Vlan Query

Answered Question
Jan 21st, 2008

Hi

I've just configured the following port on my 3560G switch:

interface FastEthernet0/48

description Link Router (2Mbit Connection)

switchport trunk encapsulation dot1q

switchport trunk native vlan 10

switchport mode trunk

speed 100

duplex full

srr-queue bandwidth share 10 10 60 20

srr-queue bandwidth shape 10 0 0 0

priority-queue out

mls qos trust dscp

auto qos voip trust

no mdix auto

The strange thing is that this port shows up in vlan 1 when I run "sh vlan br"

1 default active Fa0/48

Could someone please tell me why that is, even though the native vlan is set to 10?

Thanks

Dan

I have this problem too.
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Correct Answer by Jon Marshall about 8 years 10 months ago

Dan

Because it is not running as a trunk link. I have just done the same thing and when i shutdown the port it shows up in vlan 1.

If the port was up and running and functioning as a trunk then when you run "sh vlan brief" you won't see it attached to any vlan.

The native vlan is only the vlan that traffic will be sent untagged for. Until that port is functioning as a trunk it will remain allocated to the default vlan (unless you change it) which is vlan 1.

Jon

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Correct Answer
Jon Marshall Mon, 01/21/2008 - 03:34

Dan

Because it is not running as a trunk link. I have just done the same thing and when i shutdown the port it shows up in vlan 1.

If the port was up and running and functioning as a trunk then when you run "sh vlan brief" you won't see it attached to any vlan.

The native vlan is only the vlan that traffic will be sent untagged for. Until that port is functioning as a trunk it will remain allocated to the default vlan (unless you change it) which is vlan 1.

Jon

dan_track Mon, 01/21/2008 - 03:51

Hi

Thanks for the reply. As a follow up question, is it safe to shutdown int vlan1 then? Or am I getting my understanding confused by what shutdown means?

Thanks

Dan

Jon Marshall Mon, 01/21/2008 - 03:53

Dan

When i said shut the port down i meant the physical port not the L3 vlan interface.

Is this what you meant ?

Jon

dan_track Mon, 01/21/2008 - 04:13

Hi

Sorry what I meant was can I run

int vlan 1

shutdown

Would this in anyway affect the switch, since I assume vlan 1 by default is enabled.

I'm using a trunk link between a router that is routing for different vlans in one of our sites, other than the ones I've configured on the actual switch.

Thanks

Dan

Jon Marshall Mon, 01/21/2008 - 04:17

Dan

If vlan 1 is not being used as a vlan for clients that are active and vlan 1 is not being used as the vlan to get access to the actual switch then yes you can shutdown the L3 vlan 1 interface.

As Narayan pointed out routing all your vlans on the 3560 would appear to make more sense but then you know your topology better than we do.

Jon

royalblues Mon, 01/21/2008 - 03:46

On a dot1q trunk, the native vlan traffic is sent untagged.

Since you have not configured any switchport access vlan command, the port is by default on vlan 1. This is the vlan the port will fallback to when the port loses its trunk status.

BTW can you let me know why are you using dot1q trunks while connecting to the router? are you running router on a stick topology? Creating the SVIs on the 3560 would make more sense in this case

HTH

Narayan

glen.grant Mon, 01/21/2008 - 05:46

Narayan is corrrect because the access port was not set to anything by default it is in vlan 1 so your display is correct . If it wasn't a trunk and had a "switchport access vlan statement it would then show whatever vlan was in that statement.

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