Module 5 - STP (Part 1)

Redundancy

It is an important part of the hierarchical design for eliminating single points of failure and preventing disruption of network services to users.

Spanning Tree Protocol (STP)

_________ is a loop-prevention network protocol that allows for redundancy while creating a loop-free Layer 2 topology

Spanning Tree Protocol (STP)

_______ logically blocks physical loops in a Layer 2 network, preventing frames from circling the network forever

True

(T/F) STP compensates for a failure in the network by recalculating and opening up previously blocked ports

- MAC address table instability

- link saturation

- high CPU utilization

A Layer 2 loop can result in _______, ________, and _______ on switches and end-devices, resulting in the network becoming unusable

False - Layer 2 Ethernet does not include a mechanism to recognize and eliminate endlessly looping frames

(T/F) Layer 2 Ethernet does include a mechanism to recognize and eliminate endlessly looping frames

True

(T/F) STP was developed specifically as a loop prevention mechanism for Layer 2 Ethernet

True

(T/F) Without STP enabled, Layer 2 loops can form, causing broadcast, multicast and unknown unicast frames to loop endlessly

broadcast storm

A _______ is an abnormally high number of broadcasts overwhelming the network during a specific amount of time

True

(T/F) A host caught in a Layer 2 loop is not accessible to other hosts on the network

False - Spanning tree is enabled, by default, on Cisco switches to prevent Layer 2 loops from occurring

(T/F) Spanning tree is disabled, by default, on Cisco switches

Radia Perlman

STP is based on an algorithm invented by?

- Selecting a Root Bridge

- Block Redundant Paths

- Create a Loop-Free Topology

- Recalculate in case of Link Failure

How does the STA create a loop-free topology?

Selecting a Root Bridge

This bridge (switch) is the reference point for the entire network to build a spanning tree around

Block Redundant Paths

STP ensures that there is only one logical path between all destinations on the network

Create a Loop-Free Topology

A blocked port has the effect of making that link a non-forwarding link between the two switches

Recalculate in case of Link Failure

The physical paths still exist to provide redundancy, but these paths are disabled to prevent the loops from occurring

1. Elect the root bridge

2. Elect the root ports

3. Elect designated ports.

4. Elect alternate (blocked) ports

4 Steps to a Loop-Free Topology

Bridge Protocol Data Units (BPDUs)

During STA and STP functions, switches use ________ to share information about themselves and their connections.

Bridge Protocol Data Units (BPDUs)

______ are used to elect the root bridge, root ports, designated ports, and alternate ports

bridge ID (BID)

Each BPDU contains a _____ that identifies which switch sent the BPDU.

bridge ID (BID)

It is involved in making many of the STA decisions including root bridge and port roles

- Bridge Priority

- Extended System ID

- MAC address

3 fields of a Bridge ID (BID)

32768

The default priority value for all Cisco switches is the decimal value _____

True

(T/F) A bridge priority of 0 takes precedence over all other bridge priorities

extended system ID

The _________ value is a decimal value added to the bridge priority value in the BID to identify the VLAN for this BPDU

MAC address

When two switches are configured with the same priority and have the same extended system ID, the switch having the _________ with the lowest value, expressed in hexadecimal, will have the lower BID

False - All switches in the broadcast domain participate in the election process

(T/F) Not all switches in the broadcast domain participate in the election process of electing the root bridge

False - After a switch boots, it begins to send out BPDU frames every two seconds

(T/F) After a switch boots, it begins to send out BPDU frames every five seconds

Root ID

BPDU frames contain the BID of the sending switch and the BID of the root bridge, known as the _____

True

(T/F) At first, all switches declare themselves as the root bridge with their own BID set as the Root ID

internal root path cost

The path information, known as the ________, is determined by the sum of all the individual port costs along the path from the switch to the root bridge

root port

After the root bridge has been determined, the STA algorithm is used to select the ________

root port

The _______ is the port closest to the root bridge in terms of overall cost to the root bridge

internal root path cost

This overall cost is known as the?