protocol (RSTP), and Multiple Spanning Tree Protocol (MSTP) are as follows: STP: only supports a single instance. RSTP: supports fast convergence and a single instance. MSTP: includes the advantages of RSTP, and supports multiple instances.

What is the port ID?

Port ID is a logical interface identifier configured to participate in the STP instance. AFAIK it consists of port priority and port index. If BPDUs have the same Root Bridge ID, the same path cost to the Root and the same Sending Bridge ID (multiple links between two switches) then Port ID is used as a tie-breaker.

What does Bpdu stand for?

Bridge Protocol Data Unit
(Bridge Protocol Data Unit) A spanning tree protocol (STP) message unit that describes the attributes of a switch port such as its MAC address, priority and cost to reach. BPDUs enable switches that participate in a spanning tree protocol to gather information about each other.

What is the use of BPDU guard?

BPDU Guard feature protects the port from receiving STP BPDUs, however the port can transmit STP BPDUs. When a STP BPDU is received on a BPDU Guard enabled port, the port is shutdown and the state of the port changes to ErrDis (Error-Disable) state.

What is the sender bridge ID in BPDU?

The Sender Bridge ID is ofcourse the same as the Root BID, as it is again its own BID. With in BPDU, the Cost field is listed with a value of 0, because there is no cost between itself.

What’s the difference between a bid and a BPDU?

The BID is a global, box-wide value (within a single VLAN) that is formed from a MAC address located on the supervisor card or backplane. The source MAC is used to build the frame that carries the BPDU, whereas the BID’s MAC is contained within the actual Configuration BPDU.

What does BPDU stand for in spanning tree protocol?

The two values ( Bridge Priority + System ID Extension) together make up the Bridge ID used to elect the Root Bridge. The election process uses several STP messages sent between switches which help each switch to decide, who is the Root Bridge. These messages are called Hello BPDU where BPDU stands for Bridge Protocol Data Unit.

What are the different types of BPDUs in Cisco?

Actually, there are two types of BPDUs: Configuration BPDUs are originated by the Root Bridge and flow outward along the active paths that radiate away from the Root Bridge. Topology Change Notification BPDUs flow upstream (toward the Root Bridge) to alert the Root Bridge that the active topology has changed.