vlan SVI created but the vlan is not present in vlan database?

[adfsdafs adsfafds]

I created VLAN 3 with #interface vlan 3, however it is not shown in #show vlan. For certain Cisco platforms/releases, is a layer 2 VLAN (for the purpose of switching) treated differently than a layer 3 SVI VLAN? Where is this behavior documented?

Switch#show vlan

VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Gi0/0, Gi0/1
2 VLAN0002 active
1002 fddi-default act/unsup
1003 token-ring-default act/unsup
1004 fddinet-default act/unsup
1005 trnet-default act/unsup

VLAN Type SAID MTU Parent RingNo BridgeNo Stp BrdgMode Trans1 Trans2
---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------
1 enet 100001 1500 - - - - - 0 0
2 enet 100002 1500 - - - - - 0 0
1002 fddi 101002 1500 - - - - - 0 0
1003 tr 101003 1500 - - - - - 0 0
1004 fdnet 101004 1500 - - - ieee - 0 0
1005 trnet 101005 1500 - - - ibm - 0 0

Primary Secondary Type Ports
------- --------- ----------------- ------------------------------------------

Switch#show ip interface brief
Interface IP-Address OK? Method Status Protocol
GigabitEthernet0/0 unassigned YES unset up up
GigabitEthernet0/1 unassigned YES unset up up
Vlan2 10.65.254.226 YES manual down down
Vlan3 10.64.254.234 YES manual down down
Vlan29 unassigned YES unset administratively down down

[InayathUlla Sharieff]

Hi,

For any layer 3 vlan to come up you need to manually first add the vlan 3 in vlan database.

some switches depends on the IOS running when you create the layer 3 vlan SVI the layer 2 vlan get created for the same but some switches doesnt create the layer 2 when its relevent layer 3 SVI is created.

HTH

Regards

Inayath

[adfsdafs adsfafds]

Since the vlan SVI requires the vlan in vlan database, shouldn't there be a check to prevent the svi from being created or auto create it in vlan database just like the behavior when putting an access port into a nonexistent vlan?

If this has indeed been "fixed" (which I don't think is the case for all platforms), since which release?

[InayathUlla Sharieff]

Please do the feature navigate and you can get the platform or IOs.I dont remember it handy.

But all the latest does create the layer 2 vlan when you create the SVI.

Regards

Inayath

[adfsdafs adsfafds]

Not on vios_l2-ADVENTERPRISEK9-M), Version 15.2(4.0.55)E. 

[manoj.petshali]

Is there any cisco document which can be referred in this regard.

Means how can someone assure that just by creating interface VLAN,the Layer 2 Vlan will be created automatically

Thanks in advance

[johnd2310]

Hi,

You need to create the vlan before you can create the SVI. The SVI will not come up without the vlan.

vlan 3

 name vlan003

Interface vlan 3

ip address x.x.x.x x.x.x.x 

no shutdown

Thanks

John

[acampbell]

Hi,

Even on modern router like C891/24X we have to revert to the older method for looking vlans

router#vlan data
router(vlan)#show current

<SNIP>
VLAN ISL Id: 1
Name: default
Media Type: Ethernet
VLAN 802.10 Id: 100001
State: Operational
MTU: 1500
Translational Bridged VLAN: 1002
Translational Bridged VLAN: 1003
<SNIP>

router(vlan)#exit
router#

[Richard Burts]

In the follow up question to the old discussion this question was asked

how can someone assure that just by creating interface VLAN,the Layer 2 Vlan will be created automatically

My response is that I do not believe that it can be assured that the layer 2 vlan has been created.. The behavior is different depending on the platform. After you have created the layer 3 SVI you should check to find out if the layer 2 vlan is created or not.

HTH

Rick 

[manoj.petshali]

Thanks for useful information.

May you please let me know which platform supports this feature means creating SVI creates L2 Vlan automatically.

As i tried the same in some of Layer 3 switches (even old IOS) and it did not happen to me but i believe it happens.

Thanks in advance

Manoj Petshali

[Richard Burts]

Manoj

I do not know of a list that indicates whether the layer 2 vlan is created or not when the layer 3 SVI is configured. As you have found in your testing there are a number of switches that do not do this. So the prudent thing is that whenever you have configured a layer 3 SVI you should check on whether the layer 2 vlan exists or not.

HTH

Rick

[manoj.petshali]

Thanks a Lot for the response.

[Richard Burts]

You are quite welcome. These forums are excellent places to ask questions and to learn about networking. I hope to see you continue to be active in the forums.

HTH

Rick

[Jo6]

Hello, For anyone studying for their CCNP switch.
I was having the same question when I testing that on  
WS-C3750G-12S  -> c3750-ipservicesk9-mz.122-55.SE12.bin

interface vlan 456

ip address 192.168.54.4 255.255.255.0

no shutdown

exit 

interface gigabitEthernet 1/0/2

switchport access vlan 432

no shutdown

show vlan

Is only showing the  vlan 432

[Richard Burts]

This is another demonstration of the fact that while some versions/some platforms will create the vlan when the SVI is configured that other versions/platforms will not create the vlan when the SVI is configured. The assumption that it would happen is dangerous. The moral of this story is that when in doubt about whether the vlan was created you should check. Or perhaps the moral of this story is that if you are consistent and always create the vlan before configuring the SVI then you will always be safe.

HTH

Rick