Aboute active vlans and active ports.

Unanswered Question
Aug 27th, 2010

I am a little confused about the concepts of active vlan and active port.

I would try a definition of active vlan:

1 - The vlan must be configured.

2 - The vlan must have some ports configured in it.

3 - The vlan has not been shut down with the "shutdown vlan" command.

So, I would try a definition of active port too:

1 - The port must belong to an active vlan.

2 - The port has not been shut down.

I think that these two definitions, note that the second definition use the first one,

make sense, in particular if I consider the term active as an attribute that tell me

that the switch is doing some type of work with the vlan or port. For example, if the

vlan has not some ports configured in it, it exists but the switch does not any type

of work with it, check the mac-address-table etcetera.

What do you think about? Is it possible to give a better definition? Am I forgetting something?

Thanks.

I have this problem too.
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Richard Burts Fri, 08/27/2010 - 07:08

I think that some of us might add another characteristic in defining an active port and say that for the port to be active it needs to be connected to some live device as well as being in an active VLAN and not being shut down.

A VLAN can be active if there is at least one port in the VLAN that is connected to a live device. But a VLAN can also be active if there are no connected devices but the VLAN is included in a trunk that is active.

HTH

Rick

Giuseppe Larosa Fri, 08/27/2010 - 07:23

Hello Matteo,

in this context you have to refer to the Layer2 obejct vlan= broadcast domain

1) the vlan L2 object is defined in vlan database

example: this vlan is not associated to any port on a C4500 switch

show vlan id 101

VLAN Name                             Status    Ports

---- -------------------------------- --------- -------------------------------

101  P2POSPF4                         active

VLAN Type  SAID       MTU   Parent RingNo BridgeNo Stp  BrdgMode Trans1 Trans2

---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------

101  enet  100101     1500  -      -      -        -    -        0      0

Remote SPAN VLAN

----------------

Disabled

Primary Secondary Type              Ports

------- --------- ----------------- ------------------------------------------

switch#show spanning-tree vlan 101

Spanning tree instance(s) for vlan 101 does not exist.

! above means that not even a trunk port carries vlan 101 but it is classified active

2) a port associated with an existing vlan and in STP forwarding state

Hope to help

Giuseppe

speculor_cisco Fri, 08/27/2010 - 07:46

Thanks for the answers.

About Richard's answer, when there is not a device connected to a port, I think that the port

is in "down/down" state, isnt'it? Only in this case, as this state is different from admin down, I had forgotten it.

About Giuseppe's answer, I have not understood exactly what you wanted to mean: from the first part of

your answer it seems that the vlan is active even without port configured. Can you explain me better this concept?

Thanks.

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