Skip to main content

STP - Port state from Listening to Learning

 When Does a Switch Transition from Listening to Learning State, and Can It Revert to Blocking?


A switch moves a port from the listening state to the learning state under the following condition:

Transition from Listening to Learning:

  • Successful BPDU Processing: If the port in the listening state continues to receive BPDUs and determines that the path through this port can be part of the active spanning tree, it transitions to the learning state. In this state, the port starts learning MAC addresses but still does not forward any data frames.

At this stage, the switch is confident that the port may become part of the forwarding path, but it has not yet fully committed to forwarding traffic. Instead, it prepares by populating its MAC address table with the source addresses of the incoming frames to optimize future forwarding decisions.

Scenario: Switch Returning from Listening to Blocking

Yes, there are scenarios where a switch can transition from the listening state back to the blocking state:

  1. Receiving a Superior BPDU from Another Port: While in the listening state, if the switch receives a BPDU from another port that indicates a better path to the root bridge (lower bridge ID or path cost), the switch may decide that the current port is no longer the best candidate to forward traffic. In this case, the port will revert to the blocking state.

  2. Topology Change: If a topology change occurs during the listening state (e.g., a new root bridge is elected, or a better path to the root bridge is found), the switch might re-evaluate the role of the port. If the re-evaluation determines that the port is not needed for forwarding, it transitions back to the blocking state.

In both scenarios, the switch dynamically reconfigures its spanning tree structure to ensure that no loops occur in the network and that the most optimal path to the root bridge is maintained.

Labels:

Comments

Post a Comment

Popular posts from this blog

How to import Putty Saved Connections to mRemoteNG

Just started using mRemoteNG and its being very cool to connect to different remote connection with different protocols e.g Window Remote Desktop, VNC to Linux, SSH, HTTP connection etc. from a single application. As new user I configured some remote desktop connection which was quite easy to figure out. But when I wanted to add SSH connections, it came in my mind to import all of the saved connections in the putty. But I couldn't figure it out how can it be done, though it was quite easy and here are the steps. Open your mRemoteNG Create a folder if you want segregation of multiple networks Create a new connection Enter the IP address of remote server under connection in Config pane Under the config pane, select protocol " SSH version 2 ".  Once you select protocol to SSH version 2 you are given option to import putty sessions, as shown in the snap below. In the above snap, I have imported CSR-AWS session from my saved sessions in Putty.
1 comment
Read more

AS Path Prepending: Controlling Inbound Traffic in BGP

AS Path Prepending is a BGP feature used to make a specific path appear less preferred by artificially lengthening the AS path. This is done by adding your AS number multiple times to the AS path. It is a common method to influence inbound traffic from external networks. Longer AS Path = Less preferred route . Example Scenario : You have two ISPs: ISP1 (through CE1) and ISP2 (through CE2). You want inbound traffic from the internet to prefer ISP1 over ISP2. Network Topology : CE1 (connected to ISP1): 10.0.1.1/30 CE2 (connected to ISP2): 10.0.2.1/30 iBGP Router (Internal) connected to both CE1 (10.0.1.2/30) and CE2 (10.0.2.2/30). Configuration on CE2 (AS Path Prepending to Make ISP2 Less Preferred) : Create a route map to prepend your AS path multiple times for CE2: route-map PREPEND_AS permit 10 set as-path prepend 65001 65001 65001 Apply this route map to the neighbor in the BGP configuration for CE2: router bgp 65001 neighbor 10.0.2.1 remote-as 65002 neighbor 10.0.2.1 ro...
Post a Comment
Read more

Authoritative DNS Servers Delegation and Internal DNS Explained

DNS (Domain Name System) plays a critical role in how users and systems find resources on the internet or within internal networks. Whether it's managing an internal domain in an enterprise or delegating parts of a domain for traffic distribution, DNS setups vary widely depending on needs. In this blog post, we’ll break down the different types of DNS setups, including authoritative DNS servers, DNS delegation, and how internal DNS functions within organizations. 1. Authoritative DNS Server An Authoritative DNS server is the final source of truth for a specific domain. When someone queries a domain (e.g., example.com ), the authoritative DNS server for that domain holds the DNS records (A records, CNAME, MX, etc.) and responds with the corresponding IP address. Key Points: Who can host it? Authoritative DNS servers are often hosted by domain registrars (e.g., GoDaddy, Namecheap) or cloud DNS providers (e.g., AWS Route 53, Cloudflare). However, organizations can also host their ...
Post a Comment
Read more