Spanning Tree Protocol

Spanning Tree Protocol
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Subject Author Date
Spanning Tree Protocol vicky 06-05-2008
Posted by vicky on June 26, 2008, 2:22 am
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wrote:
> In article
>
>
> > Now my question is , weather the ports for 3 hosts (pc1, pc2 and pc3)
> > of switch 2 are also became designated port.
> > And why????
>
> Yes. Every active port (i.e., a port onto which frames are forwarded by
> a switch) is either a Designated Port or a Root Port. Each Designated
> Bridge (switch) has one (and only one) Root Port, plus one or more
> Designated Ports.
>
> While it is difficult to see your true topology (due to the ASCII art,
> which is still not aligned in my screen view), Switch 2 in your drawing
> is apparently a Designated Bridge, with its Root Port connected to
> Switch 1 (the Root Brodge), and a number of Designated Ports, three of
> which connect to PC1, PC2, and PC3.
>
> I hope this helps.
>
> --
> Rich Seifert =A0 =A0 =A0 =A0 =A0 =A0 =A0Networks and Communications Consu=
lting
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 21885 Bear Creek Way
> (408) 395-5700 =A0 =A0 =A0 =A0 =A0 =A0Los Gatos, CA 95033
> (408) 228-0803 FAX
>
> Send replies to: usenet at richseifert dot com

-----------------------------------------------------------

Hello Sir

can u plz tell me that

Is STP weather decide (when every time topology change) that
which port became trunk port or some other mechanism is used...

Thanks in advance


Vikrant

Pure Networks
Posted by Rich Seifert on June 26, 2008, 11:49 am
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In article

> can u plz tell me that
>
> Is STP weather decide (when every time topology change) that
> which port became trunk port or some other mechanism is used...
>
> Thanks in advance
>

Once again, this material is thoroughly covered in the relevant standard
(IEEE 802.1D), as well as "The Switch Book." You should read one or both
and then pose your questions.

That said, if you are using STP, then it is STP that determines the
state of each port, both before and after topology changes.


--
Rich Seifert Networks and Communications Consulting
21885 Bear Creek Way
(408) 395-5700 Los Gatos, CA 95033
(408) 228-0803 FAX

Send replies to: usenet at richseifert dot com

Posted by Martijn Lievaart on June 5, 2008, 7:16 am
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On Thu, 05 Jun 2008 03:38:03 -0700, vicky wrote:

> Hi,
>
>
> This is a physical topology of network.

Vicky,

Please switch to a fixed width font if doing ascii art. It may look good
on /your/ screen, I cannot get a good picture in either fixed or
proportional font. The recommended fix, indeed the only one, is that
everyone uses a fixed width font (or switches to fixed width if needed).

HTH,
M4

Posted by Albert Manfredi on June 5, 2008, 6:22 pm
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> Hi,
>
> This is a physical topology of network.

switch 1

switch 2

switch 3
| | |
3 hosts

> Now , by this topology a loop is formed among 3 of the above switches.
> So after spanning tree performed a loop free (logical) topology formed
> which look like......

[The loop formed by the links between the three switches is
eliminated.]

> Now my question is , weather the ports for 3 hosts (pc1, pc2 and pc3)
> of switch 2 are also became designated port.
> And why????

The ports you mention are ports that connect only to hosts. Otherwise
known as edge ports.

First, you will note in Figure 17-1 of IEEE 802.1D that edge ports are
defined to be a subset of designated ports. Why? Because they are
active ports and they provide the shortest path from that LAN to the
root port. So that fits the definition of designated port.

So the next question might be, why are these edge ports active?
Because RSTP sees no BPDUs arriving at these ports, so it can conclude
that they are edge ports and therefore cannot create loops. So the
state can be changed to forwarding as soon as this is determined.

Or, these edge ports can be administratively set to "edge port" in
managed switches. In which case the switch can immediately transition
them to forwarding state after power-up (because it knows that these
ports cannot create loops).

Bert

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