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Webcast-Catalyst9k
New Member

Beginner VLAN question...

Hi,

Ok.. lets pretend I am a beginner .

I have a cisco 3750 switch.

I am trying to create a new vlan, and an interface on the switch that will act as the default gateway for the subnet.

conf t

int vlan 61

ip add 172.16.1.10 255.255.255.0

end

conf t

vlan 61

name VLAN_CASNLB

end

if I do a show int vlan 61

Vlan61 is up, line protocol is down

if I do a show vlan br

61   VLAN_CASNLB                      active

So the vlan exist. the vlan interface exists. Why is line protocol down?

Sorry for the noob first question.. but.. well.. I am a noob

4 REPLIES

Re: Beginner VLAN question...

You have two more steps. You need to configure a switchport that will belong to that VLAN.

interface fastethernet 1/0/17

switchport mode access

switchport access vlan 61

Then you need to plug something (PC, printer, etc) into the port.

Hope it helps

Hall of Fame Super Blue

Re: Beginner VLAN question...

Just to add to Collin't post and to explain a bit.

A L3 vlan interface will only be up/up if one of the following 2 conditions are met -

1) you have an active port that is in that vlan and is up/up hence Collin's suggestion to configure a port on the switch in vlan 61 and add a PC to it

or

2) you have a trunk port on that switch that allows vlan 61

Jon

New Member

Re: Beginner VLAN question...

Thanks guys,

Jon, number 2 sounds more up my alley

2) you have a trunk port on that switch that allows vlan 61

I thought all trunk ports allowed all vlans (and that is why they are trunks)

Hall of Fame Super Blue

Re: Beginner VLAN question...

ACormier@rsmrichter.com

Thanks guys,

Jon, number 2 sounds more up my alley

2) you have a trunk port on that switch that allows vlan 61

I thought all trunk ports allowed all vlans (and that is why they are trunks)

Andrew

By default a trunk does allow all vlans but you can configure the trunk to only allow certain vlans on it and many network admins do. It gives you more control of what is allowed where and if you clear a vlan off the trunk then STP no longer needs to run across that trunk link for that vlan. So i simply meant you may have a trunk link where you have specifically configured what vlans are allowed on it. You then add another vlan and a L3 vlan interface as in your example but forget to add that vlan to the trunk link.

Jon

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