Spanning Tree Protocol: Difference between revisions

From ITCwiki
Jump to navigation Jump to search
No edit summary
No edit summary
Line 1: Line 1:
__________WORK IN PROGRESS____________________WORK IN PROGRESS____________________WORK IN PROGRESS____________________WORK IN PROGRESS__________
The Spanning Tree Protocol’s purpose is preventing bridging loops and allows a network to quick recover if the primary path fails. STP was invented by Radia Perlman from the Digital Equipment Corporation.
Spanning-Tree Protocol is a way to have redundant paths and stop loops from having. All Ethernet networks only work well if there is only one path between two points. Having many different paths will cause loops in a network. This cause frames to be duplicated. The Spanning-Tree protocol will define all switches in the network. The algorithm will automatically change the STP topology by activating or inactivating certain paths, so that only one path will be present between two points. The end-devices do not know they are connected to one network or many networks.
'''Election of the Root Switch'''
The switches in the network gather information with the exchange of data messages. These are called bridge protocol data units (BPDUs). There is an election for a root switch on every LAN segment. To stop loops STP by putting redundant switches ports into a backup state. The root switch is the place where the STP algorithm runs. All other paths not needed to reach the root switch are put in to backup mode
'''Root Switch Variables'''
{| {{table}}
| align="center" style="background:#f0f0f0;"|'''Variable'''
| align="center" style="background:#f0f0f0;"|'''Description'''
|-
| Hello Time||How often a hello is broadcasted to the other switches, so the switch knows the other switches are functioning.
|-
| Maximum Age Timer||Defines how long a bridge or switch should wait after the last received hello message before believing that the network topology has changed.
|-
| Forward Delay Timer||Time the switch has spent learning/listening before it begins forwarding traffic.
|-
|
|}
'''Information a BPDU contains'''
*MAC addresses
*Switch priority
*Port priority
*Port cost
STP Steps
Elects a root bridge
Only one bridge can exist per VLAN
Designated ports send and receive traffic and configuration trafic called BPDUs
The switch with the lowest priority will become the root bridge
Selects the root port for all other switches
One port on all switches, that are not root bridges,
This port is the lowest cost path to the root bridge.
If two ports have the same priority, the lowest port number will become the root port.
'''STP Steps'''
*Elects a root bridge
**Only one bridge can exist per VLAN
**Designated ports send and receive traffic and configuration trafic called BPDUs
**The switch with the lowest priority will become the root bridge
*Selects the root port for all other switches
**One port on all switches, that are not root bridges,
**This port is the lowest cost path to the root bridge.
**If two ports have the same priority, the lowest port number will become the root port.
'''Port Roles on a Nondesignated Switch'''
{| {{table}}
format header
result
{| {{table}}
{| {{table}}
| align="center" style="background:#f0f0f0;"|'''Port'''
| align="center" style="background:#f0f0f0;"|'''Port'''
Line 68: Line 4:
|-
|-
| Root ||The port is on nonroot bridges. It is considered to be the best path. The root port is able to send traffic in the direction of the root bridge. This port will add entries to its MAC address table. There is only one root port per bridge.
| Root ||The port is on nonroot bridges. It is considered to be the best path. The root port is able to send traffic in the direction of the root bridge. This port will add entries to its MAC address table. There is only one root port per bridge.
|-
|                ||
|-
|-
| Designated ||This port is on the root bridge and on the nonroot bridges. All switch ports are designated ports. There can only be one designated port per segment, unless it’s the root bridge where all the ports are designated ports. If there is more than one switch in the segment, an election will be held.  
| Designated ||This port is on the root bridge and on the nonroot bridges. All switch ports are designated ports. There can only be one designated port per segment, unless it’s the root bridge where all the ports are designated ports. If there is more than one switch in the segment, an election will be held.  
|-
|            ||
|-
|-
| Nondesignated ||The nondesignated port is in the blocking state. It will not add new entries to its MAC address table.
| Nondesignated ||The nondesignated port is in the blocking state. It will not add new entries to its MAC address table.
|-
|              ||
|-
|-
| Disabled ||The port is shutdown.
| Disabled ||The port is shutdown.

Revision as of 15:31, 27 April 2012

Port Description
Root The port is on nonroot bridges. It is considered to be the best path. The root port is able to send traffic in the direction of the root bridge. This port will add entries to its MAC address table. There is only one root port per bridge.
Designated This port is on the root bridge and on the nonroot bridges. All switch ports are designated ports. There can only be one designated port per segment, unless it’s the root bridge where all the ports are designated ports. If there is more than one switch in the segment, an election will be held.
Nondesignated The nondesignated port is in the blocking state. It will not add new entries to its MAC address table.
Disabled The port is shutdown.
Retrieved from "https://wiki.ihitc.net/mediawiki/index.php?title=Spanning_Tree_Protocol&oldid=5731"