Velocity Reviews - Computer Hardware Reviews

Velocity Reviews > Newsgroups > Computing > Cisco > Understanding spanning-Tree

Reply
Thread Tools

Understanding spanning-Tree

 
 
Chino
Guest
Posts: n/a
 
      11-02-2006
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?


 
Reply With Quote
 
 
 
 
Sam Wilson
Guest
Posts: n/a
 
      11-02-2006
In article <eidduh$p9b$(E-Mail Removed)>,
"Chino" <(E-Mail Removed)> wrote:

> 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?


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.

> 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.


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.

> Does it make sense to you?


I'm not sure I can answer that!

Sam
 
Reply With Quote
 
 
 
 
BernieM
Guest
Posts: n/a
 
      11-02-2006

"Chino" <(E-Mail Removed)> wrote in message
news:eidduh$p9b$(E-Mail Removed)...
> 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?


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.
>
> 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?
>



 
Reply With Quote
 
 
 
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Understanding your BIOS TYCOON Hardware 6 06-29-2005 09:54 AM
Confirm my wireless understanding please? Evil Uncle Chris Wireless Networking 1 05-01-2005 03:19 PM
Understanding voice AIMs Ghazan Haider Cisco 1 11-28-2004 03:15 PM
Re: understanding an error Alvin Andries VHDL 0 09-12-2003 11:38 AM
Why does Microsoft have such a hard time understanding what they say? George Hester ASP .Net 3 08-11-2003 09:16 PM



Advertisments