Switches connected as Access ports

[mahesh18]

Hi Everyone,

I connected to switches together under vlan 10 as access ports they have same config as below

Switch  1 is Root for vlan 10

switchport access vlan 10

switchport mode access

  spanning-tree portfast

SwitchA#sh spanning-tree int fastEthernet 1/0/15 detail

Port 17 (FastEthernet1/0/15) of VLAN0010 is designated forwarding

   Port path cost 19, Port priority 128, Port Identifier 128.17.

   Designated root has priority 32778, address 0019.e849.d380

   Designated bridge has priority 32778, address 0019.e849.d380

   Designated port id is 128.17, designated path cost 0

   Timers: message age 0, forward delay 0, hold 0

   Number of transitions to forwarding state: 1

   Link type is point-to-point by default

   BPDU: sent 3621, received 2

Switch 2

SwitchB#sh spanning-tree int fastEthernet 2/0/15 detail
Port 71 (FastEthernet2/0/15) of VLAN0010 is root forwarding
   Port path cost 19, Port priority 128, Port Identifier 128.71.
   Designated root has priority 32778, address 0019.e849.d380
   Designated bridge has priority 32778, address 0019.e849.d380
   Designated port id is 128.17, designated path cost 0
   Timers: message age 1, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type is point-to-point by default
   BPDU: sent 2, received 3800

So here As Switch 1 is root bridge so it is sending BPDUs.

So when we configure switch port  as access port and portfast is enabled and we connect it to another switch they should not send

the BPDUs right?

Is current network design is correct behaviour?

Thanks

MAhesh

[Julio A. Martinez Herrera]

Hi dude !

The command "spanning-tree portfast" is only recommended if you connect an end device on the port, like a PC or IP Phone.

http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/12.1/13ew/command/reference/S1.html#wp1070681

[mahesh18]

Hi Julio,

I know  that  i was testing how it would behave when enabled on  switch ports with connection to switches.

Seems to me that with port fast enabled  on switch ports and connection going to switches instead of PC  and with port config

as access  ports both switches still can talk to each other.

With root Bridge switch sending BPDUs and other switch receiving it.

Thanks

Mahesh

[Joseph W. Doherty · Accepted solution]

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Posting

So when we configure switch port  as access port and portfast is enabled and we connect it to another switch they should not send the BPDUs right?

I believe, it depends on whether the Portfast configured port receives BPDUs.  If it does, I beleive it drops out of Edge port mode and participates in STP.

[mahesh18]

Hi Joseph,

So one side had port fast configured it STP shows as edge port type and it is sending BPDUs.

Other side has no portfast and it is STP type P2P only and it is receiving the BPDUs.

When i config portfast  on switch 2   it is still receiving the BPDUs and port type is P2P  only does not change to edge.

So this proves what you said above is absolutely correct.

Many thanks

Regards

Mahesh

[paul driver · Accepted solution]

Hello Mahesh

It depends on where porfast is enabled:

Portfast (global or interface) = bypasses listen/learn goes into forwarding state

Bpduguard

(Global)  - goes through stp process - no blocking

(Interface) - listen state then blocks port (err-disable}

bpduguard + portfast (any variation) = jumps to forwarding from blocking - then blocks port (err-disable

Bpdufilter (global or interface) = goes through stp process (no filtering occurs)

Bpdufilter (Global) + Portfast = jumps to forwarding from blocking (no filtering occurs)

Bpdufilter (Interface) + Portfast - jumps to forwarding from blocking (filtering occurs)

res

Paul

Please don't forget to rate this post if it has been helpful.

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

pdriver wrote:
Hello Mahesh
It depends on where porfast is enabled:
Enabled From global config if bpdu's are seen only in this mode then portfast status is lost.
Enabled From port config port stills continues to be in portfast regarless ( possible loops can occur)
res
Paul

Paul I wasn't aware global portfast and individual portfast commands resulted in different behaviors.  Could you provide any reference(s) to explain this, or other, functional difference?

[paul driver]

Apologies Joseph

Not sure how i managed to post that as i have a file saved from testing all this out, Anyway I have  now corrected this, please see above.

res

Paul

Please don't forget to rate this post if it has been helpful.

[Joseph W. Doherty]

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

Paul thanks for the correction!

[mahesh18]

Hi Paul,

Thanks for adding your input  to the post.

MAhesh