Comments on: Rapid Spanning Tree Protocol RSTP Tutorial

By: Anonymous

Anonymous — Wed, 20 May 2015 08:19:45 +0000

Simple and easy to understand explanation, good work, 9tut. Thanks!

By: matt

matt — Sat, 28 Mar 2015 18:03:40 +0000

to the comment above: alternate, discarding, and *****backup***** ports are a dead giveaway that you aren’t running 802.1D flavors of spanning tree.

By: matt

matt — Sat, 28 Mar 2015 18:01:40 +0000

@Ryan.
Not totally wrong. . but when RSTP has converged the states are forwarding and ‘discarding’. Blocking is a term for ieee 802.1D common spanning tree and PVST. Blocking and discarding are almost truly synonymous, however if looking from an exam perspective, blocking would be considered a wrong answer. Also, if troubleshooting and only given partial show command that does not state RSTP as the spanning-tree mode, alternate, discarding, and blocking ports are a dead giveaway that you aren’t running 802.1D flavors of spanning tree.

By: rahul

rahul — Wed, 18 Mar 2015 05:37:16 +0000

in between two switch any possibility of edge port ?

By: rahul

rahul — Wed, 18 Mar 2015 05:35:52 +0000

what is edge port and non-edge port in rstp ?

By: Anil

Anil — Sun, 15 Mar 2015 17:33:40 +0000

Simple and straight forward explanation :)

By: Ryan

Ryan — Fri, 20 Feb 2015 16:05:42 +0000

“which two states are the port states when RSTP has converged ?
1. discarding
2. listening
3. learning
4. forwarding
5. disabled
please anyone explain ????”

Maran,

Forwarding and Blocking are the two primary port states when RSTP has converged.

By: Maran

Maran — Wed, 04 Feb 2015 08:30:01 +0000

which two states are the port states when RSTP has converged ?

1. discarding
2. listening
3. learning
4. forwarding
5. disabled

please anyone explain ????

By: Awesome stuff....this is really helpful!!!!

Awesome stuff....this is really helpful!!!! — Tue, 03 Feb 2015 15:33:46 +0000

Katrina

By: yadav

yadav — Sun, 11 Jan 2015 19:31:21 +0000

gr8 explaination

By: Mohamed

Mohamed — Fri, 02 Jan 2015 11:30:44 +0000

hi!!!!
if we connect one more link between sw2 to sw3(fa0/2 to fa0/2) what will be the status of sw3 port fa0/2? backup or alternate?if administrator put port as disable manually….what is the use of that port?

By: adeel

adeel — Wed, 26 Nov 2014 07:24:34 +0000

in above case if sw 2 has lower cost path to bridge then port from sw 3 to sw 1 selected as alternate

By: Guru

Guru — Thu, 30 Oct 2014 08:02:45 +0000

i love people taking part in this ” challenging blog”

By: amandi

amandi — Sat, 11 Oct 2014 15:17:57 +0000

awesome explanation !!!!!!!!!! best site I ever see!!!!!!!!once again thanks

By: Zameerul Haque

Zameerul Haque — Fri, 19 Sep 2014 12:16:32 +0000

EK NUMBER

By: dhanesh

dhanesh — Tue, 02 Sep 2014 08:23:57 +0000

Really he;pful…

By: Ravindra

Ravindra — Fri, 27 Jun 2014 11:01:52 +0000

awesome explanation…

Grate help … in learning

By: piush

piush — Thu, 10 Apr 2014 11:15:26 +0000

wonderfully described

By: Anonymous

Anonymous — Fri, 06 Sep 2013 07:33:47 +0000

first check priority regardless mac addressee value only use mac address if Priority tie

By: Juls

Juls — Thu, 08 Aug 2013 22:32:17 +0000

@India
1st – priority

By: India

India — Wed, 07 Aug 2013 13:26:36 +0000

when we are choosing a root bridge, what do we check first? lower priority or lower mac address?

By: Sagar

Sagar — Mon, 15 Jul 2013 14:47:49 +0000

Very easy to understand the concepts!!! btw, the statement “Because fa0/2 is inferior to fa0/3, Sw2 will select fa0/2 as its Designated port”, does it signifies that the number which is low becomes the DP ????

By: vikas

vikas — Fri, 12 Jul 2013 11:11:37 +0000

Great explanation!!!

By: Rahul Singh

Rahul Singh — Wed, 03 Jul 2013 15:08:58 +0000

Thanks for your excellent updates

By: oceandographer

oceandographer — Mon, 29 Apr 2013 18:34:04 +0000

This is an excellent article. This cleared up several questions that I had on this topic. This is the kind of thing that needs to be included in the Cisco Network Academy–Lan Switching & Wireless portion. Thanks 9tut!

By: ALI

ALI — Wed, 27 Mar 2013 18:07:45 +0000

hi KOWO cisco said right if you read the tutorial carefully again you will get you answer, 9tut say the same meaning

By: jrrivers

jrrivers — Wed, 13 Feb 2013 17:03:27 +0000

FYI… each interface on a bridge has a unique MAC address… see section 7.12.2 of IEEE 802.1D-2004.

By: Ozgun

Ozgun — Fri, 28 Dec 2012 08:56:35 +0000

is there any config. command for this mode?

By: Mohan

Mohan — Wed, 26 Dec 2012 10:07:06 +0000

Root bridge is selected based on high bridge priority(lowest value)

By: Asif

Asif — Thu, 13 Dec 2012 04:27:52 +0000

Hi 9tut,
Thanks for your excellent updates !!!!
I have one doubt, Can you please confirm me whether root bridge is selected on basis of high bridge priority or low bridge priority.
Once more thanks for your study materials!!!! :)

By: Ben

Ben — Wed, 24 Oct 2012 02:17:40 +0000

“Well, both fa0/2 & fa0/3 of Sw2 has the same “path cost to the root” and “sender bridge ID” so the third parameter “lowest port ID” will be used. Because fa0/2 is inferior to fa0/3, Sw2 will select fa0/2 as its Designated port.”

Small fix but:
Shouldn’t this be, “Because fa0/2 is SUPERIOR to fa0/3, Sw2 will select fa0/2 as its Designated Port”

By: KOWO

KOWO — Fri, 31 Aug 2012 23:51:25 +0000

So designated port are choose by lower Mac Adress or Path cost???
On scenario u choosed (designatet port SW2 (FA01) but CISCO says that
switches, the path cost is compared for a given segment. If one port is determined to have a lower path cost, it becomes the designated port for that segment. If two or more ports have the same path cost, then the switch with the lowest BID is chosen.
So please help me with this
KOWO

By: KOWO

KOWO — Fri, 31 Aug 2012 23:48:07 +0000

Please help
Designated ports are selected based on the lowest path cost to the root bridge for a segment. Since the root bridge will have a path cost of “0,” any ports on it that are connected to segments will become designated ports. For the other switches, the path cost is compared for a given segment. If one port is determined to have a lower path cost, it becomes the designated port for that segment. If two or more ports have the same path cost, then the switch with the lowest BID is chosen.

lowest root bridge id
lowest root path cost
lowest sender bridge id
lowest sender port id

By: 9tut

9tut — Wed, 29 Aug 2012 09:56:49 +0000

@Koopotang: Each switch only has 1 MAC address even they have many interfaces. Maybe you are confused about the interfaces on the switch and router: Each interface on a router does have a separate MAC address.

By: Koopotang

Koopotang — Wed, 29 Aug 2012 07:35:26 +0000

When we say “Suppose all the switches have the same bridge priority so the switch with lowest MAC address will become root bridge “…

As a switch has many interfaces, it has many MAC addresses too.. Which one would we choose ?

By: nepal

nepal — Sun, 26 Aug 2012 18:38:18 +0000

nice explained…thank you

By: learner

learner — Tue, 07 Aug 2012 08:36:15 +0000

@ropam and karthik , yes RSTP is able to respond to a physical link failure in less than 10 seconds because of the hello timers of BPDU’s , in case a neighbor misses three consecutive BPDU’s from its directly connected neighbor , it assumes the neighbor to be dead. each BPDU is sent out every 2 seconds every switch port, 3 BPDU’s means a total of 6 seconds.

By: joe

joe — Wed, 25 Jul 2012 12:54:15 +0000

pls can anybody send me a vce regestration key ,am prepering for my ccna exam next month and i could’nt get through all questions in the file i dowloaded at examcollection bcos of registration key.thanks alot email. rothitler@yahoo.com .

By: ropam

ropam — Tue, 24 Jul 2012 08:15:28 +0000

@Karthik….where did u read the 1 sec convergence time?
9tut says this about RSTP convergence time

“Rapid Spanning Tree Protocol (RSTP), which significantly reduces the convergence time after a topology change occurs in the network. While STP can take 30 to 50 seconds to transit from a blocking state to a forwarding state, RSTP is typically able to respond less than 10 seconds of a physical link failure.”

By: Karthik

Karthik — Wed, 04 Jul 2012 10:24:47 +0000

Hi,

I am having a doubt in the RSTP convergence time. How the convergence time is less than 1 seconds. If the link down happens the switch should wait for minimum 3 hello packets so it will take 6 seconds to identify the link down then how come the convergence time is 1 sec?

Can some one help me to understand this?

By: RJCCNA:)

RJCCNA:) — Sat, 16 Jun 2012 13:04:00 +0000

Wow thank a lot grate explaining ……

By: NN

NN — Sun, 03 Jun 2012 13:00:59 +0000

Sorry forgot to mention that my question is when one port is connected from Switch to hub.. Not 2 as in the example..

By: NN

NN — Sun, 03 Jun 2012 12:59:36 +0000

I have one question here.. There is a concept of edge port in RSTP.. Edge ports are those which are connected to end stations. These ports do not recieve any incoming BPDU’s on them and hence do not participate in STP algorithm.
When we connect Switch Sw2 in the above example to a hub wouldnt RSTP put both the ports in Edge mode as the hub would not send any BPDU’s to these ports?

By: mohamed

mohamed — Sat, 02 Jun 2012 04:41:34 +0000

Great explanation :)

By: Wadzi

Wadzi — Tue, 22 May 2012 09:30:52 +0000

Thank you.Well Explained

By: kurt

kurt — Fri, 18 May 2012 18:23:22 +0000

I had to read this (RSTP) a few times to understand it. Thanks 9tut for this site, is very helpful.

By: manish kevre

manish kevre — Wed, 02 May 2012 21:05:38 +0000

should have explained a link failure case .,.,or a new link added case

By: Anonymous

Anonymous — Sun, 22 Apr 2012 13:55:57 +0000

Thank you…… it is very easy to understand
….appriciateble the way of explain and scenario

By: jitu

jitu — Thu, 19 Apr 2012 12:14:34 +0000

awesome presentation

By: Anonymous

Anonymous — Tue, 27 Mar 2012 07:38:15 +0000

Guys, I have a question about RPVST.
When we elect Alternative port on switches what should we do?
1) The port of switch become AP if this switch has a bigger past cost to root switch versus the switch which has lower pat cost to root bridge? Is it right?

2) If the costs to root bridge are same we should compare MAC of the switches. If one of two switches has lower MAC than second switch, its port become DP and port of second switch become AP? Is it right?
Thanks

By: slipkorn

slipkorn — Wed, 22 Feb 2012 06:20:42 +0000

good tutorial.easy to understand.now i understand about RSTP.thanks 9tut..

By: Viji

Viji — Thu, 09 Feb 2012 23:10:10 +0000

Excellent explanation. Thanks a lot.

By: Drei

Drei — Wed, 08 Feb 2012 15:13:58 +0000

crystal clear. You should write a cisco book!

By: yogesh kumar

yogesh kumar — Wed, 25 Jan 2012 06:51:40 +0000

nice and clear explanation :-)

By: shreeram

shreeram — Wed, 18 Jan 2012 14:20:02 +0000

great presentation…i was really confused with this alt and backup port concept..thanks a lot..

By: herun

herun — Mon, 19 Dec 2011 12:36:39 +0000

Thank you very much 9tut great explanation…..

By: Nilesh

Nilesh — Sat, 17 Dec 2011 09:46:42 +0000

Simple & easy.
Thanx

By: Muhsin

Muhsin — Sun, 11 Dec 2011 17:30:57 +0000

You are great, 9tut administrator.

By: joy

joy — Fri, 25 Nov 2011 10:38:05 +0000

now i understand….thanks a lot 9tut

By: GRATEFUL

GRATEFUL — Fri, 04 Nov 2011 17:52:15 +0000

@9TUT
YOU ROCK!!!!!!!!!!!!This is the best tutorial that i have come across. it covers all that you need to know in a simplified and understandable manner. THANKS!

By: Rangga

Rangga — Mon, 03 Oct 2011 09:14:36 +0000

great tutorial….

good man…

By: Simba

Simba — Mon, 26 Sep 2011 15:40:27 +0000

Tahnk you for making learning so easy,i really appreciate

By: Sajan

Sajan — Sun, 25 Sep 2011 12:47:50 +0000

Excellent explanation.

By: 9tut

9tut — Thu, 22 Sep 2011 06:31:22 +0000

@nc: Yes, thank for your detection. I updated it!

By: nc

nc — Wed, 21 Sep 2011 18:10:59 +0000

Great article ! Thank you
In the “quick summary” second statement, is it a typo ? “discarding, listening and forwarding”, should “listening” be “Learning” ?

By: ahmed

ahmed — Fri, 16 Sep 2011 07:59:58 +0000

nice presentation

By: LA_MEL

LA_MEL — Sun, 11 Sep 2011 08:45:38 +0000

“Alternate port – A best alternate path to the root bridge. This path is different than using the root port. The alternative port moves to the forwarding state if there is a failure on the designated port for the segment.”

The alternate port will become forwarding if there is a failure in the root port (not designated port)

By: xallax

xallax — Tue, 06 Sep 2011 04:11:12 +0000

@Moloy
That’s beyond the CCNA level.

visit this link:
http://www.cisco.com/en/US/docs/switches/lan/catalyst2950/software/release/12.1_9_ea1/configuration/guide/swmstp.html#wp1039828

By: Moloy

Moloy — Tue, 06 Sep 2011 03:44:00 +0000

@9tut,
Thanks. But how it will be less than 10 seconds because it will take 6 seconds for max-age time and 15 seconds for learning to forwarding mode. So, it will take at least 21 seconds. I am getting confused, please make me clear.

By: 9tut

9tut — Mon, 05 Sep 2011 09:29:10 +0000

@Moloy: There is not a fixed time for RSTP convergence but typically it is less than 10 seconds.

By: Moloy

Moloy — Mon, 05 Sep 2011 04:27:34 +0000

@9tut,
What is the reconvergence time of rstp after link failure?

Thanks in advance

By: saran

saran — Mon, 01 Aug 2011 06:34:55 +0000

nic explanation

By: rupul

rupul — Wed, 27 Jul 2011 15:12:56 +0000

Thanks 9tut once again, you have made our listening, learning and forwarding states easier… :-)

By: Amira

Amira — Tue, 26 Jul 2011 20:04:11 +0000

Thank you 9tut

By: abdul from nigeria

abdul from nigeria — Mon, 18 Jul 2011 12:09:05 +0000

nice work u did wid RSTp tanx.

By: Deepak S

Deepak S — Sat, 09 Jul 2011 01:46:44 +0000

simplified……. Thanks

By: vinicius

vinicius — Fri, 08 Jul 2011 02:26:53 +0000

Great Tutorial! Thx!

By: BlAcK_SuNdAy

BlAcK_SuNdAy — Wed, 06 Jul 2011 07:05:28 +0000

@9tut

referring to RSTP port states:
it defines discarding, learning and forwarding states. (blocking and listening states in legacy STP are eliminated by discarding state in RSTP)

By: Vinay

Vinay — Fri, 01 Jul 2011 06:37:47 +0000

Hi,

Good presentation. I had confusion in Backup port and its essence in RSTP, now i am clear with it. Can you explain the Two way hand shake process that takes place in Point to point Ports when there is any link failure. I am asking this for the completeness of RSTP. If possible please include it in this tutorial.

Great work.

Thanks again.

Regards,
Vinay G

By: veny

veny — Thu, 16 Jun 2011 07:25:29 +0000

its too confusing topic in hole ccna study