In the STP root bridge election process, how do switches advertise themselves as the root bridge if all of the ports start in the blocking state?

dor

11/6/22, 7:06 AM

In the STP root bridge election process, all of the switches advertise themselves as the root bridge until they receive a superior BPDU. Every source about STP says that after initialisation all of the ports start in the Blocking state. If the ports are in blocking state, which means they cant forward any frames, how can the switches forward their bridge id in order for the root bridge election process to happen?

2 + 0

networking

switch

stp

Score:1

Server

vidarlo

11/6/22, 7:47 AM

Because Blocked means blocked to user frames. From wikipedia:

A port that would cause a switching loop if it were active. To prevent the use of looped paths, no user data is sent or received over a blocking port. BPDU data is still received in blocking state. A blocked port may go into forwarding mode if the other links in use fail and the spanning tree algorithm determines the port may transition to the forwarding state.

The purpose of STP is to avoid loops in the network, by blocking links that would form a loop. This means blocking frames destined for hosts.

BPDU frames can still be received by a port in the block state.

0 + 3

dor

11/6/22, 7:53 AM

i understand BPDU frames can be recieved, but lets say that we have connected 2 switches in a loop. We turn them on for the first time, if all the ports are only listening for BPDUs and no one can sends any BPDUs, how can a root bridge be elected/

vidarlo

11/6/22, 7:54 AM

One of the switches enters forwarding state as the timer runs down. It starts sending bdpu. The other switch learns about it. Done.

dor

11/6/22, 8:37 AM

thank you vidarlo

Score:0

Server

dor

11/6/22, 3:28 PM

The root bridge election process occurs when the ports are in the listening state. after the default time the ports will transition from blocking to listening, then they would be able to send and receive BPDUs, in order to advertise themselves as the root bridge

0 + 0

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: In the STP root bridge election process, how do switches advertise themselves as the root bridge if all of the ports start in the blocking state?

TH: ในกระบวนการเลือกรูตบริดจ์ของ STP สวิตช์จะประกาศตัวเองว่าเป็นรูทบริดจ์ได้อย่างไรหากพอร์ตทั้งหมดเริ่มต้นในสถานะบล็อก

RO: În procesul de alegere a podului rădăcină STP, cum se reclamă comutatoarele ca punte rădăcină dacă toate porturile încep în starea de blocare?

RU: Как в процессе выбора корневого моста STP коммутаторы объявляют себя корневыми мостами, если все порты запускаются в состоянии блокировки?

VI: Trong quy trình bầu chọn cầu nối gốc STP, làm cách nào để các thiết bị chuyển mạch tự quảng cáo là cầu nối gốc nếu tất cả các cổng bắt đầu ở trạng thái chặn?

Post an answer

Most people don’t grasp that asking a lot of questions unlocks learning and improves interpersonal bonding. In Alison’s studies, for example, though people could accurately recall how many questions had been asked in their conversations, they didn’t intuit the link between questions and liking. Across four studies, in which participants were engaged in conversations themselves or read transcripts of others’ conversations, people tended not to realize that question asking would influence—or had influenced—the level of amity between the conversationalists.