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Question
Answer
List the 3 main problems that occur when not using STP in a LAN with redundant links.
List the reasons why a switch chooses to place an interface into Forwarding or Blocking State.
List the most important fields in Hello BPDU messages.
Default Port Costs According to IEEE
Summary description of steady-state STP operations
\\\"1. The root creates and sends a Hello BPDU
2. The nonroot switches receive the Hello on their root ports. After changing the Hello to list their own bridge ID as the sender’s BID
and listing that switch’s root cost
3. Steps 1 and 2 repeat until something changes.\\\"
STP timers
Define what happens during the Listening State
\\\"Like the Blocking State
Define what happens during the Learning State
\\\"Interfaces in this state still do not forward frames
IEEE 802.1d Spanning-Tree States
How are RSTP (802.1w) and STP (802.1d) similar?
\\\"• It elects the root switch using the same parameter and tiebreakers.
• It elects the root port on nonroot switches with the same rules.
• It elects designated ports on each LAN segment with the same rules.
• It places each port in either Forwarding or Blocking State
although RSTP calls the Blacking State the Discarding State.\\\"
RSTP and STP Port States
RSTP and STP Port Roles
Compare 3 Options for Multiple Spanning Trees
STP Defaults and Configuration Options
\\\"2 branches of logic in how the \\\"\\\"spanning-tree root primary\\\"\\\" command picks a new base STP priority\\\"
\\\"• 24
• 4096 less than the current root’s base priority if the current root’s priority is 24
576 or lower\\\"
Strategy for solving STP problems on the exams
\\\"1. Determine the root switch.
2. For each nonroot switch
determine its one root port (RP) and cost to reach the root switch through that RP.
3. For each segment
determine the designated port (DP) and the cost advertised by the DP onto that segment.\\\"
Alternate port
\\\"In RSTP 802.1w
backup port
\\\"In RSTP 802.1w
Blocking State
\\\"In 802.1d STP
BPDU Guard
\\\"A cisco switch feature that listens for incoming STP BPDU messages
bridge ID (BID)
An 8-byte identifier for bridges and switches used by STP and RSTP. It is composed of a 2-byte priority field followed by a 6-byte System ID field that is usually filled with a MAC address.
BPDU
Bridge protocol data unit. The generic name for Spanning Tree Protocol messages.
designated port
\\\"In both STP and RSTP
disabled port
\\\"In STP
Discarding State
\\\"An RSTP interface state in which no received frames are processed
EtherChannel
\\\"A Cisco-proprietary feature in which up to 8 parallel Ethernet segments between the same 2 devices
forward delay
\\\"An STP timer
Forwarding State
An STP and RSTP port state in which an interface operates unrestricted by STP.
Hello BPDU
\\\"The STP & RSTP message used for the majority of STP communications
IEEE 802.1d
The IEEE standard for the original Spanning Tree Protocol.
IEEE 802.1s
\\\"The IEEE standard for Multiple Instances of Spanning Tree (MIST)
IEEE 802.1w
\\\"The IEEE standard for enhanced version of STP
Inferior Hello
\\\"When comparing 2 or more received Hello BPDUs
Learning State
\\\"In STP
Listening State
A temporary STP port state that occurs immediately when a blocking interface must be moved to a Forwarding state. The switch times out MAC table entries during this state. It also ignores frames received on the interface & doesn\\\'t forward any frames out the interface.
MaxAge
\\\"In STP
PortFast
\\\"A switch STP feature in which a port is placed in an STP Forwarding state as soon as the interface comes up
Rapid Spanning Tree Protocol (RSTP)
Defined in IEEE 802.1w. Defines an imporved versions of STP that converges much more quickly & consistently than STP (802.1d).
root port
\\\"In STP
root switch
\\\"In STP
Spanning Tree Protocol (STP)
\\\"A protocol defined by IEEE standard 802.1d. Allows switches and bridges to create a redundant LAN
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