RE: pvst and rpvst

Hello Jacek!

The confusion you are experiencing is a result of how Cisco coded the IOS
show command results. Even though the switch you are examining is running
PVST+, the show output reflects what will happen if you were to switch to
RPVST+ or MSTP modes of operation. So when you see an Alternate port under
PVST+, realize that it is indeed operating as nothing more than a legacy
Non-designated port. Should you move to one of the two newer modes of
operation, the port will indeed become a full-fledged Alternate port.

This same thing applies to your question about Edge Ports. Cisco recognizes
ports that you have configured with the PortFast treatment as Edge Ports,
for example, even though behaviors will not change until you transition the
device to the newer mode.

Since the output of the show spanning-tree vlan command behaves the way it
does, it is critical that you check the spanning-tree mode field in the
output to get your bearings on what version of STP you are actually running.

This all reminds me of a classic case like this in the IOS. When you run the
show interface trunk command, notice a Native VLAN will display for an ISL
trunk. This field obviously makes no sense unless you are talking about an
802.1Q trunk.

Continue to enjoy your studies, and congratulations on your decision to
pursue Expert-Level Cisco Certification.

Warmest Regards,
Anthony Sequeira, CCIE, CCSI
StormWind Live
http://www.stormwindlive.com

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
Jacek
Sent: Thursday, February 24, 2011 3:34 AM
To: ccielab_at_groupstudy.com
Subject: pvst and rpvst

Hello all,

Many documents talk about non-designated port in STP. Where is
non-designated port on Cisco switch running PVST? Command "sh spannin vl X"
will show only root, designated and alternate ports. Is a non-designated
port called an alternate port ? This is confusing because alternate port in
RPVST does not behave the same as in PVST.

Also I am reading that RPVST introduces edge ports. However I can see edge
ports on a switch running PVST. Actually an access port configured with
portfast will show as an edge port in both PVST and RPVST.

Anyone can please clear the confusion ?

Blogs and organic groups at http://www.ccie.net
Received on Thu Feb 24 2011 - 10:50:42 ART