Merge pull request #34 from KorelU/STP

Doc: STP (Spanning Tree Protocol) Documentation

NetworkConfigurations/NetworkDiscoveryAndManagementSubCategories/STP_SpanningTreeProtocol.md

@@ -0,0 +1,283 @@
+---
+title: STP (Spanning Tree Protocol)
+grand_parent: Network Configuration
+parent: Network Discovery and Management
+nav_order: 1
+layout: default
+---
+
+# STP (Spanning Tree Protocol)
+
+## Introduction
+
+In this guide, we will quickly explain what the
+Spanning Tree Protocol is
+and give an example implementing it.
+
+The Spanning Tree Protocol or STP is a network protocol that operates
+on the Layer 2 level of devices.
+
+The ports on a switch with STP enabled
+will always be in one of the following five port states.
+
+1. Blocking
+
+2. Listening
+
+3. Learning
+
+4. Forwarding
+
+5. Disabled
+
+The ports in a switch with STP will often begin
+in the blocking state
+and later change to the listening, learning,
+and eventually forwarding state when appropriate.
+
+**This conversion may take time as devices "learn"
+where other devices are.**
+
+STP is simple to implement using bridges and is
+important to address looping and
+wasting bandwidth. STP works by blocking
+redundant links from forwarding packets.
+
+To learn the basics of bridges, visit the following:
+[Bridging Layer 2](../VLANConfigurationSubCategories/BridgingL2.html)
+
+## Enabling Spanning Tree Protocol
+
+**By default, STP is disabled on all bridges.**
+
+To enable STP on an existing bridge, run the following command:
+
+```
+$ ip link set dev ${Bridge Name} type bridge stp_state 1
+```
+
+To enable STP on bridge creation, use:
+
+```
+$ ip link set dev ${Bridge Name} type bridge stp_state 1
+```
+
+To disable STP on a bridge, set stp_state to “0”.
+
+To show the current information about the state of the
+bridge use the following:
+
+```
+$ ip -d link show dev ${Bridge Name}
+```
+
+The brctl utility can also be used to view information
+about the current configuration.
+
+If the brctl utility is not already installed:
+
+_Do not forget to use `$ apt-get update` to
+fetch the latest version of your package lists.
+Follow this with the command `$ apt-get upgrade` to first
+review the changes in the latest versions
+and then replace the old packages by installing the new ones._
+
+Install the brctl utility with: `$ apt-get install bridge-utils`
+
+Use the following to confirm STP is enabled:
+
+```
+$ brctl show ${Bridge Name}
+```
+
+In addition to this, view other relevant information regarding the
+STP configuration of the current bridge with:
+
+```
+$ brctl showstp ${Bridge Name}
+```
+
+## Configurables
+
+The following are some of the controllable parameters
+regarding STP configurations
+
+- Bridge Priority
+- Path Priority and Cost
+- Forwarding Delay
+- Hello Time
+- Max Age
+
+### Bridge Priority
+
+The Bridge Priority is used to determine
+the probability that the bridge will be elected as the root device.
+A lower bridge priority indicates that a switch has a higher
+likelihood of becoming the root device
+
+Ex.
+
+```
+$ ip link set ${Birdge Name} type bridge priority ${Priority Number}
+```
+
+### Path Priority and Cost
+
+The Path Priority and Cost will influence the route packets take.
+A lower cost is preferred.
+
+Ex.
+
+```
+$ ip link set ${Interface Name} type bridge_slave cost ${Cost Number}
+```
+
+### Forwarding Delay
+
+The Forwarding Delay is the time spent in hundredths of a second
+in the LISTENING state and the LEARNING state before changing states.
+
+Ex.
+
+```
+$ ip link set ${Bridge Name} type bridge forward_delay ${Delay Time}
+```
+
+### Hello Time
+
+The Hello time is the set of time in hundredths of a second
+between each hello packet sent by the bridge.
+
+Ex.
+
+```
+$ ip link set ${Bridge Name} type bridge hello_time ${Hello Time}
+```
+
+### Max Age
+
+The Max Age is the timeout requirement for the hello packet.
+It reflects the time in hundredths of a second until another bridge in the
+spanning tree is assumed to be dead. It is based on the time of
+reception since the last received hello message.
+
+Ex.
+
+```
+$ ip link set ${Bridge Name} type bridge max_age ${Age Time}
+```
+
+---
+
+## Example Configuration
+
+Consider the following topology:
+
+![SpanningTreeProtocol_Topology](../../Images/ImagesForNetworkConfiguration/STP_Topology.png)
+
+Let's say we wanted to configure PC1, PC2, and PC3 to be able to communicate
+over these links and maintain the same LAN. One way we could do this is
+to create bridges on every switch and enslave all the
+connected interfaces.
+
+**However, creating a bridge on every device without STP enabled would
+begin to flood the system, as shown below.**
+
+### Flawed Example:
+
+The following was run on every switch in the given topology:
+
+```
+$ ip link add name br0 type bridge
+
+$ ip link set enp0s4 master br0
+
+$ ip link set enp0s5 master br0
+
+$ ip link set enp0s12 master br0
+```
+
+The interfaces were also brought up with:
+
+```
+$ ip link set enp0s4 up
+
+$ ip link set enp0s5 up
+
+$ ip link set enp0s12 up
+
+$ ip link set br0 up
+```
+
+The result of this configuration was
+a flood of requests in the system. The following
+is a log from one of the switch devices:
+
+```
+root@localhost:~# [  291.521985] br0: received packet on enp0s4 with own address as source address (addr:0c:6e:09:a1:00:01, vlan:0)
+[  291.530112] br0: received packet on enp0s4 with own address as source address (addr:0c:6e:09:a1:00:01, vlan:0)
+[  291.537694] br0: received packet on enp0s5 with own address as source address (addr:0c:6e:09:a1:00:01, vlan:0)
+[  291.554573] br0: received packet on enp0s4 with own address as source address (addr:0c:6e:09:a1:00:01, vlan:0)
+[  296.510152] net_ratelimit: 6194 callbacks suppressed
+```
+
+In this configuration, attempting to add a bridge to every device
+without STP enabled resulted in a loop where devices
+where receiving their own source MAC addresses.
+
+**To avoid this, enable STP by including `stp_state 1`
+upon bridge creation.**
+
+### Corrected Example:
+
+The following was run on every switch in the given topology:
+
+```
+$ ip link add name br0 type bridge stp_state 1
+
+$ ip link set enp0s4 master br0
+
+$ ip link set enp0s5 master br0
+
+$ ip link set enp0s12 master br0
+```
+
+The interfaces were also brought up with:
+
+```
+$ ip link set enp0s4 up
+
+$ ip link set enp0s5 up
+
+$ ip link set enp0s12 up
+
+$ ip link set br0 up
+```
+
+By enabling the bridges to include STP, the system flooding was
+prevented. PC1 PC2 and PC3 can now
+successfully ping one another without
+the switches receiving continued feedback
+regarding their own source MAC addresses.
+
+```
+PC1 : 192.168.1.1 255.255.255.0
+
+PC1> ping 192.168.1.2
+
+84 bytes from 192.168.1.2 icmp_seq=1 ttl=64 time=2.345 ms
+84 bytes from 192.168.1.2 icmp_seq=2 ttl=64 time=1.093 ms
+84 bytes from 192.168.1.2 icmp_seq=3 ttl=64 time=1.442 ms
+^C
+
+PC1> ping 192.168.1.3
+
+84 bytes from 192.168.1.3 icmp_seq=1 ttl=64 time=0.506 ms
+84 bytes from 192.168.1.3 icmp_seq=2 ttl=64 time=0.713 ms
+84 bytes from 192.168.1.3 icmp_seq=3 ttl=64 time=0.728 ms
+84 bytes from 192.168.1.3 icmp_seq=4 ttl=64 time=0.878 ms
+^C
+PC3>
+```
+
+**NOTE: The outputs above were tested on a Virtual Machine**

NetworkConfigurations/VLANConfigurationSubCategories/BridgingL2.md

@@ -24,9 +24,6 @@ To create a bridge, use the following command:
 $ ip link add name ${Bridge Name} type bridge
 ```
 
-NOTE: Bridges may be configured with VLAN support.
-For more information, visit VLANs (Configuring 802.1q Interfaces)
-
 ### Connecting Interfaces to a Bridge
 
 Once you have created a new bridge, connect interfaces to it