STP question...

TheEditorTheEditor Posts: 7Member ■□□□□□□□□□
Here is my question.. I understand STP but I came across this example and I swear the solution is wrong.

My question revolves around router 1. The picture shows my solution. My understanding is that STP bases its root port decision on path cost based on speed. Therefore the lowest cost link to the root bridge from Router 1 is through the 2 gigabit links, from Router 1 to Router 4 to Root Bridge.

In the solution I read the gigabit port is blocked on Router 1 and the port from Router 1 to the Root Bridge is forwarding. It's a 100Mbps link.. So that 19.. My solution is 8.

Can someone shed some light on this. .It's driving me crazy.

Thank you


  • TheEditorTheEditor Posts: 7Member ■□□□□□□□□□
    I just realized I named them all "Router". Brilliant.. Lets change all references to "router" to "switch" and please ignore the brain fart.

  • drkatdrkat Posts: 703Banned
    The only reason I could think is that the port isnt negoiated to 1000mbps?
    Married to the game but she broke her vows. That's why my bars are full of broken bottles And my night stands are full of open bibles
  • CodeBloxCodeBlox Posts: 1,363Member
    Assuming default settings? If the link is running at 1GBPS, I'd think it'd be the two gigabit links as well. That's assuming they're actually up/up
    Currently reading: Network Warrior, Unix Network Programming by Richard Stevens
  • TheEditorTheEditor Posts: 7Member ■□□□□□□□□□
    Agreed. Yes link is assumed up and negotiated to 1g. I think it was just a really wrong answer to a practice question. Thanks for the sanity check.
Sign In or Register to comment.