ch.9 Spanning Tree Protocol Concepts Flashcards
What is the 802.1D standard
STP- Spanning Tree Protocol and eventually RSTP- Rapid Spanning Tree Protocol
What is a Broadcast storm
The forwarding of a frame repeatedly on the same links, consuming significant parts of the links capacities
What is a MAC table instability
The continual updating of a switchs MAC address table with incorrect entries, in reaction to looping frames, resulting frames in which multiple copies of one frame are delivered to the intended host, confusing the host
What does STP/RSTP do
Prevents loops by placing each switch port in either a forwarding state or a blocking state
When an interface is in a blocking state in STP/RSTP what does it do
they dont process any frames
they dont learn mac address
they dont process received user frames except STP/RSTP messages
What is STP convergence
The process by which the switches collectively realize that something has changed in the LAN topology and determine whether they need to change which ports block and which ports forward
What are the three criteria STP/RSTP use to choose whether to put an interface in forwarding state
- Elects a root switch. Puts all working interfaces on the root switch in forwarding state
- Places the port with the least root cost path in forwarding state
- The switch with the lowest root cost has its interface placed as the designated port
What are the three tie breakers a switch uses to decide which route would become the designated route
- lowest neighbor bridge ID
- lowest neighbor port priority
- lowest neighbor internal port number
What is the Designated port (DP)
The switch port that advertises the lowest cost Hello onto a LAN segment
Describe the STP convergence Hello timer and its default value
The time period between Hellos created by the root
Describe the STP convergence MaxAge timer and its default value
10 times Hello timer - How long any switch should wait, after ceasing to hear Hellos, before trying to change the STP topology
Describe the STP convergence Forward delay timer and its default value
15 seconds - Delay that affects the process that occurs when an interface changes from blocking state to forwarding state. A port stays in an interim listening state, and then an interim learning state, for the number of seconds defined by the forward delay timer
What happens if a switch doesn’t receive any Hello messages from the root switch
The switch continues as normal until the MaxAge timer (default 20 seconds) , the switch makes all of its STP choices again, based on any Hellos it receives from switches, it fiugres out who should be the root switch, it then choose its RP and then its DP
Describe the Listening Temporary STP state
The interface does not forward frames, the switch removes old MAC table entries
Describe the Learning Temporary STP state
Interfaces in this state still do not forward frames, but the switch begins to learn the MAC addresses of frames received on the interface
