add BPDU Guard & BPDU Filter

21. BPDU Guard & BPDU Filter (STP Toolkit).md

@@ -7,12 +7,161 @@ tags: []
 
 # BPDU Guard & BPDU Filter (STP Toolkit)
 
+PortFast makes a port start in the Forwarding state when it is connected, but it doesn't disable STP
+on the port.
+- The port will continue to send BPDUs every 2 seconds.
+
+Because end hosts don't run STP and send BPDUs, a PortFast enabled port shouldn't receive BPDUs
+- But what if it does?
+
+If a PortFast-enabled port receives an STP BPDU, it will revert to acting like a regular STP port
+(without PortFast)
+
+## BPDU Guard
+
+### The problem
+
+PortFast should only be enabled on ports connected to non-switch devices (end osts, routers).
+- A PortFast-enabled port still sends BPDUs and will operate like a regular STP port if it 
+receives VPDUs from a neighbor.
+- If an end user carelessly connects a switch to a port meant for end hosts,, it could affect the
+STP topology.
+- *BPDU Guard* acts as a safeguard against this.
+
+### The Solution
+
+BPDU Guard protects the network from unauthorized switches being connected to ports intended for end hosts.
+It can be configured separately from [[PortFast]] but both features are usually used together.
+They both enhance STP's functionality on ports inteded for end hosts.
+
+A BPDU Guard-enabled port contibues to send BPDUs, but if it receives a BPDU it enters the error-disabled state.
+- In effect, this disbales the port.
+
+### Configuration
+
+Like PorFast, BPDU Guard can be configured in two ways:
+
+per-port:
+```Cisco
+SW3(config-if)# spanning-tree bpduguard enable
+```
+
+default
+```Cisco
+SW3(config)# spanning-tree portfast bpduguard default
+```
+
+When enabled by default *BPDU Guard* is activated on **All Portfast-enabled ports**.
+
+disableing it
+```Cisco
+SW3(config)# spanning-tree bpduguard disable
+```
+
+### Errdisable
+
+ErrDiable is a [[Cisco]] switch feature that disables a port under certain conditions, such as BPDU 
+Guard violation.
+More examples are
+- Power Policing violations
+- Port Security violations
+- DAI (Dynamic ARP inspection) violations
+
+to re-enable an err-disabled port, *first solve the underlying issue*
+- if you re0enable the port without fixing the issue, it will just be err-disabled again.
+
+You can re-enable an err-disabled  port in two ways:
+1. Manual: use *shutdown* and *no shutdown* to reset the disabled port.
+2. Automatic: *ErrDisable Recovery*
+
+#### ErrDisable Recovery
+
+ErrDisable Recovery is a feature that automatically re-enables err disabled ports after a certain period of time
+
+ErrDisable Recovery is disabled by default
+
+to view it status use
+
+```Cisco
+SW1# show errdisable recovery
+```
+
+The default recovery timer is 300 seconds (5minutes).
+- err-disabled interfaces will be automatically re-enabled after 5 minutes
+
+command to modify the interval is
+```Cisco
+SW1# errdisable recovery interval *seconds*
+```
+
+to enable ErrDisable Recovery for ports disabled by a particular cause use
+```Cisco
+SW1(config)# errdisble recovery cause *cause*
+```
+
+## BPDU Filter
+
+### The Problem
+
+A switch port connected to an end host contnues sending BPDUs every 2 seconds.
+- regardless of whether PortFast and/or BPDU GUard are enabled
+If the port doeen't connect to a switch, sending BPDUs is unnecessary and undesirable for a
+coupe of reasons
+1. Sendig BPDUs uses some bandwidth and processing power on the witch (althrough it's minimal).
+2. BPDUs contain information about the LAN's STP topology
+  - If maximum security is a concern, you should avoid sending this info to user devices.
+
+Bpdu Filter solves this by preventing a port from sending BPDUs
+
+### The Solution
+
+BPDU FIlter stops a port fro sending BPDUs
+- Unlike BPDU Guard, it does not disable the port if it receives a BPDU
+BPDU filter can be enabled in two ways:
+
+per-port:
+```Cisco
+SW3(config-if)# spanning-tree bpdufilter enable
+```
+The port will not send BPDUs
+The port will ignore any BPDUs it receives.
+In effect this disables [[STP]] on the port. *Use with caution!*
+
+default
+```Cisco
+SW3(config)# spanning-tree portfast bpdufilter default
+```
+BPDU Filter will be activated on all *PortFast-enabled ports*.
+  You can use spanning-tree bpdufilter disable to disable it on specific ports.
+The port will not send BPDUs
+If the port receives a BPDU, PortFast and BPDU Filter are disabled, and it operates as a normal STP Port.
+
+## Recommandation
+
+Enable PortFast and BPDU Guard however you prefer (per-port or by default)
+- Only enable BPDU Filter by default (global config mode).
+- Unless you have a very good reason to enable it per-port
+
+*BPDU Guard* and *BPDU Filter* can be enabled on the same port at the same time:
+
+---
+
+If BPDU Filter is enabled in global-confg mode and the port receives a BPDU:
+1. BPDU Filter will be disabled
+2. BPDU Guard will be triggered (and err-disable the interface)
+
+---
+
+If BPDU Fileter is enabled in interface config mode and the port receives a BPDU:
+- The BPDU will be ignored
+- BPDU Guard will *not* be triggered
+
 ## Review
 
 ### BPDU Guard 
-
-Automatically disab
+Automatically disables a port if it receives a BPDU, protecting the STP topology by preventing
+unauthorized devices from becoming part of the network
 
 
-BPDU Fileter
-
+### BPDU Filter
+Stops a port from sending BPDUs or processing received BPDUs