Spanning Tree (STP) Flashcards
What is the purpose of STP?
The Spanning-Tree Protocol (STP) creates one path through a switch network in order to prevent Layer 2 loops.
What is MAC Database instability?
Copies of the same frame being received on different ports.
Ethernet frames do not have a time to live(TTL) field like the Layer 3 IP header has. This means that Ethernet has no mechanism to drop frames that propagate endlessly. This can result in MAC database instability.
What is Broadcast Storms?
Broadcasts are flooded endlessly causing network disruption.
So many broadcasts frames in a Layer 2 loop use all available bandwidth and make the network unreachable → Causes DoS(Denial of service)
What is Duplicate Unicast Frames?
When the switch doesn’t have the destination MAC address in its MAC table and has to flood the frame out all ports. In looped networks this can cause duplicate frames arriving at the destination device.
What is a BDPU?
Bridge Protocol Data Unit. STP sends them between Layer 2 devices in order to create one logical path.
What is a root port?
The port on a switch that has the lowest cost to reach the root bridge.
What is a designated port?
Designated port is a non root port based on the cost of each port on either side of the segment and the total cost calculated by STP for that port to get back to the root bridge.
What happens with a port(s) that isn’t RP or DP?
The port(s) get blocked
What is a root bridge?
Layer 2 device in a switched network (a switch basically).
How does STP(Spanning-tree protocol) choose the Root Bridge?
By choosing the device with the lowest bridge ID (BID). If bridge priority is not changed, lowest MAC address becomes determinant for root bridge.
What does BID stand for?
Bridge ID. It has two fields: bridge priority and MAC address.
What is the default Bridge Priority number?
32,768
What are the consequences if STP fails/turns off?
This can cause a switched network to be unusable – Remember that there is not a TTL mechanism at Layer 2
