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Ask the Expert- SD-WAN

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Frequent Contributor

spanning-tree portfast trunk

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

2 ACCEPTED SOLUTIONS

Accepted Solutions

Re: spanning-tree portfast trunk

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

Hall of Fame Guru

Re: spanning-tree portfast trunk

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

19 REPLIES 19

Re: spanning-tree portfast trunk

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

Frequent Contributor

Re: spanning-tree portfast trunk

Hi Ganesh,

Many thanks for good reply

spanning-tree portfast trunk

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

Hall of Fame Community Legend

spanning-tree portfast trunk

Devendra,

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

spanning-tree portfast trunk

Hello,

             i will be waiting for your answer.

Thanks & Regards,

Devendra

Hall of Fame Guru

Re: spanning-tree portfast trunk

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

Frequent Contributor

Re: spanning-tree portfast trunk

Hi jon.

thanks for great reply again.

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

thanks

mahesh

Hall of Fame Guru

Re: spanning-tree portfast trunk

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

Beginner

Re: spanning-tree portfast trunk

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.

Frequent Contributor

Re: spanning-tree portfast trunk

Hi,

Thanks for more explanation

Mahesh

Rising star

I know that this is an old

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.

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Frequent Contributor

 Hi Jumora, Thank for

 

Hi Jumora,

 

Thank for updating me on this.

No post is old.Everyday we learn something new.

Best regards

MAheshg

Cisco Employee

Hi Jumora, I think i have

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.

Highlighted
Beginner

Re: I know that this is an old

thanks for this information. 

I also configure this firewall to switch trunk port with spanning tree portfast trunk.However, sometime i encounter the error disable (sometimes) on that switchport. i manually shutdown and no shut again.

any expert have any advice for this? 

thank you

 

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