CCENT, CCNA, CCNP, CCDA, CCDP, CCDE, CCIE, CCSP, CCVP, CCIP.
User avatar
rowelld
Junior Member
Posts:
75
Joined:
Sun Apr 21, 2013 4:09 pm
Certs:
CCNA Security, CCNA

PVST and RSTP Port Role Confusion

Fri Jan 03, 2014 11:26 am

I'm going through the CCNP SWITCH lab manual and notice something about the STP port roles:

Code: Select all
DLS2#show spanning-tree

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    24577
             Address     000d.bdd3.4e80
             Cost        19
             Port        2 (FastEthernet0/2)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     0011.bba6.b000
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/1               Altn BLK 19        128.1    P2p
Fa0/2               Root FWD 19        128.2    P2p
Fa0/47              Altn BLK 19        128.47   P2p
Fa0/48              Altn BLK 19        128.48   P2p

DLS2#sh run | i span
spanning-tree mode pvst
spanning-tree extend system-id
DLS2#


It was my understanding that the Alternate port role was part of Rapid-PVST. Am I missing something here?
“Success is not final, failure is not fatal: it is the courage to continue that counts.” -Winston Churchill

http://rowell.dionicio.net

User avatar
mellowd
CCIE #38070
Posts:
13814
Joined:
Wed Jun 18, 2008 7:49 am
Certs:
CCIE (RS,SP), JNCIE-SP, BC-/SPNE/NP

Re: PVST and RSTP Port Role Confusion

Fri Jan 03, 2014 11:37 am

ieee on a Cisco switch is actually running PVST - not 802.1d-1998 as you would expect.

This is a good thread about why you are seeing what you're seeing: https://supportforums.cisco.com/message/581353#581353

User avatar
that1guy15
Post Whore
Posts:
3224
Joined:
Thu Apr 29, 2010 6:12 pm
Certs:
CCNP, CCDP, CCIP

Re: PVST and RSTP Port Role Confusion

Fri Jan 03, 2014 11:38 am

Even though you are not configured for Rapid the switch is actually running in rapid but with backwards compatability for traditional 802.1d. Here is a good explanation on the Cisco Support forums
https://supportforums.cisco.com/thread/155206
http://blog.movingonesandzeros.net/

User avatar
that1guy15
Post Whore
Posts:
3224
Joined:
Thu Apr 29, 2010 6:12 pm
Certs:
CCNP, CCDP, CCIP

Re: PVST and RSTP Port Role Confusion

Fri Jan 03, 2014 11:40 am

Ha! you just inched me out Mellowd.
http://blog.movingonesandzeros.net/

User avatar
rowelld
Junior Member
Posts:
75
Joined:
Sun Apr 21, 2013 4:09 pm
Certs:
CCNA Security, CCNA

Re: PVST and RSTP Port Role Confusion

Fri Jan 03, 2014 12:03 pm

That is very interesting. Thanks for sharing that link. I thought I was going crazy.
“Success is not final, failure is not fatal: it is the courage to continue that counts.” -Winston Churchill

http://rowell.dionicio.net

'

Return to Cisco Certifications

Who is online

Users browsing this forum: No registered users and 36 guests