How long does it take for vlan interface to come up ?

[mlnsharma07]

Hi,

On Cisco 6509 IOS 15.1(2) SY3, I have a port channel configured with few vlan interfaces (configured only on this po) as below.

interface Port-channelX
 switchport
 switchport trunk allowed vlan yy,zz
 switchport mode trunk
end

After I perform a shut/no shut of the port-channel interface, vlan interfaces configured on this po come up after nearly 20-25 seconds. During this whole time, I can see that port-channel is up, but vlan-interface is down. I tried enabling "debug interface vlan", but I dont see anything in "show logging"

Is there any config setting that might cause this behavior ? Any way to overcome this ?

[Mark Malone]

A vlan interface will only come up once ports are assigned to that vlan and are up/up or there is a an STP instance for that vlan so it needs time to calculate that before it brings it up, depending on your STP your using you may be able to speed it up by using rstp which will shorten the calculation time but other than that I don't know any other way to speed it up , that sounds like expected behaviour

[mlnsharma07]

So, it looks like, when enabling spanning-tree in global configuration mode, all ports in the router become part of STP ?

I have removed the spanning-tree configuration on this port and thought that it wouldn't participate in spanning-tree. So, I thought it would move to Fwd as soon as it came up. But, I enabled portfast edge and it moves to Fwd as soon as it comes up.

So, all the ports must be participate in STP or be "portfast-ed". Am I right ?

[Mark Malone · Accepted solution]

yes all ports by default participate in some form of STP depending what type is configured to prevent layer 2 loops

portfast is used to relieve calculation on the switch , when you use that the switch knows these ports are not trunk ports and do not need to be part of the calculation so it speeds up layer 2 convergence and puts them straight into the fwd mode, portfast should only be set on access ports , pc/phones printers etc  where you know there is no path to another switch

You use portfast bpduguard as an extra force of loop security on an access port, if a bpdu is received the port will go to error disable to prevent a loop

using portfast bpdufilter disables stp on the port