Exam 350-401 topic 1 question 199 discussion

BPDU filtering allows you to avoid transmitting BPDUs on PortFast-enabled ports that are connected to an end system. When you enable PortFast on the switch, spanning tree places ports in the forwarding state immediately, instead of going through the listening, learning, and forwarding states. By default, spanning tree sends BPDUs from all ports regardless of whether PortFast is enabled. BDPU filtering is on a per-switch basis; after you enable BPDU filtering, it applies to all PortFast-enabled ports on the switch.

The 'bpdufilter default' command enables BPDU filtering on all PortFast-enabled interfaces, preventing the interfaces from sending or receiving BPDUs. BPDU filtering is disabled if a PortFast interface receives a BPDU, allowing the interface to participate in STP and continue operation. Option B is incorrect because the 'bpduguard default' command will err-disable the port if it receives a BPDU on a PortFast-enabled port. Option C is incorrect because it lacks BPDU control. Option D is incorrect because enabling BPDU Guard on an interface will put the interface in an err-disabled mode if it receives a BPDU, which is the same scenario as in Option B

bpduguard will put ports into err-disabled if bpdu received.

A. Switch1(config)# spanning-tree portfast bpdufilter default Switch1(config)# interface f0/1 Switch1(config-if)# spanning-tree portfast Explanation: The command "spanning-tree portfast bpdufilter default" enables PortFast on all access ports and applies the BPDU filter. This allows the port to immediately transition to the forwarding state and prevents the interface from sending or receiving BPDUs. The command "interface f0/1" enters the interface configuration mode for fa0/1. The command "spanning-tree portfast" enables PortFast on the interface.

Guys, C is the ANSWER 1) If you enable BPDU Filter globally on the router, it will send 11 BPDUs out when the port first comes up, but if it receives no BPDU it will stop and maintain a portfast state, however, if it receives a BPDU it will lose its portfast state. See Page 191 of the Official Study Guide

The ideal configuration would look like this: ! interface Ethernet0/2 spanning-tree portfast edge spanning-tree bpdufilter enable ! When configuring spanning-tree portfast edge bpdufilter default globally, the port still receives and sends BPDUs. Switch#show spanning-tree interface e0/2 detail Port 3 (Ethernet0/2) of VLAN0020 is broken (Port Type Inconsistent) --Output Ommited-- The port is in the portfast edge mode Link type is point-to-point by default Bpdu filter is enabled by default BPDU: sent 7, received 6 Maybe this is a bug related to EVE-NG, but only when I configure the BPDU filter on the interface it works as explained in the question.

The A one is the correct answer because is asking this two things: - 1) port going immediately to forwarding state - 2) The interface should not send or receive bpdus (by def in all intefaces bpdus are sent) https://community.cisco.com/t5/switching/why-stp-rstp-sends-bpdu-on-access-ports/td-p/4190130 - 3) If a bpdu is received the port needs to be up and running anyways Even if the command spanning-tree portfast is configured later whit the command spanning-tree portfast bpdufilter default when a port is on portfast state the bpdufilter option will be activated on that port: Switch#show running-config | sec spanning spanning-tree mode rapid-pvst spanning-tree portfast edge bpdufilter default

The question is specific to SW1 interface fa0/1, not all interfaces on SW1. spanning-tree portfast bpdufilter default is global, it impacts all interfaces on SW1.

A. but I am not sure, there are no these commands in my IOU\L2 switch from available choices, config looks like this: sw2#show spanning-tree vlan 30 detail Port 1 (Ethernet0/0) of VLAN0030 is designated forwarding Port path cost 100, Port priority 128, Port Identifier 128.1. Designated root has priority 32798, address aabb.cc00.1000 Designated bridge has priority 32798, address aabb.cc00.4000 Designated port id is 128.1, designated path cost 100 Timers: message age 0, forward delay 0, hold 0 Number of transitions to forwarding state: 6 The port is in the portfast mode by portfast trunk configuration <<<<<<<<<<<< Link type is shared by default Bpdu filter is enabled <<<<<<<<<<<<<<<<<< BPDU: sent 0, received 0 <<<<<<<< no increase counters after the clearing

a is correct

Configure global bpdufilter will still send out around 10 or 12 BPDUs at the very begining, while manually configure on the interface will not send any. Bpdu filter will prevent inbound and outbound bpdu but will remove portfast state on a port if a bpdu is received. Enabling BPDU filtering on an interface is the same as disabling spanning tree on it and can result in spanning-tree loops.

The answer is C!

The question is specific to port fa0/1, therefore global commands are ruled out, thats answers A and B off the table. Answer C is specific to port fa0/1 as requested, and portfast mode ensures all bpdu packets are ignored and maintains the port operational. Answer D has the option of BPDU guard which puts the port in err-disable upon receiving BPDU packets advertising better routes, therefore not the answer. The correct answer is C.

A At the global level, you can enable BPDU filtering on Port Fast-enabled STP ports by using the spanning-tree portfast bpdufilter default global configuration command. This command prevents interfaces that are in a Port Fast-operational state from sending or receiving BPDUs. I would say A but would configure the portfast first on the interface

The second condition is "not send or receive BPDUs" ==> we must use bpdufilter , therefore answer b and d will be eliminated. Since answer c does not have configuration part of bpdufilter, it can be taken away as well.

Portfast on fa0/1 would make it to transition immediately to a forwarding state. BPDU guard is not enabled by default, so receiving BPDUs would not make it to go errdisable state.

"At the global level, you can enable BPDU filtering on Port Fast-enabled STP ports by using the spanning-tree portfast bpdufilter default global configuration command." https://www.cisco.com/en/US/docs/switches/metro/me3600x_3800x/trash/swstpopt.html#:~:text=The%20BPDU%20filtering%20feature%20can,bpdufilter%20default%20global%20configuration%20command.