Deleting VLAN

[sivam siva]

Hi

Cisco press book says if we delete the VLAN all ports assigned to that VLAN fall back to default VLAN and port still remain up

As per my test port is not changing to VLAN 1 when I delete the VLAN.

instead, I see that VLAN is inactive. and staus is up and LED is orange 

X(config-if)#do sh int g1/0/2 sw
Name: Gi1/0/2
Switchport: Enabled
Administrative Mode: static access
Operational Mode: static access
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: native
Negotiation of Trunking: Off
Access Mode VLAN: 100 (inactive)
Trunking Native Mode VLAN: 100 (VLAN0100)
Administrative Native VLAN tagging: enabled
Voice VLAN: none
Administrative private-vlan host-association: none

X(config-if)#do sh int g1/0/2
GigabitEthernet1/0/2 is up, line protocol is up (connected)

can anyone clarify it?

Thanks 

Siva

[Giuseppe Larosa]

Hello Sivam,

what you see is correct access ports should not fallback to Vlan1 when a L2 broadcast domain Vlan is deleted.

the ports are "suspended" and this is signalled by orange LED. They are not operational because members of a not existing vlan.

However, if you go inside the port and you issue:

no switchport access vlan 100

! you put the port in Vlan 1

if you issue again

switchport access vlan 100

the Vlan 100 should be created again and active. (I didn't test this you could try and report results)

So we can say that IOS is more user friendly when creating a new Vlan then when removing one.

Hope to help

Giuseppe

[sivam siva]

Hello @Giuseppe Larosa 

Thanks for the reply

you said ports are "suspended" if VLAN is deleted.

but I could see the status and line protocol is UP

only the LED became orange, I couldn't understand the meaning of this result.

Thanks 

Siva

[Giuseppe Larosa · Accepted solution]

Hello Sivam,

the port can be up at OSI layer 1 and OSI layer 2, but it is isolated from the network if you connect a PC to it you cannot reach anything.

Even if you connect two PCs to two ports in access mode in the deleted Vlan (with LED orange) they should not be able to talk to each other.

The orange LED tells you the port is not operational and you need to take a corrective action to fix it: either you put the port in an existing Vlan or you create again the deleted Vlan.

Edit:

let see it in another way:

either the Cisco IOS should not allow to delete a Vlan until there is an access port using it, or it if allows it it has to manage those access ports in some way. Because you have deleted the vlan the associated access ports are put in a non operational state to give you time to make your changes.

Hope to help

Giuseppe

[sivam siva]

Hello 

@Giuseppe Larosa  your answer makes sense!

But can you answer the below question?

I'm thinking none of the answers are correct, answer B seems somewhat relevant but they mentioned "port go down" 

I'm struggling here.

Interfaces are assigned to a VLAN, and then the VLAN is deleted. Which state are these interfaces in after the VLAN is deleted?
A. They remain up, but they are reassigned to the default VLAN.
B. They go down until they are reassigned to a VLAN.
C. They go down, but they are reassigned to the default VLAN.
D. They remain up, but they are reassigned to the native VLAN.

Thanks 

Siva

[Giuseppe Larosa · Accepted solution]

Hello Sivam,

unfortunately some exam questions are not accurate either in the question either  in the proposed answers

A. They remain up, but they are reassigned to the default VLAN.
B. They go down until they are reassigned to a VLAN.
C. They go down, but they are reassigned to the default VLAN.
D. They remain up, but they are reassigned to the native VLAN.

A is false because ports are not reassigned to default Vlan 1 as you have seen in lab tests.

D is false because the concept of native Vlan is specific of trunk ports and trunk port simply stops to send and receive frames of the deleted vlan. In addition to this the native Vlan can be different on each trunk link (the default native vlan is again vlan 1). The question says ports are assigned to a Vlan making to think the ports are all access ports not using native vlan concept.

C is false like A because ports are not re-assigned to default VLAN.

B is not totally correct because ports are not falling down at OSI layer1, but they are not operational until you assign them to an existing VLAN.

I would choice B between the avaliable options as it is the least wrong answer.

Edit:

the key concept here is the access ports associated to the deleted VLAN are not operational and requires configuration changes to be used again. From this point of view answer B is acceptable.

Hope to help

Giuseppe

[sivam siva]

Thank you @Giuseppe Larosa