Understanding spanning-Tree

Nov 02, 2006 2 Replies
C

Hi all. I would ask something about spanning-tree, as I'm not expert to it and I'm not sure I understood well how it works.



Let's start with a question: talking about a switched LAN running more than one VLAN, where every switch partecipate in spanning tree. After a switch is elected as the root bridge for one VLAN, is it true that every packet sent by a host in that VLAN must pass through the root bridge before reaching the destination in the same VLAN?



I have a LAN splitted in two different geographical locations (they are layer 2 linked using routers with bridging). I all above is true, if I have 2 communicating hosts on one side of the LAN, and the root of their VLAN is on the other side, packets exchanged must "cross" the bridge to reach the root and then came back, wasting resources (bandwidth between the two phisical locations), as I didn't make any tuning on the spanning-tree. Does it make sense to you?


Vote
Twitter Facebook LinkedIn
S

No, but if the path between two hosts passes through the root bridge then the traffic will flow that way. There can only be one path between any two nodes in a tree.

Since the assumption about traffic passing through the root is not true neither is the example. Traffic between nodes on one side the LAN should not cross to the other side.

I'm not sure I can answer that! :-)

Sam

Vote
Twitter Facebook LinkedIn
B

No. Spanning-tree prevents layer-2 loops from forming but once the layer-2 topology has been decided normal frame forwarding occurs followinng the rules of a switch ie. mac-tables etc.

Vote
Twitter Facebook LinkedIn

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required