added BPDU guard

00. Jeremy's IT LAB CCNA course.md

@@ -33,3 +33,4 @@ tags:
 [[Protocole Spanning Tree (part2)]]
 [[PortFast (STP Toolkit)]]
 [[BPDU Guard & BPDU Filter (STP Toolkit)]]
+[[Root Guard (STP Toolkit)]]

21. Root Guard (STP Toolkit).md

@@ -0,0 +1,72 @@
+---
+id: 1779981231-AJMV
+aliases:
+  - Root Guard (STP Toolkit)
+tags: []
+---
+
+# Root Guard (STP Toolkit)
+
+STP prevents loops by electing a root bridge and ensuring that each other switch has only *one valid path* to reach it.
+
+YOu shouldn't randomly select the root bridge. Some things you should consider include:
+- Optimal traffic flow
+  - minimize latency
+  - minimize congestion
+- Stability and reliability
+
+## The Problem
+
+Within your own [[LAN]], you can easily control the root brdige by setting its priority to 0.
+- But there are cases where you might connect your LAN to other switches outside of your direct control:
+  - A service provider offering Metro Ethernet service to customers
+    - Often used to connect sites within a [[MAN]] 
+- Even if you set your root bridge's priority to 0, its role can be taken by another switch with a lower
+  [[MAC address]] .
+
+## The solution
+
+- *Root Guard* can be configured to protect your [[STP]] topology by preventing your switches from
+  accepting superior [[BPDU]]s from switches outside of your control.
+  - Superior BPDUs = a BPDU that is superior in the STP algorith (e.g Claiming a better root bridge ID).
+If you want to ensure that the root bridge rmains in your [[LAN]], you can configure Root Guard on the ports connected
+to switches outside of your control
+
+To enable root Guard on a port
+
+```Cisco
+SW1(config-if) spanning-tree guard root
+```
+
+There is no command to enable it by default from global config mode
+
+If a Root Guard-enabled port receives a BPDU, it will enter the *Broken* (Root inconsistent) state
+effectively disabling it
+- The port will not able to forward data frames and will discard any frames it receives.
+
+To re-enable a port disabled by Root Guard, you must solve the issue that disabled the port
+  - the disabled port must stop receiving superior BDPUs.
+  - tell the customer to increase the priority value of their switch.
+
+Once teh superior BPDUs received age out, the ports will automatically be re-enabled.
+  - A BPDU's Max Age is 20 seconds by default.
+
+To see the Root guard
+
+```Cisco
+SW1(config-if)# do show spanning-tree
+
+## if it's broken
+Gi0/1  Desg BKN*4       128.3   P2p  *ROOT_Inc
+
+BKN = Broken
+ROOT_Inc = Root inconsistent
+
+## if it's Work
+Gi0/1  Desg FWD 4       128.3   P2p  
+```
+
+## Review
+
+ Prevents a port from becoming a Root Port by disabling it if superior BPDUs are received,
+Thereby enforcing the current [[Root Bridge]]