Network loop causes
- Broadcast storms – formwarding of a frame repeatedly on the same links consuig significant parts of the links capacity.
- MAC table instability – Continual updating of a switch of MAC address table with incrorect etries, in raction to loooping frames being sent from the different interfaces
- Multiple frame transmission – A side effect of looping frames in which multiple copies of one frame are delivered to the intended host, confusing the host.
| Timer | Default Value | Description | |||
| Hello | 2 sec | The time period between Hellos creeated by the root. | |||
| MaxAget | 10 times Hello | How long any switch should wait, after ceasing to hear Hellos, before trying to change the STP topology. | |||
| Forward delay | 15 sec | 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. | |||
| State | Forwards Data Frames | Learns MAC based on received frames | Transitory or stable state | ||
| Blocking | No | No | Stable | ||
| Listening | No | No | Transitory | ||
| Learning | No | Yes | Transitory | ||
| Forwarding | Yes | Yes | Stable | ||
| Disable | No | No | Stable | ||
| Ethernet Speed | IEEE Cost |
| 10 Mbps | 2000000 |
| 100Mbps | 200000 |
| 1Gbps | 20000 |
| 10Gbps | 2000 |
| 100Gbps | 200 |
| 1Tbps | 20 |
Rapid STP (802.1w)
- Can be used with stp
-
Elect from
- Lowest root bridge id
-
Lowest MAC Address
-
Pretty much like stp except
- Adds a new mechanism to replace the root port, without any waiting reach a forwarding state
- Adds a new mechanism to replace a designated port without any waiting to reach a forwarding state
- Lowers wainting times for cases in which rstp must wait
| Function | Port Role | ||
| Nonroot switch best path to the root | Root port | ||
| Replaces the root port when the root port fails | Alternate port | ||
| Switch port designated to forward onto a collision domain | Designated port | ||
| Repalces a designated port when a designated port fails | Backup port | ||
| Port that is administratively disabled | Disabled port | ||
| Function | 802.1D State | 802.1w State | |
| Port is administratively disabled | Disabled | Discarding | |
| Stable state that ignores incoming data frames and is not used to forward data frames | Blocking | Discarding | |
| Interim state without MAC learning and without forwarding | Listening | Not used | |
| Interim state with MAC learning and without forwarding | Learning | Learning | |
| Stable state that allows MAC learning and forwarding of data frames | Forwarding | Forwarding | |
Show spanning-tree vlan x interface int state
Point to point – sw to sw
Point to point edge -sw to pc
Shared port – hub
Etherchannel lower stp convergence time or avoid connversiance all together.
Portfast transition immediately to blockng to forwarding, only for end device
BPDU Guard – used on access endpoint ports with portfast to prevent control root bridge
| Settting | Default | Command to change defalt |
| BID priority | Base: 32,768 | Spanning-tree vlan vlan-id root {primary| secondary} |
| Interface cost | 100 for 10 Mbps
19 for 100 Mbps 4 for 1 Gbps 2 for 10Gbps |
Spanning-tree vlan vlan-id cost cost |
| PortFast | Not enabled
Show spanning tree int int portfast |
Spanning-tree portfast
Spanning-tree portfast disable |
| PortFast Global | Spanning-tree portfast default
No Spanning-tree portfast default |
|
| BPDU Guard | Not enabled
Show spanning tree int int detail |
Spanning-tree bpduguard enable |
| BPDU Guard Global | Show spanning tree summary | Spanning-tree portfast bpduguard default
No Spanning-tree portfast bpduguard default |
| Degug | Debug spanning-tree events | |
| Mode | Spanning-tree mode pvst
Show spanning-tree vlan x |
Spanning-tree mode {pvst, rapid-pvst, mst}
Ieee = 802.1d stp |
