Day 20 Flashcards - STP
‘Classic’ Spanning Tree Protocol is IEEE […]
802.1D
Cisco switches use a version of STP called […], which runs a separate spanning tree instance in each VLAN.
PVST (Per-Vlan Spanning Tree)
Do all switches run STP by default?
Yes
How many root bridges are elected in STP?
One
If looped Layer 2 broadcast messages accumulate and congest a network, this is called a […]
broadcast storm
In an 802.1D STP network, which switch(es) send BPDUs?
Root bridge only
Interface Speed: 1 Gbps
802.1D STP cost: […]
4
Interface Speed: 10 Gbps
802.1D STP cost: […]
2
Interface Speed: 10 Mbps
802.1D STP cost: […]
100
Interface Speed: 100 Mbps
802.1D STP cost: […]
19
Interface Speed: […]
802.1D STP cost: 100
10 Mbps
Interface Speed: […]
802.1D STP cost: 19
100 Mbps
Interface Speed: […]
802.1D STP cost: 2
10 Gbps
Interface Speed: […]
802.1D STP cost: 4
1 Gbps
STP Designated ports are in a […] state.
forwarding
STP Non-Designated ports are in a […] state
blocking
STP root port selection:
1: Lowest […]
2: Lowest […]
3: Lowest […]
- root cost
- neighbor bridge ID
- neighbor port ID
STP Root ports are in a […] state.
forwarding
STP: All ports on the root bridge are […] ports (forwarding state)
designated
STP: The default bridge priority is […] (not including Extended System ID)
32768
STP: The switch with the lowest […] becomes the root bridge.
Bridge ID
STP: There must be one […] port per collision domain.
designated
STP: There must be one designated port per […].
collision domain
STP: When a switch is powered on, it assumes the role of […] bridge.
root
The messages sent by STP switches are called:
BPDUs (Bridge Protocol Data Units)
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
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 (4 bits)
Extended System ID (12 bits)
MAC Address ([…] bits)
48
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 ([…] bits)
Extended System ID (12 bits)
MAC Address (48 bits)
4
What does BPDU stand for?
Bridge Protocol Data Unit
What does PVST stand for?
Per-VLAN Spanning Tree
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
Which field in the STP BPDU is used to elect the root bridge?
Bridge ID field
[…] allows an STP port to move immediately to the forwarding state.
Portfast
Configure spanning tree in PVST mode:
SW1(config)# […]
spanning-tree mode pvst
Configure the spanning-tree root for a VLAN:
SW1(config)# […]
spanning-tree vlan vlan-id root primary
Configure the spanning-tree secondary root for a VLAN:
SW1(config)# […]
spanning-tree vlan vlan-id root secondary
Configure the STP cost of an interface:
SW1(config-if)# […]
spanning-tree vlan vlan-id cost cost
Configure the STP priority of an interface:
SW1(config-if)# […]
spanning-tree vlan vlan-id port-priority priority
Enable BPDU Guard on a switch port:
SW1(config-if)# […]
spanning-tree bpduguard enable
Enable BPDU Guard on all Portfast-enabled interfaces:
SW1(config)# […]
spanning-tree portfast bpduguard default
Enable portfast on a switch port:
SW1(config-if)# […]
spanning-tree portfast
Enable portfast on all access ports on the switch:
SW1(config)# […]
spanning-tree portfast default
If an interface with […] enabled receives a BPDU from another switch, the interface will be shut down.
BPDU Guard
PVST+ BPDUs are sent to destination MAC address:
0100.0ccc.cccd
spanning-tree vlan vlan-id root secondary sets the STP priority to […]
28672
spanning-treee vlan vlan-id root primary sets the STP priority to […], or 4096 less than the current root’s priority.
24576
Standard STP (NOT PVST) BPDUs are sent to destination MAC address:
0180.c200.0000
STP BPDUs are only forwarded on […] ports.
designated
STP default Forward delay timer:
15 seconds
STP default hello timer:
2 seconds
STP default max age timer:
20 seconds (10*hello timer)
STP: A blocking interface [can/can’t] move directly to a forwarding state.
can’t
STP: A forwarding interface [can/can’t] move directly to a blocking state.
can
STP: Do interfaces in a blocking state learn MAC addresses?
No
STP: Do interfaces in a blocking state receive BPDUs?
Yes
STP: Do interfaces in a blocking state send BPDUs?
No
STP: Do interfaces in a blocking state send/receive regular network traffic?
No
STP: Do interfaces in a Forwarding state learn MAC addresses?
Yes
STP: Do interfaces in a Forwarding state send/receive BPDUs?
Yes
STP: Do interfaces in a Forwarding state send/receive regular network traffic?
Yes
STP: Do interfaces in a Learning state learn MAC addresses?
Yes
STP: Do interfaces in a Learning state send/receive BPDUs?
Yes
STP: Do interfaces in a Learning state send/receive regular network traffic?
No
STP: Do interfaces in a Listening state learn MAC addresses?
No
STP: Do interfaces in a Listening state send/receive BPDUs?
Yes
STP: Do interfaces in a Listening state send/receive regular network traffic?
No
STP: Non-designated ports are in a […] state.
Blocking
SW1(config)# spanning-tree portfast default
This command enables portfast on which ports?
All access ports
The STP timers on the […] determine the timers used for all switches in the network.
root bridge
What are the two ‘stable’ STP port states?
Blocking, Forwarding
What are the two ‘transitional’ STP port states?
Listening, Learning
Which STP optional feature prevents a newly connected switch from becoming the root bridge?
Root Guard
Which STP optional feature shuts down an interface if it stops receiving BPDUs?
Loop Guard