cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
1113
Views
3
Helpful
7
Replies

Spanning_Tree_Protocol

kollagouthami
Level 1
Level 1

Hi ,

what are the port roles of the switch in the following scenario if it is connecting to some down stream switches and currently acting as a root bridge?




root.png




1 Accepted Solution

Accepted Solutions

Hi Bharad,

what are the port roles on the root bridge if two ports are inter connected to each other?

One of the ports is Designated Forwarding, the other is Backup Discarding.

Best regards,

Peter

View solution in original post

7 Replies 7

daniel.dib
Level 7
Level 7

What do you mean by self loop? Do you have two ports on that switch connected to each other?

Daniel Dib
CCIE #37149

Daniel Dib
CCIE #37149
CCDE #20160011

Please rate helpful posts.

devils_advocate
Level 7
Level 7

Are you asking what the port states will be when you have an active loop in the network?

I would hope you would be using BPDGuard to prevent something like this...

Hello

If you have a switch (1) which is the root and 2 other switches (2 & 3 )connected to the root switch

Then the port roles will be:

Switch 1) all interconnected links designated forwarding
Switch 2 & 3 ) interconnected link to switch 1 - root ports -forwarding
Switch 2 & 3 ) will negotiate their interconnected links between each other and one port will be the designated port for this lan segment and the other will become a Blocked port as its neither a root or designated port

Res
Paul



Sent from Cisco Technical Support iPad App


Please rate and mark as an accepted solution if you have found any of the information provided useful.
This then could assist others on these forums to find a valuable answer and broadens the community’s global network.

Kind Regards
Paul

Hi All,

what are the port roles on the root bridge if two ports are inter connected to each other?

Regards,

Bharad.

Hi Bharad,

what are the port roles on the root bridge if two ports are inter connected to each other?

One of the ports is Designated Forwarding, the other is Backup Discarding.

Best regards,

Peter

azifak
Level 1
Level 1

Hello,

if your scenario is looping f1 and f2 of Root Bridge, then

In case of pvst/rapid-pvst/mst

     F1 --> will be the desiginated forwarding

     F2 --> will be in backup bloacking

Reson for the above selection is, Root Bridge priority is tie / Root Bridge id is tie / and port path cost is tie / port priority is tie but the port identifier is different (Port identifier is the combination of port priority + the port number (this changes depends on the hardware)). please find the below example

Port 1 (GigabitEthernet1/0/1) of VLAN0001 is designated forwarding

   Port path cost 4, Port priority 128, Port Identifier 128.1.

   Designated root has priority 40961, address b4a4.e3f4.b000

   Designated bridge has priority 40961, address b4a4.e3f4.b000

   Designated port id is 128.1, designated path cost 0

   Timers: message age 0, forward delay 0, hold 0

   Number of transitions to forwarding state: 1

   Link type is point-to-point by default

   BPDU: sent 19, received 1

Port 2 (GigabitEthernet1/0/2) of VLAN0001 is backup blocking

   Port path cost 4, Port priority 128, Port Identifier 128.2.

   Designated root has priority 40961, address b4a4.e3f4.b000

   Designated bridge has priority 40961, address b4a4.e3f4.b000

   Designated port id is 128.1, designated path cost 0

   Timers: message age 16, forward delay 0, hold 0

   Number of transitions to forwarding state: 0

   Link type is point-to-point by default

   BPDU: sent 1, received 19

Regards

Azif

Hi All,

Thanks Alot for you help. 

Regards,

Bharad.

Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community:

Innovations in Cisco Full Stack Observability - A new webinar from Cisco