Day 20 | STP (part one)

If looped Layer 2 broadcast messages accumulate and congest a network, this is called a […]

broadcast storm

When a switch rapidly and continuously updates a MAC address in its MAC address table, alternating between different interfaces, this is known as […]

MAC address flapping

'Classic' Spanning Tree Protocol is IEEE […]

802.1D

Do all switches run STP by default?

Yes

The messages sent by STP switches are called:

BPDUs (Bridge Protocol Data Units)

What does BPDU stand for?

Bridge Protocol Data Unit

How many root bridges are elected in STP?

One

Which field in the STP BPDU is used to elect the root bridge?

Bridge ID field

STP: The switch with the lowest […] becomes the root bridge.

Bridge ID

STP: All ports on the root bridge are […] ports (forwarding state)

designated

STP: The default bridge priority is […] (not including Extended System ID)

32768

Three fields of the STP Bridge ID: […] (4 bits) Extended System ID (12 bits) MAC Address (48 bits)

Bridge Priority

Three fields of the STP Bridge ID: Bridge Priority (4 bits) […] (12 bits) MAC Address (48 bits)

Extended System ID (VLAN ID)

Three fields of the STP Bridge ID: Bridge Priority (4 bits) Extended System ID (12 bits) […] (48 bits)

MAC Address

Three fields of the STP Bridge ID: Bridge Priority ([…] bits) Extended System ID (12 bits) MAC Address (48 bits)

4

Three fields of the STP Bridge ID: Bridge Priority (4 bits) Extended System ID ([…] bits) MAC Address (48 bits)

12

Three fields of the STP Bridge ID: Bridge Priority (4 bits) Extended System ID (12 bits) MAC Address ([…] bits)

48

Cisco switches use a version of STP called […], which runs a separate spanning tree instance in each VLAN.

PVST (Per-Vlan Spanning Tree)

What does PVST stand for?

Per-VLAN Spanning Tree

The STP bridge priority can be changed in units of […]

4096 Possible values (you don't have to memorize these!): 0, 4096, 8192, 12288, 16384, 20480, 24576, 28672, 32768, 36864, 40960, 45056, 49152, 53248, 57344, or 61440

STP Designated ports are in a […] state.

forwarding

STP: When a switch is powered on, it assumes the role of […] bridge.

root

In an 802.1D STP network, which switch(es) send BPDUs?

Root bridge only

Interface Speed: 10 Mbps 802.1D STP cost: […]

100

Interface Speed: […] 802.1D STP cost: 100

10 Mbps

Interface Speed: 100 Mbps 802.1D STP cost: […]

19

Interface Speed: […] 802.1D STP cost: 19

100 Mbps

Interface Speed: 1 Gbps 802.1D STP cost: […]

4

Interface Speed: […] 802.1D STP cost: 4

1 Gbps

Interface Speed: 10 Gbps 802.1D STP cost: […]

2

Interface Speed: […] 802.1D STP cost: 2

10 Gbps

STP root port selection: 1: Lowest […] 2: Lowest […] 3: Lowest […]

1. root cost 2. neighbor bridge ID 3. neighbor port ID

STP: There must be one […] port per collision domain.

designated

STP: There must be one designated port per […].

collision domain

STP Root ports are in a […] state.

forwarding

STP Non-Designated ports are in a […] state

blocking