how 802.1D contain port role alternate ??

[AbdoRefky]

as i know that 802.1D shouldn't have port role alternate .

but it does . 

the question is how ! 

[Paul Chapman]

Hi -

Post results of "show spanning-tree summary"

PSC

[AbdoRefky]

but it doesn't show the port roles.i just got those photos from google . 

tell me if you still wanna the other output , i can get it from IOU or cisco packet tracer . 

[Paul Chapman]

Hi -

I guess I don't understand your question.  How do you "know" that 802.1D can't have a role of alternate?

Honestly, you did make me question my own knowledge for a minute. So to be sure I wasn't answering incorrectly I actually pulled the IEEE 802.1D specification.  You can find it here.

The document shows that Cisco correctly reflects 2 distinct attributes of an STP connection: Role and Status.

In section 7.4, the IEEE provides alignment between the 802.1D standard and the port statuses defined by the IETF: disabled, blocking, listening, learning, forwarding, and broken.

In section 9.2.9, Roles are defined as: Unknown, "Alternate or Backup", Root, or Designated

PSC

[AbdoRefky]

ahh,,,, sorry if miss guide you . 

that 802.1D 2004 version = Rapid Spanning-Tree 

the 802.1D 1998 version = Normal Spanning-Tree

so we find switches with : STP + RSTP + MSTP . 

default is STP which role is discarding doesn't appear . and instead it appears as alternate . 

now we are on 2016, did cisco integrated some of the RSTP to the STP . 

or how a cisco switch include those 3 protocols with one of them have features of another . 

[Paul Chapman]

Hi -

I quoted from the correct standard.  There may be revisions between 1998 and 2004 of 802.1D, but RSTP is a different standard.

802.1D = Spanning Tree Protocol

802.1w = Rapid Spanning Tree Protocol

802.1s = Multiple Spanning Tree

In terms of "role", discarding is not defined as a role it is defined as a "port state".  As stated before, we have 2 attributes we are dealing with here: Port state (or status) and Port Role.

PSC

[AbdoRefky]

that's as we know it, but i do quote this from CCIE Volume 1 book 

The latest 802.1D-2004
standard no longer includes the legacy STP at all (which is considered obsolete), and
instead, it covers the RSTP originally found in 802.1w. The 802.1s MSTP is integrated into
802.1Q-2005 and later revisions. With current standards, therefore, RSTP is covered in
802.1D while MSTP is covered in 802.1Q, and legacy STP has been dropped. Still, many
people are used to the old naming, with 802.1D referring to STP, 802.1w referring to
RSTP, and 802.1s referring to MSTP.

so that 802.1D 2004 is the IEEE standard for Rapid Spanning-Tree 

that screen shot from IEEE link .

and in this link you can find a nice history . 

https://en.wikipedia.org/wiki/IEEE_802.1

the simplest question will be : how switches still runs : normal spanning-tree which created at 1998 with additions that created at 2001.

another example is 801.t ( system extension ID came from this protocol )

BTW 802.1D 2004 Incorporated into 802.1Q-2014^[4]

so i think the if we want to read the latest additions of RSTP we go to 802.1Q 2014 . 

what strange world . 

[Paul Chapman]

Hi -

I guess I've never dug too deep into this before.  Cisco does have a history of doing their own thing with STP.  Realistically, the default STP mode for Cisco devices does use the legacy timers and is compatible with the original 802.1D spec, but that's as far as it goes.  Cisco's use of per-VLAN STP is completely non-spec (as much as they've tried to get it into the standard).

With that in mind, I've never considered the port roles to be non-standard.  In all the implementations that I've done I always see "Alternate" for the non-designated ports on a non-root switch.  The only difference I've seen has been that Cisco's implementation of Rapid STP uses the term "Backup" instead of "Alternate" (and often it's platform specific).

I guess the question becomes: what are you looking to get out of our exchange here?  We're debating a history lesson, not a technical issue, per se.

PSC

[AbdoRefky]

sorry for going into some history, i was pointing that 802.1D 2004 is rapid spanning-tree .

oki, my technical issue is cisco switches with the 3 STP protocols : 

1: normal spanning-tree ( 802.1D 1998)

2: rapid spanning-tree ( 802.1W/ 802.1D 2004 )

3: MSTP 

the questions . 

1 : how come a features from 802.1W & 802.1t which created at 2001 to be applied at standard created at 1998 . 

2 : where can i find a reference that cisco did add those features to the normal spanning-tree .  

[AbdoRefky]

so, any answer ?

[Paul Chapman]

Hi -

1) Clearly when the standard changed, Cisco changed IOS with it.

2) Dig though IOS release notes.

PSC

[Amer Alnassir]

Hi,

You may check "Understanding Rapid Spanning Tree Protocol (802.1w)" https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/24062-146.html

It states the following:

-"These two port roles correspond to the blocking state of 802.1D"

-"This distinction is already made internally within 802.1D. This is essentially how Cisco UplinkFast functions. The rationale is that an alternate port provides an alternate path to the root bridge and therefore can replace the root port if it fails. Of course, a backup port provides redundant connectivity to the same segment and cannot guarantee an alternate connectivity to the root bridge. Therefore, it is excluded from the uplink group."

Cisco has included those two roles in PVST/PVST+ internally. Yet, this inclusion does not affect the interoperability with non-Cisco switches. In fact Cisco switches run PVST+ (a Cisco proprietary version of IEEE 802.1D) which is interoperable with non-Cisco switches.

*802.1D refers to Legacy STP in old terminology, and to RSTP in new terminology (following IEEE 802.1D - 2004). That's one reason for much of the confusion about Spanning Tree Protocol versions. In the RSTP document above, 802.1D refers to Legacy STP, while 802.1w refers to RSTP.