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New Member

How do you keep a VLAN interface up?

Is there a method that enables you to keep a vlan "UP", even when none of the physical interfaces assigned to that vlan are connected?

6 REPLIES
Blue

Re: How do you keep a VLAN interface up?

you can use a trunk that supports the VLAN and that should keep it up. (if you can use a trunk)

unless there is at least 1 active port in VLAN, it will stay down.

New Member

Re: How do you keep a VLAN interface up?

Actually, I'm trying to keep VLAN1 (native vlan) up. I do have several interfaces, that are trunking, assigned to this vlan. Unless these interfaces are physically connected, VLAN1 stays "DOWN". The switch in question has a WAN connection through an interface in a different VLAN. This interface is up, but I cannot TELNET into the switch because VLAN1 is down.

New Member

Re: How do you keep a VLAN interface up?

If you are using vtp, you can "force" the VLAN active using those commands; depending on the switch you are using, this is done a number of different ways.

newer IOS switch running native mode -

conf t

vlan 1

state active

exit

wr mem

older IOS switch

From an enable prompt -

vlan database

[enters vlan database mode)

[Note: Newer IOS warns that this is deprecated and will not show help -- the help is as follows -

switchname#vlan database

% Warning: It is recommended to configure VLAN from config mode,

as VLAN database mode is being deprecated. Please consult user

documentation for configuring VTP/VLAN in config mode.

switchname(vlan)#?

VLAN database editing buffer manipulation commands:

abort Exit mode without applying the changes

apply Apply current changes and bump revision number

exit Apply changes, bump revision number, and exit mode

no Negate a command or set its defaults

reset Abandon current changes and reread current database

show Show database information

vlan Add, delete, or modify values associated with a single VLAN

vtp Perform VTP administrative functions.

switchname(vlan)#vlan ?

<1-1005> ISL VLAN index

switchname(vlan)#vlan 1 ?

are Maximum number of All Route Explorer hops for this VLAN

backupcrf Backup CRF mode of the VLAN

bridge Bridging characteristics of the VLAN

media Media type of the VLAN

mtu VLAN Maximum Transmission Unit

name Ascii name of the VLAN

parent ID number of the Parent VLAN of FDDI or Token Ring type VLANs

ring Ring number of FDDI or Token Ring type VLANs

said IEEE 802.10 SAID

state Operational state of the VLAN

ste Maximum number of Spanning Tree Explorer hops for this VLAN

stp Spanning tree characteristics of the VLAN

tb-vlan1 ID number of the first translational VLAN for this VLAN (or zero

if none)

tb-vlan2 ID number of the second translational VLAN for this VLAN (or zero

if none)

switchname(vlan)#vlan 1 state ?

active VLAN Active State

suspend VLAN Suspended State

switchname(vlan)#vlan 1 state active (enter)

This will make the VLAN active.

Note that it "works" even when there is no help.

There's a way to do it for CAT OS, but I only have VTP clients on my few remaining Cat OS switches.

Good luck -

Nick

(PS - if this helps, please 'rate' the answer ! :-) )

New Member

Re: How do you keep a VLAN interface up?

Hello Nick,

The native vlan, in my case VLAN1, is active by default. And even though a vlan is active, it doesn't mean that the VLAN is "UP" and the protocol is "UP". At this point it still seems that you have to have something physically plugged into an interface that is in said vlan. I think the solution to my problem is to create a loopback interface. They are always "UP" and I should be able to telnet into the switch even though the native vlan is "DOWN". Thanks for your response and input.

Re: How do you keep a VLAN interface up?

The interface vlan x (no matter if it's vlan 1 or 2 or 3) is a logical interface. It will NOT remain up unless the physical port is "connnected". the physical port can be access port belonging to vlan x or a turnk port where vlan x is part of the vlans forwarding. There is not way to keep the logical interface up if there are no connected physical port that belongs to this vlan.

New Member

Re: How do you keep a VLAN interface up?

Thank you for the clarification. It looks like I was trying to do something that's not possible. I think I found the solution though. I created a loopback interface. Even though this is a virtual interface, like a vlan, the loopback is always up and I can now telnet to my switch. Thanks for the response.

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