spanning-tree portfast trunk

Answered Question
Mar 11th, 2010
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Hi all,


i read that portfast should only be enabled on access ports  not on trunk ports.


when this command is used


spanning-tree portfast trunk?


under what cases we will use portfast command on trunk port ?


thanks

mahesh

Correct Answer by Jon Marshall about 7 years 2 weeks ago

Mahesh


You are right in what you say ie. you shouldn't use portfast on a trunk link between switches. Where i have seen the portfast trunk command used is when you have a server that supports 802.1q trunking and is running multiple vlans on it's NIC.


Jon

Correct Answer by Ganesh Hariharan about 7 years 2 weeks ago

Hi all,


i read that portfast should only be enabled on access ports  not on trunk ports.


when this command is used


spanning-tree portfast trunk?


under what cases we will use portfast command on trunk port ?


thanks

mahesh


Hi Mahesh,


You can use PortFast to connect a single end station or a switch port to a switch port. If you enable PortFast on a port that is connected to another Layer 2 device, such as a switch, you might create network loops. But you can enable portfast with router on stick case.where you have switch with trunk configured with router interface.


Hope to Help !!


Remember to rate the helpful post


Ganesh.H

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Correct Answer
Ganesh Hariharan Thu, 03/11/2010 - 23:36
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Hi all,


i read that portfast should only be enabled on access ports  not on trunk ports.


when this command is used


spanning-tree portfast trunk?


under what cases we will use portfast command on trunk port ?


thanks

mahesh


Hi Mahesh,


You can use PortFast to connect a single end station or a switch port to a switch port. If you enable PortFast on a port that is connected to another Layer 2 device, such as a switch, you might create network loops. But you can enable portfast with router on stick case.where you have switch with trunk configured with router interface.


Hope to Help !!


Remember to rate the helpful post


Ganesh.H

devendra.gawade Sat, 03/02/2013 - 21:29
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Hello Ganesh,

                        when i gone for interview ; they asked me suppose you have one L2 switch. you need to configure trunk port. when you configured trunk port ; before saving the running config you type portfast command ; what will the output ?...


waiitng for your reply.



Thanks & Regards,

Devendra

Leo Laohoo Sat, 03/02/2013 - 21:51
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Devendra,


That's a trick question.  I will never, under any circumstances, configure my uplink trunk port with STP portfast. 

devendra.gawade Mon, 03/04/2013 - 07:30
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Hello,

             i will be waiting for your answer.


Thanks & Regards,

Devendra

Correct Answer
Jon Marshall Fri, 03/12/2010 - 00:45
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Mahesh


You are right in what you say ie. you shouldn't use portfast on a trunk link between switches. Where i have seen the portfast trunk command used is when you have a server that supports 802.1q trunking and is running multiple vlans on it's NIC.


Jon

mahesh18 Fri, 03/12/2010 - 08:11
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Hi jon.


thanks for great reply again.

just to be courious which servers are these which support 802.1q trunking.


thanks

mahesh

Jon Marshall Fri, 03/12/2010 - 08:17
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mahesh18 wrote:


Hi jon.


thanks for great reply again.

just to be courious which servers are these which support 802.1q trunking.


thanks

mahesh


Mahesh


Nowadays it is VMWare servers where you see them participating in multiple vlans but before VMWare it could be any server that you wanted to be in more than one vlan and as long as the NIC supported it you could set it up that way.


Jon

You should almost never apply a spanning-tree portfast trunk command to another cisco switch.  If you go back to the basics... spanning-tree portfast allows the ports to skip the blocking to fowarding states and go immediately to forwarding.  The spanning-tree portfast trunk does the same but for trunk connections.  It is recommended to do this on vmware/ESX servers that require a multi-vlan use port, BigIPs, Netscreens, any non PAGP using device.

jumora Thu, 07/03/2014 - 12:02
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I know that this is an old post but then again I was looking for something else and crossed this conversation about portfast. You can actually enable this also against ASA firewalls that have sub interface configuration against a trunk port on a switch, specially when you have ASA failover.

mahesh18 Thu, 07/03/2014 - 20:50
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Hi Jumora,

 

Thank for updating me on this.

No post is old.Everyday we learn something new.

Best regards

MAheshg

Dilshad Ahmed Tue, 06/07/2016 - 06:08
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Hi Jumora, I think i have something similar to what you have described.

FW1---SW1---SW2---FW2 (FW 1 and 2 are also connected via failover link and have failover enabled)

When the primary switch fails we see some drops, but when it comes back we see a crazy number of drops. Could it be linked with ASA failover convergence? The host that i am trying to ping is behind FW.

I have rpvst with sw1 hardcoded to be root and don't have portfast trunk on link to FW.


If you could point me to some discussions/docs describing this scenario it would also be great.

andrespne Mon, 07/28/2014 - 15:27
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hello,

 

I have an Access Point on bridge mode passing several Vlans connected to a 4500 on a trunk port.

 

Should i enable spanning-tree portfast trunk?

 

Also whats the difference between "spanning-tree portfast" vs "spanning-tree portfast trunk" ?

 

Thanks

 

Andres

bradharrell5642 Wed, 09/10/2014 - 09:55
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I'm actually in the same situation with an access point on a trunk link, and have the same question.Im seeing constant flapping on the link that does not have port fast enabled. I checked and all other access points have this enabled on the port

CZindy1212 Sun, 12/07/2014 - 15:41
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.... and there is one more case:

 

you have access switch full of users and you want to provide them redundancy for internet connection, sou you use HSRP for example and now you have switch connected to 2 or more routers with internet links

now, those links between switch and routers are also trunks and the topology is like a triangle with the switch on the tip , omitting PCs for now , at this point the only device taken into consideration is the switch - others don't use STP because routers have configured IP addresses on subinterfaces (each for one VLAN) so they break BRdomain and computers don't care about STP. In this case, you are sure that no routing loop can occur because other devices (all of them are L3) are boundary for that L2 segment and arp requests broadcasted in your LAN stay inside.

What you've just managed to make is faster trunk transition to UP state so after reload of that switch, your users can quickly use network again.

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